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airsepvisionaire5 - caire inc

airsepvisionaire5 - caire inc

Simple to use and virtually maintenance-free, the AirSep VisionAire stationary oxygen concentrator is CAIREs tried and trusted workhorse in delivering long-term oxygen therapy to our patients. Lightweight, quiet and power efficient, this stationary oxygen concentrator is the must-have for your home oxygen delivery needs.

CAIRE Contact Form (Patients, Providers & Clinicians) Get in touch with CAIRE for more information about our products, innovative technology, or any question you may have. To help us provide you with the best customer service, please fill out each field accurately so that your request will be routed to the appropriate department. Which best describes you?*(select from dropdown)IndividualMedical Equipment ProviderClinicianDistributorGovernment EntityMedical Facility (Hospital Pipeline Oxygen Needs)How can we help?*(select from dropdown)I am looking for product and pricing informationI am looking for parts and accessoriesI have a technical issueOtherPlease describe how we can help.* First Name* Last Name* Email* Phone Number* Company* Title* Country*(select from dropdown)AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChinese TaipeiChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, the Democratic Republic of theCook IslandsCosta RicaCote d'IvoireCroatiaCubaCuraaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and McDonald IslandsHoly See (Vatican City State)HondurasHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People's Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People's Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, the former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMarshall IslandsMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNetherlands AntillesNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinian Territory, OccupiedPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRwandaSaint BarthlemySaint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaScotlandSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofViet NamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweUS State*(select from dropdown)AlabamaAlaskaArizonaArkansasCaliforniaColoradoConnecticutDelawareFloridaGeorgiaHawaiiIdahoIllinoisIndianaIowaKansasKentuckyLouisianaMaineMarylandMassachusettsMichiganMinnesotaMississippiMissouriMontanaNebraskaNevadaNew HampshireNew JerseyNew MexicoNew YorkNorth CarolinaNorth DakotaOhioOklahomaOregonPennsylvaniaRhode IslandSouth CarolinaSouth DakotaTennesseeTexasUtahVermontVirginiaWashingtonWest VirginiaWisconsinWyomingCity* Zip/Postal Code* How did you hear about us?* Comments

eclipse 5 - caire inc

eclipse 5 - caire inc

The award-winning Eclipse 5 combines portability with clinical efficiency to adapt to your needs and accommodate a variety of activities giving you the freedom to travel and enjoy life on the go. Suitable for use 24/7 use, this all-in-one oxygen therapy device delivers both continuous flow from 0.5 to 3 LPM (Liters Per Minute) and pulse doses up to a setting of 9.

CAIRE Contact Form (Patients, Providers & Clinicians) Get in touch with CAIRE for more information about our products, innovative technology, or any question you may have. To help us provide you with the best customer service, please fill out each field accurately so that your request will be routed to the appropriate department. Which best describes you?*(select from dropdown)IndividualMedical Equipment ProviderClinicianDistributorGovernment EntityMedical Facility (Hospital Pipeline Oxygen Needs)How can we help?*(select from dropdown)I am looking for product and pricing informationI am looking for parts and accessoriesI have a technical issueOtherPlease describe how we can help.* First Name* Last Name* Email* Phone Number* Company* Title* Country*(select from dropdown)AfghanistanAland IslandsAlbaniaAlgeriaAndorraAngolaAnguillaAntarcticaAntigua and BarbudaArgentinaArmeniaArubaAustraliaAustriaAzerbaijanBahamasBahrainBangladeshBarbadosBelarusBelgiumBelizeBeninBermudaBhutanBolivia, Plurinational State ofBonaire, Sint Eustatius and SabaBosnia and HerzegovinaBotswanaBouvet IslandBrazilBritish Indian Ocean TerritoryBrunei DarussalamBulgariaBurkina FasoBurundiCambodiaCameroonCanadaCape VerdeCayman IslandsCentral African RepublicChadChileChinaChinese TaipeiChristmas IslandCocos (Keeling) IslandsColombiaComorosCongoCongo, the Democratic Republic of theCook IslandsCosta RicaCote d'IvoireCroatiaCubaCuraaoCyprusCzech RepublicDenmarkDjiboutiDominicaDominican RepublicEcuadorEgyptEl SalvadorEquatorial GuineaEritreaEstoniaEthiopiaFalkland Islands (Malvinas)Faroe IslandsFijiFinlandFranceFrench GuianaFrench PolynesiaFrench Southern TerritoriesGabonGambiaGeorgiaGermanyGhanaGibraltarGreeceGreenlandGrenadaGuadeloupeGuatemalaGuernseyGuineaGuinea-BissauGuyanaHaitiHeard Island and McDonald IslandsHoly See (Vatican City State)HondurasHungaryIcelandIndiaIndonesiaIran, Islamic Republic ofIraqIrelandIsle of ManIsraelItalyJamaicaJapanJerseyJordanKazakhstanKenyaKiribatiKorea, Democratic People's Republic ofKorea, Republic ofKuwaitKyrgyzstanLao People's Democratic RepublicLatviaLebanonLesothoLiberiaLibyan Arab JamahiriyaLiechtensteinLithuaniaLuxembourgMacaoMacedonia, the former Yugoslav Republic ofMadagascarMalawiMalaysiaMaldivesMaliMaltaMarshall IslandsMartiniqueMauritaniaMauritiusMayotteMexicoMoldova, Republic ofMonacoMongoliaMontenegroMontserratMoroccoMozambiqueMyanmarNamibiaNauruNepalNetherlandsNetherlands AntillesNew CaledoniaNew ZealandNicaraguaNigerNigeriaNiueNorfolk IslandNorwayOmanPakistanPalestinian Territory, OccupiedPanamaPapua New GuineaParaguayPeruPhilippinesPitcairnPolandPortugalQatarReunionRomaniaRussian FederationRwandaSaint BarthlemySaint Helena, Ascension and Tristan da CunhaSaint Kitts and NevisSaint LuciaSaint Martin (French part)Saint Pierre and MiquelonSaint Vincent and the GrenadinesSamoaSan MarinoSao Tome and PrincipeSaudi ArabiaScotlandSenegalSerbiaSeychellesSierra LeoneSingaporeSint Maarten (Dutch part)SlovakiaSloveniaSolomon IslandsSomaliaSouth AfricaSouth Georgia and the South Sandwich IslandsSouth SudanSpainSri LankaSudanSurinameSvalbard and Jan MayenSwazilandSwedenSwitzerlandSyrian Arab RepublicTajikistanTanzania, United Republic ofThailandTimor-LesteTogoTokelauTongaTrinidad and TobagoTunisiaTurkeyTurkmenistanTurks and Caicos IslandsTuvaluUgandaUkraineUnited Arab EmiratesUnited KingdomUnited StatesUruguayUzbekistanVanuatuVenezuela, Bolivarian Republic ofViet NamVirgin Islands, BritishWallis and FutunaWestern SaharaYemenZambiaZimbabweUS State*(select from dropdown)AlabamaAlaskaArizonaArkansasCaliforniaColoradoConnecticutDelawareFloridaGeorgiaHawaiiIdahoIllinoisIndianaIowaKansasKentuckyLouisianaMaineMarylandMassachusettsMichiganMinnesotaMississippiMissouriMontanaNebraskaNevadaNew HampshireNew JerseyNew MexicoNew YorkNorth CarolinaNorth DakotaOhioOklahomaOregonPennsylvaniaRhode IslandSouth CarolinaSouth DakotaTennesseeTexasUtahVermontVirginiaWashingtonWest VirginiaWisconsinWyomingCity* Zip/Postal Code* How did you hear about us?* Comments

home | a. o. smith corp

home | a. o. smith corp

A. O. Smith ProLine water heaters are available through local plumbing contractors across the country.For more information about ProLine water heaters and installation options, visit www.hotwater.com.View ProLine

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performance evaluation of low-cost frp parabolic trough reflector with mild steel receiver | springerlink

performance evaluation of low-cost frp parabolic trough reflector with mild steel receiver | springerlink

Solar collector and concentrator system can be used for industrial process heat application in various industries. Apart from the low temperature applications, there are several potential fields of application for solar thermal energy at medium-high temperatures (80C to 300C). This paper describes the experimental results of the prototype parabolic trough made of fiberglass-reinforced plastic with its aperture area coated by aluminum foil with a reflectivity of 0.86. From Indian conditions, there is a large potential available for low-cost solar-concentrating technologies for domestic as well as industrial process heat applications. This line-focusing parabolic trough with mild steel receiver coated with black proxy material has been tested with and without glass cover. Instantaneous efficiency of 51% and 39% has been achieved with and without glass cover, respectively. Performance evaluation of the prototype system has been done during the months of April and May 2010 at Shivaji University, Kolhapur (16.42N latitude, 74.13W longitude). The total cost of the prototype system developed has been calculated as Rs10,000 (US$200).

Kalogirou et al. described a low-cost method for mass production of parabolic surfaces with fiberglass. The article indicates that the accuracy of the parabolic surface depends on the accuracy of the mold, and details of the mold production and the procedure for producing the parabolic surface are presented. The authors used fiberglass of 4-mm (mean value) thickness. The cost of the parabolic surface is US$30/m2 of aperture area with 90 rim angle [1].

Valan Arasu and Sornakumar explained the design and manufacturing of a smooth 90-rim-angle fiberglass-reinforced parabolic trough for water-heating application. The total thickness of the parabolic trough is 7 mm. The concave surface where the reflector is fixed is manufactured to a high degree of surface finish. They have found that the standard deviation of the distribution of the parabolic surface errors is 0.0066 radians from the collector performance test according to ASHRAE Standard 93 (1986), which indicates the high accuracy of the parabolic surface [2].

Martinez et al. developed a 2.37-m aperture, 1.14-m-long parabolic trough concentrator with first surface solar mirrors made over floated soda lime glasses with concave geometry and built with 16 mirrors with sizes of 0.30.6 m. This reflector yields specular reflectance around 86%. The field test of focusing such a concentrator gave a size focus of about 5.08 cm where over 90% of the reflected beam solar irradiance arrived on a simulated pipe receiver with this diameter [3].

Thomas describes a simple welded frame structure for parabolic trough concentrators suitable for developing countries. He conducted static load tests on this structure to study its deflection characteristics under various load conditions. The results show that the slope error of the reflector support corresponding to normal wind loads was found to be within the specified limits, and the structure withstood the load corresponding to extreme wind load conditions [4].

The collector's performance has been tested by Kalogirou according to the ASHRAE Standard 93(1986). The collector's efficiency and incidence angle modifier have been measured. The test slope and intercept were found to be 0.387 and 0.638, respectively. The author explained that the collector's time constant is less than 1 min and the collector's acceptance angle obtained from the test is 0.5, which in combination with the tracking mechanism maximum error ( 0.2) implies that the system works continuously at almost maximum possible efficiency [5].

Thomas and Guven have explored and reviewed the design aspects of the structural, optical, and thermal subsystems of parabolic trough concentrators. Existing methods of performance evaluation and techniques to improve their performance were also discussed by the authors [6].

Gong et al. explains that the vacuum solar receiver is the key component of a parabolic trough solar plant, which plays a prominent role in the gross system efficiency. This paper first establishes and optimizes a one-dimensional (1-D) theoretical model using MATLAB program to compute the receiver's major heat loss through glass envelope and then systematically analyzes the major influence factors of heat loss. With the laboratorial steady state test stand, the heat losses of both good vacuum and non-vacuum Sanle-3 receivers were surveyed by the authors. The authors' comparison shows that the original 1-D model agrees with the end-covered test while remarkably deviating from the end-exposed test. The authors also developed a 3-D model by CFD software to further investigate the different heat transfer processes of the receiver's end components [7].

Skeiker explains that the important parameter affecting the performance of a solar collector is its tilt angle with the horizon. This is because the variation of tilt angle changes the amount of solar radiation reaching the collector surface. Skeiker has developed a mathematical model for estimating the solar radiation on a tilted surface and to determine the optimum tilt angle and orientation (surface azimuth angle) for the solar collector in the main Syrian zones on a daily basis as well as for a specific period. The results expose that changing the tilt angle 12 times in a year maintains approximately the total amount of solar radiation near the maximum value that is found by changing the tilt angle daily to its optimum value. This achieves a yearly gain in solar radiation of approximately 30% more than in the case of a solar collector fixed on a horizontal surface [8].

A schematic sketch of the test setup of the constructed parabolic trough concentrator for domestic hot water application is shown in Figures 1 and 2. The test setup was set at the Department of Technology, Shivaji University. It consists of a solar collector, storage tank of 100-L capacity, non-return valves fitted in the pipe line to define the flow direction, and control valve used to regulate the flow rate through the circuit. The necessary instruments are attached to the apparatus and then connected to the data acquisition system. For performance evaluation of a system, data collection is important, and for the data collection, measuring instrument is needed. The following instruments were used.

For construction of the parabolic trough, a composite material is used. E-glass fiberglass-reinforced plastic (FRP) has been selected as material for collector. There are a number of benefits obtained from using FRP composite; these benefits and characteristics were considered during the design and development process. The parabolic trough was constructed by the hand lay-up method. First, the mold was made of a plywood-type wooden material. The accuracy of the fiberglass-reinforced parabolic trough surface depends on the accuracy of the mold; therefore, extreme care has been taken during the construction of the wooden mold. The wooden mold has been constructed with plywood ISI BWR IS 303, which has been manufactured using high-density timber from selected hardwood layers of uniform thickness for good strength and stability. The thickness of the plywood was 20 mm. Firstly, a parabolic rib having a width of 110.23 cm was manufactured. Two parabolic pieces of the same type of were manufactured using a saw machine; these two parabolic pieces were positioned in such a way that the space between the adjacent forms on either side is equal. Small recesses were cut on the mold frame to accommodate the parabolic forms, and the parabolic forms were nailed perpendicularly on the mold frame and then connected by means of a wooden strip.

On top of these parabolic forms, a 6-mm smooth-surface plywood was fixed with nails. Wood putty was used to eliminate any marks left by the nails that were polish by sandpaper after the wood putty was set; plane smooth sunmica (a type of smooth plywood) was stuck on the plywood surface with sticky materials (Fevicol, Pidilite, Mumbai, India). A thin film of plastic, 200-m thick, with size equal to the parabola mold was laid on the wooden parabolic mold. The thin film was used as a release agent and to get a smooth surface inside the parabola. Then, 450-m chopped strand fiberglass was placed on top of the thin film. The catalyst or Methyl Ethyl Ketone Peroxide Hardener and accelerator cobalt were mixed in polyester resin in a separate bowl. The mixed resin was applied by brushes to the surface of the chopped strand mat, and then, another layer of chopped strand mat was placed on the mixed resin. The fiberglass mat was saturated with the resin by rolling the surface with a brush. The resin was applied on the mat by brushing. A brush was used to work the resin in to the fiber. During the process, extreme care was taken so that the material is securely attached to the mold, and no air is trapped in between the fiberglass and mold. The rolling action of the squeeze assists in removing air bubbles that could prove detrimental to the laminate performance. This process of laying alternate layers of polyester resin and chopped strand fiberglass mat was repeated until a 2-mm-thick fiberglass-reinforced laminate was obtained. Table 1 shows the parameters and dimensions of the terms used in the experimentation.

The experiment procedure was started by flushing the system. Then, the system was filled with water and the flow rate was adjusted to the required value. The solar collector was allowed to run for over 20 min to achieve quasi-steady-state conditions before starting the experiments, and the proper working of all measuring instruments was checked, including the connection of the temperature indicator to the temperature sensor, pyranometer, anemometer, and tracking of parabolic trough. Cold water from the storage tank enters the mild steel receiver of the parabolic trough collector. The tank was located above the level of the collector to assure the natural flow of water. As water in the receiver tube, which is located at the focal axis of the trough, is heated by solar energy, heated water flows automatically to the top of the water tank and is replaced by cold water from the bottom of the tank. When the water gets heated upon rising to the collector, its density will decrease and the lighter-density water will move up and be stored on top of the storage tank. Higher-density water from the bottom of the tank again enters the parabolic trough and gets heated and moves up and stored in the top of the storage tank. Data of all readings of ambient, fluid, receiver body, and storage tank temperatures and total solar radiations with wind speed every half an hour were collected. The experiment has been performed for 7 h over the day from 0930 hours to 1530 hours. The experiment has been continued with changing input parameters, such as receiver materials and mass flow rate of water.

During the experimentation, a cylindrical parabolic collector has been oriented with its focal axis pointed in the eastwest (E-W) orientation so that the focal axis is horizontal. Sun tracking was provided to the parabolic trough collector. Manual tracking was provided to the parabolic trough collector. The trough was rotated about a horizontal (E-W) axis and adjusted manually so that solar beam makes minimum angle of incidence with the aperture plane at all times.

where q u is the useful energy delivered from the concentrator (W); m, mass flow rate(kg/s); To, outlet fluid temperature (C); Tin, inlet fluid temperature (C); Cp, specific heat of water (kJ/kgC); C, concentration ratio; S, incident solar flux absorbed in the absorber plate (W/m2); Ul, overall heat loss coefficient (W/m2C); Ta, ambient temperature (C); F', collector efficiency factor; Do, outer diameter of the tube (m); and L is the length of the concentrator (m).

where qu is the useful energy gain per unit of the collector length; Tr, mean receiver surface temperature (C); W, width of the parabolic reflector (m), and where F is the collector efficiency factor defined by Equations 5 and 6 [1, 5, 9, 10].

where Tc is the temperature of the cover; hw, wind heat transfer coefficient(W/m2-K); p, emissivity of absorber surface for long-wavelength radiation; and c, emissivity of the cover for long-wavelength radiation.

The convective heat transfer coefficient hf on the inside surface of the absorber tube can be calculated. For Reynolds number greater than 2,000, the flow is turbulent and the heat transfer coefficient may be calculated from Equation 14 [9, 10]:

Figure 3 shows the variation of inlet and outlet temperatures of the water. The trend explains that, as solar radiation on the receiver enhances, outlet water temperature increases. In comparison, the receiver with glass cover yields much higher outlet water temperature than the receiver without glass cover. The glass cover over the mild steel receiver acts as an insulator, and outlet water temperature and temperature gradient between inlet and outlet water rise sharply. It has been observed that, with glass cover, outlet water temperature and temperature gradient increase by 29% and 68%, respectively.

Figure 4 explores the variation of receiver temperature. From Figure 4, it is clear that the receiver temperature increases with increase in solar radiation. When the receiver is exposed to atmosphere, there are heavier convective heat losses from the receiver as compared to the receiver with glass cover. As said earlier, the glass cover acts as an insulator and also helps in concentrating more solar radiation at the receiver. It has been observed that, with glass cover, receiver temperature has been increased by 23%, which assures hotter water temperature at the outlet.

Figure 5 indicates useful heat gained by the water flowing through the receiver throughout the day. Useful heat gained by the water is affected by various parameters such as wind speed, receiver temperature, and solar radiation. Receiver temperature is the average of three values over the space and not over the time. Temperature was measured at four locations over the length of the receiver. This plotted variation shows that as the receiver surface temperature increases, it increases the thermal conductivity of the air surrounding the receiver. When air conductivity increases, heat losses also increase, but this is not the only cause of heat loss. Figure 5 shows that, with glass-covered receiver, it is possible to achieve more useful heat gain. It has been observed that as the beam solar radiation incident on the collector increases, more optical energy is captured by the receiver. Compared to the decrease in solar radiation and wind velocity by 4% and 7%, respectively, useful heat gained by the receiver with glass cover increases by 22% throughout the day, and average receiver temperature increased by 23%.

Figure 6 explains the variation of collector efficiency and convective heat loss coefficient. The higher the wind speed, the higher will be the convective heat loss and the lower will be the collector efficiency at an instant. It has been observed that the average decrease in heat loss coefficient is 70% when the receiver was covered with glass. When the heat loss coefficient decreased by 70%, the instantaneous efficiency of the collector still increased by 13% with the glass-covered receiver. Instantaneous efficiency of 51% has been achieved with the glass-covered receiver. Radiative heat losses are very small, so their effect on collector efficiency is very small. The main cause for heat loss is temperature gradient between the receiver and surrounding and wind velocity at an instant which therefore increase convective and radiative heat losses from the receiver. An average receiver temperature has been determined to provide accurate receiver loss predictions. Also, wind velocity affects the variation of convective heat loss coefficient. This heat loss also depends upon solar radiation at an instant.

From Indian conditions, low-cost FRP parabolic trough system can prove to be beneficial for industrial heating applications as well as domestic heating. With the system described in this paper, the following conclusions are drawn:

AS, M. Tech, Principal at New Satara College of Engineering & Management, Head of Solar Thermal Research Lab, is involved in research and development programs of solar thermal energy technology in Maharashtra, India, with more than 6 years of experience in the field of solar thermal energy. He was also invited as a solar expert for IEA workshops on the road map of solar heating and cooling at Germany, China, and Australia. SA, M.Tech in Energy, is working as a lecturer at the Amrutvahini College of Engineering and is involved in research activities in the field of thermal energy technology at Shivaji University, Kolhapur, Maharashtra, India. NS, a coordinator and associate professor at the Department of Energy Technology, has 30 years of experience in the field of energy-related issues. He is involved in various energy research projects of the Department of Technology at Shivaji University, Kolhapur, Maharashtra, India. He has more than 150 publications under his name.

Valan Arasu A, Sornakumar T: Design, manufacture and testing of fiberglass reinforced parabola trough for parabolic trough solar collectors. Sol. Energy. 2007, 81(10):12731279. 10.1016/j.solener.2007.01.005

Martinez I, Almanza R, Mazari M, Correa G: Parabolic trough reflector manufactured with aluminum first surface mirrors thermally sagged. Sol. Energ. Mat. Sol. C. 2000, 64(1):8596. 10.1016/S0927-0248(00)00068-4

AS and SA carried out all the computations and system designing and drafted the manuscript. NS conceived of the study and participated in its design and coordination. All authors read and approved the final manuscript.

Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Sagade, A.A., Aher, S. & Shinde, N.N. Performance evaluation of low-cost FRP parabolic trough reflector with mild steel receiver. Int J Energy Environ Eng 4, 5 (2013). https://doi.org/10.1186/2251-6832-4-5

a review of the beneficiation of copper-cobalt-bearing minerals in the democratic republic of congo - sciencedirect

a review of the beneficiation of copper-cobalt-bearing minerals in the democratic republic of congo - sciencedirect

Mining is increasingly taking place at depths where sulphide bodies are present, which has led to a need to reinvent beneficiation methods.Gravity separation is used either as a preconcentration step or during the extraction of rich concentrates from process tails.Sulphidisation followed by flotation is the preferred beneficiation technique for oxidised copper-cobalt ores.The integration of CPS systems into the flotation circuits can help minimise reagent overconsumption.Application of selective flotation can help a concentrator to produce separate oxide and sulphide concentrates.

Copper and cobalt (CuCo) are strategic metals for the Democratic Republic of Congo (DRC), and nearly 20% of the country's GDP is supported by their exports. At present, the country classifies itself as the leading copper producer in Africa with an output in the region of a million tonnes and possesses nearly 60% of the world's reserves of Co; a metal exclusively exported in the form of salts or semi-finished products. Concentrators play a very important role in the growth of CuCo metal production, which is needed in order to meet rapidly growing global demand and to increase government revenues through mining royalties. This article reviews the major process flow sheets and reagent suites in practice at concentrators operated in the DRC for the beneficiation of CuCo values from various ore types. The comprehensive compilation of pertinent laboratory and industrial data is intended to provide practising specialists, metallurgists, and academics conducting research on Congolese CuCo ores with a single well-detailed reference source. Emphasis is placed on froth flotation as the major technique for the beneficiation of CuCo minerals.

exporthub: online b2b marketplace - connecting buyers & suppliers smartly

exporthub: online b2b marketplace - connecting buyers & suppliers smartly

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The service rendered by exporthub is truly the best I have ever experienced in my experience with any B2B site. My KAM John Murphy is a consummate professional and they delivered on their promise of finding us reputable buyers in less than a month. I will like to recommend their service to any company interested in exploring and expanding thier market for foreign buyers

Since I joined Exporthub, I have been getting good support from My account manager Mr. John Murphy and whenever I have any query my KAM is always available for my help. Recently I have managed to close different orders & some are in pipelines worth $30,000+ & we have found one importer now he will be our regular client. I suggest others to join exporthub and get good services for their business

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modern technologies for the thermal treatment of municipal solid waste, and prospects for their implementation in russia (review) | springerlink

modern technologies for the thermal treatment of municipal solid waste, and prospects for their implementation in russia (review) | springerlink

The data on the state-of-the-art of the thermal processing of municipal solid waste (MSW) in the United States, China, Europe, and other countries are presented. The analysis of technologies for MSW incineration in layered furnaces using fire-grates and fluidized-bed furnaces, as well as using gasification and pyrolysis, is performed. It is shown that the best technology for the energy-producing MSW utilization consists in MSW incineration in layered furnaces with the use of mechanical shearing fire-grates. It is noted that, since all the enterprises for the energy-producing MSW utilization (in fact, these are TPPs, whose main fuel is municipal solid waste) are currently equipped with multistage gas purification facilities, the problems of their environmentally safe operation are completely solved. Therefore, research is mainly aimed at improving the energy efficiency of these enterprises, including through the integration of the units for MSW incineration into the thermal circuit of a TPP operating based on fossil fuel. Examples are given of foreign operating installations for the energy-producing MSW utilization with an electrical efficiency of 2731% as well as those operating in a heating cycle with a high energy efficiency. The state-of-the-art of MSW thermal processing and the prospects for the implementation of modern technologies for the energy-producing MSW utilization in Russia are presented. Despite the fact that there is no sufficient experience in this field in Russia (only three plants have been constructed in Moscow, whose installed electric operating capacity does not exceed 12 MW), it is planned to construct four relatively large thermal power plants in Moscow oblast with an electric operating capacity of 70 MW each, in order to incinerate 700000 t of solid waste per year. A TPP with the energy-producing utilization of 360000 t of MSW per year with an installed electric operating capacity of 24 MW is the most promising for Russia. Such a TPP could already be in demand in more than two dozen large Russian cities.

J. B. Kitto, M. D. Fick, Jr., and L. A. Hiner, World-class technology for the newest waste-to-energy plant in the United States Palm Beach renewable energy facility No. 2, Technical Paper No. BR-1935, Presented at Renewable Energy World International, Orlando, Fla., Dec. 1315, 2016. https://yandex.ru/search/? text=World-Class-Technology-for-Waste-to-Energy-Plant-2016-Renewable-Energy-World-Article&lr=213

Clean Technologies and Stable Development, in Information Bulletin: EY, Services in the Field of Clean Technologies and Sustainable Development, Iss. 5: Incineration as a Way to Solving the Problem of Municipal Waste (Ernst & Young, 2018) [in Russian]. https:// www.ey.com/Publication/vwLUAssets/EY-cas-newsletter-march-2018/$File/EY-cas-newsletter-march-2018. pdf

W. B. Lim, E. Yuen, A. R. Bhaskar, Governments Across the Emerging Markets are Eager to Tap into Waste-to-Energy (WTE) Technologies, but Many are Learning that It Takes More. https://home.kpmg/xx/en/home/insights/2019/10/waste-to-energy-green-solutions-for-emerging-markets.html

Globalization on Waste-to-Energy Market Continues: Press Release of Ecoprog GmbH, 27 November 2018. https:// www.ecoprog.com/fileadmin/user_upload/pressemitteilungen/ecoprog_press_release_Waste_to_Energy_2018-2019.pdf

Review of State-of-the-Art Waste-to-Energy Technologies: Stage Two Case Studies (WSP, London, 2013). http:// www.epa.wa.gov.au/sites/default/files/Publications/WSP %20Waste%20to%20Energy%20Technical%20Report% 20Stage%20Two.pdf

Report and Recommendations of the Environmental Protection Authority and the Waste Authority, Report No.1468 Waste-to-Energy s16(e) (2013). https:// www.epa.wa.gov.au/sites/default/files/Publications/ Rep%201468%20Waste%20to%20energy%20s16e% 20040413.pdf

Stadt Zrich ERZ Entsorgung + Recycling. Thermische Verwertung von Abfall. https://www.stadtzuerich.ch/ content/dam/stzh/ted/Deutsch/erz/Zuerich_Waerme/ Publikationen_und_Broschueren/ZW_Thermische_ Verwertung_Hagenholz_1708.pdf

Decree of the Government of Moscow No. 313-PP of April 22, 2008 On the development of the technical base of the municipal waste management system in Moscow. http://mosopen.ru/document/313_pp_2008-04-22

Directive 2000/76/EC of the European Parliament and of the Council of 4 December 2000 on incineration of waste, Off. J. Eur. Communities, Dec. 28 (2000). https://eurlex.europa.eu/LexUriServ/LexUriServ.do? uri=CONSLEG:2000L0076:20001228:EN:PDF

Tugov, A.N. Modern Technologies for the Thermal Treatment of Municipal Solid Waste, and Prospects for Their Implementation in Russia (Review). Therm. Eng. 68, 116 (2021). https://doi.org/10.1134/S0040601521010183

gold smelting & refining process

gold smelting & refining process

Gold can be concentrated and recovered by applying different gold refining process methods and the final product has variable quality. In this way, it is necessary to have a better marketable product so that the incomes can be improved. Then, we have two smelt and cast the gold into bars called bullion or Dore. The name bullion is restricted to the precious metals, refined or unrefined, in bars or ingots that contain small contaminants.

For many years, the term bullion made reference to coins and the name base-bullion is for pig-lead or copper bottoms obtained in smelting operations of lead and copper concentrates. The last product is characterized for containing small amounts of gold and silver. The treatment of these products depends on the metallurgical extractive process of lead and copper.

It has been shown that concentrates obtained by gravity devices and cathodes can be smelted directly most the time. Silver-gold concentrates can be smelted too. Under this consideration, a concentrate must contain at least 20 oz/t of gold. Obviously, if the higher grades are better and 50 oz/t is a good average value. It is important to mention that a silver-gold concentrate obtained by flotation has a high silver content. For example a concentrate assaying 1400 oz/t Ag and 8 oz/t Au can be smelted directly.The smelting process involves several operations, retorting, smelting and refining.

The most known gold alloys are made with silver. The proportion between gold and silver changes the alloy color. In this way, there are yellow and white alloys and the last ones present different metallurgical properties. Alloys are influenced by the presence of other minerals or metals. The next table shows the melting point of many elements and minerals that usually are in gold concentrates.

Basically, gold can form alloys with the metals mentioned in the table. There are other metals, but the alloys are no stable. For example, arsenic and antimony are decomposed by mercury. Only some metals such as zinc, silicon, iridium and cobalt can be used to prepared good alloys without modifying the gold properties too much.

Alloys based on the gold-silver-copper system can be employed for many applications. They can be rolled, flattened and stamped easily. It has been investigated the effect of different elements and compounds on gold bullion properties. For example, deoxidizers are added in order to minimize the formation of oxides (e.g. copper can be oxidized easily) when is necessary. The presence of zinc or silicon reduces the formation of oxidized copper compounds, but other oxides more stable are produced.

Especially zinc oxides that are difficult to eliminate. Phosphorous and boron are good deoxidizers, but an excessive addition or presence is a problem because the metallic product can be brittle. So, we have to analyze the gold concentrate and the additives to be added in order to have a good alloy.

Elements have influence on the grain size. For example, large grains tend to create a peeling effect, this can produce losses when the bar is transported and handled. The presence of barium salts is good due to acts as a grain refiner. In general, some elements and compounds form fine disperse centers where the crystallization starts.

Silicon is not very soluble in gold and silver. In this way, a low melting eutectic point is produced which modify the melting point of the alloy. Normally the compound is formed on grain boundaries making the alloy a little brittle. If the gold concentrate has copper, silicon can form alloys with copper easily avoiding or minimizing the brittle effects. Other problem with silicon is the grain size, it tends to grow. When some corners are brittle, they were cause by silicon. Brittle points or located areas will produce gold losses. Then, it is important to know the material to be smelted and the fluxes or additives to be added.

Amalgams are other important group of alloys. Quicksilver (Mercury) reacts with gold at ordinary temperature, and forms alloys of variable composition. An amalgam containing 90% Hg is liquid, 87% Hg is pasty and 85% Hg is solid. Amalgams with smaller contents of mercury can be produced by heating the alloy at different temperatures. When amalgams are heated near of the boiling point of Mercury, the gold content is higher and reaches the maximum point when all the mercury was distillated.

Gold concentrates, precipitates, and Merril-Crowe product can have mercury is variable proportion. If we smelt the charge directly at 1100 oC, mercury will be released to the environment and the smelting place can be a dangerous place. In order to avoid this situation, is necessary to eliminate mercury by retorting. The same considerations taken in the amalgamation process are valid for this stage. The small amount of elemental mercury that is extracted from the host rock can affect workers health. Considering the fact that cyanidation is the main gold recovery process and indirectly mercury by a factor of 2,000 5,000. The last one needs a small volume of high grade gold solution that is suitable for final recovery. Elemental mercury vapor is released when the pregnant leach solution undergoes the recovery process required to produce dore bars.

The hazards associated with mercury exposure include inhalation, absorption and ingestion. As an air contaminant, the main concern is inhalation of vapors as results of releases. Acute exposure to high levels can lead to severe lung damage and death. This poisoning has three phases, initial exposure results in flu like symptoms lasting between one to three days, followed by signs and symptoms of severe pulmonary toxicity; the final phase is mouth sores and ulcers with memory loss, depression and insomnia. It must be mentioned that these symptoms are characteristic of high exposures. Then, this step is very important. OSHA has established a permissible exposure level of 0.05 mg/m3 based on eight hours average time.

There are several types of retorts and the final selection is based on gold production, mercury recovery system, and safety conditions. The charge is heated slowly until boiling point of mercury is reached. At this point the mercury is eliminated and condensed in cooling tubes passed through water. Obviously, some losses can be produced and this can be estimated as 0.065 grams per 255 grams of mercury. The process takes two to three hours. The final product is composed by gold, silver, sulphides and base metals.

Although the process is simple, the elimination of mercury is not totally perfect. The problem has two causes; first, flouring or tiny mechanical reduction of size during grinding. The second cause is due to chemical reactions that forms coatings or layers of some impurities. These coatings can be oxides, sulphides, or sulphates of some base metals that present in the ore. The employment of mercury which contains with base metals improves mercury elimination. Oxides are formed by weathering and they are not soluble in mercury, and then float on its surface. Gangue minerals are other possible source of coatings due to recovery and concentration processes are no totally efficient.

The mercury retort must be located in a special place. Basically, the room should be kept under a negative pressure with respect to the rest of the building, which can be accomplished by using either fans or local exhaust ventilation. The makeup air vents for the room exhaust ventilation system must be located on the wall opposite the refiner fresh air supply plenum. The retort has to be operated and maintained in accordance with the vendor recommendations. Test must be performed to know the optimum operating parameters prior to start its service. This will minimize the potential of sending mercury contaminated to the flux mixing station and furnace section. During the operation the retort must work under vacuum and the air exiting the water condensation system has to be scrubbed with a mercury vapor removal system such as a filer with activated carbon. Then, the flow can be introduced into the vacuum system. The scrubber system is required due to the water condensation system is not efficient.

The condensed mercury vapor is trapped in a condensation pot. Normally, liquid mercury can be removed from the container by opening a valve and draining into another container. The mercury is then poured into a flask. This procedure must be done carefully.

Once performed the retorting process, the product obtained is heated in a furnace in the presence of slag forming fluxes at temperatures over the melting point of all the components of the change, commonly between 1150 to 1450 oC. This operation is performed for around two hours to ensure complete separation of impurities from the precious metals. Gold and silver form an alloy that is heavier than the slag and sinks to the bottom of the furnace. Once the smelting is complete, the slag is removed and the precious metals are casted in ingots. The slag contains gold and silver and must be reprocessed in order to minimize the losses of precious metals.

A very important element in the smelting process is the flux, which is added to charge in order to remove base metals and other impurities from the Dore bar. The mixing of charge and fluxes has to be done in ventilated areas. A good practice is to vacuum the flux and charge from the retort pans either directly into the furnace or into a hopper that will feed the mixture into the crucible. In this way, personnel will not be in direct contact with the flux or any residual mercury vapor. In general, the flux and the retorting product must be mixed with safety.

The flux is a mixture of several reagent chemical such as borax, silica, sodium nitrate, sodium carbonate and fluorspar. Borax is a white crystalline mineral used in glass and ceramic enamel mixes. In the smelting process, borax helps to reduce the gold smelting point of the charge and capture metallic oxides. The addition of this reagent must be controlled; otherwise the slag will be extremely hard and non-homogeneous. Other negative effect is to avoid the separation of phases into the molten charge. Silica is an acid flux and reacts with metallic oxides forming stable silicates. Excessive addition creates slags with high viscosity and metallic oxides are no trapped with efficiency. Normally, the borax/silica ratio is 2/1. Sodium nitrate is an oxidant for iron, copper and zinc. When the charge is near 500 oC, sodium nitrate produces oxygen. Sodium carbonate is an alkaline flux whose melting point is 850 oC and reacts with silica forming sodium silicate. The latter reacts with oxides and produces other oxidized compounds. Sodium carbonate must be added with caution due to an excessive addition creates sticky slags that are difficult to remove. Fluorspar modifies slag viscosity because modify the silicates formed during the smelting process. An excessive addition attacks the crucible and reduces borax action on metallic oxides.

When the flux and the charge are mixed in the right proportion, the slag will take the right smelting point, density and viscosity are low, fluidity is good, metallic oxides are eliminated easily; precious metals losses are reduced at minimum and can be broken easily. Separation efficiency between precious metals and slag is evaluated by taken slag samples and perform assays for gold and silver. The performance depends on the charge properties, gold and silver content and fluxes efficiency.

During the smelting process, any residual mercury contained in the concentrate will be eliminated in the first moments. An exhaust hood must be placed over the furnace to extract mercury and other fumes released during the heating process. In the market exists two types of hood, one considers and annular hood mounted on the top of the furnace, and the other design considers an enclosure around the furnace. Depending on the silver content, the process can produce silver fumes. Then the Dore bar should be allowed to cool in the molds to facilitate removal of the bars after they have cooled. An exhaust hood must be considered in case silver fumes can be a problem.

The molten charge has to be sampled by using a glass vacuum tube or a simple ladle to take a deep sample. Dore bars are cooled after they are poured and then chipped to remove slag. This step can be done by using a pneumatic chipping gun or automatic descaler. Probably, considering the daily production, the best option must be chosen.

Once the slags were removed and cooled, will be stored for further processing. Precious metals can be recovered by gravimetric devices and cyanidation. A common practice is to crush the material until 100% passing 20 mesh. The material is processed in a shaking table and the concentrate is smelted again and the tails is crushed again in order to have a finer size, which must be appropriate for cyanidation. Intensive cyanidation is a good option, but obviously, the material can be sent to the leaching process employed to treat the raw ore. Gold and silver recoveries are between 99.5 to 99.7%. Although slag production weight is variable, a typical operation can generate 10 kilos of slag per 1000 oz of gold.

The precipitate obtained in the Merrill-Crowe process is very sensitive during the smelting process due to the process employ diatomaceous earth as a filtration medium. This material contains silica. Then, it is important to know the silica content in the cement so that the fluxes can be added in the right proportion in order to avoid unexpected problems in the process. Also the final product quality is influenced because the silver/gold proportion is modified. Other very interesting point is the degree of oxidation generated by the flux. If the oxygen liberated is high, there will be produced a foaming effect during the smelting process. The foam contains water vapor, metallic oxides fumes and combustion products and creates an appropriate environment to trap gold and silver into the slag. When this happen, it is necessary to observe the molten charge so that we can be sure the foam disappeared. This operation can takes time, but the losses are minimized.

The recipe to be used in variable and is based on the charge composition. For example, 1 ton of concentrate or cement can be mixed with 300 kg borax, 100 kg silica, 10 kilos sodium carbonate, 5 kilos sodium nitrate and 0.5 kg fluorspar. As was mentioned before, the flux has influence on the slag properties and Dore bar composition. Precious metals contents are between 98 to 99%.

There is an alternative process that employs fluxes, carbon and lead oxide (litharge). In this case carbon helps to reduce oxides and distribute the temperature correctly in the crucible. Flour is the most known source of carbon. When the charge is taken high temperatures lead oxide is reduced and metallic lead is produced. This metallic lead in liquid state traps gold and silver. As slag and metallic charge have different densities, lead and precious metals go to the bottom of the crucible and the slag floats. In other words, lead reduces the losses of precious metals into the slag. The mixture of heat, fluxes, carbon and lead assure an appropriate reducing environment. When the smelting process is complete, the charge is poured into a mold. Once the slag is cool, this can be separate from lead and precious metals by using a hammer or any device than can break the slag. The metallic product is named button and have to be processed in the other smelting process called cupellation. By this second stage, lead and precious metals are separated. The button is placed in cupels which are porous containers. These empty spaces will absorb lead oxide and the Dore metal is formed. Cupellation is performed under oxidation environment in order o oxide metallic lead to PbO.

A brief description on slags was mentioned briefly in the previous item. Slags are a very important part of the process because they may tell us if the smelting was carried out in the right way. As was mentioned, in the making of Dore bars (Gold Bullion) oxides and other impurities are eliminated by means of high temperature reactions with fluxes. Most of the impurities and fluxing agents combine to form a liquid silicate called slag that float above the liquid Dore metal and is removed from the crucible. Normally, crucibles are fed with a retorting product and reprocessed slags from previous operations due they can contain precious metals in variable proportion. Slags are glassy, stony, hard and compact; and their properties mainly on how the material was cooled. The cooling procedure has influence on how a particular slag can be reprocessed.

In general, slag from smelting process arises from extraneous materials such as rust and oxides; oxidation of elements in the charge (e.g. iron, copper, zinc); residues from fuels; fluxes employed in the process (silica, borax, sodium nitrate, sodium carbonate, fluorspar); crucible erosion. Then, slag can vary in appearance and chemical composition.

Slags can be categorized in three groups. The first one is formed by allowing the molten slag to cool relatively slow under ambient conditions and the final cooling can be accelerated with water spray. The second one is cooled through a water jacket that leads to rapid steam generation and formation of several cavities within the slag. These cavities modify the slag density. The third group is formed by granulated slag that is formed by quenching molten slag in water. The very rapid cooling causes solidification of the slag as sand sized particles of glass.

Refining processes are employed to improve the gold product quality. There are several types of refining procedures employed, but some of them are selected according to the daily production. It is important to mention that the gold purity is variable according to the process employed and the workers experience. If the final content is important, some assays must be performed. This point is valid when there is a previous commitment on gold quality. Other aspect very important to mention is about impurities, if they are difficult to remove, the process selected must be changed. Ensuring that most of gold is recovered is a very important aspect so that the production cost can justify the operation. Finally, there are aspects related to health, safety and contamination that have certain influence in the process.

The techniques employed are Cupellation, Inquartation and Parting, Miller Chlorination Process, Wohwill Electrolytic Process, Fizzer Cell, and Aqua Regia Process. The final election is based on the initial gold content. For example, the Whohwill Process is selected if the gold content is not less than 98%, the Aqua Regia process is a good option when the silver content is less than 5%. It the charge to be refined contains platinum group metals such as platinum and palladium, the Inquartation and Parting Process can be selected. In general the final selection is not easy and is good practice to equip a facility to perform more than one process.

The Cupellation process is employed in very small scale and is based on the fire assay process. The final product can collect gold and platinum group metals. Perhaps, small miners can considers this option when there are economical restrictions and the final product quality is not very important. The Inquartation and Parting Process is based on the solubility between gold, silver and copper. Initially there is an impure product obtained by smelting that must be grained to improve the surface area so that the metallic product can be attacked with nitric acid in order to dissolve copper and silver and the leaching residue is metallic gold. During the acid attack, platinum and palladium forms part of the rich solution. However, Iridium, Ruthenium, Rhodium and Osmium are not dissolved. The gold purity is close to 99.99% when the platinum group metals content is very low.

The Miller chlorination process is well know and has been practised for a long time in the gold refining industry. The process consists of chlorine addition into the molten Dore by using an immersed tubing system. Initially there is a slow reaction of chlorine gas with base metals forming volatile compounds. Once is complete the initial reaction, there is a fast generation of non-volatile compound called Miller Salt that must be removed from the surface of the molten charge. It is important to avoid the formation of gold chlorides in order to avoid losses. One solution is to the problem is to cover the molten charge with mixture composed by borax and silica. The end of the process is noted when appear purple fumes of chloride gold. Platinum group metals are not removed and gold purity is between 99.5 to 99.8%. Although this technique is old, the process has to be operated by skilled workers and the facilities must have an excellent exhaust system in order to avoid contamination by chlorine.

Other process used for a long time is the Wohlwill Process and is considered as the second part of the Miller process due to refine its product. This is an electrolytic process based on the dissolution of gold in an acid bath prepared with chlorine gas and hydrochloric acid. The final product is a gold cathode with 99.99% purity. Although the process is efficient, there is an issue related to the cost due to it is necessary to heat and apply a specific current density such as 110 amperes per square foot. Platinum group metals and silver are reported on anode slimes and the remaining base metals are in solution.

The Fizzer Cell Process is an improved Wohlwill Process whose main change is the cathode design. There is a porous ceramic container that works like a membrane whose purpose is to avoid gold losses and adhesion of some impurities on cathode surface. The electrolytic cell is drained and filtered. A very important aspect of this process is referred to the possibility of treating impure anodes, basically when the silver content is as high as 10%.

The Aqua Regia Process is appropriate to be employed in small scale and the metallic gold to be obtained is as pure as 99.9%. The main steps of the process are to dissolve the precious metals and some impurities. Since the Aqua Regia is a mixture between nitric acid and hydrochloric acid, part of the silver will remain in solution and other part will form a silver chloride precipitate. Then, it is important to be careful with the silver content. It must be mentioned that the silver chloride formation has a negative effect on gold dissolution. Once the dissolution is performed, the solution and the precipitate are separate by filtration operations. The solution contains gold and is treated with reducing agents such as ferrous sulphate, sulphur dioxide or sodium bisulphate. Gold powder of high purity is obtained and can be melted later. When gold precipitates, platinum group metals remain in solution and have to be recovered by other procedure.

Metallurgical processes need to know the metallic content of the different products obtained in recovery and refining processes. If we have to know about gold assay, it is important to mention the Fire Assay Process that has been employed in the mining industry for a long time. Basically the ore is mixed with a mixture of fluxes and during the smelting process precious metals are liberated and most of heavy metals are trapped by the fluxes. However, lead is the key element due to collect precious metals. The latter product is reprocessed by a cupellation stage so that we can have a gold-silver alloy that will be leached selectively to calculate the gold content.

One aspect very important is to know the minerals present in the sample to be assayed due to they have influence on the flux to be added. Obviously, this knowledge is fruit of experience and study. Basically, minerals can be identified by specific gravity, color, streak, luster, hardness, magnetic susceptibility, and reaction with any special reagent such as hydrochloric acid. The number of minerals is large and assayers have to be focused in the main minerals such as sulphides or sulphides. Carbonates react easily with nitric or hydrochloric acid and this is a common characteristic of alkaline samples.

A good procedure to estimate the minerals is to perform a gravimetric separation by using a watch glass or a curved plate. This procedure is called vanning. In this case, is necessary to take 10 to 30 g of sample and mix it with water in the watch glass. The idea is to separate minerals according to their specific gravity like a panning gold operation. Heavy minerals stay in the center and the lighter minerals at the border. When the vanning is well done, it is possible to identify minerals of different color and densities due to they are distributed in different zones. The size of these zones will tell us the main minerals and the possible nature of the sample.

This is a substance added to a material to aid in its fusion. Other action is to act as a reducing agent to dioxide or decompose impurities and remove them as slags. In this way, we can insure complete decomposition of the ore. One of the components is a lead oxide that is reduced to metallic lead. This metallic element collects gold and silver. The weight of flux is 25 grams. Basically, the flux must be able to control viscosity, degree of acidity, change the melting point of the ore and decompose the ore. The main fluxes are listed below:

Calcium oxide. This is an alkaline flux that modifies the viscosity and fluidity of the charge. Also reacts with alumina. Lead oxide. Litharge is the yellow lead monoxide is a desulphurizing flux and provides lead to the process. Potassium carbonate. Is employed with sodium carbonate in order to modify the melting point of the sample. Sodium carbonate. This flux can be added alone or not and its main action is to react with sulphides. Kt can be replaced with sodium bicarbonate. Borax. This is an acid flux and is appropriate to separate metallic oxides. If the addition is excessive, part of gold will be lost and the remaining part reacts with alkaline fluxes. Silica. This is other acid flux that changes the melting point. Excessive addition creates a molten charge with excessive viscosity. Fluorspar. This a neutral flux that improves decomposition and fluidity. Refractory ores needs fluorspar to avoid gold losses. Sodium nitrate. It is an oxidizing agent whose addition is oriented the oxide base metals. Excessive addition changes dramatically the lead button size. Reducing agents. They help to convert lead oxide to metallic lead. There are several types of reducing agents, some of them are flour, and charcoal.

The weight of sample is based on the called one-assay ton (29.166 g). Laboratories normally employs one assay ton, and other half assay ton. Obviously, the experience is the best tool to estimate the weight. The fluxes to be added are the remaining part of the charge. The mixture of fluxes must contain lead oxide and sodium carbonate. Typically the lead bottom weight is between 18 to 25 grams. The other fluxes are added is minor proportion. The main criterion is to consider the weight of metallic lead to be produced; otherwise there will be more than one problem with the Dore metal obtained at the end of the process. The oxidizing and reducing properties of the sample have influence on the lead button weight. Some minerals such as hematite, magnetite and pyrolusite have direct influence on oxidizing properties. Similarly, galena, chalcocite, chalcopyrite, pyrite, sphalerite and arsenopyrite change the reducing properties according to its sulphur content. It means more sulphur content, more reducing power.

A recipe can be composed of 25 g litharge, 20 g sodium carbonate, 1 g flour, 8 g silica, and 25 g ore sample. This proportion can work for a neutral ore and the components can be modified in order to test other samples. The lead button is the best proof of the mixture fluxes efficiency.

Black sand samples must follow a special smelting procedure due to they are difficult to melt at common temperatures. The fluxes to be used must be chosen with detail in order to avoid wrong results. The sample preparation is other problem since these materials contains free gold. A good recipe has the following composition, 30 g litharge, 30 g sodium carbonate, 25 g borax, 5 g flour, 8 g fluorspar, 30 g silica and 20 g ore sample.

First and foremost the crucible (scorifier) must be preheated, and then add the mixture sample-fluxes. Ore sample and fluxes melt at different temperatures and the order of these reactions has a very important role in the efficiency of the process. Once the charge is totally melted, it is important to add 15 to 30 more minutes in order to assure a good diffusion of the button and precious metals collection.

When temperature is near 550 oC, lead metal is formed from a reaction between lead oxide and flour. The charge forms a porous mass with borax and sodium carbonate. Sulphides react with carbonates and forms alkali sulphates that replaces gold in the crystalline structure. Borax melts at 740 oC and reacts on metallic oxides. At 850 oC, sodium carbonate is melted and reacts with silicates. Since part of the lead oxide was not smelted, when temperature reaches 885 oC, all the lead is transformed in oxide. At this moment the remaining free gold and silver particles are collected and go to the bottom of the crucible. The final point is near 1068 oC and is expected that all the reactions are complete.

There are several factors that affect the efficiency of the melting process. Some of them are the following: ore sample particle size must be very fine in order to have the right surface area and the reactions can be favored. Then, the ore must be pulverized in the right way. Other aspect is the right addition of fluxes. If they are not in the minimum amount, reactions will be completed and some of gold and silver will be trapped into the slag. The excessive addition of fluxes is not a good choice due to melting of the charge and the lead metal formations are under different phases. This situation creates losses of gold and silver. The temperature must increase its value in the proper way. It means if the final is reached very fats, the reactions are not complete and lead metal is formed to fast without having enough time to collect precious metals. In order to assure the right order of reactions, the sample and the fluxes have to form a homogenous mass without segregations. The contact between ore particles and fluxes is very important.

During the melting process is expected to obtain several layers of different material due to reagents have different solubility and density. Under this consideration, at the top there is an alkali layer composed oxidized sulphides (sulphates). The following stratus is formed by heavy metal oxides and chemically is a borosilicate. This layer must not be thick or lumpy; otherwise some minerals will not be dissolved and melted. The balance of silica and borax is very important. Sometimes, there is a matte layer and is produced when the flux is inappropriate. This layer is composed by lead, zinc, iron and copper sulphides. Also, when the flux was selected wrongly, some compounds of arsenic and antimony with iron and copper are formed. This layer is called speiss. At the bottom is located the lead button with gold and silver.

Slag appearance is a good indicator of the process. Although iron minerals have influence on color slag, it is possible to draw some conclusions according to the color. For example, a blue color is symptom of copper minerals. The presence of manganese minerals is note for a lavender color slag. Green is synonymous of iron minerals and most of slags present this color. If the iron minerals are not a very important part in the sample, a yellow color indicates presence of lead and a white color is typical of silicates of calcium or magnesium.

This is an oxidizing process that must separate lead metal and precious metals. The lead button obtained is placed in cupels that absorb lead oxide. The process is based in the fact that lead can be oxidized at high temperatures and precious metals no. under this consideration, the separation is possible. The initial temperature is 860-880 oC and the final is at 900-920 oC. Cupels must be capable of resist high temperatures, absorb oxides, but no liquid metals. Typically, cupels are fabricated with magnesia, calcium sulphate, lime and clay, and a mixture between calcium sulphate and lime-clay.

The initial step is to preheat the cupel at 860 oC. Then the lead button is placed on the cupel and after 30-40 minutes the oxidation and absorption process is complete. During this process is necessary to check the temperature and the lead button condition. The final point is obtained at 900 oC. When the cupel is cooled, the surface condition around the Dore metal let us know if the smelting process was performed efficiently. For example, cracks mean an excess of antimony, residual slag is an indication that lack of cleaning, and stains are sign of impurities.

The initial step is to weight the Dore metal. Since silver is leached by nitric acid and gold no, the next step is to attack the Dore metal with a hot diluted solution of nitric acid. The acid dissolves the silver and leaves the gold that has to be rinsed, dry, and weight on a scale of high sensibility such as 0.001 mg. We need a capsule to perform the acid attack.

environmental economics - an overview | sciencedirect topics

environmental economics - an overview | sciencedirect topics

Environmental economics has carved out a niche within economics by pushing at the boundaries of anthropocentric economic utilitarianism, for example, by incorporating environmental values into the benefit cost accounts, and by extending market logic and market institutions as deeply as possible into the environmental domain.

Environmental economics is a kind of practical economics its practitioners are trying mostly, I think, to do good in the world or at least that part of the world they can hope to influence. They do not always agree on what might constitute good for more than 40 years, I have listened closely when my fellow environmental economists talk shop casually among themselves, and I have heard claims that our role is to ensure that environmental concerns are fully considered in the arguments and calculations that economists produce, and that it is to knock some economic commonsense into those greenies and any public agencies that might be influenced by them, with roughly equal frequency. Nor do environmental economists agree at a level of principle the century-old debates between those who think government can and should do more to address the issues that do not get much attention in unfettered markets, and those who are quite sure that markets are the best institutions conceivable for getting things right in an imperfect world, are played out yet again in everyday discourse among the environmental economists. Nevertheless, there is a body of beliefs and assumptions that commands majority allegiance among environmental economists, if by no means unanimous assent. For example, most of those who would prefer a more activist role for government in environmental regulation and most of those who would prefer a more hands-off stance agree in considerable detail about what is meant by benefits and costs, and many of them would offer similar reasons as to why policy should be attentive to benefits and costs.

While explicitly acknowledging the intellectual diversity among us, when I characterize the beliefs and assumptions of environmental economists in what follows, for example, to contrast them with those of environmental ethicists, I am referring, unless otherwise indicated, to this body of mainstream beliefs and assumptions.

Environmental, economic and social aspects of the sustainable development can be improved by recycling, depending upon the local circumstances. However, there are several technical aspects, which influence the extent to which the desirable practice of recycling water from plant practices is possible,. As the chemistry of the system is altered, it could affect the process efficiency. This applies specially to flotation, which (as explained in Chapter 3), is principally governed by the chemistry of the ore pulp.

The quality of the external water can range from very high quality, soft water derived from melting snow, or poor quality, hard water (with high levels of dissolved calcium and magnesium) from underground aquifers, and to even lower quality sea water (with very high concentrations of dissolved salts). Some underground water may be more saline than the ocean water. Occasionally, a different source of water is used in the wet and dry seasons. Sewage water from cities is becoming a potential external source with sustainability implications. If the initial quality of the external water is high, the scope for recycling of water from all the products is maximized. Such reuse of recycle water from the products allows chemical species from the oxidation of the ore and from other inputs to the process such as reagents to increase in concentration in the water returned to the plant Such accumulation of species often has negative effect on the performance of the process. There are, however, instances, where, depending upon the chemistry of the process, recycle water is found to have positive effect on the process.

The recycling of water from the various solid-liquid separations on the concentrate and tailing streams is called internal reuse. Reclamation of water from tailing pond areas, usually more distant from the concentrator, is called external reuse (Rao and Finch, 1989). The opportunities for recycling water from plant products (concentrate and tailing) are schematically shown in Figure 11.1.

Figure 11.1. Some opportunities for recycling water in a semi-arid region in Australia. Typical values for percent solid have been used. Note that the use of a thickened tailing disposal system or underground past fill may require an extra water removal step after the tailing thickener. It is assumed that 40 percent of the water reaching the tailing dam can be recycled, the remainder being lost by evaporation and retained within the tailing dam, with minor input of water to the tailing dam from annual rainfall. (Johnson, 2003).

The maximization of recycling of water is achieved when there is (I) maximum removal of water from each of the product streams; and (ii) return of water to the processing from all of the product streams.

A more complex example of the recycling of water for a concentrator could include inputs of water from an underground mine to the concentrator and/or to the tailings area. There could also be an output of water from the concentrator to the mine through the use of backfill or paste fill. (See Chapter 9 for discussion on backfill).

There are many methods by which the hazards risk management team can assess the mitigation options that it has generated for each identified hazard risk. One method, or framework, as it is often called, that has been developed by the US Federal Emergency Management Agency (FEMA) is the social, technical, administrative, political, legal, economic, environmental (STAPLEE) method.

Each of these terms represents an opportunity or constraint to implementing a mitigation option. Because communities are generally unique in their overall makeup, a single mitigation option analyzed according to the STAPLEE criteria may produce different outcomes among various places.

Each criterion considers a different aspect of the community and requires specific methods of information collection and analysis. There is no definable or identifiable priority or weight assigned to any of these criteria; the order of letters in the acronym was determined by the word they formed (which was meant to be easy to remember).

Social. A mitigation option will be viable only if it is socially accepted within the community where it is implemented. The public is instrumental in guiding decisions such as these through their support or lack of it. Even with public support, a proposed mitigation option might not work, but without public support, the action taken will almost certainly fail. Disaster risk managers must have a clear understanding of how the mitigation option will affect the population. They must investigate several questions that will guide their interpretation of this criterion:Will the proposed action adversely affect any one segment of the population? Will it give some disproportionate benefit to only one segment?Will the action disrupt established neighborhoods; break up legal, political, or electoral districts; or cause the relocation of lower-income people?Is the proposed action compatible with present and future community values?Will the actions adversely affect cultural values or resources?

Technical. If the proposed action is investigated and found not to be technically feasible, it is probably not a good option. In addition, when looking into the technical feasibility of each option, it is important to investigate whether it will help to reduce losses in the long term and whether it has secondary effects that could nullify its benefits. By addressing the following questions, the hazards risk management team can determine the suitability of their proposed actions based on the actual degree of help those actions will ultimately provide:How effective is the action in avoiding or reducing future losses? It is important that the measures taken are able to achieve the anticipated results, not a fraction of them.Will it create more problems than it fixes?Does it solve the problem or only a symptom?

Administrative. This measure investigates the communitys capabilities for carrying out the projects required to implement each mitigation option. Specifically, the disaster managers will look at each options requirements in terms of:StaffingFundingMaintenance

The community may be able to implement some options on their own using their own resources, whereas other options will require (often significant) outside assistance. The questions disaster managers must answer include:Does the jurisdiction have the capability (staff, technical experts, and/or funding) to implement the action, and can it be readily obtained?Can the community provide the necessary maintenance work required to maintain the method of mitigation?Can the implementation project be accomplished in a timely manner, without excessive disruption to the community?

Political. Mitigation actions tend to be highly political. Like most other government actions, they tend to entail spending local funds and using local services, require permits and permissions, involve some alteration to the fabric of the community, may involve some use of public lands, and involve a certain amount of risk for the political leaders who authorize the actions. The political nature of each option will likewise be an influential decision-making factor when options are being chosen for implementation. Disaster managers will need to be aware of or will need to investigate how local, regional, and national political leaders feel about issues related to agenda items such as the environment, economic development, safety, and emergency management. Logically, actions that go against the current administrations political ideology in any of these areas are likely to receive less support than those that are in line with its beliefs. It is common for proposed mitigation actions to fail because they lack this much-needed political support.

Disaster managers can measure political support for their mitigation options by addressing the following questions:Is there political support to implement and maintain this action?Have political leaders participated in the planning process so far?Is there a local champion willing to see the action to completion?Who are the stakeholders in this proposed action, and how do they feel about the changes that will occur as a result of the action?Is there enough public support toward which political leaders are likely to lean, to ensure the success of the action?Have all of the stakeholders been offered an opportunity to participate in the planning process?How can the mitigation objectives be accomplished at the lowest cost to the public?

Legal. Many mitigation options require actions to be taken that need legal authority to be lawfully conducted. Disaster managers must determine whether they will be able to establish the legal authority at the national, provincial, state, or local levels to implement the proposed mitigation actions. It may even be necessary to propose the passage of new laws or regulations to accommodate the needs of the mitigation measure if such legal authority is weak or nonexistent. However, this legal authority is best established long before the mitigation action is taken because of the exhaustive process of making or changing laws.

Depending on the country where the mitigation actions are being conducted, government entities at each structural level may operate under their own specific source of delegated authority. Local governments may operate under enabling legislation that gives them the power to engage in certain activities, or under informal governance systems based on tribal or other forms of law.

Disaster managers need to identify the unit of government that ultimately has the authority to grant or deny the permission to undertake actions necessary to implement the mitigation action. They are well served to understand the interrelations among the various levels of government to anticipate political roadblocks or challenges that may arise. Much of this information can be obtained by asking:Does the government in question have the authority to grant permissions or permits for the work to be conducted?Is there a technical, scientific, or legal basis for the mitigation action (i.e., does the mitigation action fit the hazard setting)?Are the proper laws, ordinances, and resolutions in place to implement the action?Are there potential legal consequences?Will there be issues of liability for the actions or support of actions, or lack of action, by any of the mitigation stakeholders?Is the action likely to be challenged by stakeholders who may be negatively affected?

Economic. Like all community projects, mitigation options must prove to be cost-effective to the community before they are considered viable for implementation. The mitigation measures must also be affordable to those who will be funding the project. Mitigation projects often require maintenance, at the expense of the community where it is implemented, long after the project is completed. For this reason, affordability means many things, including being able to be funded without restructuring local budgets, able to be financed but with some budget restructuring required, able to be funded but requiring a special tax to be imposed, able to be financed but requiring external loans, and so on.

Mitigation measures that are cost-free to the community or that can be financed within a current budget cycle are much more attractive to government officials who are making funding decisions than are options that require general obligation bonds or other forms of debt that ultimately draw on future community funds.

Communities that have little money to support mitigation actions (a common condition) are likely to be more willing to support a mitigation option if it can be funded, in part or in whole, by some alternative (outside) source or sources. Disaster managers should ask the following questions when considering the economic aspects of mitigation options:Are there currently sources of funds that can be used to implement the action?What benefits will the action provide?Does the cost seem reasonable for the size of the problem and likely benefits?What financial burden will be placed on the tax base or local economy to implement or maintain this action?Will the result of the action negatively affect the economy in some secondary manner, such as reducing some form of income generation that was dependent on the existence of the hazard?Does the action contribute to other community economic goals, such as capital improvements or economic development?

Environmental. Many mitigation measures affect the natural environment, positively or negatively, and occasionally both positively and negatively to some degree. Disaster managers must consider these effects, because their actions could have long-term effects on the community and could negate any positive gains of the mitigation action.

Benefits to the environment often arise from implementing a mitigation measure, which must be considered when choosing options. Floodplain buyout programs, for instance, which include acquisition and relocation of structures out of identified floodplains, help to restore the natural function of the floodplain. Vegetation management, which is often performed to control the wildfire hazard risk to humans and property, also provides the same protection to the environment.

Questions that disaster managers should ask when considering the environmental factors associated with particular mitigation options include:How will this action affect the environment (including land, water, and air resources and endangered species)?Will this action comply with environmental laws and regulations?Is the action consistent with the communitys environmental values and goals?

International economic, environmental, and technological advances over the past decade have contributed toward the consideration of CBM recovery and CO2 sequestration together. The idea is to geologically sequester CO2, while at the same time recovering the methane already in them. The CO2 would be injected via wells drilled into the coal, and the CO2 would drive the methane out of the coal through the wells to the surface, where it would be collected. This two-birds-with-one-stone idea is feasible because bituminous coal stores twice the volume of CO2 than it stores methane. The net result would be less CO2 in the atmosphere, no significant new methane added to the atmosphere, and enhanced recovery of methane to help pay for the process.

What about the logistics and cost of this CBM/CO2 strategy? Most US power plants are within 35miles of a coalbed (not necessarily a suitable one). For a plant near a gassy coalbed (or multiple beds, for coal often occurs in multiple seams), pipeline length would be minimal to convey CO2 from the plant into the coal, and to pipe recovered methane back to the power plant.

The environmental impacts and economic feasibility are often evaluated across different scenarios for comparison. For example, Clare et al. (2015) compared the economic and carbon abatement potential of straw pyrolysis for biochar and electrical energy production with two design scenarios (straw briquetting and combustion for heat generation and straw gasification for electrical energy production) and two baseline scenarios (straw reincorporation into the soil and straw burning on the field). Harsono et al. (2013) compared the energy balances, GHG emissions, and economics of biochar production from the slow pyrolysis of empty fruit brunches in a palm oil mill with that of a baseline case where empty fruit brunches were applied to the trees in the palm oil plantation. Homagain et al. (2016) compared the economics of four scenarios of biochar-based bioenergy production and soil application in terms of high or low feedstock availabilities and with or without soil application. The scenario setting also echoes the reference scenario selection during LCA that may significantly affect the resulting carbon abatement potential. Shabangu et al. (2014) compared the economic feasibility of pine to biochar and methanol based on three technological scenarios, that is, slow pyrolysis at 300 and 450C, and gasification at 800C, with the same processing of the volatiles into syngas and the conversion of the syngas into methanol. Baseline scenarios could be selected based on the existing biomass utilization practice together with multiple design scenarios for system optimization and selection. The LCA and CBA results could vary significantly across different scenarios.

Although environmental economics focuses strongly on the problems of achieving economic efficiency and maximizing social welfare, reliance on both market-oriented economic institutions and democratic political institutions is based on an approach that emphasizes the protection of fundamental rights and freedoms as the basic moral foundation of society. Libertarians, for example, stress the sanctity of property rights that were acquired justly in accordance with the requirements of the law and respect for the rights of others. Egalitarian liberals, in contrast, emphasize the concept of equality of opportunity, though they agree with libertarians that public policies should be structured to support people's freedom that is, their ability to define and pursue their own conception of the good life. These theories treat rights as fundamental and do not see maximizing social welfare as a well-defined, ex ante policy objective. Liberal theories, however, do see a role for democratic governments to promote a conception of the public interest that is legitimated through (and limited by) the consent of the governed.

On the one hand, a perceived right to pursue individual self-interest in markets might be construed as conferring a right to release carbon dioxide and other pollutants into the atmosphere without constraint by government. Clearly, this value judgment plays a role in political debates over climate change policy.

On the other hand, democratic societies are grounded on the principle that individuals' positive freedom to pursue self-interest is limited by other people's negative freedom to be protected against uncompensated harms, including bodily harms and damage to private property. In English and American law, it is well established that economic actors have no right to undertake actions that inflict a risk of serious harms that jeopardize other people's lives, health, and livelihoods. Such actions are regulated by both torts law and by environmental statutes such as the Clean Air Act and the Clean Water Act. Moreover, these statutes are premised on a principle known as the public-trust doctrine, which holds that certain types of environmental resources are the joint property of each member of society. Rights to enjoy the benefits of public trust resources are usufructuary in nature the utilization of such resources comes with an obligation to insure that similar benefits are available for the enjoyment of others and that the integrity of the resource base is conserved from each generation to the next.

What are the implications of rights-based ethics for climate change policy? As noted above, the United Nations Framework Convention on Climate Change calls for stabilizing greenhouse gas concentrations to avoid dangerous anthropogenic interference with the Earth's climate. The achievement of this goal is believed to be consistent with the short-run utilization of fossil fuels and other sources of greenhouse gas emissions as a gradual transition is made from current to post-carbon energy technologies. In this sense, this criterion allows for some exercise of positive economic freedoms.

On the other hand, this language deems it illegitimate to allow greenhouse gases to accumulate in the atmosphere beyond the 2C temperature warming limit established by the Copenhagen Accord. This limit reflects decision-makers' judgment concerning the level of climate change that should be considered dangerous, taking into account both the projected benefits of climate stabilization and the uncertain but well-established risk that unmitigated climate change would inflict catastrophic ecological, social, and economic costs, thereby violating the right of future generations to freedom from uncompensated harms.

Critics have argued that this approach to climate policy is unsound because there is no bright line, technical definition of what constitutes danger or exactly how the rights of today's polluters and members of future generations are to be balanced except through subjective judgment. The approach seems to change the role of economists and other analysts from prescribing optimal policies to gauging the impacts of alternative policies on various stakeholder groups (including future generations) and on natural systems. Importantly, the emphasis on risk implies a need to employ techniques from decision science and statistics for characterizing the likelihood of low-probability, high-consequence events. In decision science, rational decisions are sometimes driven by a desire to advert the prospect of highly adverse outcomes even if they are unlikely to occur. This calls into question the common practice of studying climate change policies in deterministic optimization models that abstract away from uncertainty and that impose a priori value judgments through the choice of the objective function.

Critics also argue that taking aggressive steps to stabilize climate would be economically inefficient and might actually serve to reduce the welfare of future generations by adversely affecting the rate of economic growth. Here, it is important to note that the current generation of models suggests that climate stabilization would confer large expected net benefits on people living in the twenty-second century and beyond. Simply put, climate stability may be viewed as a productive form of natural capital that contributes positively to long-run human flourishing.

The efficiency question is less clear-cut. While deterministic models that employ high discount rates suggest that climate stabilization might be economically inefficient, stochastic models that assume a plausibly high degree of risk aversion suggest that the present-value net benefits of climate stabilization are positive if the analysis allows for a degree of uncertainty concerning climate dynamics and climate change damages that is consistent with the current state of the scientific literature.

The literature on environmental economics has derived various conditions for designing efficient policies. However, the policies implemented rarely satisfy those conditions. The deviation mainly results from politics. To better understand the formation of environmental policy and its welfare consequences, an analysis based on political economy is needed.

According to the public-choice theory, a government is not a unitary being; instead, it is regarded as a set of institutions through which individuals reach collective decisions. The process of policy formation contains several players, including voters, interest groups, bureaucrats, political parties, a judiciary, and so on. This article focuses on two of them: special-interest groups and voters. Such treatment definitely does not mean that other political agents are unimportant; it just reflects the fact that most of the related literature concentrates on these two facets of the political process. In addition, this article is confined to the theoretical literature and overlooks empirical studies.

This article introduces lobbying models in the section Special-Interest Groups. Among the various approaches dealing with lobbying, here the focus is on the common-agency (or menu-auction) approach. This approach, which has been widely applied to the determination of other public policies, is regarded as the most promising approach to a positive theory of environmental regulation.

Then the voting mechanism is discussed in the section Voting and Election. The central part of this section is the widely used median-voter theorem. Two types of democratic structures have been distinguished: direct democracy and representative democracy; each has its unique issues.

The coastal and marine natural resources of an LME are capital assetsin effect representing wealth embodied in its marine natural resources. Capital assets, natural or otherwise, can provide valuable services (interest) over time if maintained, much like savings in a bank provide a flow of interest income.

Underlying much of environmental economics is the notion of resource valuation (i.e., valuing nature's services). Resource valuation involves the use of concepts and methods to estimate the economic value the public holds for natural resource services.16 These services may be direct or indirect; and they may or may not be bought and sold in the marketplace.

Direct services include on site use of marine parks, beaches, commercial fishing, exploitation of marine minerals, or harvesting of fish, shellfish or wood from mangroves. Indirect services occur off site, for example, when fish produced by a mangrove are harvested many miles away. Some natural resources services are exchanged in organized markets, such as commercial fisheries, oil and other minerals, some coastal property, or tourism. However, a central feature of many, if not most, marine resource issues is that the services provided are not traded on markets. The services provided, as for example, by mangroves, corals, and sea grasses, water quality, recreation, scenic amenities and biodiversity are not bought and sold on markets and, as a result, often are given inadequate attention in public policy.

Four types of value are associated with resource services. First, use value is the benefit received from on site or physical use, such as harvesting of fish, exploitation of oil or beach use. Second, passive use value is the enjoyment one gets from a resource above and beyond any direct use.17 Passive use losses may arise if individuals feel worse off when they learn of the loss of an endangered species, closure of beaches or other adverse impact on other natural resources, even if they do not use these resources themselves. People might be willing to pay to prevent such losses, much as they might pay to preserve, say, an historically or culturally significant building or site, even if they never actually visit it. Third, total value is the sum of use and passive use value. Fourth, individuals also may think of a resource as having an option value when either supply (e.g., threat of extinction; the outcome of a policy) or demand is uncertain. Option value may be thought of as what would be paid to keep the opportunity open to later use a site or resource.

Resource valuation usually is not an end in itself, except in the case of commodities such as oil or other minerals, or of fish, where the government might lease public resources to private businesses.18 Instead, estimates of the value of particular resource services normally are more useful as contributions to policy for improving resource management. Most policy decisions involve specific proposals affecting resources and their services at the margin; hence, resource valuation most often will involve assessments of the marginal value of resource services rather than the aggregate value.

Social and cultural factors correspond to and reinforce the need for economic valuation, but their focus and the use of sociocultural analysis is also quite different. Indicators such as income, employment, and economic sector performance are elements of both types of investigation. However, sociocultural analysis takes a step away from strict enumeration of these elements and focuses on people's knowledge and views (norms and values) about their work, and how this affects their perceptions and actions towards LME resources (Brainerd et al. 1996). Although this is not easily measured on a monetary scale, these factors are considered significant by those involved in resource use. Sociocultural analysis has the capacity to contribute to management by considering the values of cultural and social elements of the community, and the potential costs associated with social and economic disruption and dislocation.

Social and cultural factors are closely linked to governance, users and uses of LME resources. One way to account for these linkages is to view human action within the context of Natural Resource Communities (NRCs) (Dyer et al. 1992). The interface between a regional system of extractive NRCs, their service flows and the associated LME is here defined as a Natural Resource Region (NRR).19 Dyer et al. (1992) define NRCs as populations whose sustainability depends upon the utilization of renewable natural resources. By broadening the definition to include those dependent on non-renewable aspects of the marine environment as well, they and their aggregations as NRRs represent the LME-dependent communities within a coastal region.

The Natural Resource Region (NRR) includes social, cultural, human, economic and biophysical capital and their interactions within networks of LME-dependent communities (Dyer and Poggie 1998). These forms of capital are defined as follows:

Social capital refers to the interactive networks of humans that occurs within and between natural resource communities. Social capital is key to the flow of other forms of capital, as well as central to the dynamics of governance and resource utilization.

Biophysical capital, as explained above, is used to denote those natural resources of an LME that directly or indirectly generate flows of goods and services used by humans. The value of these natural resources is derived from the dynamic between human action and the natural environment. These include potential resources, identified but not actively utilized in extractive processes, or those having primary value in passive recreational activities (e.g. the whale as resource to the whale watching industry).

Fishing is a good example of the interactions of some of these forms of capital. A fishing boat out at sea is a production-extraction unit of the NRR, relying directly on the productivity of the fish resources of the LME (the NRR biophysical asset). The fishing boat is thus an extension of the NRC from which it came, carrying with it social, cultural, human, and manufactured capital in its hunt for fish resources.

The conceptualization of capital interactions within an NRR network lends understanding to the occupational valuation placed on way of life. For example, Doeringer, Moss and Terkla (1986) show how kinship support systemsa form of social capital in our formulationallow fishermen to maintain labor linkages to the fishing industry in defiance of seemingly debilitating economic conditions, usually associated with declines in volume and value of fish catch, as well as severe management restrictions on fishing.

In the interface with LMEs, primary units of human-environment interactionindividuals, families, households or communitiesare to be viewed as interconnected within regional networks held together by shared values and forms of capital. The NRC is a nodal form of human organizational structures, regional and capital interactions, and provides for points of spatial reference by which to study the LME-NRR dynamic.

Networks of Natural Resource Communities within NRRs act as conduits through which total capital is exchanged, shared, and transformed by human action. For example, we can consider the NRC20 as a regional contributor to whatever commerce is stimulated by LME-related activities, and as a means of providing sustainable support to LME-related households and families as they contribute products and services to the region and nation in which they are embedded. While only a subset of the NRC interact directly with the marine environment and its resources (e.g. fishermen, shipping vessel operators), these individuals are nevertheless connected to more differentiated communities and towns, contributing to the economic and food security of those communities and towns and buffering coastal development in a way that contributes to social and economic diversity.

Social impact assessment variables point to measurable change in the human population, communities, and social relationships resulting from policy change (ICGP 1993). The Interorganizational Committee on Guidelines and Principles (1993) identified a list of social variables under the general headings of (1) population characteristics, (2) community and institutional structures, (3) political and social resources, (4) individual, household and family changes, and (5) community resources. Definitions of each heading considered by the Committee are given below.

Community and institutional structures mean the size, structure and level of organization of local government to include linkages to the larger political systems. The historical and present patterns of employment and industrial diversification. The size and level of activity of voluntary organizations and interest groups and finally, how these institutions relate to each other.

Political and social resources refer to the distribution of power and authority, the identification of interested and affected parties as well as the leadership capability and capacity within the community or region.

Individual, household and family changes refer to factors which influence the daily life of the individuals, households and families, including attitudes, perceptions, family and household characteristics and social networks. These changes range from attitudes toward the policy to an alteration in family and household relations and social networks to perceptions of risk, health and safety.

Community resources include patterns of natural resource and land use; the availability of housing and community services to include health, police and fire protection and sanitation facilities. Key to the continuity and survival of human communities are their historical and archaeological cultural resources. Under this collection of variables we also consider possible changes for indigenous, ethnic and religious sub-cultures.

Sociocultural elements may also be assessed by performance indicators related to equity issues such as the distribution of benefits among stakeholders, the nature of access to LME resources, and the reliance of communities on LME resources (Clay, per. com., 1998). The distribution of income is a measure of equity within natural resource communities and between communities and wider society. Benefits distribution can take other forms such as the pattern of fish consumption and distribution, and allocation of and/or access to resources. The nature of access to LME resources considers property rights as well as the local involvement in resource management. Community reliance on LME resources may take several forms including employment and other economic factors, food security and cultural factors. The relative importance of different social variables will vary depending on the specific community and its relationship to the resource in question.

Dyer and Griffith (1996) isolated five variables that help identify fishing community dependence on an LME. It will become obvious that the five variables overlap somewhat; thus, they must be considered together. These are:

Relative isolation or integration of LME resource users into alternative economic sectors. To what extent have users (e.g., fishermen, processors) segmented themselves from other parts of the local political economy or other fisheries?

User types and strategies of users within a port of access to LME resources. What impact does the mix of types (e.g., fixed fishing gearweirs, fish corralsversus mobile fishing gear) across ports and States have on the long-term sustainability of LME resource stocks?

Degree of regional specialization. To what extent have users from related areas and use-sectors moved into the region? Clearly, those users who would have difficulty moving into alternative use-sectors are more dependent on LME resources than those who have histories of moving among several sectors in an opportunistic fashion.

Percentage of population involved in LME resource-related industries. Those communities where between five and ten percent of the population are directly employed in LME resource-related industries are more dependent on the LME than those where fewer than five percent are so employed.

Competition and conflict within the port, between different components of use sectors. Competition between smaller scale and industrial scale users can create conflict between users within the same portas well as between different actors in a use-sector (such as boat owners, captains, and processors). Dependence may have a strong perceptual dimension, with users perceiving the resources they are extracting to be scarce and that one user group's gain (e.g. industrial trawling, purse seining) is another user group's loss (e.g. gill netting).

These five variables can be adapted and broadened to cover the full range of LME-related activities. A fundamental assumption of the NRR model is that there is some degree of reliance on the natural resources (i.e., biophysical capital) of an LME. In an LME-linked NRC, biophysical capital reliance manifests itself as learned social behaviors of LME-related activities. The combined social, cultural and economic interactions arise from the conditions that increase or decrease access to the LME and its biophysical capital. Furthermore, dependence on natural resources limits the occupational roles of community members, and can intensify cultural assimilation for those immigrating into an NRC.

Disruption of LMEs is occurring more frequently as NRRs are stressed by human factors that push resources beyond their ability to renew themselves and permanently degrade physical structures such as bottom topography. Such resource degradation patterns in an NRR can be found in conditions of severe poverty, overpopulation, the practice of destructive extraction techniques (e.g. blast fishing in Philippine reef systems), or the development of overcapacity in a fishery (e.g. the groundfish fisheries of New England, Dyer and Griffith 1996). In an idealized condition, an effective state of environmental awareness is generated among NRC residents and NRR networks that allows for sustainable utilization of biophysical capital in an LME. Less idealized conditionsmost real world ecosystems and their human actorsrequire some form of management appropriate to the political ecology and cultural and environmental history of the region in question. Thus, although a generic LME/NRR management framework for the Bay of Bengal and the Gulf of Maine may be conceptually similar, operationalizing the model cannot proceed without considering site-specific human-environmental dynamics.

The interdependence of economic, social, cultural and governance elements is readily apparent. They overlap, complement, and conflict with one another in different situations. Their relative importance and tradeoffs between different sociocultural and economic values will depend on the interplay of the community, LME resources, and larger society.

Economic instruments can be defined as mechanisms that force economic agents to internalize all or part of the social costs associated with environmentally harmful activities and that rely on market forces to promote efficiency. In doing so, they seek to impose additional costs on producers that harm the environment and reward those that improve environment outcomes, while utilizing market forces to improve the allocation of resources. (Some analysts include subsidies among economic instruments but as they are voluntary and economic agents are not forced to internalize the social costs they are more appropriately classified as voluntary instruments.)

This approach to environmental protection is usually associated with environmental economics, a school of economic thought that is a subdiscipline of neoclassical economics. According to environmental economists, environmental problems arise because of the existence of externalitiesimpacts involuntarily incurred by a person or persons without compensation or payment as a result of the actions of another. Because of the existence of externalities, markets are unable to guarantee the efficient allocation of resources. For example, if producers emit pollution into the atmosphere without paying for it, the price that consumers pay for the producers outputs will not reflect the full social cost of the transaction. As a result, there will be excessive output and consumption of the relevant good or service. If producers are forced to internalize the social costs associated with the air pollution, there would be a more efficient tradeoff between air pollution and output, leading to higher net social welfare.

The more recent trend in environmental economics has been to characterize environmental problems as being a product of the incomplete allocation of property rights. According to this approach, if a property right over the relevant environmental resource were appropriately defined and allocated to individuals, and there was perfect information and no transaction costs, the operation of market forces would lead to efficient outcomes. For example, if the atmosphere were owned by someone and producers had to pay to emit pollution, then negotiation between the owner and producers would ensure the most efficient allocation of atmospheric resources. On the basis of these theories, economic instruments either

place a restriction on the amount of pollution that can be emitted or resource that can be used and then allow pollution or resource entitlements to be traded among economic agents (called marketable permit or cap-and-trade schemes, e.g., tradable emission, water, catch and development rights schemes); or

seek to create well-defined, secure, and transferable property rights over environmental resources and allocate these to relevant individuals or groups (pure property rights approaches, e.g., land titles and fishing area rights).

Marketable permit schemes and pure property rights approaches are similar in that both rely on the creation and exchange of property rights to promote environmental and economic outcomes. But pure property rights approaches place no external restrictions on the use of the relevant resource and rely on market incentives to achieve the desired environmental outcome, while marketable permit schemes rely on a cap or limit on the use of the relevant resource to achieve the desired environmental outcome.

One of the major benefits associated with economic instruments is that by utilizing market forces they can encourage a more efficient allocation of resources. For example, when tradable emission quotas are used, the operation of market forces should ensure that the necessary emission reductions are achieved at least cost (i.e., the equimarginal principle should be satisfied). Further, economic instruments provide an incentive for producers to reduce pollution, which encourages innovation. Advocates of economic instruments also claim they are more flexible than regulatory instruments, although this is not always the case.

Although economic instruments can be more efficient than alternative policy mechanisms, they can suffer from a number of weaknesses. In relation to pollution fees, individual liability and pure property rights approaches, there can be a considerable amount of uncertainty associated with environmental outcomes. For example, producers may choose to absorb the increase in costs associated with a pollution fee, or demand may be unresponsive to price rises, meaning the level of pollution may not decline by the desired amount. Consequently, where policy-makers are faced with uncertainty regarding environmental risks and questions regarding irreversibility, alternative approaches can be preferable.

Like regulatory approaches, marketable permit schemes (or cap-and-trade approaches) can place an upper limit on the permissible amount of pollution or resource extraction. Hence, they can be useful in dealing with uncertainty and threshold effects. The advantage that marketable permit schemes offer is that having set a specified limit on pollution or resource extraction, they allow market forces to determine the allocation of pollution or extraction rights among producers. One of the most successful marketable pollution permit schemes has been the United States Environmental Protection Agencys Sulfur Dioxide Program, which is part of the broader Acid Rain Program. The cost of reducing emissions was substantially lower than predicted because producers had an incentive to find cheaper ways to do so.

Problems arise with marketable permit schemes when there is a lack of equivalence between the environment or pollution units that producers are expected to trade (i.e., the resource is not homogeneous). For example, tradable development permit schemes that place a limit on the amount of development in an area but allow developers to exchange development rights can lead to the rights moving toward the developments with the highest economic returns. However, they will not necessarily achieve biodiversity objectives as each parcel of land may contain different biodiversity values. Similar problems can arise with emission schemes that allow emission permits to be generated through the enhancement of sinks (i.e., there can be uncertainty about whether the enhancement of sinks will offset the additional emissions).

Transaction costs can also pose problems for economic instruments. Devising schemes that can be administered in a cost-effective manner can sometimes be difficult. Further, if there are excessive costs associated with the negotiation and exchange of marketable permits, the efficiency benefits may not materialize.

As with all environmental policy mechanisms, politics can impede the effective use of economic instruments. However, economic instruments can be especially vulnerable to political influences if it is necessary to constantly adjust the price signals provided through the scheme. For example, if a carbon tax is used to address climate change, it will be necessary to adjust the tax over time to account for unexpected events and new information. Special interest groups may impede this process, thereby undermining the efficacy of the tax.

There has been a tendency in the past for regulatory instruments and economic instruments to be presented as substitutes. In practice, these two types of instruments are generally used as complements and economic instruments always require a regulatory framework. Indeed, there is a growing recognition of the need for policy packages or policy mixes that use a range of instruments to achieve environmental protection objectives.

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