magnetic separation description

magnetic separation process - xinhai

magnetic separation process - xinhai

Magnetic separation places the leading position in iron ore separation. For weak magnetic and lean iron, Xinhai adopts gravity separation, magnetic separation, flotation, and roasting magnetic separation; used for strong magnetic iron ore, magnetic separation

It is used to low grade magnetite. Due to the strong magnetic and easy to grind, one stage grinding is adopted for magnetite with coarse particle distribution, conversely the multi stages grinding. At present the fine grinding technology promoted by Xinhai improves the concentrate grate from 61% to 67%

In two stages grinding, stages separation, single weak magnetic flow, fine grinding means adding fine screen regrinding process to separate fine minerals timely and reduce the over-grinding. It improves the capacity of ball mill and concentrate grade by 2%

A magnetite in Inner Mongolia, the main mental mineral was magnetite with disseminated structure and fine particle distribution. The iron content was about 12-16%. This plant adopted the grinding-weak magnetic process and obtained 65% concentrate grade and 90% recovery rate, but the operation cost is too high after a long time running. It authorized Xinhai to reform the process. Xinhai did not only keep the original indexes, but also reduce the operation costs. Indexes comparison as follow

Due to the low grade of the iron ore, the stages grinding and stages separation could reduce energy consumption. Cost saving is the key of developing the mine. The fine grinding process has guide significance for similar iron ore

Two-stage closed-circuit crushing and screening-two-stage closed-circuit grinding and classification-magnetic separation process of one-stage roughing and three-stage concentration concentrates and tailings filtering and dewatering.

Crushing and screening: the final product size was -12mm. Advanced and cost-effective equipment was adopted;crushing and screening processes shared the plant for convenience; the crushing product was fine so that crushing and grinding costs were cut.

Grinding and classification: the first- and second-grinding fineness was -200 mesh (67%) and -325 mesh (88.47%) respectively. Bearing-drive energy-saving ball mill was adopted so that grinding costs were significantly reduced. Upgraded spiral classifier and fine screen were adopted in the first- and second-stage classification respectively to control the particle size strictly.

Concentrates and tailings transportation: iron concentrates were dehydrated in the permanent magnetic filter and then transported by belt conveyor to the iron concentrates powder dump, and tailings flowed by gravity to the ditch outside the plant.

The project adopted advanced, sound and energy-saving equipment and simple auxiliary facilities to cut construction costs and increase output. There was no environmental pollution, meaning that no waste water was discharged.

Iron concentrates dewatering: iron concentrates were pumped to the permanent magnetic filter and dehydrated together with already produced concentrates; filtrate returned to the system for recycling and filter cake was transported by belt conveyor at three times to the dump.

While increasing the efficiency of resources exploration, Xinhai paid attention to environmental protection. Effective solutions were adopted to address the spread of dust and noise and the disposal of waste water and tailings so that green development of the mine was ensured.

magnetic separation - an overview | sciencedirect topics

magnetic separation - an overview | sciencedirect topics

Magnetic separations take advantages of natural magnetic properties between minerals in feed. The separation is between economic ore constituents, noneconomic contaminants and gangue. Magnetite and ilmenite can be separated from its nonmagnetic RFM of host rock as valuable product or as contaminants. The technique is widely used in beneficiation of beach sand. All minerals will have one of the three magnetic properties. It is ferromagnetic (magnetite, pyrrhotite etc.), paramagnetic (monazite, ilmenite, rutile, chromite, wolframite, hematite, etc.) or diamagnetic (plagioclase, calcite, zircon and apatite etc.). Commercial magnetic separation units follow continuous separation process on a moving stream of dry or wet particles passing through low or high magnetic field. The various magnetic separators are drum, cross-belt, roll, high-gradient magnetic separation (HGMS), high-intensity magnetic separation (HIMS) and low-intensity magnetic separation (LIMS) types.

Drum separator consists of a nonmagnetic drum fitted with three to six permanent magnets. It is composed of ceramic or rare earth magnetic alloys in the inner periphery (Fig. 12.34). The drum rotates at uniform motion over a moving stream of preferably wet feed. The ferromagnetic and paramagnetic minerals are picked up by the rotating magnets and pinned to the outer surface of the drum. As the drum moves up the concentrate is compressed, dewatered and discharged leaving the gangue in the tailing compartment. The drum rotation can be clockwise or counterclockwise and the collection of concentrate is designed accordingly. Drum separator produces extremely clean magnetic concentrate.

Cross-belt separator consists of a magnet fixed over the moving belt carrying magnetic feed (Fig. 12.35). The magnet lifts the magnetic minerals and puts across the field leaving the gangue to tailing. The system is widely used in mineral beach sand industry for separation of ilmenite and rutile. However, it is replaced by rare earth role magnetic and rare earth drum magnetic separators.

Carrier magnetic separation has been proposed for more effective separation of water and solids from acid mine water to generate very pure water (Feng et al., 2000). As discussed in Chapter 10, dissolved heavy metals like zinc and copper can be recovered from acid mine drainage (AMD) by selective precipitation controlling the pH for the precipitation of specific metals. Following this recovery step, the remaining solution is treated with lime to a pH ~12 to precipitate the residual metal ions. The water thus produced is satisfactory for recycling in mineral processing, but not of the quality for domestic use as it still contains some heavy metal ions. That is because, some of the metal hydroxides are amphoteric and their hydroxides re-dissolve at very high pH. For example, the concentration of lead ion increases from nearly zero at pH 9 to 0,12mg/L at pH 12 as the precipitated lead hydroxide dissolves producing plumbate:

Magnetic filtration has been applied in place of lime treatment by Feng and coworkers (2000). Ultrafine magnetic particles are used as magnetic seeds. At a dosage of 0.5 g/L magnetite, all fine precipitate flocs can be rendered strongly magnetic. The mine water is treated with hydrogen peroxide (to oxidize ferrous iron and manganese), followed by the addition of lime and magnetite to raise the pH to 5, Sodium sulfide and more lime are then added to raise the pH to 8. The heavy metal sulfide precipitates are filtered magnetically using a high gradient magnetic separator with a permanent magnetic assembly. This produces an effluent with heavy metal ion (Cu, Zn, Pb, Cd, Cr, Mn, Ti,) well below the discharge limits. The effluent thus freed from heavy metals is then passed to an ion exchange step, where the calcium ion is removed by a cationic resin and sulfate ions by an anion exchange resin. In the elution step, the cation resin is treated with sulfuric acid and the anion resin is treated with sodium hydroxide and lime. High quality gypsum (calcium sulfate) is produced by both elutions. This is a useful byproduct, which helps to offset the cost of the process for the effective removal of toxic metal ions.

A similar process to separate various metal ions in acid mine water by magnetic seeds has been described by Choung and coworkers (2000). In their laboratory study the metal ions are precipitated as hydroxides and magnetite is added as a magnetic seed. The metal hydroxide precipitates are thought to be locked by the magnetic seed, which is then separated by a hand magnet.

The technique has so far been demonstrated only on a laboratory scale. While it may have considerable potential in removing toxic metals from relatively dilute streams of acid mine water, it has not been applied on a pilot plant scale. Economic factors, in particular, the quantity of magnetite required for large scale treatment is an important factor to be considered.

Lyman and Palmer (1993b) studied the roasting(magnetic separation or selective leaching process). The roasting here aimed at oxidizing neodymium while leaving iron as metallic form at a controlled H2water vapor mixture on the basis of the thermodynamic consideration showing a common stability region of Nd2O3 and Fe. Although selective roasting was successful, the subsequent process such as magnetic separation and acid leaching were not because of the extremely fine grain size of the oxidized scrap. Thus, they discontinued the study in this direction and changed the strategy to total dissolution process as has been described previously.

When large quantities of ferrous scrap are to be separated from other materials magnetic separation is the obvious choice. The two types of magnets are permanent magnets and electromagnets. The latter can be turned on and off to pick-up and drop items. Magnetic separators can be of the belt type or drum type. In the drum a permanent magnet is often located inside a rotating shell. Material passes under the drum on a belt. A belt separator is similar except that the magnet is located between pulleys around which a continuous belt travels. Magnetic separation has some limitations. It cannot separate iron and steel from nickel and magnetic stainless steels. Also, composite parts containing iron will be collected which could contaminate the melt. Hand sorting may be used in conjunction with magnetic separation to avoid these occurrences. (See Chapter 3 for discussion of magnetic separation techniques).

Nickel is mainly extracted from its sulfide ores which are concentrated by magnetic separation and a froth flotation process. After concentration by these processes the concentrated ore is mixed with silica and subjected to a number of roasting and smelting operations. During these operations the iron and sulfide contents are reduced by their conversion first into oxide and then to silicate, which is then removed as slag. The resulting matte of Ni3S2 and Cu2S is allowed to cool for few days, when Ni3S2, Cu2S, and nickel/copper metal form distinct phases which can be separated mechanically. The metal is obtained from the matte electrolytically by casting it directly as an anode with a pure nickel sheet as a cathode and aqueous NiCl2, NiSO4 as an electrolyte. At a temperature of around 50C and at atmospheric pressure, the obtained nickel, which is impure, is then reacted with the residual carbon monoxide to produce the volatile nickel tetra carbonyl which gives back the pure metal and carbon monoxide at 230C.

Adsorption using magnetic adsorbents has emerged as an exigent water remediation technology particularly for wastewater treatment while eliminating filtration shortcomings of nonmagnetic adsorbents. Magnetic separation not only simplifies isolation but also opens the ground for easy washing followed by redispersion. Moreover, mechanisms controlling the adsorption process are also enhanced. Pyrolysis, coprecipitation, and calcination are the methods frequently used for preparation of good-quality and high yield of magnetic biochar (Thines et al., 2017).

Conventional heating and microwave-assisted heating have been used in laboratory scale to generate magnetic biochar adsorbents. Conventional pyrolysis has been successfully integrated in industrial production of magnetic biochars using modified furnace. Cottonwood, pinewood, date pits, pine needles, hydrochar waste, orange peels, and pine bark underwent conventional pyrolysis after being treated with magnetic precursors like FeCl36H2O, Co(NO3)26H2O, natural hematite, Fe(NO3)39H2O, etc., to create magnetic biochars (Yang et al., 2016; Zhu et al., 2014; Zahoor and Ali Khan, 2014; Harikishore Kumar Reddy and Lee, 2014; Wang et al., 2015c; Zhang et al., 2013a,d; Theydan and Ahmed, 2012; Chen et al., 2011a; Liu et al., 2010). All these magnetic biochars used for adsorption of phosphate, arsenate, methylene blue, aflatoxin B1, triclosan, Cd2+, Pb2+, and metallic Hg showed improved performance in magnetic response and adsorptive removal from aqueous phase due to incorporation of the more active sites required for adsorption and enhanced physical properties. This can be attributed to uniform and dispersive reinforcement of -Fe2O3, Fe3O4, and CoFe2O4 forming strong mechanical bonds with biochar matrix. The oxide particles embedded showed particle size within 20nm to 1m with variable shapes such as cubic or octahedral. However, reduction in surface area (Wang et al., 2015c; Zahoor and Ali Khan, 2014; Chen et al., 2011a) and lowered adsorption capacity upon reinforcement of magnetic oxide (Khan et al., 2015) did not appear significant indicating minimum hindrance in adsorptive removal of pollutants by these composites.

Microwave-assisted pyrolysis has also found its way in the production of magnetic biochars from bamboo and empty fruit branch used for the remediation of Cr(VI), Cd2+, methylene blue, and Pb2+ from aqueous phase (Ruthiraan et al., 2015; Mubarak et al., 2014; Zhang et al., 2013d; Wang et al., 2013, 2012, 2011). These magnetic biochars containing hydrous Fe2O3, cobalt oxide, binary CoFe oxide, and metallic Ni crystals adsorbed these contaminants through electrostatic attraction, ion exchange, inner sphere surface complexation, and physisorption. Superparamagnetic cotton fabric biochars were obtained following both conventional pyrolysis and microwave-assisted pyrolysis by ZHu et al. (2014) in order to compare their properties. The authors found that microwave-heated biochar showed no apparent agglomeration and was characterized by more controlled size and dispersion of oxide particles. Modification of magnetic biochar to further improve its functionality has also been reported. For example, chitosan modification of magnetic biochar obtained from invasive species Eichhornia crassipes provided more oxygenated functional groups for greater electrostatic interaction and therefore enhanced Cr(VI) remediation (Zhang et al., 2015a).

Coprecipitation is another process by which magnetic biochar can be fabricated. Yu et al. (2013) employed sugarcane bagasse as the raw material for the production of magnetic-modified sugarcane bagasse through the chemical precipitation of Fe2+ and Fe3+ over the sugarcane bagasse particles in an ammonia solution under ultrasound irradiation at 60C. A large amount of carboxyl groups found on the surface of biochar, which made the surface more negatively charged. Thats why better adsorption was found for the removal of Pb2+ and Cd+ due to the ion-exchange mechanism (Yu et al., 2013). A comparison of two synthesis methods including chemical coprecipitation of iron oxides onto biochar after pyrolysis and chemical coprecipitation of iron oxides onto biomass before pyrolysis for preparing magnetic biochars was studied by Baig et al. (2014). The results suggested that the chemical coprecipitation of iron oxides before pyrolysis led to greater Fe3O4 loading, higher saturation magnetization, improved thermal stability, and superior As(III, V) adsorption efficiency of the biochars (Baig et al., 2014).

Magnetization in biochar can also be introduced via calcination in which biochar is subjected to heat treatment to remove water and drive off CO2, SO2, and other volatile constituents. The simplicity of this process was the main reason behind the wide application of this process in the production of magnetic biochar composites. For instance, calcination of rice hull and ferric acetylacetonate in tube furnace generates magnetic biochar consisting of good dispersion of Fe3O4 particles on the surface. The biochar showed improved lead removal performance through hydroxide precipitation followed by suitable magnetic separation.

Magnetic mineral separation techniques are invariably selective, and not fully representative of the grain size and composition of magnetic minerals present in the sample; however, magnetic separation may be necessary for SEM/TEM, X-ray, Mossbauer, or chemical analyses. The importance of fine SD grains as remanence carriers emphasizes the necessity of making the separation technique as sensitive as possible to the fine grains. As grain shape has become an important criterion for distinguishing detrital and biogenic magnetite, separation procedures to prepare representative extracts for SEM and TEM observation have become more important. A recommended procedure which has been successful for extracting magnetite (including the SD fraction) is as follows: (i) Crush the sample (if necessary) in a jaw crusher with ceramic jaws, (ii) Use a mortar and pestle to produce a powder. (iii) Dissolve carbonate with 1N acetic acid buffered with sodium acetate to a pH of 5, changing the reagent every day until reaction ceases (several weeks), (iv) Rinse the residue with distilled water, (v) Agitate the residue ultrasonically in a 4% solution of sodium hexametaphosphate to disperse the clays. (vi) Extract the magnetic fraction using a high-gradient magnetic separation technique (Schulze and Dixon, 1979), or alternatively, pass the solution (several times, if necessary) slowly past a small rare earth magnet.

Seed receipt and preparation: Following receipt, the seeds are sent for mechanical preparation. This consists of mechanical screening and magnetic separation to remove any impurities which may be present. Following separation are the processes of crushing, flaking, and cooking.

Oil Extraction: The prepared seeds are mixed with hexane in a continuous counter current system to produce a hexane-oil mixture (miscella) and seed cake. The seed cake is separated from the miscella, dried cooled, pressed, and used to produce animal feed. The hexane is recovered from the miscella under vacuum (using direct and indirect steam) and reused in the system. The remaining crude oil is then cooled and sent for refining.

Oil refining packaging: Crude oil and ghee are processed using the following steps:Degumming (for sunflower seeds or soybean) and neutralization gums are removed in a batch process, using phosphoric acid. Neutralization is done by adding caustic soda to remove free fatty acids from crude oil to produce semi-refined oil.Bleaching color is removed from the oil using fuller's earth followed by filtration.Deodorization unpleasant odours are removed from oil by high temperature vacuum distillation.Packaging the reined, bleached, and deodorized (RBD) oil is bottled in automatic filling lines.

Degumming (for sunflower seeds or soybean) and neutralization gums are removed in a batch process, using phosphoric acid. Neutralization is done by adding caustic soda to remove free fatty acids from crude oil to produce semi-refined oil.

Soap and glycerin production: Fats are saponified in a batch process, by mixing with caustic soda and heating with direct and indirect steam. After saponification, soap is separated from the lye solution to be dried, blended with additives, homogenized, cut, and pecked. Glycerin is separated from the lye solution and distilled.

The two main sources of energy are mazot and electricity. Mazot and solar are used in the boilers to generate steam. Average annual consumption 15,000 tons of mazot and 600 tons of solar. Annual electricity consumption is around 10.5 million kWh.

The factory consumes an average of 16,800 m3/day of water of which 1,800 m3/ day is process water, and 1,500 m3/day cooling and vacuum water. This water is taken entirely from group water boreholes within factory premises. Approximately 35 m3 of drinking water is taken from the public network every day.

The factory generates about 16,000 m3/day of industrial wastewater from different factory steams, including process effluents, boiler blow down, cooling water, vacuum water, and steam condensate. The wastewater is discharged to Akhnawy drain near the factory.

Iron-containing residues generated in steel plants contain several toxic elements and require further processing In an integrated process described by Eetu-Pekka and coworkers (2005) the residues go through a magnetic separation step. In the second stage they are agglomerated, before the reduction of iron oxides. The element, which is most problematic is sulfur. Some of it is transferred in to the gas phase during reduction as hydrogen sulfide and carbonyl sulfide (COS). There would still be a large amount of sulfur in the residue after the reduction phase. One way to decrease the amount of sulfur is to separate the residues with high sulfur content before the processing and leave them outside of recycling. Other possible methods suggested are to enhance the transfer of sulfur into the slag phase by controlling the slag composition or by ensuring the carbon saturation of iron. The slag composition can be controlled to enhance the transfer of sulfur by addition of lime to the residue material. Excessive lime should be avoided to prevent precipitation of solid phases like dicalcium silicate. Sulfur content of iron can be lowered by increasing the carbon and silicon content in metal, by adding carbon into the residue material. Optimum quantity depends upon the original composition of the residue material. The process is schematically shown in Figure 8.25

MWI-bottom ash is the solid residue from combustion of municipal waste or in a Municipal Waste Incineration Furnace. Often MWI-bottom ashes have been subjected to a post treatment consisting of magnetic separation of iron and sieving and comminution of particles > 40 mm. Fly ashes from Municipal Waste Incineration are kept separate from the MWI-bottom ash. In the Dutch situation it is forbidden to prepare mixed ashes from fly ash and bottom ashes. In 1996 800,000 tons of MWI-bottom ash were produced in the Netherlands. The last years MWI-bottom ash is utilized for 100%, primarily in granular form as embankment material up to a hight of 10 m or more or as a road base material.

MWI-bottom ashes are supplied to the market with a certificate for its technical and environmental behaviour. The environmental part of this certificate is based on old legislation. MWI-bottom ashes up to now always comply with the demands for environmental certification.

The Building Materials Decree enforces more severe demands than the present regulations. Because of that a large part of the MWI-bottom ashes does not comply with the demands from the Building Materials Decree. To safeguard its outlet to the market the Dutch Ministry of the Environment has developed a Special Category for MWI-bottom ashes. In this category MWI-bottom ashes can be utilized under a set of isolation measures. With the Municipal Waste Incineration sector the appointment has been made to pursue steady quality improvement of its byproducts so that MWI-bottom ashes can be utilized as Category 2 Building Materials in future.

magnetic separation, magnetic separation process, magnetic separator machine - xinhai

magnetic separation, magnetic separation process, magnetic separator machine - xinhai

Xinhai mineral processing equipment mainly include: grinding equipment, flotation equipment, dewatering equipment, magnetic separation equipment, and so on. Some of the equipment is Xinhai independent research and development, and has been awarded national patent. View details

Gold CIP Production Line adsorbs gold from cyaniding pulp by active carbon including 7 steps: leaching pulp preparation, cyaniding leaching, carbon adsorption, gold loaded carbon desorption, pregnant solution electrodeposit, carbon acid regeneration, leaching pulp. View details

Magnetic separation places the leading position in iron ore separation. For weak magnetic and lean iron, Xinhai adopts gravity separation, magnetic separation, flotation, and roasting magnetic separation; used for strong magnetic iron ore, magnetic separation.

It is used to low grade magnetite. Due to the strong magnetic and easy to grind, one stage grinding is adopted for magnetite with coarse particle distribution, conversely the multi stages grinding. At present the fine grinding technology promoted by Xinhai improves the concentrate grate from 61% to 67%.

In two stages grinding, stages separation, single weak magnetic flow, fine grinding means adding fine screen regrinding process to separate fine minerals timely and reduce the over-grinding. It improves the capacity of ball mill and concentrate grade by 2%.

A magnetite in Inner Mongolia, the main mental mineral was magnetite with disseminated structure and fine particle distribution. The iron content was about 12-16%. This plant adopted the grinding-weak magnetic process and obtained 65% concentrate grade and 90% recovery rate, but the operation cost is too high after a long time running. It authorized Xinhai to reform the process. Xinhai did not only keep the original indexes, but also reduce the operation costs. Indexes comparison as follow

Due to the low grade of the iron ore, the stages grinding and stages separation could reduce energy consumption. Cost saving is the key of developing the mine. The fine grinding process has guide significance for similar iron ore

Two-stage closed-circuit crushing and screening-two-stage closed-circuit grinding and classification-magnetic separation process of one-stage roughing and three-stage concentration concentrates and tailings filtering and dewatering.

Crushing and screening: the final product size was -12mm. Advanced and cost-effective equipment was adopted;crushing and screening processes shared the plant for convenience; the crushing product was fine so that crushing and grinding costs were cut.

Grinding and classification: the first- and second-grinding fineness was -200 mesh (67%) and -325 mesh (88.47%) respectively. Bearing-drive energy-saving ball mill was adopted so that grinding costs were significantly reduced. Upgraded spiral classifier and fine screen were adopted in the first- and second-stage classification respectively to control the particle size strictly.

Concentrates and tailings transportation: iron concentrates were dehydrated in the permanent magnetic filter and then transported by belt conveyor to the iron concentrates powder dump, and tailings flowed by gravity to the ditch outside the plant.

The project adopted advanced, sound and energy-saving equipment and simple auxiliary facilities to cut construction costs and increase output. There was no environmental pollution, meaning that no waste water was discharged.

Iron concentrates dewatering: iron concentrates were pumped to the permanent magnetic filter and dehydrated together with already produced concentrates; filtrate returned to the system for recycling and filter cake was transported by belt conveyor at three times to the dump.

While increasing the efficiency of resources exploration, Xinhai paid attention to environmental protection. Effective solutions were adopted to address the spread of dust and noise and the disposal of waste water and tailings so that green development of the mine was ensured.

magnetic separation in the mining industry - mainland machinery

magnetic separation in the mining industry - mainland machinery

One of the greatest challenges facing the mining industry is the separation of unwanted material generated by the extraction process from the valuable material. Mining, whether done through open seam or underground means, creates a huge amount of waste product in the form of worthless or low value minerals and unusable man-made materials. These materials can be extremely difficult to separate from the valuable materials miners are after. Perhaps the most efficient way of separating these materials is through magnetic separation.

Magnetic separation machines consist of a vibratory feeding mechanism, an upper and lower belt and a magnet. The bulk material is fed through the vibrating mechanism onto the lower belt. At this point, the magnet pulls any material susceptible to magnetic attraction onto the upper belt, effectively separating the unwanted metals from the rest of the bulk.

Magnetic separation has been used in the mining industry for more than 100 years, beginning with John Wetherills Wetherill Magnetic Separator, which was used in England in the late nineteenth century.

Magnetic separation is most commonly used in the mining industry to separate tramp ore, or unwanted waste metals, from the rest of the bulk material. Tramp ore typically consists of the man-made byproducts created by the mining process itself, such as wires from explosive charges, nuts and bolts, nails, broken pieces from hand tools such as jack hammers and drills or tips off of heavy duty extraction buckets.

Magnetic separation machines are usually placed at the beginning of a mines materials processing line to remove tramp ore before it can cause harm to downstream equipment such as ore crushers and conveyor belts, which can be easily damaged by metal shards or other sharp objects.

The type of magnetic separator used by a mine depends on what material they are extracting and how much tramp ore is generated by their process. As a result, separators of different magnetic flux, or power, can be used. There are 2 types of magnetic separators; electromagnetic and permanent.

Electromagnetic separators generate a magnetic field by switching power from alternating current to direct current. Electromagnetic separators are useful for removing large pieces of tramp ore from the bulk material. These separators are typically suspended over a conveyor belt and draw the unwanted material upward. Electromagnetic separators are easy to clean as removing the tramp ore that they separate from the bulk is as simple as turning off the power that creates their magnetic field.

Permanent magnets consist of materials that generate their own magnetic field. Though not as powerful as electromagnetic separators, permanent magnets are better at attracting strongly magnetized materials such as nickel, cobalt, iron and some rare earth metals. Some permanent magnets are now being made with rare earth metals that have the ability to attract even stainless steel, which is typically not susceptible to magnetic pull. In order to clean permanent magnets, a stainless steel scraper must be used to remove any metal parts from the magnets surface.

Magnetic separation definitely is one of the most important parts of this process. I think magnetic separators are often taken for granted when it comes to processing, whether that processing is in mining or in food processing. Many people dont even know the work that goes into making food safe or mining materials pure.

magnetic separation and characterization of vivianite from digested sewage sludge - sciencedirect

magnetic separation and characterization of vivianite from digested sewage sludge - sciencedirect

For the first time, vivianite was separated from sludge via a wet magnetic technique.The study focuses on the analysis of the extracted vivianite and recovered P.The product contains vivianite (5060%), organic matter (20%), quartz and siderite.Phosphorus was recovered and purified from vivianite through alkaline treatment.After purification, heavy metals are in line with P rock and future legislation.

To prevent eutrophication of surface water, phosphate needs to be removed from sewage. Iron (Fe) dosing is commonly used to achieve this goal either as the main strategy or in support of biological removal. Vivianite (Fe(II)3(PO4)2*8H2O) plays a crucial role in capturing the phosphate, and if enough iron is present in the sludge after anaerobic digestion, 7090% of total phosphorus (P) can be bound in vivianite. Based on its paramagnetism and inspired by technologies used in the mining industry, a magnetic separation procedure has been developed. Two digested sludges from sewage treatment plants using Chemical Phosphorus Removal were processed with a lab-scale Jones magnetic separator with an emphasis on the characterization of the recovered vivianite and the P-rich caustic solution. The recovered fractions were analyzed with various analytical techniques (e.g., ICP-OES, TG-DSC-MS, XRD and Mssbauer spectroscopy). The magnetic separation showed a concentration factor for phosphorus and iron of 23. The separated fractions consist of 5262% of vivianite, 20% of organic matter, less than 10% of quartz and a small quantity of siderite. More than 80% of the P in the recovered vivianite mixture can be released and thus recovered via an alkaline treatment while the resulting iron oxide has the potential to be reused. Moreover, the trace elements in the P-rich caustic solution meet the future legislation for recovered phosphorus salts and are comparable to the usual content in Phosphate rock. The efficiency of the magnetic separation and the advantages of its implementation in WWTP are also discussed in this paper.

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