phosphate rocks crushers

crushed rock phosphate

crushed rock phosphate

Rock Phosphate is a mined rock that contains limestone, silica and clay as well as high concentration of phosphorus. Being a natural compound, Organic Material Review Institute (OMRI), USA listed rock phosphate in organic farming, agriculture, gardening and food production. Rock phosphate is the cheapest source of phosphorus. Phosphorus is essential in building a biological soil and crucial for plants to develop healthy root systems, assimilate nutrients for good plant growth, hastens crop maturity, encourages earthworms and beneficial soil bacteria, and set flowers and fruits.

Rock Phosphate is a mined rock that contains limestone, silica and clay as well as high concentration of phosphorus. Being a natural compound, Organic Material Review Institute (OMRI), USA listed rock phosphate in organic farming, agriculture, gardening and food production. Rock phosphate is the cheapest source of phosphorus. Phosphorus is essential in building a biological soil and crucial for plants to develop healthy root systems, assimilate nutrients for good plant growth, hastens crop maturity, encourages earthworms and beneficial soil bacteria, and set flowers and fruits.

phosphate rock - an overview | sciencedirect topics

phosphate rock - an overview | sciencedirect topics

Phosphate rock used for fertilizer is a major NORM due to both uranium and thorium. Phosphate is a common chemical constituent of fertilizer. It is principally mined from apatite and phosphate rocks (phosphorite) in which the concentration of phosphate has been enhanced by sedimentary, igneous, weathering, and biological processes. Uranium can also be concentrated in these processes so that a high phosphate content generally coincides with high uranium content (50300ppm). Thorium is more likely to be present in igneous phosphorite. The radioactivity of these ores (due to uranium, thorium, and radium) can be as high as 10,000Bq/kg. Significant phosphate mining operations take place in many countries, with large outputs from the USA, Morocco, and China, the world total being 156 Mt in 2007 (Table 2.8).

Reproduced with permission from International Atomic Energy Agency, Extent of Environmental Contamination by Naturally Occurring Radioactive Material (NORM) and Technological Options for Mitigation, Technical Reports Series No. 419, IAEA, Vienna (2003).

Phosphoric acid is an intermediate step in almost all phosphate applications. Production requires first the beneficiation of the ore, followed by acid leaching and separation. In general, the beneficiation stage does not result in a reduction of NORM in the ore.

Treatment with sulfuric acid leads to the production of gypsum (phosphogypsum), which retains about 80% of Ra-226 and 30% of Th-232 and 14% of U-238. This means that uranium and thorium are enhanced to about 150% of the value of the beneficiated ore, making it a significant NORM. This gypsum can either be sold or disposed of. In the USA, the use of phosphogypsum with a radioactivity greater than 370Bq/kg is banned by the Environmental Protection Authority. Gypsum can either be disposed of in piles or discharged to rivers and the sea. Some leaching from the material is possible. Gypsum wastes can have radioactivity levels up to 1700Bq/kg. Scales from the sulfuric acid process are formed in the pipes and filtration systems of plants and need to be cleaned or replaced periodically. While much smaller in volume than gypsum, these wastes can be much more radioactiveeven over 1MBq/kg (Table 2.9).

Processing phosphate sometimes gives rise to measurable doses of radiation to people. Phosphate rocks containing up to 120ppm U have been used as a source of uranium as byproductsome 17,000tU in the USA and are likely to be so again.

European fertilizer manufacturing gave rise to discharges of phosphogypsum containing about 4TBq/year of Ra-226, Pb-210, and Po-210 into the North Sea and North Atlantic. This reduced to about half the amount in the 1990s and was overtaken as a source of radioactivity by offshore oil and gas production in Norwegian and UK waters, releasing over 10TBq/year of Ra-226, Ra-228, & Pb-210. This means that together they contribute 95% of the alpha-active discharges in those waters (two orders of magnitude more than the nuclear industry, and with this NORM having higher radiotoxicity).

Ground rock phosphate (90% passing through 100mesh sieve) is mixed with sulphuric acid (55 to 75%) in a specially designed mixer which discharges the product to a wide belt conveyor. The reaction is completed in the belt conveyor:

The reacted mass is then sent to a curing shed where the product is stored for 3 to 4weeks for curing and drying. The cured product is dried, milled and screened to obtain the product SSP. Where granulation is practiced, the cured SSP is granulated in the presence of steam. The manufacturing process is given in Figure712.

For 71% of the phosphate rock processing, a wet process, involving the production of phosphoric acid, is used for the acid digestion and in most cases large amounts of phosphogypsum are produced as a by-product.

During the wet production process, the contaminants are distributed between the different (by-)products depending on the type of acid (sulfuric acid, hydrochloric acid, or nitric acid) used for digestion. In the case of sulfuric acid digestion, which is frequently used for fertilizer production, one processing road leads via the production of phosphoric acid and phosphogypsum and the following reaction can occur (IAEA, 2013b):

As a non-renewable ore, phosphate rock is a very important strategic resource. However, in the process of the exploitation and utilization, there are severe waste and environmental pollution problems which are disadvantageous to the sustainable development of phosphorus resources. In order to promote the sustainable development of Chinas phosphorus resources industry, this research proposes a system dynamics model with two sub-models for thermal phosphoric acid and wet phosphoric acid separately, considering to the actual situation of regional phosphorus resources industry. This model focuses on industrial, financial, technological and environmental policies for the development of phosphorus resources industry, such as phosphorus resources exploitation, product structure adjustment, waste management and other policies. To find the optimum policy combination of sustainable development, the model which employs resource productivity, economic benefits, ecological efficiency and social satisfaction as objects, explores development situations of phosphorus resources industry and assesses the impacts of the policies by comparative policy scenarios. Results show that under the condition of excess capacity, optimization of phosphate fertilizer product portfolio is more advantageous compared with capacity expansion to increase production value of phosphorus chemical industry. And the combination of total consumption control policy of phosphate rock and acts to promote technical progress improves resource productivity. The implementation of waste recycling policies is conducive to improve continuously the eco-efficiency, and is not conducive to increase economic benefit due to more investment cost. Finally, this study indicates that an effective combination of total consumption control policy, product structure adjustment and appropriate environmental protection will be beneficial to the sustainable development of phosphorus resources industry. In addition, it contributes not only to the conservation of natural resources, but also to a reasonable disposition of the investment which can promote technological progress in industrial weak links. Moreover, the results can provide relevant references for policy makers to make appropriate decisions.

In the production of superphosphate fertilizer from phosphate rock, the rock is normally pulverized, mixed with sulfuric acid, and discharged into a den where the reaction between rock and acid proceeds. The fresh superphosphate is then removed from the den by an elevator and conveyed to storage for curing. Exhaust gases containing fluorine compounds are drawn from the mixing and den operations and, in some instances, from the elevator and other units.

Typical Florida pebble phosphate rock contains about 3.6% fluoride expressed as elemental fluorine, and approximately 32% of this is released during the acidulation process (Pettit, 1951). Almost all of the fluoride vapors are evolved in the mixer and den although a slight evolution of vapor occurs during subsequent handling and storage operations. The composition of mixer gases and total flue gases from a plant handling Morocco rock is presented in Table 6-15. The fluorine evolved from this rock corresponds to approximately 1% of the weight of the rock or 25% of the fluorine originally present.

Comparative data on three types of scrubbers used in superphosphate plants are presented by Pettit (1951 A, B). Although no conclusions are drawn in the study, the data, which are summarized in Table 6-16, indicate that the horizontal scrubber offered the highest efficiency with the lowest water-flow rate. The high efficiency of this unit probably resulted from the use of high-pressure nozzles and the long tortuous path which the gas stream was forced to follow.

Data on 13 scrubbers handling superphosphate-den gas have been presented by Sherwin (1954). Ten of these are more or less conventional spray-tower systems, one is a packed tower, and one is a jet-exhauster system. The spray towers show values for KGa ranging from 0.62 to 2.65; the packed tower, a KGa of 3.7, and the jet exhauster, a KGa of 15.6. The volume for the jet exhauster is based on the volume of the tower which would enclose the vertical venturi pipe from the jet level to the level of the liquid in the tank below. The system obviously gives a very high volume-coefficient of performances; however, power consumption was reported high and overall fluorine-removal efficiency for two units in series was not as high as that of the majority of the spray installations. A portion of the data on these units is summarized in Table 6-17.

It will be noticed that the two-stage spray tower (installation 4) gives slightly better performance than the six-stage spray tower. The two major reasons for this appear to be (a) the lower gas velocity which allows the mist formed to settle out and (b) the appreciably higher water-circulation rate. Silica-deposition problems generally favor the use of a spray tower for this service over the more compact packed tower.

Hansen and Danos (1982) report on experience with a large (18 ft 8 ft 46 ft) crossflow scrubber in a phosphoric acid plant. The scrubber consisted of a spray chamber followed by multiple packed beds of plastic woven mesh. With regard to the spray chamber section of the scrubber, they conclude that a spray nozzle pressure over 60 psig is required to attain 80% fluoride removal efficiency (1.5 transfer units); the amount of spray chamber water should be about 20 to 30 gpm/1,000 acfm; and full cone spray nozzles directed counter-current to the gas flow are preferred. The plastic woven mesh may be irrigated with low-pressure co-current sprays; however, the nozzles should be mounted so that they are equidistant from the packing face and should be designed so that, when partially plugged, they do not create a single jet of water that can wear holes in the woven mesh.

Data on a commercial water spray installation for removing HF and other fluoride compounds from the exhaust gases of a nodulizing kiln have been reported in considerable detail by Magill et al. (1956) and are reproduced in Table 6-18. Limited data are also available on a large jet scrubber operating at a TVA installation manufacturing high analysis superphosphate (Anon., 1962). The unit is used to pull and scrub 12,500 scfm of air containing silicon tetrafluoride vapor and entrained phosphate dust and to develop a suction head of minus 1 in. of water. The ejector has a 36-in. diameter suction chamber and is almost 16 ft high. The spray nozzle has a 5-in. diameter bronze spiral insert covered with 3/16 in. thick neoprene. The scrubber discharges downward into a brick-lined concrete sump. Liquor is recycled to the nozzle by means of a centrifugal pump at a rate of 744 gpm, a pressure of 60 psig, and a maximum temperature of 135F.

The principal source of uranium in unconventional resources is rock phosphate, or phosphorite. Estimates of the amount available range from 9 to 22MtU. The IAEAs World Distribution of Uranium Deposits (UDEPO, IAEA, 2009) database tabulates 14Mt, though the 2014 Red Book tabulates only 7.6Mt, while suggesting that the 22Mt may be realistic.

With uranium as a minor byproduct of phosphates, the potential supply is tied to the economics of phosphate production, coupled with the environmental benefits of removing uranium from the waste stream and/or product. World phosphorous pentoxide (P2O5) production capacity is about 50Mt/year according to PhosEnergy, 9.5Mt in North America, 9.4Mt in Africa, and 19.2Mt in Asia.

About 20% of US uranium came from central Floridas phosphate deposits as a byproduct in the mid-1990s, but recovery then became uneconomic. From 1981 to 1992, US production from this source averaged just over 1000tU/year, then fell away sharply and finished in 1998. The IAEA Red Book (OECD NEA & IAEA, 2009) also reports significant US production of uranium from phosphates from 19541962. With higher uranium prices today, the US resource is being examined again, as is a lower-grade resource in Morocco. Plans for Florida extend only to 400tU/year at this stage.

In Brazil, where uranium is essentially a coproduct with phosphate, the Santa Quitria joint venture between the government company, Indstrias Nucleares do Brasil, and Galvani phosphates has a prime customer in the form of Eletrobras, owner of the national nuclear power operator Eletronuclear. This project based on the Santa Quiteria and Itataia mines will produce both uranium concentrate and diammonium phosphate in a single integrated process. The mine was expected to produce 970tU/year from 2015, and ramp up to 1270tU/year in 2017 as byproduct or coproduct of phosphate. Reserves are 76,000tU at 0.08% U, though resources are reported as 140,000tU at Santa Quiteria and 80,000tU at Itataia, grading 0.054% U in P2O5.

In the United States, Cameco and Uranium Equities Ltd have run a demonstration plant using a refined processPhosEnergyand estimate that some 7700tU could be recovered annually as byproduct from phosphate production, including 2300tU in the US. The prefeasibility study on the PhosEnergy process was completed early in 2015 and confirmed its potential as a low-cost process.

Phosphogypsum is a waste by-product from the processing of phosphate rock in plants producing phosphoric acid and phosphate fertilizers, such as superphosphate. The wet chemical phosphoric acid treatment process, or wet process, in which phosphate ore is digested with sulfuric acid, is widely used to produce phosphoric acid and calcium sulfate, mainly in dihydrate form (CaSO42H2O):

Annual world production of phosphogypsum is estimated to be ~300Mt (Yang et al., 2009). This by-product is contaminated by various impurities, both chemical and radioactive, and is usually stockpiled within special areas. The problem of contaminated phosphogypsum has already become an international ecological problem. For example, a huge amount of phospho-gypsum has accumulated in Florida (more than 1 billion (!) tons), in Europe (where the contaminated phosphogypsum is discharged into the River Rhine close to the North Sea), in Canada, Morocco, Togo, India, China, Korea, Israel, Jordan, Syria, Russia, and other parts of the world.

The building materials industry seems to be the largest among all the industries which is able to reprocess the greatest amount of this industrial by-product and benefit man. However, because of the contamination, only 15% of world phosphogypsum production is recycled as building products and asset retarder in the manufacture of Portland cement (a small amount is recycled as agricultural fertilizer or for soil stabilization amendment), while the remaining 85% is disposed of without any treatment (Tayibi et al., 2009). Disposed phosphogypsum is usually dumped in large stockpiles, occupying considerable land areas and causing serious environmental damage due to both chemical and radioactive contamination.

Typical concentrations of radium (226Ra) in phosphogypsum are 2003000Bqkg1(US Environmental Protection Agency, 1990). They are similar to those in phosphate ores. Digestion with sulfuric acid causes the selective separation and concentration of naturally occurring radium (226Ra), uranium (238U) and thorium (232Th): about 80% of 226Ra is concentrated in phospho-gypsum, while nearly 86% of 238U and 70% of 232Th end up in phosphoric acid (Tayibi et al., 2009). In other words, most of the 226Ra follows phospho-gypsum, which is responsible for its enhanced radioactivity, and most of the 238U and 232Th remain in the phosphoric acid product.

In addition to radionuclides, phosphogypsum contains some trace contaminants which may pose health and environmental hazards, such as arsenic, lead, cadmium, chromium, fluorine, zinc, antimony, and copper (US Environmental Protection Agency, 1990). These trace elements may be leached from phosphogypsum, as radionuclides, migrate to the nearby surface and ground water, and cause fluorescence on the surface of building elements.

The key problem restraining the utilization of phosphogypsum in construction is its radiological effect on the human population, and it is not solved yet. Unfortunately, no effective technologies are known for processing phosphogypsum and for its utilization in the construction industry. The main problem is the slightly elevated radioactivity of phosphogypsum, which is due to the high activity concentration of 226Ra, while the remaining impurities can be extracted relatively easily, for example by using phase transformations between different kinds of calcium sulfate hydrate and filtering the obtained solution. Traditional technologies of purification of phosphogypsum from radium are not effective, because of the similarity of chemical properties of radium sulfate and calcium sulfate salts, when the radioactive salt is isomorphously included in the gypsum crystal lattice (Kovler, 2004).

There have been several attempts to manufacture building materials from phosphogypsum in different countries. For example, phosphogypsum was used some time ago by a New Jersey company for the manufacture of wallboard, partition blocks, and plaster for distribution in the northeastern United States (Fitzgerald and Sensintappar, 1978). Due to the absence of low-cost natural gypsum and the lack of long-term storage place, phospho-gypsum has been used extensively for wallboard and other building materials and also as a cement retarder in Japan and South Korea.

Among European countries phosphogypsum is used in limited amounts (or was formerly used) in Austria, Belgium, Germany, the Netherlands, the United Kingdom, Finland, Greece and some other countries that are not members of the EU (RP-96, 1997). However, the modern environmental norms, which are getting stricter year by year in different countries, leave almost no chance for commercial application of phosphogypsum in construction without previously solving the awkward problem of its elevated radioactivity. No wallboard containing phosphogypsum is commercially manufactured now in the USA, and the situation is not going to change in the near future.

In nature, phosphorus is available in the mineral deposits in the form of phosphate rocks.Phosphorus is mined from phosphate rocks for production of chemical fertilizers. The relative abundance of phosphate rocks in the earth's crust is limited and unequally distributed. For example, about 65% of global phosphorus is produced in just three countries, i.e., Morocco, China, and the US [69]. Most other countries depend on the imports for phosphate fertilizers for growing crops, thus phosphorus availability in a nation is linked to food security. Phosphorus has received public attention mainly because of bothpollution as well as scarcity. Phosphorus is a limiting nutrient in aquatic water bodies,thereby controlling the growth of phototrophic organisms in aquatic waters and coastal marine systems. Release of phosphorus into surface waters affects the natural phosphorus cycle and can promote eutrophication of lakes, reservoirs, estuaries, and oceans. On theother hand, the quality sources of phosphate rock are finite and nonrenewable. It hasbeen estimated that phosphorus demand for its use in chemical fertilizers will outstripsupply by 2033 and the quality phosphate rocks will get depleted within 100years in the absence of a sustainable approach [70]. In this context, waste streams are increasingly considered as potential secondary sources for phosphorus. Also, removal of phosphorus from wastewaters is required to limit the eutrophication potential in receiving waters.

Phosphate fertilizers are obtained from phosphorites of sedimentary or magmatic origin. Sedimentary phosphate rock usually is strip-mined and contains high concentrations of 238U (8005200Bq/kg), 230Th (20016,000Bq/kg), 232Th (5170Bq/kg), and 226Ra (25900Bq/kg). Apatite Ca2[(PO4)3(OH),F,Cl)], the predominant mineral, also contains trace amounts of 210Po (Merkel & Hoyer, 2012). The mining and processing of phosphate fertilizers contaminate the surrounding soil and the application of the fertilizer over time tends to increase the concentration of radionuclides in agricultural soils, and thus transfer radionuclides through the food chain.

As discussed in Chapter 4, PG is a by-product from processing phosphate rock to produce fertilizers and other chemicals. The phosphate rock processing industry ranks fifth in the mining industry in the United States. In making fertilizer, phosphoric acid is produced from phosphate. To procure 1 tonne of phosphoric acid, approximately 45 tonnes of by-product, PG, is also generated. In 2013, 32 million tonnes of phosphate rock was processed in the United States; approximately 22 million tonnes of PG was produced in that year. Fig. 4.1 presents the phosphate rock processing and products. PG to date has not received enough attention with regard to utilization in the United States. Currently, a high proportion of the PG is either dumped or stacked. The decision to dump is partly affected by the relative leniency of environmental laws where PG is seen as essentially safe, but of no value; the decision to stack is partly affected, notably in the United States, by regulations that describe PG as low in radioactivity and hence subject to use only under permit. PG was reportedly used as synthetic construction aggregate in the United States and some European countries in the production of gypsum board, and for highway pavement, foundation, and embankment materials. The low utilization rate is due to lack of usability criteria and guidelines.

There is growing consensus that it is imperative to explore the rational applications of PG, and finding the right application for PG is pivotal to the turning point. The best way is blending use with other material such as slag.

The reason for PG not currently being fully utilized is often due to a general lack of quantification work on the properties of PG and the performance requirements of the end products (uses). Unfortunately, the impact of past utilization mistakes is very difficult to overcome even for proven uses. The blending use of slag and PG will possibly open new avenue for the use of PG in rational applications in construction, Fig. 6.8 shows stockpiled PG approximately 120 ft high.

phosphorite ore crushers selection - eastman rock crusher

phosphorite ore crushers selection - eastman rock crusher

For the phosphate ore processing plant,1) Rough crushing: crushing 1500-350mm material to 350-100mm is coarse crushing,2) Medium crushing: 350-100mm broken to 100-40mm,3) Fine crushing: 100-40mm crushed to 30-10mm.

According to the particle size of the phosphate ore and the allowable feed size of the mill, the common screening and crushing processes are two-stage open-circuit process, two-stage closed-circuit process, three-stage open-circuit process, and three-stage closed-circuit process.

In this article, we require more than 80% of the phosphate rock with a particle size of less than 100 mesh after grinding treatment. To ensure the fineness of the grinding product, the particle size of the phosphate rock entering the mill is required to be less than 15mm. Therefore, a three-stage crushing process is adopted.

The mill feeding capacity of this project is 180t/h. According to the experience, check the return amount of screen material to ensure that it is not more than 10%, and the capacity of screening machines and crushers at all levels can be calculated.

The selection of crushing equipment is mainly related to the nature of the processed phosphate rock material (hardness, density, viscosity, clay content, moisture, maximum particle size of the ore, etc.), processing capacity, crushed product particle size and equipment configuration and other factors.Commonly used crushing equipment mainly includes jaw crushers, gyratory crushers, impact crushers, hammer crushers, cone crushers, and counter-roll crushers.

The coarse ore crusher generally uses a jaw crusher or a gyratory crusher, and an impact crusher can also be used when processing medium-hard phosphate ore. The processing capacity of the gyratory crusher is generally 2.5-3 times that of the jaw crusher, but the equipment is complex in structure, heavy in the body, high in equipment, and expensive. For 180tph processing capacity in this article, jaw crusher can be selected.

The medium crushing capacity is 144t/h, the feed size is less than 200mm, and the output size is less than 30-80mm. The processing capacity of the roller crusher is too small, and the investment in the standard cone crusher is too high. Therefore, it is recommended to choose hammer crushers and impact crushers for medium crushing crushers.

The crushing capacity is 160t/h, the feed size is less than 80mm, and the output size is less than 15mm. The processing capacity of the fine crushing jaw crusher is low, and the equipment investment of the short-head cone crusher is high. For the fine crushing machine, hammer crusher and impact crusher are recommended.

Due to the low hardness of the phosphate rock in this project, from the perspective of reducing equipment investment, jaw crushers should be selected for coarse crushing, and hammer crushers or impact crushers should be selected for medium crushing and fine crushing.

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