Phosphate rock beneficiation

Figure 5.17a. Florida G eralized Scheme of Phosphate Rock Beneficiation Wcishiiig.

Calcination. Phosphate rock normally is used as a dry rock or in slurry form. However, in some cases, particularly where the raw phosphate is high in carbonaceous matter or it is desirable to have a clean acid, the rock is calcined. Also, in a few cases, the phosphate rock is calcined, the product slaked, and free lime separated as a beneficiation step. Calcination is energy intensive and produces a less reactive rock and, in some cases, a less filterable gypsum. Therefore, the use of calcination is diminishing, and is being replaced by a wet oxidation step to produce green acid.16 In separating calcium carbonate, flotation, where it is successful, is favored over calcination because of its lower cost. 

Nofal, A. M., Egyptian Phosphate Rocks Important Factors Affecting Thek Economic and Technical Evaluation, in Beneficiation of Phosphate Theory and Practice, Society for Mining, Metallurgy, and Exploration, Inc., 1993. 

Natural gas, naphtha, fuel oil, and sulfur have fairly definable specifications. In contrast, phosphate rock and coal are products that can vary significantly in composition and other characteristics. These variations can affect the processes used to upgrade the as-mined ores or the processes for manufacture of fertilizers from beneficiated products. Potash ores also vary greatly in composition depending on origin however, the end products of mining,... 

Lehr, J. R., and McClellan, G. H., Phosphate Rocks Important Factors in Their Economic and Technical Evaluation, CENTO Symposium on the Mining and Beneficiation of Fertilizer Minerals, pp. 192-242, November 19-24, 1973. 

Phosphate rock deposits contain uranium (U), radium (Ra), thorium (Th), and other radionuclides as contaminants. Uranium in phosphate rock deposits throughout the world range from 3 to 400 mg kg (Guimond, 1978). It has been estimated that 1000 kg of Florida phosphate rock contains about 100 pCi each of" U and Ra and 4 pCi of °Th (Menzel, 1968). Some of these elements are retained in the HjPO and the remainder are transferred to the by-products during fertilizer manufacture. For instance it is estimated that 60% of the radioactivity in mined Florida phosphate rock remains with slime and sand tailings during beneficiation (Guimond and Windham, 1975). 

About 33% of the U in beneficiated phosphate rock concentrate feed for acidulation by the wet-process method was found in the phosphogypsum (PG) byproduct. The remainder of the U was found mainly in the H2PO4, which subsequently is processed to several types of P fertilizers. 

Phosphate rock preparation—Domestic phosphate rocks are essentially fluorapatite admixed with various proportions of other compounds of calcium, fluorine, iron, aluminum, and silicon. Phosphate rock preparation involves beneficiation to remove impurities, drying to remove moisture, and grinding to improve reactivity. Phosphate rock, when very finely pulverized, has limited direct use as a fertilizer. However, it is mainly used as a raw material for the manufacture of phosphate acid, superphosphate, phosphorus, and phosphorus compounds. 

After beneficiation, the washed rock may contain 7%-20% moisture, which is reduced to between 1% and 2% moisture using direct-fired rotary dryers. Emissions expected from the dryer consist primarily of fine rock dust. Some sulfur dioxide may also be present in the dryer exhaust from the combustion of sulfur in the fuel. Phosphate rock dryers are usually equipped with dry cyclones, followed by wet scrubber systems for control of rock dust. The scrubber systems will operate at typical particulate collection efficiencies of 97%-98% with emissions ranging from 0.1 to 0.3 kg/t of phosphoric anhydride (P2O5) [77]. 

Phosphate rocks can be applied directly to soils to furnish P, and they have been used for the past century. With their limited solubility, however, they are most beneficial on very acidic soils (pH below about 5.2). Most PR must be ground to a fairly fine state to improve its reactivity in soils, which make it less convenient to handle than granulated fertilizers. There are large differences in the reactivity of PRs, which increases with the amount of substitution of carbonate for phosphate in the apalMic mineral structure. Warm climates with adequate soil moisture and acidic soils have the potential for PR to be... 

The determination of the type and amount of apatite, in a phosphate rock is very important. Sedimentary phosphate rocks containing the most highly carbonate-substituted apatites can only be beneficiated to maxi-mumrgradesrofr33-34 wt % P2O5. Depending on the amount of carbonate substitution, the grade can increase to a maximum of about 42 wt % P2O5 for sedimentary apatites with essentiaDy no substitution. In order to reach... 

Abu-Eishah, S. 1., et al. 1991. Beneficiation of Calcareous Phosphate Rocks Using Dilute Acetic Acid Solutions, International Journal o/Min-... 

Contaminants of Concern - All phosphate ore contains traces of radioactive elements, and some contain a number of metals. These impurities are studied in relation to their impact on health and the environment. During the processing of the phosphate rock they are partitioned between ore beneficiation process waste, add process waste, and final product. 

It has been established that about 60% of the radionuclides remain in bcneficiation tails. Two-thirds of those remaining in the beneficiated phosphate rock is trans— ferred to the phosphoric acid, and the remaining third is disposed of with the phosphogypsum 122]. 

Establishment of the phosphate, mining and benefh elation operations only for one medium-size plant may not prove competitive with imported phosphate raw materials. Therefore, countries with large phosphate rock deposits have developed national industries that export phosphate rock, phosphoric acid, and fertilizers. These industries would supply the world market with stable volumes of raw materials at comparatively stable prices. A similar situation exists with beneficiation of potash and potash muriate. 

Phosphate rock mining, beneficiation (i.e., processes whereby extracted ore from mining is separated into mineral and gangue),... 

A vast majority of phosphate ores yield commercial phosphate rock only after the removal of impurities by beneficiation. Also known as mineral dressing and ore processing, beneficiation may involve a variety of operations such as size reduction, size separation, mineral separation, and thermal processing. 

Energy requirements for producing phosphorous fertilizers add up to as little as 15 GJ/t P for phosphate rock and as much as nearly 30 GJ/t for complex P-containing compounds. Mining, crushing, and beneficiation of potash (KCl) usually does not cost more than 10 GJ/t of the nutrient. As we will see in the next chapter, only a small part of synthesized ammonia is used directly as a fertilizer conversion of NHj to liquid and solid nitrogen fertilizers that dominate the field applications requires a considerable amount of additional energy. ... 

Helsel (63), pp. 182-183. Phosphate rock can be applied directly to fields after grinding, beneficiation, and drying, but most of it is used to produce phosphoric acid (H3PO4) by the reaction with H2SO4. The acid is the base for synthesis of such widely used fertilizes as triple superphosphate and mono- and diammonium phosphate see UNIDO (32), pp. 295-399. 

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