Phosphate rock defluorinated

The phosphate manufacturing and phosphate fertilizer industry includes the production of elemental phosphorus, various phosphorus-derived chemicals, phosphate fertilizer chemicals, and other nonfertilizer phosphate chemicals [1-30], Chemicals that are derived from phosphorus include phosphoric acid (dry process), phosphorus pentoxide, phosphorus penta-sulfide, phosphoms trichloride, phosphorus oxychloride, sodium tripolyphosphate, and calcium phosphates [8]. The nonfertilizer phosphate production part of the industry includes defluori-nated phosphate rock, defluorinated phosphoric acid, and sodium phosphate salts. The phosphate fertilizer segment of the industry produces the primary phosphorus nutrient source for the agricultural industry and for other applications of chemical fertilization. Many of these fertilizer products are toxic to aquatic life at certain levels of concentration, and many are also hazardous to human life and health when contact is made in a concentrated form. 

On the other hand, defluorinated phosphate rock is utilized as an animal feed ingredient. Defluorinated phosphoric acid is mainly used in the production of animal foodstuffs and hquid fertilizers. Finally, sodium phosphates, produced from wet process acid as the raw material, are used as intermediates in the production of cleaning compounds. 

Figure 4 Defluorinated phosphate rock fluid bed process (from Ref. 8).

Parameter (mg/L except pH) Phosphorus production (A) Phosphorusconsuming (B) Phosphate (C) Defluorinated phosphate rock (D) Defluorinated phosphoric acid (E) Sodium phosphate (F)... 

Table 12 Effluent Limitations (mg/L except for pH) for Subpart D, Defluorinated Phosphate Rock...

Defluorinated Phosphate Rock. There is substantial production of defluorinated phosphate rock for fertilizer use in Japan (about 100,000 mt/year). Ground, high-grade rock is mixed with small proportions of sodium carbonate or sulfate and wet-process acid. The mixture is calcined at a temperature of 1350°C in an oil-fired rotary kiln 45.0 m in length and 2.7 m in diameter. The product contains 38-42 percent P205 of which more than 90 percent is soluble in neutral ammonium nitrate solution and is an effective fertilizer on acid soils. During the production of defluorinated phosphate rock, substantially all fluorine is driven off. Sodium bifluoride (NaHF2) is recovered as a byproduct. A similar product is made in the United States, but it is mainly used for animal feed supplement. 

About 87%, or about 32 million tonnes of the phosphate rock consumed in the U.S.A. in 1978 went to agricultural uses, the remainder going as feedstock for elemental phosphorus production [6]. Phosphate rock of fluorapatite stoichiometry (CaFi 3Cas(P04)2), which is destined as a mineral supplement for animal feeds or as a bulking agent in fertilizers is normally defluorinated. 

Finely ground phosphate rock (Ca3(P04)2) is occasionally added to fertilizer formulations as a diluent or filler. However, because phosphate rock has only a very limited water solubility its action as a phosphate nutrient is small and very slow. Hence, this ingredient is not allowed to be included in the % P2O5 analysis appearing on fertilizer packaging. Before use as a filler, phosphate rock is normally defluorinated by heating with silica and steam to decrease the risk of soil contamination by fluoride (Chap. 10). 

TVA has stucfied defluorination of lower grade phosphate rock through fusion processes. Ten pilot plants arxi two demonstration-scale plants were built and operated. The more successful plant operated for 10 years (1945-55) and produced about 170,(X)0 tonnes of product containing 28% P2O5 from low-grade TcnncsseeL rock. The results of the studies have been published [6]. 

Minerals. Supplementation of macrominerals to mminants is sometimes necessary. Calcium and phosphoms are the minerals most often supplemented in mminant diets. One or both may be deficient, and the level of one affects the utilization of the other. Limestone, 36% calcium, is commonly used as a source of supplemental calcium. Dolomite, 22% calcium oyster sheUs, 35% calcium and gypsum, 29% calcium, are sources of calcium. Bone meal, 29% calcium, 14% phosphoms dicalcium phosphate, 25—28% calcium, 18—21% phosphoms and defluorinated rock phosphate, 32% calcium, 18% phosphoms, are sources of both calcium and phosphoms. Diammonium phosphate, 25% phosphoms phosphoric acid, 32% phosphoms sodium phosphate, 22% phosphoms and sodium tripolyphosphate, 31% phosphoms, are additional sources of phosphoms (5). 

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