Clean Defluorination Technology For Making Feed-grade Dicalcium Phosphate With Wet-process Phosphoric Acid

Phosphate rock's average quality is not high in China. There are many noxious elements in them, including fluorine. Phosphate rock is the indispensable raw material for producing feed-grade dicalcium phosphate,but our country's national standard requires that F-content doesn't exceed 0.18%. Therefore, deflourination is the key problem.The dicalcium phosphate was prepared by leaching the phosphate rock with hydrochloric acid and phosphoric acid respectively, in which the effects of acid concentration, reaction time, reaction temperature, retention time, neutralization pH, blow rate on fluorine content was deeply and systematically investigated. Through adjusting technical parameters and optimizing experimental conditions, the dissolution of fluorine was reduced. The acid leaching reaction and defluorination process were simultaneously progressed. Finally, the crude phosphoric acid after simple filtration and neutralization can prepare the feed-grade dicalcium phosphate which meets national standard. Besides, this research gained optimum conditions.The study results showed as follows: (1) Under the optimum conditions of leaching the phosphate rock with hydrochloric acid the fluorine content of feed-grade dicalcium phosphate can reduce to 0.12%. The optimum blow rate was 700mL/min, The optimum hydrochloric acid concentration was 5.3mol/L. The optimum reaction time and retention time was respectively 2h and 2.5h. The optimum reaction temperature was 65℃. The optimum dosage of HCl and H2O were both 17mL (Hydrochloric acid concentration was 12mol/L).The optimum adding acid time was 60s. The optimum neutralization pH is 5.4-5.8. The optimum meshes of sieve was 150 courses (0.1mm). (2) Under the optimum conditions of leaching the phosphate rock with phosphoric acid the fluorine content of feed-grade dicalcium phosphate can reduce to 0.087%. The optimum phosphoric acid concentration was 6.4mol/L. The optimum reaction time and retention time was respectively 6h and 1h. The optimum blow rate was 700mL/min. The optimum reaction temperature was 60℃. The optimum dosage of H2O and H3PO4 was respectively 20mL and 15mL ( Phosphoric acid concentration was 15mol/L). The optimum adding acid time was 90s. The optimum neutralization pH is 5.2-5.8. The optimum meshes of sieve was 140 courses (0.105mm).