Study On Preparation Of Feed-grade Defluorinated Calcium Phosphate

Defluorinated calcium phosphate(DFP) is a kind of inorganic feed additive with a prominent performance on markedly increasing production and gaining weight when it is fed to domestic animals and poultries. Meanwhile ,with the characteristic of short flow, low invest and cost, and good profit, DFP has been extensively manufactured and used abroad. During the course of production whether the fluorin is effectively eliminated from the reaction system or not plays a key role on the quality of product, so it is quite necessary to investigate the factors affecting defluorination and the reaction mechanism, because these are very important for deepening understanding the essence of the reaction , broadening the approach of using middle and low-grade quality phosphate rock, meeting the increasing market needs of this product. Firstly, by making use of Sichuan phosphate ore as material, several factors of affecting defluorination, that is, temperature, phosphorous acid concentration, the ratio of phosphorous acid added into the feed material, reaction time, were studied in detail with thermal-acid method in this paper. The results indicated that temperature and the ratio of phosphorous acid play an important part in defluorination reaction, because there is a compact relation between the quantity of liquid yielded during the course of toasting and the two factors. Reaction time has great effect on defluorination, because enough time is required for a sufficient reaction and the elimination of compounds containing fluorin formed in production. The study also showed that the effect of phosphorous acid concentration is not distinct. Through experiments the optimum conditions of manufacturing DFP with Sichuan phosphate ore as material were obtained. The temperature is 1180~1230℃,the ratio of phosphorous acid added into the feed material is about 30%,reaction time is above 120min, phosphorus acid concentration is about 45%。Under the conditions the products can be obtained with the quality of the content of P available 17.20%,Ca available 26.88%,F 0.11% all meeting the quality standards of feed DFP established by enterprise at home. Secondly, the effect of temperature on defluorination was investigated with a material of Guizhou phosphate ore. By comparing the experiment results under different temperatures it was observed that the reactivity of Guizhou phosphate rock is better than that of Sichuan ore, which was manifested by a higher conversion of feed material and a higher content of P and Ca available, and a lower content of F in the products. And the best toasting temperature for Guizhou phosphate ore manufacturing DFP is 1140~1180℃. Finally, experiments of defluorination reaction were carried out by using pure phosphorite as material , and the experiments showed that pure phosphorite's reaction activity is worst, Sichuan phosphate ore's worse and the Guizhou's best by comparing the results. Meanwhile the effect of phosphate ore property on defluorination was analyzed based on the results of experiments. In the end of the paper the reaction mechanism was primarily studied according to the X-ray diffraction of Sichuan and Guizhou phosphate ores'sinter specimens.