New Low-Temperature Technology of Producing Calcium Feed Phosphate with Microelements

The possibility of producing feed calcium phosphates in a way ensuring a low physical water content in the product was investigated in laboratory conditions. For this purpose the process use of a phosphoric acid solution with a higher (than in conventional methods) P₂O₅ content (53-63% by wt. P₂O₅) with CaO (molar fraction of 0.5-0.8) and CaCO₃ in the phosphoric acid neutralizing mixture was tested. Phosphates with a high content of phosphorous forms highly assimilable by animals, soluble in 0.4% HCl (94-99%), were obtained. The physical water content of 1-4% by wt. H₂O was obtained when a phosphoric acid solution with a 59% by wt. P₂O₅ content and a CaO molar fraction of 0.8 in the neutralizing mixture were used and for a phosphoric acid solution with a 63 % by wt. P₂O₅ content. A temperature above 160°C was obtained when respectively phosphoric acid with a 59% by wt. P₂O₅ content and the highest CaO fraction in the neutralizing mixture and a phosphoric acid solution with a 63% by wt. P₂O₅ content were used. An elevated CO₂ content in the products, indicating an increase in the unreacted calcium carbonate content, was found when a phosphoric acid solution containing 59% by wt. P₂O₅ and a CaO fraction of 0.8 in the neutralizing mixture were used and also for a phosphoric acid solution with a 63% by wt. P₂O₅ content and a CaO fraction of 0.7-0.8 in the neutralizing mixture. By supplementing extraction phosphorous acid composition with microelements (Se, Cu and Zn compounds) at the stage of extraction phosphoric acid production one can obtain a product with a homogenous content of the elements, but this entails losses as high as 70-80% caused by the separation of phosphogypsum from the phosphorous material decomposition product. Because of the different mass fractions of microelement salts and feed phosphates a homogenous selenium compound content in feed phosphate is obtained only after 8 hours of mixing. Mixing time is twice shorter for copper and zinc.