The use of wet phosphoric acid purification step waste filtration cakes for making animal feed-grade phosphates

摘要

The Fe(III) and Al impurity phosphates precipitating at pH = 3.0-3.4 and 3.8-4.5, resp., on neutralizing (pH > 7) desulfated wet H_3PO_4 with Na_2CO_3 (to make (2:1) Na orthophosphates and further Na tripolyphosphate, Na_5P_3O_(10)), wee collected by filtration (about 300 kg/ton of acid's P_2O_5), allowed to solidify, and neutralized with CaO, 1:0.5 to 1:0.75 w/w. The water (45%) contained in the cake hydrated CaO (temp. rose to 393 K) and evaporated to leave the semi-product (<=5% H_2O) that was dried, screened, milled, and re-screened to collect the undersize (<200 #mu#m). this was used as a substitute for natural products to prepare feed-grade dicalcium phosphate that met Polish Standard PN-R-64803 requirements (P, min. 16%; Ca, 21-30%; F, max. 0.2%). This product was 15-20% cheaper than that made from natural products only.