METHOD OF PRODUCING HIGHLY PURE CALCIUM CARBONATE AND NITROGEN-SULPHATE FERTILISER DURING COMPLEX PROCESSING OF PHOSPHOGYPSUM Russian patent published in 2014 - IPC C01F11/18 C01C1/18 C01C1/24 C05G1/00 

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry when processing phosphogypsum - a wet-process phosphoric acid production waste. Highly pure calcium carbonate and nitrogen-sulphate fertiliser are obtained by converting phosphogypsum with ammonium carbonate solution to obtain ammonium sulphate solution and phosphochalk. The phosphochalk is dissolved in nitric acid and the insoluble residue is filtered off from the calcium nitrate solution. Further, the calcium nitrate solution is reacted with ammonium carbonate to obtain a product pulp of calcium carbonate in ammonium nitrate solution, followed by deposition of highly pure calcium carbonate therefrom and processing the ammonium nitrate solution into nitrogen-sulphate fertiliser. The product pulp is divided into two parts, one of which is taken for filtration to separate the residue of highly pure calcium carbonate, and the other is taken for premixing with ammonium carbonate solution until concentration of ammonium carbonate in the liquid phase is equal to 4.0-8.0%. During deposition of highly pure calcium carbonate, temperature is kept at 40-45°C and concentration of excess ammonium carbonate in the liquid phase of the pulp is kept at 0.5-1.0%. Ammonium nitrate solution obtained after separating the calcium carbonate residue is mixed with ammonium sulphate solution obtained after converting phosphogypsum. The mixture is evaporated, granulated and dried.

EFFECT: invention increases effectiveness of complex treatment of phosphogypsum, efficiency of filtering at the step of depositing highly pure calcium carbonate, output of ammonium nitrate into the liquid phase.

2 cl, 2 tbl, 4 ex