METHOD OF EXTRACTING RARE-EARTH METALS AND PRODUCING GYPSUM PLASTER FROM PHOSPHOGYPSUM HEMIHYDRATE Russian patent published in 2014 - IPC C22B59/00 C22B3/06 

FIELD: chemistry.

SUBSTANCE: method includes consecutive steps of recrystallising phosphogypsum and dissolving rare-earth metals. Recrystallisation of calcium sulphate hemihydrate or anhydrite into a dihydrate is carried out in the presence of a soluble calcium salt in concentration of 0.075-3.75 M with respect to Ca²⁺ in a weakly acidic medium at pH>1. Dissolution is carried out with a strong acid with pKa<0 in concentration of 0.2-8 M with respect to H+. The degree of extraction of rare-earth metals into the solution is less than 95% and the residual content of phosphorus, fluorine and alkali metal impurities in the calcium sulphate dihydrate is not more than 0.3 wt %, 0.1 wt % and 0.05 wt %, respectively.

EFFECT: more effective extraction of rare-earth metals with simultaneous purification of calcium sulphate from phosphorus and fluorine.

3 cl, 3 tbl, 7 ex