Nature of influence exerted by Na2SiF6 on REE recovery from orthophosphoric acid solution in the course of CaSO4 center dot 0.5H(2)O crystallization

摘要

Chemical and X-ray phase analyses were used to study the influence exerted by Na2SiF6 on the isomorphic inclusion of cerium into the structure of CaSO(4)a (TM) 0.5H(2)O precipitates formed from solutions of phosphoric acid hemihydrate (38 wt P2O5). The poorly soluble suspensions of CaSO(4)a (TM) 0.5H(2)O precipitates can serve as adsorbents for cerium compounds, with CaSO(4)a (TM) 0.5H(2)O-NaCe(SO4)(2)a (TM) H2O and CaSO(4)a (TM) 0.5H(2)O-CePO(4)a (TM) 0.5H(2)O solid solutions formed. The introduction of Na2SiF6 makes the sorption properties CaSO4a (TM) 0.5H2O several times better because the Na2SiF6 phase is a source of sodium cations and creates the necessary Na: Ce ratio of 1: 1 for extracting cerium from the liquid phase into a precipitate in the form of a CaSO(4)a (TM) 0.5H(2)O-NaCe(SO4)(2)a (TM) H2O + CePO(4)a (TM) 0.5H(2)O solid solution. Under the industrial conditions in which extraction phosphoric acid is manufactured, a similar isomorphous capture of rare-earth elements of the cerium group (La-Sm) may occur in joint precipitation of CaSO(4)a (TM) 0.5H(2)O and Na2SiF6.