An environmental friendly Na 2 CO 3 -roasting decomposition strategy for the mixed rare earth concentrate

Abstract

Abstract The decomposition of the mixed RE (rare earth) concentrate bastnaesite (RECO 3 F) and monazite (REPO 4 ) has been investigated extensively for a few decades. In this work, a novel environmental friendly Na 2 CO 3 -based roasting decomposition strategy for the mixed RE concentrate has been proposed. It is a two-step strategy combining air-oxidation and Na 2 CO 3 -roasting. In the first step of air-oxidation, almost all of bastnaesite decomposes. While more than 95% of monazite decomposes in the second Na 2 CO 3 -roasting step. Thus, the consumption of Na 2 CO 3 in the current proposed process would decrease greatly. The Na 2 CO 3 -roasting phenomena were compared among the reactions of Na 2 CO 3 -mixed RE concentrate, Na 2 CO 3 -pure bastnaesite and Na 2 CO 3 -the first leaching residue by H 2 SO 4 . The air-roasting temperature was optimized. In particular, the roasting temperature for the reaction of Na 2 CO 3 and H 2 SO 4 -leaching residue has been optimized according to P- and Ce-leaching percents. Finally, following the proposed flowsheet under the optimized conditions, taking 50 g of mixed RE concentrate as feedings, the final solid residue occupies around 2.4%. In addition, about 70% of F and 87% of P can be transferred into H 2 SO 4 -leaching liquor and H 2 O-leaching liquor, respectively. 93.7% of Th and 96.6% of RE can be leached. Finally, a H 2 SO 4 -leaching liquor containing Th, Ce(IV), RE(III) and F can be obtained for the subsequent separation.