An environmental friendly Na2CO3-roasting decomposition strategy for the mixed rare earth concentrate

• A novel two-step decomposition strategy for mixed RE concentrate is proposed.
• Bastnaesite (RECO3F) can be decomposed at the first air-oxidization step.
• Monazite (REPO4) can be decomposed at the second Na2CO3-roasting step.
• Both the roasting processes have no apparent lumps produced.
• Respective recovery of F, P, Th, RE can be expected from H2SO4-leaching liquors.

The decomposition of the mixed RE (rare earth) concentrate bastnaesite (RECO3F) and monazite (REPO4) has been investigated extensively for a few decades. In this work, a novel environmental friendly Na2CO3-based roasting decomposition strategy for the mixed RE concentrate has been proposed. It is a two-step strategy combining air-oxidation and Na2CO3-roasting. In the first step of air-oxidation, almost all of bastnaesite decomposes. While more than 95% of monazite decomposes in the second Na2CO3-roasting step. Thus, the consumption of Na2CO3 in the current proposed process would decrease greatly. The Na2CO3-roasting phenomena were compared among the reactions of Na2CO3-mixed RE concentrate, Na2CO3-pure bastnaesite and Na2CO3-the first leaching residue by H2SO4. The air-roasting temperature was optimized. In particular, the roasting temperature for the reaction of Na2CO3 and H2SO4-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 H2SO4-leaching liquor and H2O-leaching liquor, respectively. 93.7% of Th and 96.6% of RE can be leached. Finally, a H2SO4-leaching liquor containing Th, Ce(IV), RE(III) and F can be obtained for the subsequent separation.

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