Non-ammonia enrichment of rare earth elements from rare earth leaching liquor in a magnesium salt system I: Precipitation by calcium oxide

Abstract

Combining the environmental advantage of magnesium salt compound leaching agent, calcium oxide was used as a precipitant to enrich rare earth elements from rare earth leaching liquor in a magnesium salt system. The use of magnesium salt compound leaching agent and calcium oxide precipitant can achieve the effective circulation of Ca and Mg, and finally solve the ammonia-nitrogen pollution problem in the whole extraction process of the weathered crust elution-deposited rare earth ore. The study suggested that alkaline rare earth sulfates and rare earth hydroxides could generate in the precipitation process, which was proved by the Hazen model calculation and the calcium oxide addition experiments. What's more, it was showed that, under the optimum precipitation conditions, the precipitation efficiency of rare earth was 99.72% and the purity of rare earth concentrate is 82.21%, and the SO3 content in the rare earth concentrate was as high as 13.44% because of the formation of alkaline rare earth sulfates during the precipitation process. In order to reduce the SO3 content, the stirring washing of the precipitation enrichment with an sulfate removal agent was proposed in this paper. The anion of the sulfate removal agent could compete with sulfate ions in the stirring washing process. As a result, sodium hydroxide could be the first choice for further detailed study. When the precipitation enrichment was washed with sodium hydroxide, the purity of the rare earth concentrate was 88.03% and the SO3 content was 7.51% respectively. Hence, a feasible operation would be provided for the non-ammonia enrichment of rare earth from leaching liquor in a magnesium salt system. The research in this paper could have great significance for environmentally-friendly extraction of the weathered crust elution-deposited rare earth ore and the improvement of resource utilization.