Behavior of sulfate in preparation of single light rare earth carbonate by Mg(HCO3)2 precipitation method

The precipitation of the water-leaching solution of Baotou mixed rare earth (RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate. To solve the serious problem of ammonia-nitrogen pollution, new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product (SO42- <1.8 wt% in RE carbonates products). In this paper, we studied the effects of feeding modes on the behavior of SO42- during the preparation of light RE carbonate (RE = La, Ce, Pr, Nd) from their sulfate solutions using Mg(HCO3)(2) as a precipitant. The results indicate that the contents of SO42- in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La-2(CO3)(2.15)(SO4)(0.85)center dot 4H(2)O and Ce-2(CO3)(2.15)(SO4)(0.85)center dot 3H(2)O, while those of the Pr and Nd precipitates are 4 wt%-5 wt% since they exist in the form of n-carbonate. The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO42- enclosed in the precipitation. The content of SO42- in the RE carbonate obtained using reverse feeding mode is the lowest. Among them, the content of SO42- in La precipitate is only 1.40 wt%. Both synchronous and reverse feeding modes can effectively reduce the content of SO42- in RE carbonate, which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)(2) precipitation method. (C) 2021 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

Automated summary

This study investigates the effects of feeding modes on the behavior of SO42- during the preparation of light RE carbonates, finding that the synchronous and reverse feeding modes can effectively reduce the content of SO42- in the product. The results provide theoretical guidance for the preparation of qualified light RE carbonate products using Mg(HCO3)(2) precipitation method.