Leaching process of rare earth elements, gallium and niobium in a coal-bearing strata-hosted rare metal deposit—a case study from the late permian tuff in the zhongliangshan mine, chongqing

Abstract

The tuff, a part of coal-bearing strata, in the Zhongliangshan coal mine, Chongqing, southwestern China, hosts a rare metal deposit enriched in rare earth elements (REE), Ga and Nb. However, the extraction techniques directly related to the recovery of rare metals in coal-bearing strata have been little-studied in the literature. The purpose of this paper is to investigate the extractability of REE, Ga and Nb in the tuff in the Zhongliangshan mine using the alkaline sintering-water immersion-acid leaching (ASWIAL) method. The results show that ASWIAL can separate and extract REE, Ga and Nb effectively under the optimized conditions of calcining at 860◦C for 0.5 h with a sample to sintering agent ratio of 1:1.5, immersing at 90◦C for 2 h with 150 mL hot water dosage, and leaching using 4 mol/L HCl at 40◦C for 2 h with a liquid-solid ratio of 20:1 (mL:g). The final leaching efficiencies of REE and Ga are up to 85.81% and 93.37%, respectively, whereas the leaching efficiency of Nb is less than 1%, suggesting the high concentration of Nb in the leaching residue, which needs further extraction.