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Lanthanum recycling from La2O3-containing oxide slag via synthesis and separation of the Si-La alloy

Minpeng Lei,Yun Lei,Shiding Wang,Dongfang Yang,Shaoyuan Li,Wenhui Ma

Spent nickel-metal hydride (NiMH) batteries are a significant secondary resource for recovering rare earth elements (REEs), particularly lanthanum (La). However, extracting La from the La 2 O 3 -containing oxide slag generated during pyrometallurgical recycling remains a major challenge. This study proposes a novel approach to address this issue by synergistically extracting La from La 2 O 3 -containing oxide slag while simultaneously upgrading metallurgical-grade silicon (MG-Si, 99.2%) to high-purity Si (99.991%). The process begins with the extraction of La from the La 2 O 3 -containing oxide slag using MG-Si as a reductant, yielding a useful Si-La alloy. This is followed by a three-stage leaching process to further separate the Si-La alloy and purify the Si powder. In the primary leaching stage, the Si-La alloy powder is separated into a La-containing acidic solution and residual Si powder using HCl solution. In the secondary leaching stage, Fe impurities in the residual Si powder are removed using a mixed acids solution of HF and HCl. In the tertiary leaching stage, the Si powder is further purified to 99.991% using HCl. Finally, the La ions in the La-containing acidic solution are selectively precipitated using hydrofluoric acid (HF) and ammonia (NH 3 ·H 2 O), respectively, resulting in high-purity LaF 3 (96.2%) and LaOCl (99.4%). This new method simultaneously recovers La from La 2 O 3 -containing oxide slag and enhances Si purity from 99.2 to 99.991%.