Synchronized removal of non-rare earth ions (Al3+, Fe3+, Th4+, U6+, and F−) from rare earth leach solutions using lanthanum‑cerium oxides for pH adjustment

Abstract

Eliminating non-rare earth anions and cations is a challenge for Chinese rare earth producers due to the increase in the contamination with non-rare earth impurities in leach solutions. Based on the decontamination mechanism of conventional alkaline reagents, a procedure for the synchronized removal of non-rare earth anions and cations from rare earth leach solutions was developed. In this work, the principal non-rare earth anions and cations in the solution (initial pH of 1.12) was decontaminated by adding lanthanum–cerium oxides to adjust the pH to 4.0 with the addition of a 20 g/100 mL aluminum-based carrier at a water bath temperature of 30 °C. The lanthanum‑cerium oxides were mixed at a lanthanum‑cerium molar ratio of 4:1 and roasted at 1000 °C. The removal efficiencies of Al³⁺, Fe³⁺, Th⁴⁺, U⁶⁺, and F⁻ were 97.5 %, 92.7 %, 91.7 %, 97.4 %, and 95.7 %, respectively. The solid produced after decontamination could be transformed into a new aluminum-based carrier for repeated use after washing, drying, and roasting. The variation in non-rare earth anion and cation removal efficiencies was less than 3 % after three cycles. The removal of non-rare earth impurities was significantly improved, with a decrease in the loss of rare earths from 5 % to approximately 2 %. This process opens new application scenarios for highly abundant lanthanum and cerium and avoids the risk of introducing new impurities from conventional alkali sources. This process has practical significance for the green and healthy development of rare earth producing enterprises.