Effect of Leaching Parameters Towards Leaching Efficiency and Rare Earth Element Phases Partitioning of Malaysian Ion Adsorption Clay

Abstract

Ion adsorption clay (IAC) has attracted attention as a valuable source of rare earth elements (REEs) because it has lower levels of radioactive elements concentrations as well as its simple in-situ leaching method used for extraction that reduces environmental impact and often lowers operational cost. However, variation in REE phases partitioning of IAC and high content of Al and Fe impurities in the pregnant leach solution (PLS) provide significant challenges for designing optimum in situ leaching and subsequent REE enrichment process. This study aims to establish understanding of leaching parameters towards REE leaching efficiency, impurities concentration and resulting REE phases partitioning. The sequential extraction results show that IAC samples chosen constitute up to 68.61% of ion-exchangeable phase REE, indicating enrichment of leachable REE in horizon B. Leaching test was conducted via agitation method by using ammonium sulphate and ammonium acetate as lixiviants at varied concentrations of 1.0% and 1.5% and varied initial pH 3, 5 and 7. The leaching test results show that ammonium acetate lixiviant produced the highest recovery of REE and the lowest Al concentration in the PLS when leached at initial pH 3. It can also be noted that leaching conducted at lower pH results in higher REE recovery and higher Al and Fe concentrations in PLS regardless of lixiviant type and concentrations. Sequential extraction performed on soil leach residue indicates that leaching at lower pH shows tendency to leach both ion-exchangeable and colloidal phase REE, proven by reduction of REE concentration of these phases.