Phase study of REEs speciation: Sequential extraction of Malaysian acid mine drainage precipitate and tailing

Abstract The recovery of rare earth elements (REEs) from acid mine drainage (AMD) has emerged as a promising and popular secondary source of REEs worldwide in recent years. Characterizing this type of source is essential for a comprehensive understanding, particularly concerning Malaysian samples, including chemical speciation and rare earth content in order to develop the optimal recovery process. This study investigates AMD treated precipitates at pH 7.50 and an original raw tailing from a Malaysian tin tailing mine. The REEs enrichment of precipitate produced from raw acid mine drainage by using selective precipitation process yield almost 3 times magnitude from original concentration. A chemical test of 5 step - sequential extraction was conducted, revealing that the majority portion of rare earth elements (78.74%) resided in the Fe-Mn oxide phase at pH 7.50 of AMD treated precipitate, and (81.83%) in the organic matter phase in raw tailing. Additionally, the portion of REEs in the ion-exchangeable phase constitutes the minority (less than 5%) in both samples, suggesting its less suitability for in-situ leaching (ISL) technique, commonly used in ion adsorption clay sources. Understanding the distribution of REEs in these samples holds the potential for optimizing local REEs recovery methods.