Sulfuric Acid Leaching of Heavy Rare Earth Elements (HREEs) from Indonesian Zircon Tailing

Abstract

Solid pollution has been an issue in mineral processing for decade. One of these pollutants is zircon sand mining waste (zircon tailing). Due to the concentration of rare earth minerals in zircon tailing and the increasing demand of REE in advanced technologies, studying zircon tailing as a potential source of REE had become an interest for us. Our experiments consisted of mineral characterization and an alkaline fusion process, followed by a leaching process. The characterization process was carried out to obtain actual information from zircon tailing samples. This process showed total rare earth elements (REEs) content of 58.62%, at 9%, 1%, 1.2%, 1.7%, and 1.5% for Y, Gd, Er, Dy, and Yb, respectively. A sieving process was carried out since it was known that most heavy rare earth elements (HREEs) content occurs at a larger size. The alkaline fusion process was applied with an intent to break the phosphate bonds present in the REE-carrying minerals (xenotime and monazite) and convert phosphate bonds to hydroxide bonds in rare earth metals. During the alkaline fusion process, as much as 75%, 66.45%, and 60% of the phosphate, silica, and zirconium, respectively, were reduced. The leaching process was carried out in a flat-bottom three-neck flask. The optimum point of leaching experiments occurs at 0.5 M H2SO4, 60°C, and a solid-to-liquid (S/L) ratio of 10 g/100 mL. In these conditions, as much as 89%, 99%, 94%, 92%, and 90% of Y, Gd, Er, Dy, and Yb, respectively, were recovered as an HREEs2-(SO4)3 product solution.