Separation of rare earth elements via pickering emulsion: A sustainable approach to physicochemical beneficiation

Abstract

• A novel method for separating rare earth minerals using Pickering emulsions is proposed; • Minerals’ surface properties and operating conditions investigated for a selective extraction; • Pickering emulsions efficiently separates monazite and bastnaesite from carbonate minerals; • Emulsions offer a sustainable and environmentally friendly alternative for recovering fine REE minerals. Separating rare earth elements (REE) bearing minerals from their associated gangue minerals, such as dolomite and calcite, is challenging, particularly for fine particle size, due to their similar physicochemical surface properties. To exploit the small differences in surface properties between the gangue and the REE minerals, a solid stabilized emulsification (SSE) process was developed to concentrate the fine REE minerals, bastnaesite, and monazite, from carbonate minerals. Our study examines the minerals’ surface properties, contact angle, and zeta potential, on the resulting mineral-oil–water emulsion systems. The mineral separation occurred naturally, without surface modifiers, using key operating parameters, like moderate agitation (450 rpm), low oil viscosity (< 20 cSt), and a pH ranging from 6 to 10. In the fine ore (< 38 µm), REE-bearing minerals, predominantly liberated or highly exposed, had a strong affinity for the oil phase (contact angle > 59°), compared to the carbonate minerals (contact angle < 48°), which remained in the aqueous phase. As monazite and bastnaesite, particularly monazite, tended to attach to the oil, a 68 % REE recovery and an enrichment ratio of 2.9 occurred in a single-stage emulsification process. This study showcases SSE as a promising sustainable solution for rare earth beneficiation.