An environmentally friendly route for beneficiation of rare earth-bearing minerals by Pickering emulsification: adjusting the interfacial and formulation parameters
The performance of the Pickering emulsification process to selectively separate rare earth-bearing minerals from the associated gangue and to concentrate them in a novel environmentally friendly approach was enhanced by adjusting the interfacial conditions and the formulation parameters. The present study investigated the effects of interfacial tension, oil polarity and viscosity on the selective separation. Modifying the emulsion formulation and selecting an appropriate oil, oil to water volume ratio, and solid mass fraction can enhance the recovery and grade of rare earth bearing minerals in the product when compared with conventional flotation. Various oils with different viscosities and chemical compositions (silicone oil, oleic acid, paraffin, and kerosene) supplemented with an additive (1% 1-hexanol) to modify the interfacial tension, and a continuous phase other than water (i.e., 90% ethylene glycol) were tested. An oil viscosity of 200 cSt, oil-to-water ratio of 10%v, and a solid particle concentration of 5 wt% provided the best selectivity. Since silicone oil is not economically feasible at industrial scale, paraffin oil, which is less expensive, was tested and provided better selectivity. We employed a Niobec ore containing bastnäsite and monazite with total rare earth elements of 3.3 wt%. The recovery of a one-stage emulsification was improved significantly by up to 56% using paraffin oil. It also resulted in a product enrichment ratio of approximately 2.7.