Thorium ion exchange separation from rare earth elements ore samples following a combined attrition and dissolution procedure

Abstract

Autogenous grinding (without grinding media) may provide some advantages if satisfactory lixiviation efficiency can be achieved on larger grain sizes. This grinding strategy requires less energy and offers important cost savings and reduction of GHG emissions in the mining industry compared to other commonly used approaches. Two attrition cells (1.2 L, 12 L) were designed to conduct a wet autogenous grinding. The combined grinding and leaching experiments were performed using six Canadian rare earth elements (REEs) ore samples to solubilize the REEs while grinding the ore in a modified attrition mill. Sulfuric, hydrochloric and nitric acids were compared under various operating conditions on three different types of ore samples (carbonatite, sedimentary, peralkaline). The addition of an alkaline step was also investigated. Metals dissolution in the 1.2 L attrition mill with or without NaOH addition (T = 20 °C, solid/liquid ratio = 20%, acid concentration [HNO3] = 7.5 M, time = 1 h) was found effective for the carbonatite ore (solubilization efficiencies of 91–99% Th, 29–32% U, 85–91% LREEs, 84–94% HREEs) and the sedimentary ore (solubilization efficiencies of 89–99% Th, 98–99% U, 22–83% LREEs, 48–99% HREEs). Actinide elements often comprise a significant component in REEs ore samples and are considered impurities. Their presence in primary REE mineral resources is problematic from a regulatory and health physics perspective. To overcome these issues, anionic, cationic and chelating resins were tested to remove Th from the nitric leaching liquor. Best separation results were obtained with the impregnated resin Lewatit VPOC 1026. To the best of our knowledge, this is the first time that Lewatit VPOC 1026 was reported in the literature for Th separation from REEs.