An experimental design approach for the separation of thorium from rare earth elements

As a part of technological evaluation of Eskisehir-Beylikahir thorium ore of Turkey, a novel study on the separation of thorium from oxalate concentrate including Th, La, Ce, Pr, Nd, Sm, Eu, Gd were carried out. As a first step, thorium-rare earth elements (REEs) oxalate concentrate was precipitated from nitric acid solution by the addition of 100% excess of oxalic acid amount necessary for stoichiometry. The concentrations of Th and REEs in the oxalate concentrate were chosen to simulate the oxalate intermediate product previously obtained from leach liqueur. Separation of thorium from REEs is mainly based on their significant solubility differences in ammonium oxalate solution. The dissolution conditions of thorium-REEs oxalate concentrate were investigated using central composite design (CCD) with three independent variables at five levels. The effect of independent variables such as contact time, amount of precipitate and the concentration of ammonium oxalate (AOX) solution on the thorium dissolution yield (%) were investigated. Analysis of variance (ANOVA) revealed that the effect of precipitate amount and the effect of ammonium oxalate concentration were found significant on the separation of thorium from Th-REEs concentrate. Probability F-value (F = 7 x 10(-6)) and correlation coefficient (R-2 = 0.96) indicate that a proposed model fits the experimental data well. At the optimum conditions the thorium dissolution yield was achieved to 96.66 +/- 2.16%.