Optimization of the process of obtaining RE2O3 from xenotime using statistical design

Abstract

The study of the production of the mixed rare earth oxide (RE2O3) from xenotime via hydrometallurgy was performed to evaluate the significance of the effects of three factors including the melting temperature (A), the ratio of NaOH/xenotime (B), and time (C) for the first stage of alkaline fusion by using full 23 factorial design. Also, seven factors were studied including liquid/solid ratio (LS), inert (I1), excess HNO3 (EA), temperature (TL), inert (I2), time (HL), and inert (I3) for the second and third steps, which were the oxalic acid leaching and precipitation, using Plackett-Burman design (PBD). Optimizing factors for significance were performed using plots of interactions, analysis of variance (ANOVA), Pareto charts, surface charts, analysis of Student’s t-test and F test. A regression model was suggested and satisfactorily adjusted for the experimental data of the process of alkaline fusion, revealing an elevated coefficient of determination (R2=0.92) to a Fcalculated value well above the Ftabulated value, at a 95% confidence level. The RE2O3 was characterized by chemical analysis, X-ray diffraction, scanning electron microscopy, and specific surface area. This process resulted in a material with identical physical and chemical properties to the isolated compounds of rare earths and can be used as an alternative sintering additive in advanced ceramics, and indicated that the cost of final production of RE2O3 can be lower compared to commercial Y2O3.