A solution chemistry approach to the study of rare earth element precipitation by oxalic acid

A solution chemistry approach is developed to study oxalic acid efficiency (OAE) in recovering rare earth (RE) elements from the leachates of weathered clays. The optimal pH for precipitation (approximately 2) to obtain the highest RE recovery with the highest purity is identified experimentally and confirmed by solution chemistry calculations. Applying the solution chemistry approach to three case studies, the cause for a larger oxalic acid consumption than that calculated from stoichiometry of RE oxalate precipitation is identified. A typical OAE of approximately 60 pct was determined with 40 pct of excess oxalic acid consumed by precipitating and complexing non-RE elements while maintaining a low residual RE element concentration. Both solution chemistry calculations and experimental results showed that OAE can be improved by processing leachates of high initial RE concentrations.