Recovery of oxalate from scrubbing solution containing rare earths and iron produced during uranium recovery from phosphoric acid

A solution containing oxalate complexes of rare earths, yttrium and iron (III) is obtained during the processing of wet process phosphoric acid for uranium recovery by solvent extraction. A process is described to recover oxalic acid from such a solution. The process is based on the conversion of iron (III) oxalate into calcium oxalate by calcium chloride followed by the metathesis of calcium oxalate with sulphuric acid to produce calcium sulphate and free oxalic acid. Data is presented to illustrate the influence of various parameters such as pH, temperature, digestion time and amount of calcium chloride on effective conversion of calcium oxalate. Under optimized conditions of pH 1, digestion time 2 h, twice the stoichiometric ratio of calcium chloride at ambient temperature (30±1°C) the recovery of calcium oxalate was found to be >94%. An overall schematic material balance flow -sheet for treating the oxalate solution of rare earths, yttrium and iron (III) to oxalic acid recovery has been presented. An improvement in the second cycle of patented process flow-sheet based on 1.5 M D2EHPA + 0.2 M TBP incorporating oxalic acid scrubbing / recycle for uranium recovery from phosphoric acid has been tested and found to be simple in terms of operations and capable of meeting product specifications.

Process parameters including pH, digestion time, temperature and amount of calcium chlo- ride have been optimized for the recovery of oxalic acid from iron bearing scrubbed solution obtained in second cycle of 1.5 M D2EHPA + 0.2 M TBP solvent extraction process during uranium recovery from WPA. The feasibility of using the recovered oxalic acid at scrubbing stage for iron removal from loaded extract comprising of 1.5 M D2EHPA + 0.2 M TBP + 14.0 g/L U3O8 + 1.12 g/L Fe(III) is established. An improved flow sheet based on 1.5 M D2EHPA + 0.2 M TBP for second cycle for uranium recovery and oxalic acid recycle was found to be efficient.