Extraction equilibria of cerium(IV) with Cyanex 923 followed by precipitation kinetics of cerium(III) oxalate from sulfate solution

Abstract

The phenomenon studies on solvent extraction of cerium(IV) using Cyanex 923 followed by the precipitation kinetics and recovery of cerium(III) oxalate has been investigated from the sulfate media. The extraction equilibria investigated with varying concentrations of extractant into the organic phase and acid into the aqueous phase could reveal the solvation of [Ce(SO4)2·2L·HSO4-]org species. The thermodynamic properties determined at different temperatures exhibited the exothermic nature of extraction (ΔH°, −12.2 kJ·mol−1). The quantitative extraction and back-extraction of cerium(IV) in sulfate media could be achieved in three stages of counter-current contact at an organic-to-aqueous ratio of 2/3 and 3/2, respectively. Ce-enrich stripped solution was subsequently recovered as cerium(III) precipitates by treating with oxalic acid. Precipitation with the optimized dosage of Ce:H2C2O4 as 1:≥10 yielded the oxalate products of unlike physico-chemical characteristics, while precipitating at different temperatures. The precipitation kinetics was found to have good fits to the Avrami equation; where, n values < 1 indicated for instantaneous nucleation that leads to flakes-shape growth of precipitates and supported by the surface morphological study. Evaluation of the apparent activation energy (Ea, 8.6 kJ·mol−1) indicated that the precipitation reaction follows a diffusion-controlled mechanism as supported by the surface site saturation of cerium(III) oxalate through the constants of Avrami equation. The findings of the present study may supply a potential way of extracting cerium(IV) from sulfate leach liquor of rare earths ores and the precipitation recovery of cerium(III) oxalate as the suitable precursor of (nano)crystalline ceria.