Thermodynamic Study of Adsorption behaviors of Trivalent Metal Ions onto Chelating Resin: Comparison between Scandium(III) and Other Metal Ions

Abstract

Scandium (Sc) has no commercially viable independent deposits and is mainly recovered as a by-product of the smelting of other ores. In the process of recovering nickel from laterite ores, Sc is recovered from sulfuric acid leachates. An ion-exchange resin method is an effective way to recover low concentrations of Sc(III) in sulfuric acid leachates. In addition to Sc(III), the leachates also contain trivalent metal ions Cr(III), Al(III), and Fe(III). This study proposes optimal adsorption conditions for the selective separation and recovery of Sc from other trivalent cations in sulfuric acid solutions using CR11. The adsorption behaviors of the trivalent ions Sc(III), Cr(III), Al(III) and Fe(III) were thermodynamically investigated. With increasing temperature, the equilibrium adsorption amounts of Cr(III) and Al(III) increased, that of Fe(III) decreased below 10 mmol L-1 and increased above 10 mmol L-1, while that of Sc(III) changed little. The adsorption data were measured and fitted by three models, namely, the Langmuir, Freundlich, and Langmuir-Freundlich models. The values of the coefficient of determination (R2) show that the Langmuir-Freundlich model is more suitable than the other models. The co-adsorption with SO42- anions after 0.4 - 0.8 mmol g-1 adsorption of trivalent cations may be one reason for the fit to the Langmuir-Freundlich model. In this study, column tests with synthetic solutions were also investigated. Apparent distribution coefficients of metal ions and apparent separation factors of Sc(III) versus other metals were defined as indicators of the optimal solution volume to be fed for scandium recovery.

Keywords

• ion exchange
• chelating resin
• trivalent metal ion
• scandium
• adsorption
• isotherm