Enhanced extraction of scandium and inhibiting of iron from acid leaching solution of red mud by D2EHPA and sodium chloride

Abstract

D2EHPA (P204), tri-butyl-phosphate (TBP) and sodium chloride (NaCl) were attractive for selective extraction of scandium from acid leaching solution of red mud. The extraction parameters of P204 concentration (X_P204), NaCl concentration (C_NaCl), pH value, reaction time, stirring speed and O/A were investigated to extract scandium and separate iron from the acid leaching solution. The extraction mechanism was analyzed by Fourier transform infrared spectroscopy (FT-IR) and thermodynamic theory. The single-stage extraction efficiency of scandium, iron and β_(Sc/Fe) were 99.1%, 9.4% and 1061.2, respectively, with C_NaCl of 75 g/L and X_P204 of 0.75 at solution pH value of 1.2 and stirring speed of 200 r/min for 6 min, in which a good separation effect of scandium and iron was obtained. The vibration absorption peak Sc—O was contributed to the extraction of scandium with P204. The complex [FeCl_n]³⁻ⁿ existed in the solution with adding NaCl into the acid leaching solution. The value of n was higher and the valence state of the complex [FeCl_n]³⁻ⁿ was lower with an increase of chloride concentration, which restricts the extraction efficiency of iron with P204. The extraction of three stages in the counter-current simulation experiments was carried out according to the McCabe-Thiele diagram. Gibbs free energy change (ΔG) of −5.93 kJ/mol, enthalpy change (ΔH) of 23.45 kJ/mol and entropy change (ΔH) of 98.54 J/(mol·K) were obtained in the solvent extraction proces, which indicate that the extraction reaction is easily spontaneous and endothermic and a proper increase of temperature is conducive to the extraction of scandium.

Keywords

scandium / selective extraction / D2EHPA/sodium chloride / leaching solution / red mud

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