Enhanced extraction of scandium and inhibiting of iron from acid leaching solution of red mud by D2EHPA and sodium chlorideD2EHPA/氯化钠强化萃取赤泥酸浸液中钪及抑制铁的实验研究

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 (XP204), NaCl concentration (CNaCl), 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 CNaCl of 75 g/L and XP204 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 [FeCln]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 [FeCln]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.