LAUSR

Abstract Niobium consumption has burgeoned owing to the increasing application of niobium in critical industries, including the aerospace and oil and gas industries. Conventional metallurgical technologies and separation methods for niobium extraction use highly concentrated HF, which is hazardous to both humans and the environment. A solvent extraction system comprising trioctyl tertiary amine (N235) and 4-methyl-2-pentanone (MIBK) that can extract and separate niobium from an oxalate-containing H2SO4 solution is proposed in this paper. Niobium solutions tend to contain titanium and iron impurities; therefore, the effects of various conditions on the separation of the three elements were investigated. The extraction mechanism and thermodynamics of the process were also examined. Over 82% niobium was extracted at an organic-to-aqueous phase ratio of 1:1 and the H+ concentration of 8.29 mol/L using an organic phase with 50 vol% N235 and 50 vol% MIBK as the extractants at 20 °C. Only 18.4% titanium and 3.35% iron were co-extracted. Two stripping processes, both of which further separated niobium and titanium, are also proposed herein. The possible composition of the niobium-containing extraction complex was [(R3NH)·NbO(C2O4)2(H2O)2], as supported by a Fourier transform infrared spectroscopy (FT-IR) analysis and ultraviolet–visible (UV–vis) spectrophotometry. The extraction mechanism was inferred to be the association of R3NH+ in N235 with the [NbO(C2O4)2(H2O)2]− from the acidic niobium-containing solution, and the stripping mechanism was concluded to be anion exchange. The enthalpy change (∆Ho) of the extraction system was −11.0 kJ/mol at 288.15–313.15 K, which indicated that niobium extraction from the H2SO4 solution with oxalate using N235 and MIBK was an irreversible exothermic process.