Separation and extraction of niobium from H2SO4 solution containing titanium and iron impurities

A fluoride-free solvent extraction method for niobium separation in leached sulfuric mother liquor of ilmenorutile was proposed in this paper. The extraction system comprising trioctyl tertiary amine (N235) and 4-methyl-2-pentanone (MIBK) demonstrated good extraction efficiency and selectivity of niobium over titanium and iron impurities in sulfuric acid–oxalate solutions. Details of extraction, scrubbing, and stripping processes were investigated herein, and its practical effectiveness in both batch and multi-stage simulated counter-current modes was verified. Over 73.8% niobium was extracted under optimum conditions, and only 2.8% titanium and 1.7% iron were co-extracted. The recovery of niobium reached 99.1% in the four-stage simulated counter-current extraction tests. In the three-stage simulated counter-current stripping tests, the stripping efficiency of niobium reached 99.7% with 2.0 mol/L HNO3. Qualified niobium oxide products were prepared. The enthalpy change, entropy change, and the standard Gibbs free energy change (ΔHo, ΔSo, and ΔGo, respectively) corroborated the exothermicity, orderliness, and spontaneity of the reaction. The possible composition of the extraction complex was [NbO(C2O4)2(H2O)2]−, as supported by a Fourier transform infrared spectroscopy and ultraviolet–visible spectrophotometry. The extraction mechanism was inferred to be the outer-sphere complexation through physical binding which was the association of R3NH+ in N235 with the [NbO(C2O4)2(H2O)2]−. A preliminary mass balance indicated that 203.92 g Nb2O5 was generated from 1000 g raw material ilmenorutile.