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 countercurrent 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 (Delta H-0, Delta S-0, and Delta G(0), 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