Separation of titanium from vanadium and iron in leach solutions of vanadium slag by solvent extraction with trioctyl tertiary amine (N235)

Abstract

The separation of titanium (Ti) (IV) in acidic leach solutions of vanadium slag by solvent extraction with trioctyl tertiary amine (N235) is proposed. Because the leach solutions contain a lot of vanadium (V) and iron (Fe) impurities, the effects of various conditions on the separation of Ti, V, and Fe were investigated. Then, the extraction mechanism and thermodynamics of the process were discussed. Upon using 35% (v/v) N235 and 65% (v/v) sulfonated kerosene as the extractant, over 82% Ti was extracted at a 2:1 organic to aqueous phase ratio (4 min at 298.15 K in a single-stage contract) with only 5% V and 10% Fe co-extracted. After the three-stage extraction, over 97% Ti, 7% V, and 18% Fe were extracted. By washing with 1.25 mol/L ammonium sulfate, most of the V and Fe impurities were removed with an insignificant amount of Ti wasted. Upon stripping with 1.0 mol/L ammonia at a 1:1 organic to aqueous phase ratio, approximately 90% Ti was recovered from the purified organic liquor. Other impurity elements such as Mn, Al, Mg, Ca and Si have little effect on the Ti separation. The possible composition of Ti-containing extract may be (R3NH)2·TiO3, and Fourier transform infrared spectroscopy (FT-IR) analysis confirmed that the characteristic peaks representing NTiO and TiO were in the extracted compound. The mechanism of the extraction included the association of R3NH+ from N235 with TiO32− from the acidic leach solutions. Furthermore, thermodynamic calculations showed that Ti separation from the leach solutions of vanadium slag using N235 is an exothermic, irreversible, and possible reaction at 298.15–338.15 K.