Abstract
An environmentally friendly approach was reported for recovering vanadium (V) from aqueous media with aqueous two-phase system (ATPS) formed by poly (ethylene glycol) 2000 (PEG2000) and sodium sulfate with octadecyl amine ethoxylate ethers as extractants. The effect of aqueous pH, the type of extractants and phase-forming salts, vanadium concentration and extracting temperature on the extraction performance of vanadium was investigated. The researched results indicated that the extraction rate of vanadium has remarkable relationship with vanadium species in aqueous phase, and the selected extractants can extract efficiently vanadium from salt-rich to PEG200-rich phase. The initial and equilibrium pH in aqueous phase has no relationship with vanadium concentration, and there is no new covalent bond generation between polyvanadate anion and extractant in PEG 2000-rich phase by FTIR, which can be deduced that polyvanadate anion is extracted into PEG 2000-rich phase due to the electrostatic attraction interaction between protonated extractant and polyvanadate anion. Adding chloride and nitrate in aqueous two-phase system could remarkably decrease the extraction rate of vanadium, and then sulfate is in favor of extracting vanadium. The extraction rate of vanadium decreases with increasing temperature from 40.0 °C to 60.0 °C, which showed the phase transfer of vanadium from salt-rich phase to PEG2000-rich phase is exothermal, resulting from the difference of interaction energy among all compositions in aqueous two-phase system. The vanadium can be easily separated out from the solution containing Fe(III), Co(II), Ni(II), Cu(II), Zn (II), Al(III), Cr(III) and Mn(II) under the suitable conditions. The stripping rate and precipitation rate of vanadium can be easily achieved to 90% and 80%, respectively, in single stage stripping with ammonium carbonate solution as stripping agent and phase-forming salt.
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