New process consisting of oxidative stripping of vanadium from loaded D2EHPA organic solution with H2O2 and direct precipitation with sulfuric acid

Abstract

Abstract The traditional process of extracting V(IV) with di(2-ethylhexyl) phosphoric acid (D2EHPA) uses H2SO4 for V stripping and ammonium salt for V precipitation, leading to excessive consumption of H2SO4 and NH3·H2O, which results in a large volume of ammonia‑nitrogen wastewater. To solve this issue, a novel stripping reagent, H2O2, with the multifunction of oxidation and stripping, and a new method of precipitating vanadium from a solution of vanadium peroxy compounds were introduced to replace the traditional stripping reagent and ammonium salt precipitation, which requires separate stripping, oxidation, neutralisation and precipitation steps. The oxidative stripping of V from the loaded organic system consisting of 10% D2EHPA and 5% tri-butyl phosphate (TBP) in sulfonated kerosene using H2O2 was systematically investigated. The results indicated that 98.7% of the vanadium was stripped by three-stage cross-flow stripping under mild optimal conditions. Moreover, it was found that VO(O2)2–in the strip solution decomposed into VO(O2)+under oscillating conditions and the cation was synergistically re-extracted by D2EHPA and TBP, which resulted in a significant decrease in the stripping of vanadium and poisoning of the organic phase. The use of D2EHPA alone as the extractant can effectively prevent the problems encountered when H2O2 is used as the stripping reagent. The strip liquor could be used for direct precipitation of vanadium. A precipitation efficiency of 87% was obtained by adding a small amount of H2SO4. This new process combines oxidation, stripping and direct precipitation and exhibits the advantages of a short process flowsheet, with reagent savings (~95% decrease in H2SO4 consumption and no NH3·H2O consumption compared with traditional processes), and wastewater that is free of ammonia /nitrogen.