Simultaneous stripping and regeneration of chelate structure of vanadium through vanadium reduction and conversion in vanadium-bearing shale extraction

Abstract

Chelating extractants have shown excellent selectivity in vanadium extraction. Nevertheless, the resulting extraction complex is stable, making the stripping of chelating extractant a challenge. The H2C2O4-H2SO4 system was proposed to stripping vanadium from the loaded organic phase of chelating extractant Mextral 984 H. The effects of process parameters of H2C2O4-H2SO4 system on the vanadium stripping percentage was investigated. The results show that the single-stage vanadium stripping percentage reached 93.12%, and the vanadium concentration in the single-stage stripping solution reached 13.44 g/L under optimum conditions: the H2SO4 concentration of 1.87 mol/L, the H2C2O4 concentration of 0.16 mol/L, the temperature of 80 °C, the time of 30 min, and phase ratio(O/A) of 4:1. In addition, the high extraction efficiency (>85%) was maintained after 10 cycles, indicating that the developed system can be used in the Mextral 984 H stripping system. The mechanism of stripping was also analysed using FT-IR and 1H NMR combined with thermodynamic and quantum calculations. It was summarized that after H2C2O4 reduces V(V) to V(IV), H+ can replace V(IV), the free V(IV) in organic phase is more prone to coordinated with C2O42- and SO42- and then goes into aqueous phase. Thus the stripping and regeneration of the loaded organic phase of Mextral 984 H can be occurred simultaneously. Meanwhile, the introduction of H+ can speed up the stripping process. The innovative method of the reduction stripping of vanadium is proposed in the black shale extraction field.