Separation of V(V) and Cr(VI) from vanadium-containing solutions based on E-pH diagrams of V-Cr-S-H 2 O system

The extremely similar physicochemical properties of vanadium and chromium lead to the difficulty in separating from each other. In this study, a novel hydrometallurgical process was devised to selectively precipitate chromium from vanadium-containing solutions, facilitating the efficient separation of V(V) and Cr(VI) while enabling the recovery of both vanadium and chromium species. The speciation of vanadium and chromium in solutions was investigated through the construction of E-pH diagrams for V-Cr-S-H2O system at 298 K, 363 K, and 453 K. The results revealed that under conditions of pH approximately 12 and temperature 363 K, the reduction potential of SO42-/S2- was found to lie between that of CrO42-/Cr(OH)3 and VO43-/V2O3. This suggests that selective reduction of Cr(VI) could be achieved using S2- as reducing agent. In order to validate the theoretical findings, single-factor experiments were conducted on a laboratory scale. The effects of various parameters including initial pH, sodium sulfide dosage, reaction time, temperature, and initial concentration of vanadium-containing solutions on the chromium precipitation ratio and vanadium loss ratio were investigated. The experimental outcomes showed that the chromium precipitation ratio reached 99.8 % while the vanadium loss rate was only 3.5 % when the experiment was conducted at the optimal conditions: the initial pH was set to 12, sodium sulfide dosage was 2.0 times of the theoretical dosage, reaction time was 60 min and the temperature was 363 K. Then, the chromium concentration in the solution decreased from 2407 mg/L to 3.3 mg/L. Ultimately, V2O5 with a purity of 99.0 % and Cr2O3 with a purity of 97.2 % were successfully obtained.