Safe utilization of chromium-bearing vanadate residue by recovery of vanadium and chromium based on calcium circulation

Abstract

A safe, economical treatment of hazardous chromium-bearing vanadate residue (CVR) will significantly benefit the clean production of chromate-bearing salts. This study investigated recovery of sodium vanadate and sodium chromate from CVR in sodium bicarbonate solution. Results indicate that the stability of calcium vanadate and calcium chromate depends on pH and [HCO3–]. CaV2O6·4H2O transforms into CaV2O6·4H2O, CaV2O6·2H2O, CaV2O6, Ca2V2O7·2H2O, and Ca5(VO4)3(OH) when pH increases from 7.51 to 12.32. Increasing pH and reducing CVR dosage improve the vanadate extraction rate, and high V2O5 and Na2Cr2O7·2H2O extraction rates are achieved in dilute NaHCO3 solution. Moreover, addition of NaOH positively contributes to the recovery of vanadate and chromate from CVR. Over 95% V2O5 and Na2Cr2O7·2H2O in CVR can be extracted from 60 g/L NaHCO3 and 30 g/L NaOH solutions at 90 °C for 2 h. In order to reduce the hazardous residue containing chromate after recovery of CVR, calcium circulation is presented. Results show that more than 60% lime can be saved with fresh residue addition to remove vanadate from sodium chromate solution due to the active CaCO3. Moreover, no lime is required in removal of vanadate when the roasting residue is added. Therefore, a novel process is developed for utilization of CVR.