Separation And Purification Of Chromium Oxide From Chromium Slag Precipitated In Waste Water

The technique difficulties still exist during the process of harmlessness and reclamation of chromium slag in China.Therefore,the research on studying a practical way to reduce the hazard and reclaim the chromium slag is significant to the sustainable development.In this study,focusing on purifying the chrome from slag for recycling,the sample of trivalent chromium slag is precipitate in waste water.This is different from common hexavalent chromium slag,and the contents of chromium should above 50%.The redox purification is used in this study.First,the optimum condition of roasting process is mixed the slag with 120%Na2CO3 and 10%CaO,heated to 800?,kept for 50mins.In this condition,the leaching rate of chrome is highest.Second,the optimum condition for leaching process is mixing the 20%sulphuric acid with liquid-solid ratio of 20:1 in 80? for 50min.Then,1 mixed leaching agent with reducing agent.The highest recovery rate of chrome will be generated,by mixed the 80%Na2SO3 solution,kept pH to 3.0 for 10min in 80?.Next,adjusting pH by NaOH to deposit chrome in pH 8.0 for 40min in a temperature of 80? could maximum the recovery rate.Last,the optimum condition for calcination of Cr(OH)3 is to heat to 900?for 120min.After roasting,the grade of Cr2O3 can reach up to 92%.After redox purification,acid-alkali purification is used to increase the recovery ratio.The optimum condition for acid leaching is 33.3%of HCl at a temperature of 70?for 60 min,with liquid-solid ratio of 15:1.The maximum ratio of iron removal by 140%oxalic acid is performed best with 80%NaSO3,at a temperature of 30? for 20min.Then,I used NaCO3 to redeposit Cr(OH)3.The highest ratio of deposition is in temperature:90C,time:50 min,pH:9.0.The last step is purify the roasted Cr2O3 in NaOH solution.Using NaOH 4mol/L,heating the Cr2O3 in 90? for 60min,the grade of Cr2O3 increased to 95%.