Research Of Cyclic Metallurgy Process For Recovery Of Vanadium And Chromium From Chromium-Containing Vanadate Solution By Transformation Precipitation

Vanadium and chromium are strategic metals,which are widely applied in metallurgical,material and chemical industries.The chromium-containing vanadium slag produced during the smelting process of vanadium-titanium magnetite is the main raw material for the production of V₂O₅.At present,the mainstream process of vanadium extraction from vanadium slag is sodium roasting of vanadium slag-water leaching-precipitation vanadium with acid ammonium salt.The chromium in vanadium precipitated solution is recovered by reduction and neutralization,and the neutralized solution is disposed by evaporation and concentration.However,the V-Cr-bearing reduction slag obtained by reduction and neutralization and the mixture of Na₂SO₄and（NH₄）₂SO₄obtained by evaporation and concentration are all hazardous solid wastes.Their composition are complex,and the resourcization and harmless dispose of them has become a thorny problem faced by vanadium extraction industry.In view of the defects in the process of extracting vanadium from sodium roasting vanadium slag,the paper takes the leaching solution of sodium roasting vanadium slag（chromium-containing vanadate solution）as the research target,a cyclic metallurgy process for recovery of vanadium and chromium by transformation precipitation is proposed,specifically involves selective recovery of vanadium by Ca（OH）₂from chromium-containing vanadate solution,recovery of chromium by Pb CO₃from vanadium precipitated solution,the recycling use of calcium salt and lead salt and the recovery of sodium carbonate salt.Selective recovery of vanadium by mechanical activation of calcium salts.Vanadium can be selectively precipitated by calcium salt.The precipitation efficiency of V is 99.34%by adding Ca（OH）₂according to Ca/V molar ratio 1.8 into chromium-containing vanadate solution and ball milling for 60 min at room temperature.The vanadium precipitate obtained by ball milling has good reactivity.The leaching efficiency of V reached 99.35%by adding Na HCO₃into water according to Na HCO₃/V molar ratio 2.8 to leach V from the vanadium precipitate with L/S ratio 4:1 ml/g and stirring for 6 min at room temperature.Mechanical activation can not only improve the effective utilization of Ca（OH）₂,but also can significantly improve the leaching performance of vanadium precipitate,which lays a foundation for the development of cyclic metallurgy process for recovery of vanadium by calcium salt from leaching solution of sodium roasting vanadium slag.Cyclic metallurgy process for recovery of vanadium by calcium salt from leaching solution of sodium roasting vanadium slag was studied.Under the optimized conditions,the precipitation efficiency of V is99.34%,while the content of Cr in the precipitate is about 0.041%,the leaching efficiency of V reached 99.35%.The CaO obtained by calcination of CaCO₃leaching residue can be returned to the process of vanadium precipitation for recycling.The crystals of NH₄VO₃can be obtained by adjusting the Na HCO₃leaching solution p H to 8.0 and then adding NH₄HCO₃according to NH₄⁺/V molar ratio 1.0 stirring for 8 h at room temperature.The crystallized solution can be returned to the process of leaching vanadium precipitate.In the whole cycle process,the leaching efficiency of V always maintained above 99%,and the recycling utilization of CaO and Na HCO₃in vanadium extraction process can be realized.Cyclic metallurgy process for recovery of chromium by lead carbonate transformation precipitation from vanadium precipitated solution produced with calcium salt was studied.Under the weak base conditions,the concentration of Cr in the solution decreases to 0.001 g/L by adding Pb CO₃and controlling the final p H to 8.5.Under the strong base conditions,the concentration of Cr in the solution can be decreased to 0.016 g/L by adding Pb CO₃and adjusting the initial p H to 12.5.Chromium can effectively leached from chromium precipitate with Na₂CO₃solution.Under the optimized leaching conditions,the leaching efficiency of Cr reaches 96.43%and 96.47%by adding weak base chromium precipitates and strong base chromium precipitates into Na₂CO₃solution.The base leaching solution can be used to circularly leach the chromium precipitates until Na₂Cr O₄near saturation.The base leaching residue containing Pb CO₃can be returned to the chromium precipitation process,which realized the recycling of lead salt.Electrodialysis concentration can recover the sodium carbonate salt from chromium precipitated solution.The concentrated water is cooled to crystallize Na HCO₃and fresh water is returned to the process of leaching vanadium slag clinker,which realized the closed circulation of sodium carbonate and water in the process of extraction vanadium,and the whole process of the cyclic metallurgy process of separation and recovery vanadium and chromium from the chromium-containing vanadate solution can be completed.In addition,the above-mentioned cyclic metallurgy process is also applied to the recovery of chromium from acid vanadium precipitated solution produced by the current vanadium extraction process from vanadium slag,and the leaching of vanadium from calcification roasted clinker of vanadium slag.Adjusting the p H of acidic vanadium precipitated solution to 12with lime,after filtration,the concentration of Cr decreased to 0.002 g/L by adding Pb SO₄into the solution according to Pb/Cr molar ratio 2.5.The chromium precipitate is the mixture of Pb Cr O₄?Pb O and Pb SO₄.The leaching efficiency of Cr reaches near 99%by adding chromium precipitates into 12%Na HSO₄solution with L/S ratio 10:1 ml/g and stirring for 100 min at 80℃.The acidic leaching solution containing chromium can be reused to circularly leach chromium precipitates until Na₂Cr₂O₇near saturation and the acid leaching residue containing Pb SO₄can be returned to the chromium precipitation process.The leaching efficiency of V reaches 97.34%by adding calcification roasted clinker into 10%Na HCO₃solution with L/S ratio5:1 ml/g and stirring for 120 min at 95℃.The leaching process is calculated by the shrinkage unreacted core model,and the apparent activation energy is 38.10 k J/mol.After the crystallized solution heated and deaminated for 30 min at 95℃,the concentration of NH₄⁺in the solution changed little with the further increase in time.Calcification roasting clinker was added into deaminated solution to leach vanadium directly,the sodium bicarbonate solution and the deamminated solution have the same leaching effect.The residual NH₄⁺in the deamminated solution have not adverse effect on the leaching of vanadium.There are 90 figures,19 tables and 124 references in this thesis...