Separation And Recovery Of Chromium And Vanadium From High-chromium Vanadium Slag

Vanadium-titanium magnetite is the major characteristic of multi-metallic mineral resources in China, which provides enough steel smelting iron ore resources and sufficient vanadium and titanium source of raw materials for non-ferrous metal smelting, vanadium slag from converter residue of steel-smelting is the main resources of vanadium. Leaching of vanadium and chromium from high-chromium vanadium slag by sodium roasting-water extraction was studied firstly, separation and recovery of vanadium and chromium by ammonium vanadium precipitation and reduction of chromium, the reaction mechanism of ammonium vanadium precipitation and reduction of chromium, process parameters are investigated; finally, exploring a new method which separated and recovery of V and Cr, the reaction mechanism of process, the factors and process parameters are studied.Sodium roasting-water leaching was carried out by high-chromium slag as raw material, sodium carbonate with a certain amount of low-grade magnesite, the basic parameters of roasting process was determined which was a1.6of sodium carbonate ratio at750℃for lh, the best leaching rate of V and Cr were80%,70%under the optimum condition. The result showed that, the effect of roasting, amount of sodium carbonate and solid-liquid rate on leaching rate of V and Cr were significant, bigger solid-liquid rate, higher leaching rate of V and Cr; the effect of extraction on leaching time was not apparent.Effects of impurities such as Cr、P、Si、Cl-、SO42-on ammonium poly-vanadium are investigated. The results showed that increase of the Cr concentration can significantly reduce the rate of sedimentation, especially the low concentration of Vanadium is influenced obviously; the effect of Si on precipitating is low, precipitation of Vanadium on P is influenced heavily, when the concentration of P is upon0.1g/L, the sedimentation of Vanadium is below75%; the effect of low concentration of Cl" is not noTable, however, when the concentration of NaCl up to100g/L, the precipitation of Vanadium is below20%; precipitation of Vanadium on SO42-is influenced slightly.Then exploring a new method which was modest reduction roasting-alkali leaching, with an appropriate amount of reduction agent that can restore Cr(Ⅵ) and V(Ⅴ) to Cr (Ⅲ) and V (Ⅳ), a small amount of vanadium and most of chromium were precipitated, the filtrate was vanadium-rich liquid, vanadium was extracted by alkali leaching after precipitate was calcined, vanadium and chromium were separated from vanadium-containing chromium solution. The best process parameters of modest reduction and precipitate was that:the amount of sodium sulfite was50%of what can restore Cr(Ⅵ) and V(V) to Cr(Ⅲ) and V(Ⅳ), the origin pH was2.0～2.5and precipitate pH was5.0～5.5, at room temperature for30min, the sedimentation ratio of vanadium and chromium was15～20%and90～95%. appropriate roasting conditions is at850～950℃for more than1h, it was found that in the process of roasting Cr (Ⅲ) and V (Ⅳ) generated CrVO4, then CrVO4was decomposed of Cr2O3and V2O5; the effect of leaching by NaOH was better than Na2CO3and effect of extraction on leaching temperature is not significant; it is benefit to leach more of V2O5by increasing extraction medium concentration and time; under the optimum leaching conditions (3mol/LNaOH, leaching for1.5h at90℃the leaching solution contained V:1.76g/L, Cr<0.01g/L, and the residue was Cr2O3powder with purity of96%.