| This study was designed to recover vanadium, chromium, tungsten and molybdenum from residues and spent catalysts by solvent extraction using primary amine as the extractant. Mechanism and pathways of solvent extractions were discussed, and the novel processes of waste utilization were developed. Results were as below:1) To investigate the relationships between oxometallate species in aqueous phase and extraction complexes in organic phase, pH-1gC diagram, slope method and spectra wereapplied. The reaction pathways of solvent extraction were suggested:V(V) was extracted as H6V10O28 in organic phase and extraction complex was [(RNH2)6(H6V10O28)](o) in the beginning of extraction. The predominant extraction complex in equilibrium status was [(RNH2)2(H3V3O9)](o)with the extraction rate of 99.89%, when mH:mv=1.25.W(VI), Mo(VI), and Cr(VI) were extracted as H6W12O39, H6Mo7O24, and H2CrO4 in the beginning of extraction, respectively. The predominant extraction complex of W(VI) in equilibrium status was [(RNH2)(H2WO4)](o)with the extraction rate of 99.15%, when mH:mw=2.35. The predominant extraction complex of Cr(VI) in equilibrium status was [(RNH2)(H2CrO4)](o)with the extraction rate of 98.77%, when mH:mMo=2.86. The predominant extraction complex of Mo(VI) in equilibrium status was [(RNH2)3/2(H2MoO4)](o)with the extraction rate of 93.67%, when mH:mMo=3.8.A positive correlation was found between distribution ratio and the concentration of metal and H+ in aqueous phase. The extraction equilibrium constants and Pizter equation parameters were compared, the priority of primary amine extracting metal was suggested as V>W>Cr>Mo, which was testified by experiments examining extraction rate, distribution ratio and separation coefficient.2) Separation of V(Ⅴ) and Cr(Ⅵ) by primary amine was studied. The results showed that V(Ⅴ) could be selectively extracted in solvation mechanism with the extraction rate of 97.15% while Cr(Ⅵ)’s extraction rate was 18.74%, when mH:mmetal=0.7. and Chromate’s hydrolysis showed positive effect on V(Ⅴ) extraction by providing H+. When mH:mmcta1>0.7, Cr(Ⅵ)acted as an extraction competitor instead.Study on the separation of V(Ⅴ)-W(Ⅵ) and V(Ⅴ)-Mo(Ⅵ) showed that:when mH:mmetal<2.5, the solvent extraction conducted in solvation mechanism and V(Ⅴ) was in priority, while W(Ⅵ)/Mo(Ⅵ) was in priority and the mechanism was anion exchange when mH:mmctal>2.5.3) Based on lab-scale experiments of using simulated leaching liquor, the processes suggested were verified. Results of the separation of V(Ⅴ) and Cr(Ⅵ) showed that V2O5 with the purity over 99.9% was prepared. Results of extraction of V(Ⅴ) and W(Ⅵ)showed that the extraction rates of V(Ⅴ) and W(Ⅵ) were 99.96% and 99.12%, respectively. Results of the separation of V(Ⅴ) and Mo(Ⅵ) showed that H2MoO4 and V2O5 were prepared with the purity over 99%.4) The industrial experiments on resource recovery of residue containing V(Ⅴ) and Cr(Ⅵ) were operated for 9 months. The results showed that V(Ⅴ)’s average extraction rate was 98.6%, that separation coefficient was 1524 on average, that the stripping liquor of loaded organic phase contained 45-50 g/L V(Ⅴ) and 0-1 g/L Cr(Ⅵ), and that V2O5 with the purity over 99.5% was prepared. The novel process was stable and could recover values from hazardous residue. |
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