Solvent Extraction And Separation Of Molybdenum From The Wastewater

With the increasing discharge of the wastewater containing molybdenum, chromium and zinc, more and more metal resources are lost and molybdenum with low toxiticy and more toxic chromium do more harm to the environment. So it is important to recover molybdenum, chromium and zinc from the effluents. Among the methods for molybdenum recovery, solvent extraction is a more efficient method due to its advantages such as the big handing capacity, simplicity of operating and ease serialization. This work was focused on the recovery of molybdenum form the effluents containing 0.5 g/L zinc, 0.5 g/L molybdenum and 0.05 g/L chromium. The synergistic effect of the extraction of molybdenum by the mixture of di-2-ethylhexyl phosphoric acid (P₂₀₄) and trialkylamine (N₂₃₅) was also studied.The results showed that molybdenum, zinc and chromium can be extracted by the extractant N₂₃₅ in the diluent sulfonated kerosene. In the system of 10% extrctant, 1/10 (O/A) phase ratio, pH=3.00 and [Cl^-]/[SO₄^2-]=1/1, the extraction rate of molybdenum is of 90.4%, while that of chromium being of 61.43% and that of zinc being of 11.58%, and the separation factors between molybdenum and zinc or chromium reaches 72.06 and 5.93, respectively. The results of stripping experiments indicated that strong aqua ammonia can strip the molybdenum efficiently with the 1/10 (O/A) phase ratio.Synergistic effect in the extraction of molybdenum by the mixed extractants of P₂₀₄ and N₂₃₅ was observed. An obvious enhancement of the molybdenum extraction was observed when the mole fraction of N₂₃₅ is of about 0.7. In weak acidy conditions (pH=2.0), the coefficient of synergistic extraction is 2.24. The effect of the concentration of P₂₀₄ or N₂₃₅ and temperature on the extraction of molybdenum was further studied. In the range of temperature from 291K to 321K, the extraction rate of molybdenum increases with the reducing of temperature. The reaction mechanism was deduced and the extracted species was decided to be (R₃NH)₃·HMo₈O₂₆·(HA)₂. The reaction can be written as follows: FT-IR spectra of the mixed extractants and the loaded organic phase were also examined.