Separation of vanadium, tungsten, and arsenic from alkaline leachate of spent SCR catalysts via coextraction and stepwise stripping

Abstract

The application of sodium hydroxide solution in the treatment of spent SCR catalysts has emerged as a prevalent technique for the recovery of titanium dioxide. Nonetheless, this method yields a substantial quantity of wastewater containing vanadium, tungsten, and arsenic, posing significant challenges for recycling, and resulting in the unnecessary disposal of valuable metals. In this study, the separation of vanadium, tungsten, and arsenic from alkaline leachate of spent SCR catalysts was investigated using modified Aliquat 336 with SO42− (MA336-S). Firstly, 98.88 % and 97.93 %, and 13.27 % of vanadium, tungsten, and arsenic were coextracted by MA336-S, and the electrospray ionization mass spectrometry and fourier transform infrared spectroscopy were employed to verify the formation of [(R3CH3N)2HVO4] and [(R3CH3N)2WO4]. Afterwards, the effective separation of vanadium, tungsten, and arsenic in organic phase was achieved by stepwise stripping. When Na2SO4 was used as the stripping agent, the stripping efficiency for arsenic reached 96.06 %. The selective stripping of vanadium and tungsten was achieved using 2.5 M NaOH and 1 M Na2SO4 + 1 M NaOH, respectively, resulting in stripping ratios of 99.59 % for vanadium and 99.15 % for tungsten. An extremely high separation factor of vanadium and tungsten (βV/W, 2388) can be achieved. Subsequently, the organic phase was preserved for recycling. A comprehensive process flowsheet was clarified for the efficient separation of vanadium, tungsten, and arsenic from the alkaline leachate of spent SCR catalysts, thereby facilitating a synergistic and enhanced recovery of these valuable metals from waste resources.