Tuning of vanadium valence for value-added recycling and utilization of vanadium from spent Selective Catalytic Reduction Catalysts

Spent hazardous selective catalytic reduction (SCR) catalysts are both wastes and secondary resources. The harmless disposal and value-added utilization are necessary. In this paper, we propose a green route to sus-tainable reutilize vanadium from hazardous wastes as vanadium dioxide (VO2) cathodes for aqueous zinc ion batteries. The valence tuning from V5+, V4+, and V3+ in spent catalysts to V4+ in leaching solution has been realized by reduction acid leaching to ensure the complete recycle. The leaching rate of vanadium is 93.6%, and the vanadium content in the slag phase is less than 0.04%. Most V and few Fe and Al are extracted by P204 in organic phase, then diluted sulfuric acid is used for stepwise stripping from mixed V, Fe, and Al solution. Then high-purity (99.9%) vanadyl sulfate (VOSO4) solution is obtained after extraction and purification, which is used for the preparation of VO2 materials The assembled batteries by prepared VO2 exhibited a discharge capacity of 204.6 mA h g(-1) at the first five cycles, and 172.5 mA h g(-1) after 100 cycles at 0.1 A g(-1). The capacity retention rate is 84.31% after 100 cycles. The mechanism and environmental analysis of greenhouse gas emission of reduction acid leaching are discussed, which reduces carbon emissions by 89.50% compared with routine acid leaching. Moreover, the phase transformation, metal element flow as well as species evolution are described for the deep understanding of valence tuning at molecular level. This paper presents a prospective approach for the short-cut and value-added utilization recovery of vanadium from hazardous wastes.