A promising treatment method for Cr(VI) detoxification and recovery by coupling Fe0/Fe3C/C fine powders and circulating fluidized bed

Abstract

This study reports an innovative and efficient method of coupling highly active Fe0/Fe3C/C powders and circulating fluidized bed (Fe0/Fe3C/C CFB) for the treatment of Cr(VI) containing water via detoxification and Cr recovery. It can overcome the shortcomings of Fe/C micro-electrolysis in the conventional fixed bed such as descending chemical reactivity and hydraulic permeability. The effects of inlet Cr(VI) concentration, initial solution pH, gas velocities, solid holdup and hydraulic retention time on the reactor performance were detailedly investigated. The results proved that Fe0/Fe3C/C CFB showed a much high superficial liquid velocity and it favor the increase of reaction dynamics, whereas the surplus solid holdup caused a significant hydrogen evolution. Moreover, due to its inhibited particle self-agglomeration and preserved gap structure, CFB has a much higher performance in terms of efficiency and longevity compared with fixed bed. Based on the qualitative characterizations (XPS, XRD and in-situ Raman), 100% Cr(VI) conversion concurrent with microcrystalline Fe derivatives were found on the surface of Fe0/Fe3C/C in CFB. Quantitative analysis (Mossbauer and acid extraction) demonstrated that the exposed crystallite of selectively catalytic adsorbed Fe(II) speciation was responsible to successive electron transfer in Cr(VI) treatment. Hence, 47% Fe0 utilization and 91.7% Cr(III) recovery proved satisfied compatibility between Fe0/Fe3C/C and CFB. In general, the Fe0/Fe3C/C CFB would provide theoretical basis and technological guidance for the improvement of Fe/C process in industry.