American Chemical Society
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Understanding the Reduction Kinetics of Aqueous Vanadium(V) and Transformation Products Using Rotating Ring-Disk Electrodes

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journal contribution
posted on 2017-09-13, 00:00 authored by Gongde Chen, Haizhou Liu
Vanadium­(V) is an emerging contaminant in the most recent Environmental Protection Agency’s candidate contaminant list (CCL4). The redox chemistry of vanadium controls its occurrence in the aquatic environment, but the impact of vanadium­(V) speciation on the redox properties remains largely unknown. This study utilized the rotating ring-disk electrode technique to examine the reduction kinetics of four pH- and concentration-dependent vanadium­(V) species in the presence and the absence of phosphate. Results showed that the reduction of VO2+, HxV4O12+x(4+x)– (V4), and HVO42– proceeded via a one-electron transfer, while that of NaxHyV10O28(6–xy)– (V10) underwent a two-electron transfer. Koutecky–Levich and Tafel analyses showed that the intrinsic reduction rate constants followed the order of V10 > VO2+ > V4 > HVO42–. Ring-electrode collection efficiency indicated that the reduction product of V10 was stable, while those of VO2+, HVO42–, and V4 had short half-lives that ranged from milliseconds to seconds. With molar ratios of phosphate to vanadium­(V) varying from 0 to 1, phosphate accelerated the reduction kinetics of V10 and V4 and enhanced the stability of the reduction products of VO2+, V4, and HVO42–. This study suggests that phosphate complexation could enhance the reductive removal of vanadium­(V) and inhibit the reoxidation of its reduction product in water treatment.