Competing Ion Behavior in Direct Electrochemical Selenite Reduction

Abstract

Anthropogenic selenium (Se) released in industrial and agricultural wastewaters presents toxicity challenges for local ecosystems. Se direct electrochemical reduction (SeDER) is an effective and thermodynamically favorable approach for Se(IV) removal, but evaluating the feasibility of SeDER in application requires a comprehensive understanding of system performance in complex water matrices. This study evaluates both the cathodic and anodic competing ion behavior in a SeDER process, including both four-and six-electron Se(IV) reduction pathways. The results suggest that sulfate promotes electrochemical Se(IV) removal efficiency by 11−23%, but nitrate hinders Se(IV) removal (2−11% decrease) by occupying cathodic reaction sites. The anodic competing ions, especially chloride, decrease SeDER performance by generating strong oxidants and disrupting Se(IV) reduction pathways. We also find that four-electron Se(IV) reduction outperforms its six-electron counterpart when treating simulated fluegas desulfurization wastewater (with 7 g L −1 Cl − ), with a lowest effluent Se level of 0.23 mg L −1 , a highest removal efficiency of 96.9%, and a threshold deposition capacity of 3.5 g m −2 in a 7-day semicontinuous operation. Electrochemical Se(IV) removal using our prototype batch reactor is not competitive for treating low-Se concentration agricultural wastewaters (up to 24% removal). The results suggest the need for future work to evaluate alternative electrodes and reactor design that reduce water splitting reactions, enhance Faradaic efficiency, and promote mass transfer to the electrode surface.

Cost-Effective Cathode Materials To Electrochemically Tackle Aquatic Selenite Pollution

“…Mechanical Se recovery utilizes a scraper to physically separate Se(0) from the cathode surface . Electrochemical Se recovery leverages either anodic stripping to oxidize Se(0) to Se­(IV) or Se­(VI) in an enriched solution, or cathodic stripping to further reduce Se(0) to Se­(-II) in the form of recoverable CuSe precipitates. , …”

“…48 Electrochemical Se recovery leverages either anodic stripping to oxidize Se(0) to Se(IV) or Se(VI) in an enriched solution, or cathodic stripping to further reduce Se(0) to Se(-II) in the form of recoverable CuSe precipitates. 49,50 ■ ASSOCIATED CONTENT * sı Supporting Information…”

Selenium (Se) recovery for technological applications from environmental matrices based on biotic and abiotic mechanisms

“…Moreover, it is cleaner and environmentally friendly than other abiotic methods. Future studies about reactor design optimization, electrode modification of electrochemical systems are also needed for more energy and cost-effective Se removal and recovery [175,176].…”

Prospects of metal recovery from wastewater and brine

“…Most elements classified in this list are not main group elements (that is, groups I-II and XIII-XVIII in the periodic table), with the exception of lithium, magnesium, gallium, germanium and antimony-a listing that suggests that main group elements are generally less attractive targets for recovery. Beyond this principle, criticality designations offer limited guidance in choosing recovery targets from wastewater and brine, as the number of critical wastewater 16 -using innovative separation methods with little consideration for practical, large-scale feasibility.…”