From removal claims to engineering evidence: electrochemical treatment and selective recovery of heavy metals in wastewater

Abstract

The evaluation of the efficacy of electrochemical treatment of heavy-metal-bearing wastewater has evolved from a focus on peak removal in simplified solutions to a consideration of selectivity, stability, and product value to withstand the complex chemical processes occurring in industrial streams. The present review employs a systematic approach to evaluate the extant literature on the subject. This approach involves a series of steps, including decomposition, capture, separation/concentration, and purification/recovery. The review places a premium on studies that report on real or chemically complex wastewaters, metal speciation or release, normalized energy use, continuous operation, effluent quality, product purity, and residual-stream fate. Ligand-rich Cu- and Ni-bearing wastewaters serve as the primary evidence base due to their combination of strong complexation, competing ions, high salinity, organic interference, and relatively mature recovery-oriented data. These wastewaters also expose failure modes relevant to other heavy-metal systems. Across a range of electrochemical processes, including electrooxidation, electroreduction, electrocoagulation, electrodialysis, bipolar membrane electrodialysis, capacitive deionization, and electrodeposition, the central finding is that removal, recovery, and product-end validation are distinct claims requiring different evidence. The efficacy of removal is substantiated by engineering evidence when it is associated with species transformation, stable stream control, energy and boundary accounting, product purity, impurity carryover, and the fate of residual liquid or solid streams. The resulting evidence-oriented reporting framework is intended to translate laboratory electrochemistry into continuous, resource-recovery-oriented treatment of complex heavy-metal wastewater.