Treatment of Cr(VI) present in plating wastewater using a Cu/Fe galvanic reactor

•Batch and continuous Cu/Fe systems for chromium plating wastewater were studied.•Sulfate, nitrate and chloride ions seriously compete with Cr(VI) reduction at pH > 1.5.•The 100%, 92%, 50% and 38% of Cr(VI), Cl−, NO3− and SO4−2 was removed in batch.•A maximum reduction capacity of 189.6 mg Cr(VI)/g iron was obtained for GCR980.•Electricity and hydrogen gas cogeneration was detected in all Cu/Fe GCR.

In this study, we present the reduction of Cr(VI) present in chromium electroplating wastewater using batch and continuous systems with a galvanic Cu/Fe configuration. The chromium plating wastewater used in this work exhibited the presence of nitrate and sulfate ions, which are capable of competing with the reduction of chromium and copper in low quantities. As a result, the system was optimized by increasing the proton concentration to ensure a faster rate of 100% chromium reduction; thus, a shorter duration (less than 20 min) was found when a pH value of 1.5 was used. In all of the systems, iron and copper release was registered; however, because lower than theoretical iron quantities were detected in the Cu/Fe system, additional copper cathode mechanisms are proposed for the reduction of Cr(VI). The monitoring of the ions present in the system showed that all nitrate, sulfate, and chloride ions were removed simultaneously (50.3%, 37.7%, and 91.8%, respectively), and copper was likely the major element responsible of for the removal of these ions. The continuous experiments also revealed that Cr(VI) reduction could be performed efficiently with a maximum reduction capacity of 189.6 mg Cr(VI)/g iron, which is higher than that obtained in other recent electrochemical works. The SEM/EDS and XRD results definitively confirm that anodic and cathodic Cr(VI) reduction was taking place and that the formation of sludge occurred principally by precipitation of iron. The cogenerated energy and gas (H2 and N2) are valuable subproducts that enhance the sustainability of the process, and the system also has the following known advantages: no energy input into the reactor, lower sludge generation, cathode reuse and the possibility to discharge the treated wastewater to national waters or reuse it in the rinsing process.

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