CuS-Cu₂S/γ-Fe₂O₃ for efficient Cr(VI) elimination from electroplating wastewater: The role of surface-active Cu-based...

Conventional adsorbents for Cr(VI) elimination from electroplating wastewater are constrained by limited uptake capacity, poor recyclability, and inadequate management of retained chromium. To tackle these issues, a magnetically recoverable CuS/γ-Fe₂O₃ composite was developed as a reusable adsorbent. Upon thermal annealing, a partial phase transformation from CuS to Cu₂S occurred, yielding a mixed CuS-Cu₂S/γ-Fe₂O₃ hybrid. This hybrid exhibited enhanced Cr(VI) capture, achieving 87.2 mg g^-1 at pH 4.0, 25 °C, 0.5 g L^-1 adsorbent dosage, and 50 mg L^-1 initial Cr(VI). Elimination process proceeded via the adsorption-reduction route, governed by surface reductant availability and affinity aqueous Cr(VI) and H⁺. Although the CuS-to-Cu₂S transformation reduced total reductant sites, it improved Cr(VI) and H⁺ adsorption, likely due to the unique surface properties of Cu₂S; hence, the CuS-Cu₂S/γ-Fe₂O₃ composite outperformed its single-phase counterpart. Moreover, this composite also showed good stability and reusability, maintaining 100% Cr(VI) removal over fifteen cycles while retaining magnetic recoverability. Furthermore, repeated adsorption enabled efficient Cr(VI) enrichment from electroplating wastewater onto CuS-Cu₂S/γ-Fe₂O₃, allowing the spent adsorbent to serve as a potential substitute for chromium ore. In summary, these findings highlighted CuS-Cu₂S/γ-Fe₂O₃ as a highly promising adsorbent for treating Cr(VI)-bearing electroplating wastewater.