Construction of Magnetic S-Doped CoWO₄ Composite for Efficient and Selective Recovery of Gold from Wastewater via Adsorption–Reduction Pathway

The design and synthesis of efficient adsorbents for the recovery of precious metals from secondary resources are of great environmental and economic significance. Herein, a magnetic sulfur-doped composite CoFe₂O₄@S–CoWO₄ (CF@S–CoWO₄) is developed through a hydrothermal synthesis method, which is used to selectively recover gold in aqueous media. Significantly, CF@S–CoWO₄ exhibits the best overall performance with gold ions adsorption capacity (Q_max) and distribution coefficient (K_d) are 1049 mg g⁻¹ and 4.4 × 10⁶ mL g⁻¹, respectively, which are much higher than those of other gold adsorption materials. The selectivity coefficients (K) toward other metal ions (Pd²⁺, Ca²⁺, Mg²⁺, Cd²⁺, Al³⁺, Li⁺, Ni⁺) are also higher, which suggests that CF@S–CoWO₄ had a preferential selectivity for Au³⁺ in coexisting ion solutions. Moreover, the antianion interference of the composite follows the order: SO₄²⁻ > PO₄³⁻ > NO₃⁻ > CO₃²⁻, and it also shows very good reusability with adsorption efficiency at 81.78% after four repeated cycles. Based on characterizations and calculation, it is found that Au(III) mainly undergoes chelation and reduction reactions in the S sites in CF@S–CoWO₄, which indicates the important role of S sites. Hence the CF@S–CoWO₄ composite demonstrates a promising application for the recycling of gold ions from electronic wastewater.