Efficient Removal of Hg2+ from Wastewater by a Novel Cu-Modified Attapulgite: Adsorption Performance and Mechanism

The development of low-cost and highly efficient adsorbents is essentially needed for removing Hg²⁺ species from desulfurization sludge leaching wastewater. In this study, a series of novel Cu-modified attapulgite (Cu–ATP) adsorbents were synthesized via a simple HNO₃ treatment combined with an improved impregnation method. The Hg²⁺ removal efficiency of these Cu–ATP adsorbents was investigated in simulated leaching wastewater. The effects of HNO₃ concentration, Cu precursor, Cu-loading content, and other adsorption conditions on Hg²⁺ removal using Cu–ATP were investigated. The results demonstrated that Cu–ATP prepared with CuSO₄ as the precursor and treated with 3 mol/L HNO₃ showed excellent Hg²⁺ removal performance. Moreover, with increasing adsorbent content and adsorption time, the Hg²⁺ removal efficiency of Cu–ATP first increased and then stabilized. However, with an increase in pH value, the Hg²⁺ removal efficiency first increased and then decreased, whereas the removal showed a decreasing trend with increasing initial Hg²⁺ concentration. The adsorption kinetics results indicated that Hg²⁺ adsorption on Cu–ATP was well described by the pseudo-second-order model. Furthermore, various characterization methods, including Brunauer − Emmett − Teller analysis (BET), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), were employed to analyze the physicochemical properties of the adsorbents. The analyses confirmed that the superior Hg²⁺ removal efficiency of Cu–ATP was mainly due to the complexation of Hg²⁺ with chemisorbed oxygen produced by Cu doping and S species generated from the Cu precursor (CuSO₄). These findings underscore the potential of Cu–ATP as a cost-effective adsorbent for removing Hg²⁺ from wastewater.