Hydrothermal Conversion of Electrolytic Manganese Residue into Silicate-Based Adsorbent for Removal of Cu(II) from Wastewater.

A novel silicate-based adsorbent (M-EMR) was synthesized via a hydrothermal process using electrolytic manganese residue (EMR) and calcium carbide slag (CS) in a NaOH medium. The adsorption behavior of M-EMR for Cu(II) ions from aqueous solution was systematically investigated under varying conditions. The adsorption kinetics followed a pseudo-second-order model with a high correlation coefficient ( = 0.9999), suggesting chemisorption as the rate-limiting mechanism. Equilibrium data were best fitted by the Langmuir isotherm ( > 0.999), with maximum adsorption capacities of 174.22, 185.19, and 232.56 mg/g at 288.15, 298.15, and 308.15 K, respectively. Thermodynamic analysis revealed a spontaneous and endothermic process, characterized by negative Δ° values and positive Δ° (41.25 kJ/mol) and Δ° (203.88 J/mol·K). Competitive adsorption studies showed that Pb(II) significantly interfered with Cu(II) uptake, while Co(II) and Ni(II) exhibited negligible effects. M-EMR demonstrated high selectivity for Cu(II) and strong resistance to interference from coexisting cations (K, Ca, Na, Mg). Mechanistic analysis confirmed that ion exchange, surface precipitation, and complexation were the primary removal pathways, further supported by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) results. Cu(II) could be efficiently desorbed using 30 mmol/L EDTA, achieving a recovery efficiency of 96.62%. This study provides a cost-effective and environmentally sustainable approach for the valorization of industrial waste and the treatment of Cu(II)-contaminated wastewater.