Study on the\nAdsorption Mechanism of Cu<sup>2+</sup> by ZnAl-LDH-Containing Exchangeable\nInterlayer Chloride Ions

Different Zn/Al ratios of Cl<sup>–</sup> intercalated\nZnAl-layered\ndouble hydroxide (ZnAl-LDH) were prepared using the coprecipitation\nmethod, and their adsorption performance for Cu<sup>2+</sup> in aqueous\nsolution was evaluated. The factors affecting adsorption properties,\nsuch as dosage, reaction time, and pH, were determined by adsorption\nexperiments. Then, the adsorption kinetics and isotherm models were\nfitted to evaluate the adsorption mechanism. The results show that\nthe Zn/Al ratio has a great influence on the adsorption effect, the\nbest adsorption effect is obtained when the Zn/Al ratio is 4:1, and\nthe maximum adsorption capacity of Cu<sup>2+</sup> is 213 mg/g. The\nmechanism study shows that the adsorption of Cu<sup>2+</sup> by ZnAl-LDH\nis mainly an isomorphic substitution. Additionally, during the adsorption\nof CuSO<sub>4</sub>, the presence of SO<sub>4</sub><sup>2–</sup> undergoes interlayer anion exchange with Cl<sup>–</sup>,\nand the process of SO<sub>4</sub><sup>2–</sup> entering the\ninterlayer facilitates the isomorphic substitution of Cu<sup>2+</sup> and Zn<sup>2+</sup>. X-ray diffraction (XRD) analysis shows that\nas the Zn/Al ratio increases, the interlayer spacing of ZnAl-LDH increases,\nand the crystallinity decreases. The adsorption process conforms to\nthe pseudo-second-order kinetic process and the Langmuir isotherm\nadsorption model. Therefore, the adsorption type of ZnAl-LDH for Cu<sup>2+</sup> is monolayer chemical adsorption. The adsorption thermodynamic\nresults indicate that the adsorption of Cu<sup>2+</sup> is a spontaneous\nendothermic process. The research results revealed the mechanism of\nZnAl-LDH adsorbing Cu<sup>2+</sup>, providing ideas for removing and\nrecovering copper-containing electroplating wastewater.