Investigation of the mechanism of Cu(II) removal using Mg-Al layered double hydroxide intercalated with carbonate: Equilibrium and pH studies and solid-state analyses

Layered double hydroxides (LDHs) are effective in removing metal cations from aqueous solutions, but the mechanism of the process has not been thoroughly investigated. In this study, we conduct the removal of Cu(II) from aqueous solutions using the CO₃·Mg-Al LDH and investigate the mechanism of the process based on equilibrium and pH studies and solid-state analyses. Adsorption isotherms show that the equilibrium removal of Cu follows the Freundlich and Halsey models (R² = 0.973), inducing a multilayer adsorption process. pH studies show that Cu is removed at pH < pH_PZC(=12.1), consistent with chemical binding, rather than electrostatic attraction, as the predominant mechanism of removal. XRD reveals the formation of CuCl₂·3[Cu(OH)₂] and retention of the LDH structure, and SEM images show a thick-layer morphology. Solid-state analyses confirm the formation of CuCl₂·3[Cu(OH)₂] and its multilayer accumulation on the LDH surface, in accordance with the equilibrium and pH studies.