Effect of Multi-Metal Composition on Arsenic Sorption by LDHs: A Comparative Study of MgCuZnAl-LDH and MgAl-LDH.

Multimetallic layered double hydroxides (LDHs) are promising oxyanion sorbents, but their practical use requires evaluation of sorption efficiency and chemical stability. This study examined how introducing Cu2+ and Zn2+ into the LDH structure affects As(V) sorption, comparing binary Mg3Al1 and four-component Mg2Cu0.5Zn0.5Al1 in carbonate and chloride forms. The materials were synthesised by the co-precipitation method and characterised using XRD, FTIR, SEM, BET, and XPS, while their layer metal composition was determined by ICP-OES. The sorption studies were supplemented by chemical stability analysis (pH 4-11) and As(V) desorption experiments. Equilibrium data were evaluated using the Redlich-Peterson isotherm model. The four-component LDH showed higher As(V) sorption capacity than the conventional MgAl system, with the best performance observed for chloride forms: 37.5 mg/g for MgCuZnAl-LDH and 22.5 mg/g for MgAl-LDH. The sorption kinetics are well described by the pseudo-second-order and Elovich models, indicating a significant contribution from chemisorption. The results suggest that As(V) removal involves the combined action of anion exchange, electrostatic interactions and inner-sphere complex formation, controlled by the composition of the LDH layer and the type of interlayer anion. The introduction of Cu2+ and Zn2+ promoted additional active sites and stronger As(V) surface interactions. The results indicate that MgCuZnAl-LDH, particularly in the chloride form, exhibits promising As(V) sorption performance under model conditions involving a single solute.