Removal of sulfate from wastewater via synthetic Mg-Al layered double hydroxide: An adsorption, kinetics, and thermodynamic study

Abstract Sulfate-contaminated water is a major environmental problem that alters the taste of water, disturbs the digestive systems of animals and humans, and erodes both soil and metals. In this study, the layered double hydroxide (LDH) 4Mg2Al.NO3 and LDH 8Mg2Al.NO3 were prepared using a co-precipitation technique, and applied in the adsorption of SO42- from an aqueous solution. The reaction is well described by the Langmuir adsorption model. LDH 4Mg2Al.NO3 and LDH 8Mg2Al.NO3 afforded maximum SO42- adsorption values of 135.14 and 92.59 mg/g, respectively. The reaction is best explained by a pseudo-second-order mechanism, which suggests that chemisorption is the rate-determining step. The activation energies of LDH 4Mg2Al.NO3 and LDH 8Mg2Al.NO3 indicate that the adsorption of SO42- on synthetic LDHs predominantly follows an anion-exchange mechanism, wherein SO42- ions in the aqueous medium replaces intercalated NO3- ions in the synthetic LDHs. The thermodynamic parameters (ΔH, ΔS, and ΔG) were also calculated. The reaction was endothermic, and the synthetic LDHs afforded feasible and spontaneous adsorption of SO42-.