Novel composites of activated carbon and layered double oxide for the removal of sulfate from synthetic and brackish groundwater.

Sulfate (SO) is a major water and environmental concern that causes severe diarrhea, death of invertebrates and plant species, and clogging of industrial pipes. In the current work, treatment of SO from synthetic and real groundwater having 3901 mg(SO)/L was investigated for the first time using Zn-Al and Mg-Al layered double oxides doped granular activated carbon (GAC/Mg-Al LDO and GAC/Zn-Al LDO). The co-precipitation method was followed to synthesize the GAC/LDO composites using an Mg or Zn to Al molar ratio of 3:1. The GAC/Mg-Al LDO possessed a higher specific surface area (323.9 m/g) compared to GAC/Zn-Al LDO (195.1 m/g). The GAC/Mg-Al LDO demonstrated more than 99% removal of SO from synthetic water, while it was 50.9% for GAC/Zn-Al LDO and less than 1% for raw GAC at an initial concentration of 50 mg/L. The GAC/Mg-Al LDO was selected for further batch experiments and modeling investigation. The equilibrium data followed the Redlich-Peterson and Langmuir models with determination coefficients of 0.943 and 0.935, respectively. The maximum Langmuir adsorption capacity was 143.5 mg/g. In the real groundwater adsorption study, the screening experiment revealed high selectivity towards SO with 62% removal efficiency. The optimum dosage was found to be 50 g/L with an uptake capacity of 61.5 mg/g. The kinetic data of SO removal from synthetic and brackish water were in excellent agreement with the pseudo-second order model, and the equilibrium was attained in 5 h. Accordingly, it can be concluded that the GAC/Mg-Al LDO is an efficient material for treating SO from real groundwater and can be utilized as a pretreatment unit for high sulfate water resources.