Adsorption system for Mg²⁺ removal from aqueous solutions using bentonite/γ-alumina nanocomposite

Calcium and magnesium are the most common sources of water hardness. These divalent ions can react with soap anions decreasing the cleaning efficiency and hence, high consumption of detergents occurred as a result. Development of novel low-cost adsorbents for metals removal has attracted a great attention. In this study, bentonite/γ-alumina nanocomposites were used to remove Mg²⁺ from water. Effects of process parameters including γ-alumina content, initial ion concentration, adsorbent dosage, contact time and pH on adsorption process were investigated. Increasing the amount of alumina in composite from 1 to 3 and 5 wt%, caused a negative effect on the amount of adsorbed magnesium ions per gram of adsorbent; while increasing the initial ion concentration from 60 ppm to 100 ppm resulted in higher uptake per unit mass of the adsorbent from 2.15 mg/g to 2.80 mg/g, respectively. Langmuir, Freundlich and D-K-R isotherm models were used for data analysis, among which the Langmuir model was found to be more successful (R² = 0.9955), obtaining the maximum adsorption capacity (Q_m) of 3.478 mg/g. Moreover, calculation of the adsorption energy (E) from DKR isotherm model depicted the physical nature of the adsorption of Mg²⁺ onto bentonite/γ-alumina nanocomposite powder.