Equilibrium, thermodynamic and kinetic studies on adsorption of Sb(III) from aqueous solution using low-cost natural diatomite

The equilibrium, thermodynamics and kinetics of antimony(III) adsorption from aqueous solution using low-cost natural diatomite were investigated using batch adsorption parameters such as pH and ionic strength. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were applied to describe the isotherm models. The maximum adsorption capacity of diatomite for Sb(III) was found to be 35.2 mg/g at pH 6. The percent Sb(III) adsorbed in the presence of 0.001 M NaNO3 at pH 6 was 68%, compared to 56 and 48% and at the same pH but in the presence of 0.01 and 0.1 M NaNO3, respectively. From the D–R model, the mean adsorption energy was calculated as 7.32 kJ/mol, indicating that the adsorption of Sb(III) onto diatomite was physically carried out. The high stability of diatomite permitted a slightly decrease as about 10% in desorption yield and about 3% in adsorption yield after ten times of adsorption/desorption cycles. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the adsorption of Sb(III) onto diatomite was feasible, spontaneous and exothermic. Evaluation of the experimental data in terms of adsorption kinetics revealed that the adsorption of Sb(III) onto diatomite followed well the pseudo-second-order kinetic model.