Potential of nano crystalline calcium hydroxyapatite for Tin(II) removal from aqueous solutions: Equilibria and kinetic processes

The potential of the synthesized nano hydroxyapatite to remove Sn2+ from aqueous solutions was investigated in a batch reactor under different experimental conditions. The study also investigates the effects of process parameters such as initial concentration of Sn2+ ions, temperature, and adsorbent mass. Various thermodynamic parameters, such as ΔGo, ΔHo and ΔSo have been calculated. The thermodynamics of an Sn2+ ion onto nano HAp system indicates a spontaneous and endothermic nature of the process. Tin uptake was quantitatively evaluated using the Langmuir, Freundlich and Dubinin-Kaganer-Radushkevich models. The adsorption data follow the adsorption equilibrium described well by the Langmuir isotherm model with maximum adsorption capacity of 2500 mg/g of Sn2+ ions on nano HAp. Using the second-order kinetic constants, the activation energy of adsorption (Ea) was determined as 4.125 kJ mol−1 according to the Arrhenius equation.