Kinetic and thermodynamic studies of Cd and Pb sorption using diatomite from aqueous solutions

In this study, kinetic and thermodynamic of Cd and Pb sorption from aqueous solutions were studied using diatomite. Kinetic sorption of heavy metals was analyzed by pseudo-first-order, pseudo-second-order, Elovich and power function equation in terms of their fitness. Freundlich, Langmuir, Temkin, Dubinin-Radushkevich (D-R) isotherm models have also been used for fitness of adsorption data in different temperatures (283, 293, 303 and 313 K). The results showed that the sorption of Cd and Pb by diatomite is intensified by increasing contact time and temperature. Kinetic sorption of heavy metals data showed the best fitness with the pseudo-second-order equation (R2=0.99) and a good fitness with Langmuir and D-R equations. The thermodynamic parameters such as Gibb's Free Energey (ΔG), Enthalpy (ΔH) and Entropy (ΔS) indicated that the adsorption of Cd and Pb ions were spontaneous and endothermic at 283–313 °K. Regarding to the adsorption energy of D–R model, Cd adsorption by diatomite (E< 8 kJ mol− 1) is probably followed by a physical process, but Pb adsorption by diatomite (E> 8 kJ mol− 1) is probably followed by a chemical process Diatomite has a greater efficiency for removal of Pb (RE=99%) than that of Cd (RE=86%) from aqueous solutions. Therefore, diatomite could be used as an efficient sorbent for the sorption of Pb and Cd (II) from polluted water resources.