Sorption of Cu and Zn from aqueous solutions on diatomite: The kinetic and thermodynamic

Heavy metals enter the environment through the discharge of industrial wastewater and urban wastewater. Zinc (Zn) and copper (Cu) are considered as an essential element for life and act as micronutrients when present in trace amounts, too much Zn and Cu can still cause eminent health problems. There are several method to remove the heavy metals from aqueous solutions that adsorption by cheap minerals is one of the best method.

The raw diatomite as a sorbent for removal of Cu and Zn used in this investigation was prepared as a natural resource from, Birjand mine. In this study, batch experiments were conducted for evaluation of the kinetic and thermodynamic adsorption of Cu and Zn from aqueous solutions by diatomite. The kinetic parameters of metal ions sorption by diatomite (0.1g) were determined with 25mL solutions containing 100 mg L-1 Cu and Zn concentrations at 0, 10, 20, 30, 40, 50 sen 2, 5, 10, 20, 40, 60 min 2, 4, 6 hr at (at background solution 0.03 mol L-1 NaNO3). For thermodynamic studies the solutions were stirred in a thermally controlled shaker at 10, 20, 30 and 40 ºC .The adsorption behavior of heavy metals (Cu and Zn) in different time was conducted by pseudo-first-order, pseudo-second-order, Elovich and fractional power models. Also, Freundlich, Langmuir, Tempkin, Dubinin-Radushkevich isotherms models have also been used to the equilibrium adsorption at data 10, 20, 30 and 40 ºC.

The results showed that the adsorption capacity of diatomite increased with increasing contact time. The time required creating equilibrium between the adsorbed metals on the solid surface and the fraction remaining in the solution for Cu and Zn were 40 and 120 minutes, respectively, and the amount sorption of Cu was more than Zn by diatomite. The maximum adsorption of Cu and Zn (qmax) by diatomite at 20 ° C was 56 and 27 mg g-1, respectively. Among adsorption kinetic models, pseudo-second-order model was better fitted for experimental data (R2=0.99). The values of adsorption by diatomite, increased with increasing temperature, the adsorption data were well fitted with Langmuir (R2: 0.96-0.99). The thermodynamic parameters (ΔG, ΔH and ΔS) indicated that the adsorption of Cu and Zn ions were feasible, spontaneous and endothermic at 10–40ºC. The sorption energy parameter (E) of Dubinin-Radushkevich isotherm values indicated probably physical sorption reaction of the metals by the sorbent (E

Because of the presence of heavy metals in contaminated water and the importance of their removal, use of diatomite as one of the cheap and accessible absorbents can be effective in the removal of heavy metals from industrial contaminated water sources, especially Cu and Zn.