Removal of Cd, Cu and Zn ions from aqueous solutions using natural and Fe modified sepiolite, zeolite and palygorskite clay minerals

Metal ions such as Cu, Cd, and Zn are toxic and considered as hazardous pollutants due to their stability in the environment. In this study, the natural and Fe (III) modified sepiolite, palygorskite, and zeolite clay minerals were used for the removal of Cu, Zn, and Cd ions from aqueous solutions. The iron chloride 1 M was used for mineral modification and the capacity of sorbent was assessed in a batch experiment containing six starting concentration of sorbents ranging from 10 mg L-1 to 140 mg L-1. Results of the study showed higher removal efficiency for modified compared to natural clays. Removal efficiency of Cd, Cu, and Zn for zeolite was increased by 15.5, 30.2 and 21.4%, respectively, after modification. Zn removal by sepiolite remained unchanged after surface modification, whereas Cu and Cd removal was increased respectively by 13.6 and 21.2%. Palygorskite modification process also increased 38.14% of Cu, 25.5% of Zn, and 28.4% of Cd sorption compared to its unmodified form. Equilibrium sorption isotherm studies showed that the experimental data were better fitted by the Freundlich sorption isotherm (r(2) > 0.99) than the Langmuir (r(2) > 0.82). In general, the investigated minerals are suggested as efficient sorbents for the removal of Cd, Cu, and Zn ions from contaminated aqueous solutions.