Sorption Characteristics of Heavy Metals onto Natural Zeolite of Clinoptilolite Type

ABSTRACT: Adsorption isotherms of Pb, Cd and Zn were studied on natural zeolite of clinoptilolite type for single, binary and ternary systems with initial concentrations of 0.15 to 3 mM. The adsorption data for Pb, Cd and Zn showed highly significant fit to the Freundlich adsorption isotherm in all single, binary and ternary systems. The KF value, the metal adsorbed by solid phase at the equilibrium concentration of unity, was the highest for Pb followed by Zn and Cd, respectively. Metals adsorption data were also acceptably fitted to the Langmuir adsorption isotherm. Zeolite showed greater sorption capacity and bonding strength for Pb than Zn and Cd as evidenced by the quantities of KL and bL coefficients. Sorption capacities of Cd and Zn decreased but sorption bonding strengths of these two metals increased in ternary system as compared to the single system. Sorption capacity of Pb on zeolite was kept but its sorption bonding strength decreased in ternary system in comparison with single system. The quantities of distribution coefficient (Kd), the affinity of metal for retention onto solid phase, was the highest for Pb followed by Zn and Cd, respectively. Due to the lower Kd values of Cd, it assumed that this element has higher potential to be bioavailable in the solution and hence is more hazardous among the metals studied. Due to the high sorption capacity, being plentiful and low cost it is concluded that the use of zeolite as an appropriate adsorbent is promising for the removal of heavy metals especially Pb from contaminated sites.