Competitive sorption characteristics of heavy metal ions in multi-metal systems on natural clinoptilolite from Baiyin, China

Heavy metal pollution has become a more serious environmental problem. The sorption behavior of natural clinoptilolite from Baiyin, China was studied with respect to Cu2+, Cd2+ and Zn2+ in water system in order to evaluate its application potential to remedy the soil contaminated by heavy metals. Batch experiments were conducted to investigate kinetics and thermodynamics for Cu2+, Cd2+ and Zn2+ sorption on natural zeolite in single-, binary- or ternarymetal system, and to ascertain competitive characteristics among heavy metal ions and reaction mechanism. The pseudo-second order model was found to be more appropriate for kinetic sorption analysis compared to the pseudo-first order model. The Langmuir, Freundlich and DKR isotherms fitted well with the experimental data. The sequence of heavy metal ions adsorbed preferentially was Cu2+ > Zn2+ > Cd2+ in binary-system and Cu2+ > Cd2+ and Zn2+ in ternary-metal system, which could be related to the radius, hydration radius, electronegativity and initial concentration of metal ion. The competitive sorption coefficients were calculated and compared. The correlativity between the competitive sorption coefficients showed that antagonistic sorption effect occurred between Cu2+ and Cd2+ and between Cu2+ and Zn2+, and synergistical sorption effect occurred between Cd2+ and Zn2+ in ternary-metal system. © Research India Publications.