Abstract
Sequential desorption of adsorbed Zn(II) and Hg(II) ions using distilled water (physical interaction), 1 M KNO 3 (electrostatics), HONH 2 HCl in 25% (v/v) CH 3 COOH (hydrogen bond) and 0.1 M Na 2 EDTA (complexation) • Selective adsorbent of heavy metals based on dithizone immobilization on bentonite. • Significant enhanced performance of the adsorbent towards Hg(II) and Zn(II) ions. • Simultaneous adsorption kinetics of Hg(II) and Zn(II) follow pseudo-2 nd order model. • Isotherm adsorption of Zn(II) follows Langmuir, Hg(II) fits well Freundlich model. • Electrostatic interactions for Zn(II), hydrogen bond and complexation for Hg(II). Simultaneous adsorption of Zn(II) and Hg(II) in the presence of alkaline earth metal, Mg(II) on dithizone-immobilized bentonite has been done by batch method. The study was begun by activation of natural bentonite with HCl followed by immobilization of dithizone on bentonite surface. Some parameters influencing the adsorption such as pH, interaction time and initial concentration of metal ions were optimized. Types of interaction between metal ions and adsorbent were assessed by conducting sequential desorption of the adsorbed metals using H 2 O, KNO 3 , HONH 2 HCl and Na 2 EDTA. XRD and FTIR characterizations suggest that dithizone has been successfully immobilized on the surface of bentonite. Optimum conditions for simultaneous adsorption of Hg(II) and Zn(II) in the presence of Mg(II) are at pH 6 and interaction time of 60 minutes. Capacity, affinity and selectivity of dithizone immobilized bentonite towards Hg(II) and Zn(II) are better than those of non-immobilized activated natural bentonite, but the interaction types of the two metal ions with adsorbents are different. Zn(II) ion mostly interacts with adsorbents through physical and electrostatic interactions, while Hg(II) ion interacts via hydrogen bond and complexation. Upon immobilization of dithizone on the surface of bentonite, the interaction of Hg(II) with adsorbent changes significantly from hydrogen bond to complexation. Moreover, the presence of Mg(II) ion gives no significant influence on metal adsorption, indicating that dithizone-immobilized bentonite is quite selective towards heavy metal ions.
Published Version
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