Murari, Prasad and Sona, Saxena (2004) Sorption Mechanism of Some Divalent Metal Ions Onto Low-Cost Mineral Adsorbent. Ind. Eng. Chem. Res., 43. pp. 1512-1522. ISSN 0888-5885

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Abstract

This paper investigates the underlying mechanism of uptake from aqueous solution of divalent metal cations (Pb2+, Cu2+, and Zn2+) by a low-cost mineral adsorbent. Batch adsorption studies were carried out for the concentration ranges of 24.1−2410 μmol/L for lead, 78.65−7865 μmol/L for copper, and 76.45−7645 μmol/L for zinc solutions under natural conditions. Two simple kinetic models, that is, pseudo-first-order and pseudo-second-order models, were tested to investigate the adsorption mechanism. All of the parameters of these models were calculated and are discussed. Rate constants were found to be nearly constant at all metal concentrations for the first-order model, whereas they gradually decreased with increasing metal concentration in the order Pb2+ > Cu2+ > Zn2+ for the second-order model. The sorption kinetics appears to be mainly controlled by liquid-film diffusion. External-diffusion and film-diffusion models were tested to evaluate mass-transfer coefficients and film-transfer constants at different initial concentrations of solute (metal cation). Both mass-transfer and film-transfer constants were noticed to be affected by the initial metal concentration. They gradually decreased with increasing initial concentration of metal cation in the order Pb2+ > Cu2+ > Zn2+. The film-diffusion model was found not to be applicable for the adsorption of lower concentrations of divalent cations. The equilibrium data were described to a lesser extent by Freundlich model, and the Langmuir model seemed to be more appropriate, giving maximum fixation capacities for Pb2+, Cu2+, and Zn2+ of 90.9, 270.2, and 250.0 μmol/g, respectively. The crystallographic dimensions of the treated mineral adsorbent samples were measured by X-ray diffraction (XRD), which revealed appreciable expansion of the crystal size as a result of the incorporation of divalent cations in the place of exchangeable cations of the adsorbent. The affinity order for the adsorption of cations by the mineral adsorbent is validated by ionic radius theory. Cation exchange along with complexation were found to be the most probable mechanisms for the sorption of divalent cations. An attempt was made to quantify the ion-exchange and complexation mechanisms.

Item Type:	Article
Subjects:	CSIR-800 > Environmental Studies/Chemistry
Divisions:	UNSPECIFIED
Depositing User:	Mr. B.K. Prasad
Date Deposited:	30 Jul 2013 11:40
Last Modified:	30 Jul 2013 11:40
URI:	http://ampri.csircentral.net/id/eprint/177

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