Abstract
This paper presents the adsorption of Cr(III) and Cr(VI) ions from aqueous solutions and water samples in a laboratory batch scale mode by eggshells as a low-cost sorbent, which is available, cheap, and may represent an environmental problem. The adsorption process and extent of adsorption are dependent on the physical and chemical characteristics of the adsorbent, adsorbate and experimental conditions. The effect of process parameters (i.e., solution pH, initial concentration of Cr(III) ions, sorbent dose, shaking time, temperature, and various ions) on the adsorption of Cr(III) was studied. It was found that crushed eggshells possess relatively high sorption capacity, when comparing with other sorbents. Moreover, the sorption capacity increased with the increase of Cr(III) and sorbent concentrations and temperature. Thermodynamic parameters viz. the change in Gibbs free energy change (∆Gº ), enthalpy (∆Hº ) and entropy (∆Sº ) were also calculated. These parameters indicated that the adsorption process of chromium(III) on eggshell sorbent was spontaneous and endothermic in nature. Under the optimum experimental conditions employed, the removal of ca. ~100% of Cr(III) and Cr(VI) ions in a mixture (1:1), after reduction of Cr(VI) to Cr(III), was attained. The procedure was successfully applied to remove chromium ions from aqueous and different natural water samples. Keywords: Chromium(III), chromium(VI), sorption, eggshells, low-cost sorbent, water samples.
Highlights
Toxic heavy metals are constantly released into the environment
The best solution is to prevent the entrance of toxic metals into the ecosystem (Chubar et al, 2003)
The composition of by-product eggshell has been characterized by chemical analysis as follows: calcium carbonate (94%), magnesium carbonate (1%), calcium phosphate (1%) and organic matter (4%)
Summary
Uptake by eggshell (2000 mg/l) with shaking time at pH 7. Plot of Log log [Ci /(Ci-qm)] vs log t gives a straight line (Fig. 6) These results show that the diffusion of Cr(III) ions into eggshell pores played a role in the adsorption process and were similar to those described elsewhere (Akhtar & Qadeer, 1997; Qadeer & Hanif, 1994). Such results may either be attributed to the creation of some new active sites on the sorbent or to the acceleration of some originally slow adsorption steps. If high concentrations of the investigated foreign ions were used, they could affect the removal of Cr(III) and
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