Use of eggshell powder as low-cost adsorbent for effective Cr(VI) and Co(II) ion removal.

In this work, eggshell powder was used as a low-cost adsorbent for the removal Cr(VI) and Co(II) ions from aqueous solutions as a function of contact time, adsorbent concentration, adsorbate concentration, pH and temperature. Eggshell powder was characterized by X-ray diffraction, scanning electron microscopy and N₂ physisorption measurements. The kinetic studies showed that the experimental data of both solid–liquid systems studied were well adjusted to pseudo-second order kinetics and Langmuir isotherm models. The results showed that the metal ion adsorption equilibrium was attained after 300 min of contact time for the Cr(VI) ion and 180 min for the Co(II) ion. The Co(II) ion adsorption capacity of eggshell powder was found to be approximately four times greater than the Cr(VI) ion. From the Langmuir isotherms, the maximum adsorption capacities of 0.6815 and 2.2888 mg/g were found for Cr(VI) and Co(II) ion, respectively. The thermodynamic parameters were evaluated and showed that Cr(VI) and Co(II) ion adsorption onto eggshell powder were endothermic and spontaneous processes under the studied conditions. These findings demonstrate the important role of eggshell powder as a readily available and low-cost adsorbent for the efficient removal of Cr(VI) and Co(II) ions present in aqueous media. [ABSTRACT FROM AUTHOR]