Eggshell and coral wastes as low cost sorbents for the removal of $Pb^{2+}$, $Cd^{2+}$ and $Cu^{2+}$ from aqueous solutions

Abstract

Rapid industrialization in Korea has led to the discharge of heavy metals to water, posing a threat to the environment. The use of natural materials as low cost sorbents for the removal of heavy metals from aqueous solutions has recently received increasing attention. The present study was conducted to evaluate the effectiveness of eggshell and coral wastes for the removal of $Pb^{2+}$, $Cd^{2+}$ and $Cu^{2+}$ from aqueous solutions. Batch equilibrium experiments were conducted using heavy metal solutions with waste eggshell and coral powders. Langmuir and Freundlich adsorption models were used for the mathematical description of sorption equilibrium. The maximum amounts of metals ($Cu^{2+}$, $Pb^{2+}$ and $Cd^{2+}$) adsorbed were found to be 32.3, 22.9 and 4.47 mmol $kg^{-1}$ for eggshell and 6.77, 5.52 and 1.03 mmol $kg^{-1}$ for coral wastes, respectively. At low initial concentrations the adsorption of heavy metals onto both sorbents can be described as H-type (except for the Cd adsorption onto coral), indicating high-affinity isotherms and strong adsorbate-adsorptive interactions such as inner sphere complexes. However, the metal adsorption was described by L-type isotherm at high initial concentrations. Based on the distribution coefficient ($K_d$) values and the percentage of metal removed, the selectivity sequence in eggshells and coral wastes was found to be $Pb^{2+}$ > $Cu^{2+}$ > $Cd^{2+}$. The $K_d$ values and the percentage of metals removed were higher in eggshells than coral with its higher capacity to adsorb heavy metals. Based on the results of the present study, eggshell and coral wastes can be used for the removal of heavy metals from aqueous solutions.

Keywords

• Eggshell;
• Coral;
• Heavy metal removal;
• Distribution coefficient;
• Langmuir isotherm;
• Biosorption