Sorption of Cd²⁺ and Pb²⁺ on Aragonite Synthesized from Eggshell

In the present work, waste eggshells were used as a precursor for the synthesis of aragonite crystals through the wet carbonation method. Cadmium (Cd²⁺) and lead (Pb²⁺) were removed by the synthesized aragonite from synthetic wastewater. The influence of initial solution pH, contact time, Cd²⁺ and Pb²⁺ concentration, and sorbent dosage were evaluated. The major sorption was observed in the first 100 mins and 360 mins for Pb²⁺and Cd²⁺ respectively reaching sorption equilibrium at 720 mins (12 hr). The sorption capacity toward Pb²⁺ was much higher than toward Cd²⁺. Both heavy metals displayed high sorption capacities at initial pH 6. The pseudo-second-order kinetic model fits well with the experimental data with a higher correlation coefficient R². Two isotherm models were also evaluated for the best fit with the experimental data obtained. Langmuir isotherm best fits the sorption of the metals on aragonite synthesized from eggshells. X-ray diffraction (XRD) and Scanning electron microscopy (SEM) results of sorbent after sorption showed that the mechanism of sorption was dominated by surface precipitation. Therefore, aragonite crystals synthesized from waste eggshells can be a potential substitute source for the removal of Cd²⁺ and Pb²⁺ from contaminated water.