Mechanistic study of Pb²⁺+ removal from aqueous solutions using eggshells

This study investigates the impact of eggshell particle size and solid-to-water (s/w) ratio on lead (Pb²⁺+) removal from aqueous solution. Collected raw eggshells were washed, crushed, and sieved into two particle sizes (<150 and 150-500 μm). Batch Pb²⁺+ removal experiments were conducted at different s/w ratios with initial Pb²⁺+ concentrations of up to 70 mg/L. The contribution of precipitation to Pb²⁺+ removal was simulated by quantifying removal using eggshell water, whereas sorbed Pb²⁺+ was quantified by acid digestion. Results indicated that eggshell particle sizes did not affect Pb²⁺+ removal. High removal (up to 99%) of Pb²⁺+ was achieved for low initial Pb²⁺+ concentrations (<30 mg/L) across all s/w ratios studied. However, higher removal capacity was observed at lower s/w ratios. In addition, results confirmed that precipitation played a major role in the removal of Pb²⁺+ by eggshells. Yet, this role decreased as the s/w ratio and initial concentration of Pb²⁺+ increased. A predictive relationship that relates the normalized removal capacity of eggshells to the s/w ratio was developed to potentially facilitate the design of the reactor.