This study evaluates the potential of calcined oyster and clam shells as low-cost materials for the removal of heavy metal ions Pb2+, Cd2+, and Cu2+ in aqueous solutions. The materials were collected, cleaned, and calcined at 700 °C to produce carbon monoxide (CaO)-rich materials. Material characterization was performed using fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM,) and Brunauer-Emmett-Teller analysis (BET). The FT-IR results confirmed the partial conversion of CaCO3 to CaO, while SEM images showed a strongly aggregated particle structure and dense surface. BET analysis revealed very low specific surface areas (1.049 and 0.373 m2/g for oyster and clam shells, respectively), indicating poorly developed capillary structures. Despite this, both materials achieved high removal efficiency, particularly for Pb2+(>90% at a concentration of 150 mg/L). The treatment efficiency followed the order Pb2+ > Cd2+ > Cu2+, consistent with the physicochemical properties and precipitation capabilities of the metal ions. The results showed that the removal mechanism was not dominated by physical adsorption but mainly involved chemical processes, including CaO hydration to create an alkaline environment, precipitation of hydroxides and carbonates, and ion exchange. The study demonstrated that calcined seashell material is an effective, sustainable, and low-cost solution for heavy metal treatment in water.