Excess phosphate in water bodies causes algae bloom and this phenomenon can reduce the amount of dissolved oxygen in the water bodies, resulting in the death of aquatic life. The major focus of this study is to prepare adsorbent from three waste shells for phosphate adsorption from aqueous solution and to compare their effectiveness. This study used adsorbents made marsh clamshells, waste mussel shells, and eggshells. PO43– adsorption by these shells was analysed using several parameter values, with an initial PO43− concentration of 10 mg L−1, solution volume of 100 mL, adsorbent dosage of 2 g, and various contact times. The pseudo-second-order kinetic model fitted the batch experimental data better as evidenced by the R2 values for raw marsh clamshell (0.9991), calcine waste mussel shell (0.9999), and calcine eggshell (0.9997), indicating that the adsorption between the various adsorbents and PO43− is a chemisorption process. Calcined eggshell showed the best PO43− removal efficiency (99%), followed by calcined waste mussel shell (96%) and raw marsh clamshell (73%). The application of waste material to adsorb phosphate from aqueous solution shows the potential of a new adsorbents for use in real adsorption wastewater treatment technologies.