Comparative studies on the use of activated snail (Achanita fulica) and periwinkle shells (Typanotonus fuscatu) in the removal of heavy metal ions from aqueous solutions

Abstract

This study seeks to compare the application of activated snail and periwinkle shells in the removal of heavy metal ions from aqueous solution. Snail and periwinkle shells obtained from local markets in Warri, Nigeria, were carbonized, activated and characterized. Batch adsorption experiment was carried out to determine the effect of pH, concentration, adsorbent dose and contact time on the adsorption process. Data obtained were examined using adsorption isotherms. Characterization result showed that activated carbon obtained from periwinkle shells had higher values of pH, pore volume, moisture content and porosity than the values obtained for activated snail shells. The maximum pH obtained for the adsorption of Pb²⁺ and Cd²⁺ ions using activated  periwinkle shell carbon (APSC) and activated snail shell carbon (ASSC) were 7 for Pb²+ and 4 – 10 for Cd ²⁺ . The percentage adsorption of these ions onto APSC were 96.70% Pb²⁺ and 100% Cd²⁺ while that of ASSC were  95.00% Pb⁺² and 68.80% Cd²⁺ . The optimum adsorbent dose and contact time for the removal of these ions, using both adsorbents, were 3 g and 90 min, respectively. Results revealed that APSC had better adsorption capacity than ASSC for most parameters studied. Of the four adsorption isotherms models used for this study,  Langmuir had the highest regression coefficient (R² = 0.9852 for APSC and 0.8950 for ASSC). Data for adsorption kinetics exhibited a good  compliance with pseudo-second order kinetic model