SIO-REMOVAL OF CADMIUM FROM WATER USING LEMON PEEL AND GREEN COCONUT SHELL POWDER

Abstract

Cadmium is one of the most toxic heavy metal and has the potential to cause several diseases such as renal disturbances, lung insufficiency, bone lesions, cancer and hypertension. It is a conservative pollutant and thus can be harmful for long term consumption of Cd containing water even at lower concentration. Cadmium finds its way to waste stream from electroplating, smelting, alloy manufacturing, pigments, plastic, cadmium-nickel batteries, fertilizers, mining, pigments and dyes, textile operations etc. Therefore removal of cadmium from water is of special concern. Among the various techniques such as precipitation, ion exchange, membrane separation, etc. available for cadmium removal from water, adsorption is the most popular process due to its high efficiency, easy handling and economic feasibility. However, nowadays many researchers are focusing in developing suitable and low cost adsorbents. Therefore, the present study has been undertaken to develop suitable low cost agro based biosorbents for cadmium.removal from water as these materials are abundantly available and of zero cost. In the continuing search to achieve the desired objective, lemon peel and green coconut shell powder have been evaluated as biosorbents for the removal of cadmium from aqueous solutions. Batch experiments have been performed to study the adsorption of cadmium ions on these biosorbents. Characterization of both biosorbents has been carried out using various techniques such as proximate and ultimate analysis, FTIR, SEM, EDAX etc. The influence of cadmium initial concentration, pH, adsorbent dosage, time, temperature was studied in batch method. Adsorption process reveals that the initial uptake is rapid and equilibrium is established about in 3 h for green coconut shell powder and_5 h for2lemon peel. To facilitate mathematical modeling, adsorption kinetic models as well as adsorption isotherms have been developed. Adsorption of Cd on both the adsorbents has been found to follow pseudo second order kinetic model. Equilibrium data are fitted to Langmuir and Freundlich isotherm models. The maximum adsorption capacity (max) for lemon peel and green coconut shell powder is found to be 11.24 mg/g and 14.49 mg/g respectively. Various thermodynamics parameters such as Gibb's free energy change (AG°), enthalpy change (OH°) and entropy change (AS°) indicate the nature of process. The negative values of AG° and OH° show that the process is spontaneous and exothermic, respectively.