REMOVAL OF HEAVY METAL IONS FROM AQUEOUS SOLUTIONS BY ACTIVATED CARBON, DERIVED FROM AGRICULTURAL WASTE

Abstract

Low cost oxidized and un-oxidized activated carbon samples were prepared from saw dust and seed shells of Ziziphus jujube by chemical activation with phosphoric acid (H3PO4), followed by carbonization at 450 oC. The prepared carbon samples were characterized and utilized for the adsorptive removal of toxic heavy metals from aqueous solutions such as chromium (VI), cadmium (II) and lead (II) ions. All samples were found to be microporous in nature with low ash content, sufficient BET surface area and pore volumes. The effect of various parameters like solution pH, contact time, initial concentration, temperature, carbon dosage and shaking speed, on adsorption of metal ions was investigated. The adsorption of Cr (VI) decreased while that of Cd (II) and Pb (II) increased by increasing pH. Maximum adsorption of Cr (VI) was observed in the pH range of 2–4 at equilibrium time of 300-420 min. Equilibrium time for Cd (II) and Pb (II) adsorption was found to be 420-480 min at all temperatures. Batch experiments revealed that the adsorption of all the metal ions increased with increase in contact time, initial concentration, temperature and carbon dosage, etc. Thermodynamic studies indicated the feasibility, spontaneity and endothermic nature of the adsorption process. Among different isotherm and kinetic equations, Langmuir’s model and pseudo - second order equation were found to better describe the experimental data. The adsorption capacity of oxidized samples was found to be higher than that of un-oxidized samples for Cr (VI) but lower for Cd (II) and Pb (II). In comparison to Cd (II) ions, the removal of Pb (II) ions was higher. The results suggested that the prepared activated carbon samples could be used effectively as eco-environment friendly adsorbents for removal of Cr (VI), Cd (II) and Pb (II) ions from aqueous solutions. Keywords: Activated carbon; Ziziphus jujube; Adsorption; Heavy metals; Chromium; Cadmium; Lead; Thermodynamic; Kinetic