Comparison of copper adsorption from aqueous solution using modified and unmodified Hevea brasiliensis saw dust

Raw rubber wood (Hevea brasiliensis) saw dust (RSD) was modified using phosphoric acid and sodium hydroxide with different impregnation ratios (IR) to improve adsorption capacity for the removal of copper from aqueous solutions. The modified saw dusts using phosphoric acid (PMSD4, IR 1:2) and sodium hydroxide (SMSD3, IR 1:1) were evaluated through SEM and FTIR. Equilibrium and kinetic adsorption studies were carried using RSD, PMSD4 and SMSD3. The effects of various operating variables such as solution pH, adsorbent dose, initial copper concentration, temperature on the removal of copper ions have been studied. The copper adsorption data were fitted to various isotherm models. The data were also fitted to kinetic models such as pseudo first order, pseudo second order, Elovich and intraparticle diffusion models. The optimum pH for the adsorption was 6. The adsorption data were found to follow the Langmuir and Freundlich models better than the other models. The adsorption of the metal ions increased with increasing temperature indicating the endothermic nature of the adsorption process. Thermodynamic parameters such as free energy, enthalpy and entropy change were calculated. An appreciable increase in adsorption capacity was observed when studies were carried out using SMSD3 to PMSD4 and RSD.