Study of the Convergence of Equilibrium Time and lead (II) Adsorption Efficiency by Rice Husk and Activated Carbon at Low Concentrations

In this research, rice husk and activated carbon adsorbents were used for removal of lead ion from aqueous solution at pH= 6. In the batch tests experimental parameters were studied, including contact time and initial metal ions concentration.Survey of the equilibrium time at different concentration showed that equilibrium time is reduced with decrease of initial concentration of solution from 50 mg/l to 1 mg/l for both of the adsorbents, and they are closed to each other. In this state is obtained equilibrium time 45 and 60 min for activated carbon and rice husk, respectively. With the increase of initial concentration of solution from 50 mg/l to 500 mg/l, the equilibrium time is also decreased and they converge. In this condition, is obtained equilibrium time 60 min for activated carbon and rice husk and and are closed to each other. Maximum equilibrium time is obtained 120 and 90 min for rice husk and granular activated carbon adsorbent. Study of the adsorption efficiency at different concentrations indicated that adsorption efficiency is increased with decrease of initial concentration of solution for both the adsorbents, and they are closed to each other. The maximum adsorption efficiency for rice husk and activated carbon at initial concentration of 1 mg/l was found. The attained adsorption efficiency in this concentration was approximately %98 and %99.7 for rice husk and activated carbon adsorbents. In this study, kinetic adsorption models were also studied and Ho et al. (1996) model rather than the lagergren (1898) described data better. Also, fitting langmuir and freunlich adsorption isotherm models on experimental data showed that freundlich model described experimental data better.