Adsorption of lead by activated carbon developed from rice husk

Activated carbons were prepared from rice husk for the adsorption of Pb(II) from aqueous solution. The textural properties of the prepared carbons were characterized from the adsorption of nitrogen at 77 K and scanning electron microscopy. Fourier-transform infrared spectroscopy, base and acid neutralization capacities, pH of the active carbon slurry, and pH point of zero charge (pH(pzc)) were used to characterize the surface oxygen functional groups. The effect of experimental parameters such as pH, initial concentration, contact time, and temperature on the adsorption was investigated. The equilibrium data were analyzed by the Langmuir and Freundlich models, which revealed that Langmuir model was more suitable to describe the lead adsorption than Freundlich model. The adsorption kinetics could be expressed by the pseudo-second-order model where boundary layer diffusion tends to be the rate-limiting step. Solution pH exhibited remarkable impact on the adsorption process and the maximum amount adsorbed was obtained at pH 5. The adsorption capacity of the carbon sample is related to the porosity and the surface chemistry, which are dependent on the method of activation.