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Adsorption onto activated carbons is a potent method for the treatment of dye-bearing effluents because it offers various advantages. In this study, activated carbons, prepared by a new technique from low-cost rice husk by sulfuric acid and zinc chloride activation, were used as the adsorbent for the removal of crystal violet, a basic dye, from aqueous solutions. The effects of various experimental parameters, such as adsorbent dosage and size, initial dye concentration, pH, contact time, and temperature, were investigated in batch mode. The kinetic data were well fitted to the Lagergren, pseudo-second-order, and intraparticle diffusion models. It was found that intraparticle diffusion plays a significant role in the adsorption mechanism. The isothermal data could be well described by the Langmuir and Freundlich equations. The maximum uptakes of crystal violet by sulfuric acid activated (RHS) and zinc chloride activated (RHZ) rice husk carbon were found to be 64.875 and 61.575 mg/g of adsorbent, respectively. The results indicate that RHS and RHZ could be employed as low-cost alternatives to commercial activated carbon in wastewater treatment for the removal of basic dyes.

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Nuts of Terminalia Arjuna, an agricultural waste, were used to prepare activated carbons by zinc chloride activation under four different activation atmospheres, to develop carbons with substantial capability, and to adsorb phenol from dilute aqueous solutions. Experiments were carried out at different chemical ratios (activating agent/precursor). Effect of carbonization temperature and time are the important variables, which had significant effect on the pore structure of carbon. Developed activated carbon was characterized by SEM analysis. Pore volume and surface area were estimated by Hg porosimetry and BET surface area analyses. The carbons showed surface area and micropore volumes of around 1260 m 2 /g and 0.522 cm 3 /g, respectively. The activated carbon developed shows substantial capability to adsorb phenol from dilute aqueous solutions. The kinetic data were fitted to the models of intraparticle diffusion, pseudo-secondorder, and Lagergren model which followed more closely the pseudo-second-order chemisorption model. The isotherm equilibrium data were well-fitted by the Langmuir and Freundlich models. The maximum removal of phenol was obtained at pH 3.5 (about 93% for adsorbent dose of 10 g/L and 100 g/L initial concentration).