Alkali - treated Carbonized Rice Husk for the Removal of Aqueous Cr(VI)

Rice husk was chemically modified for the preparation of activated carbon . Rice husk was treated with nitric acid and carbonized at 700 C. After carbonization, the resulting rice husk char was treated with NaOH at room temperatur e. The 5 M NaOH - treated rice husk ha d the highest surface area ( 750 m 2 /g ) . Proximate analysis of activated ca rbon confirmed that NaOH treatment remove d silica completely. T emperature programmed decomposition (TPD) graphs showed that the total gas contents (CO and CO 2 ) liberated by CRH and H 2 O - treated CRH and CRH5M were 2l5 μmol/g, 390 μmol/g , and 970 μmol/g, respectively. The adsorption studies of the activated carbon during Cr (VI) removal from the aqueous medium indicated that CRH5M showed the highest rate of adsorption. The eff ect of adsorbent dosage, Cr (VI) concentration, pH , and temperature were studied to determine the best removal efficiency. With a decrease in pH from 4.4 to 2, the adsorption capacity increased from 3 mg/g to 25.2 mg/g. T he adsorption of Cr (VI) followed pse udo - second - order behaviour. The change s in Gibbs free energy, enthalpy , and entropy affected by thermodynamic parameters were found to be negative, which conf irmed that the adsorption of Cr (VI) on CRH5M is spontaneous, exothermic , and favours low temperatu re s