Adsorbents from Bio-waste for water purification

Rice Husk was used as a source to prepare activated carbon by physical and chemical activation methods. The physical activation was employed with CO2 and steam at high temperature of 850oC while chemical activation with nitric acid ,sodium hydroxide, phosphoric acid and Zinc chloride at an ambient temperature. The treatment with nitric acid before carbonization and with sodium hydroxide after carbonization we got high surface Area (750 m2/g). The adsorption studies of Cr (VI) ion on the activated carbon of rice husk were investigated. Also, the effects of various experimental parameters like contact time, adsorbent dosage, Cr (VI) ions concentration, temperature and pH were studied using batch adsorption experiments. The characterization of the activated carbon was accomplished by using BET-N2 adsorption, Temperature programmed decomposition (TPD), Raman Spectra, point of zero charge (PZC) and Thermo gravimetric analysis (TGA). The results obtained from adsorption studies follow that highest adsorption 88 % and highest adsorption capacity is 8.17 mg/g. The kinetic studies of adsorption were analyzed by different kinetic models like pseudo second order and intra-particle diffusion. Among these, the pseudo second order was found to be the most appropriate to study the adsorption of Cr (VI) ions on physically activated carbon. The process was found to be endothermic with enthalpy change, ΔH of 13.25 kJ/mol and entropy change, ΔS of 53.96 J K-1 for the temperature change of 300-330 K. The negative values of ΔG of -4.99 kJ/mol (NCRH5M), -2.06 kJ/mol (NCRH3M), -0.82 kJ/mol (NCRH1M) and -0.27 kJ/mol (CRH) suggest the spontaneous adsorption of Cr (VI) ions on activated carbon. For the determination of total hardness and TDS of tap water results found before and after treatment are 190, 155 and 80, 50 mg/L respectively. For the Fluoride Removal of tap water results before and after treatment are 0.93 and 0.51 respectively