Removal of Hexavalent Chromium from Aqueous Solution by Adsorption on Raw Powder and Chemically Activated Carbon of Hibiscus rosa-sinensis Flowers

Adsorption using low cost adsorbents is one of the cheapest methods that can be used for removal of hexavalent chromium from water. In this study, a comparison has been carried out on adsorption using raw Hibiscus rosa-sinensis flowers and activated carbon prepared by impregnation of the Hibiscus rosa-sinensis flower. Hibiscus rosa-sinensis flowers are low cost adsorbents available throughout the year and easily biodegradable, and hence cost effective. Impregnation of the flower powder with different ratios of sulphuric acid was carried out. Adsorption using carbon is found to be more efficient as compared to the raw flowers. The optimum adsorbent dosage for the carbon was found to be 200mg/100mL, and for the raw flower 400mg/100mL. Both, Langmuir and Freudlich isotherms were studied and from the values of coefficient of determination obtained, it was concluded that the Langmuir isotherm fits well. Kinetic studies were also conducted. This included the pseudo first order and pseudo second order kinetics. The q_e,cal values obtained for pseudo first order kinetics for the carbon and raw flower were 7.799 mg/g and 29.459mg/g respectively. This showed a large variation from the experimental value. But for the pseudo second order kinetics only a slight variation from the experimental value was observed. Hence, it was concluded that the adsorption process followed pseudo second order kinetics.