Equilibrium, kinetics and thermodynamic studies for adsorption of As(III) on activated alumina Tony Sarvinder Singh, K.K. Pant* Department of Chemical Engineering, Indian Institute of Technology, HauzKhas, New Delhi 110016, India Received 10 March 2003; received in revised form 27 June 2003; accepted 27 June 2003 Abstract Contamination of drinking water due to arsenic is a severe health hazard problem. Most of the techniques developed for pentavalent arsenic [As(V)] species are not very effective for trivalent arsenic ions [As(III)] which are more toxic and mobile than arsenate ions. Present investigation aims to remove arsenite ions [As(III)] by activated alumina. Effect of adsorbent dose, solution pH, and contact time has been investigated. Kinetics reveal that uptake of As(III) ion is very rapid in the first 6h and equilibrium time is independent of initial As(III) concentration. The arsenite removal was strongly dependent on pH and temperature. Equilibrium studies show that As(III) ions have high affinity towards activated alumina at pH 7.6. Both Freundlich and Langmuir adsorption isotherms were well fit to the experimental data. Thermodynamic parameters depict the exothermic nature of adsorption and the process is spontaneous and favorable. The results suggest that activated alumina can be used effectively for the removal of AflTD ions. Keywords: Adsorption; Arsenite; Equilibrium; Adsorption kinetics; Activated alumina 1. Introduction Arsenic is an ubiquitous element in the earth's crust and ranks 20th among most abundant element [1]. Arsenic occurs in both organic and inorganic forms in natural waters but organic arsenic is of lit- tle importance as it goes through bio transformation and detoxifies through methylation. Inorganic arsenic occurs in - 3 , 0, +3, and +5 oxidation states in aquatic systems. The elemental state -3 and 0 are extremely rare whereas +3 and +5 oxidation states are commonly found in water systems depending on the prevailing redox conditions. Under reducing environment As(III) is found primarily as H3AsO3, H 2 As0 3 -, HAsO 3 2 ", and AsO 3 3 " whereas differ- ent hydrolysis species of As(V) such as H3AsO4, E^AsCU", HAsCU 2 ", and AsCU 3 " can be present in water with dissolved oxygen/oxidizing environ- ment [2]. Although environmental restrictions and regulations have limited the production and uses of arsenic and its compounds, they are still extensively used in metallurgy, agriculture, forestry, electronics, pharmaceuticals, glass, and ceramic industry. It is introduced into the environment through weathering of rocks, mine tailings, industrial wastes discharge, fertilizers, agricultural employments of pesticides,