Toxicological & Environmental Chemistry Vol. 91, No. 6, August 2009, 1055–1067 Removal of arsenic ions from aqueous solutions by adsorption onto biopolymeric crosslinked calcium alginate beads Tulika Dewangan a , Alka Tiwari a * and A.K. Bajpai b a Department of Chemistry, Research Centre, Govt. V.Y.T.P.G. Autonomous College, Durg, India; b Department of Chemistry, Bose Memorial Research Laboratory, Government Autonomous Science College, Jabalpur, India (Received 13 April 2008; final version received 23 October 2008) The present article discusses the removal of As (V) ions from dilute aqueous solutions by adsorption onto biopolymeric beads of crosslinked calcium alginate. The beads were characterized by FTIR spectroscopy and their water sorption capacity was investigated. The process of adsorption of arsenic ions was monitored and various adsorption parameters were evaluated. The experiments were conducted to optimize the removal capacity and study the influence of various experimental factors such as pH, initial metal ion concentrations, contact time, and solid-to-liquid ratio. The adsorption data were applied to Langmuir and Freundlich isotherm equations, and various static parameters were calculated. Keywords: adsorption isotherm; biosorption; immobilization; calcium alginate Introduction One of the major pathways of adult and child exposure to contaminants such as heavy metals and organic compounds is through the food chain (Emongor, Meulenberg, and Phole 2004). Pollution of the environment with toxic metals and radioactive waste has dramatically increased since the beginning of the industrial revolution (Emongor, Ramolemana, and Machacha 2005). Arsenic occurs in the environment as a result of several inputs that contain this element in organic and inorganic forms. It is introduced in the aqueous system through geochemical reaction, industrial waste discharge, or even agricultural use of arsenical pesticides (Loukidou, Malis, and Zouboulis 2003). The problem of arsenic contamination in the ground water is a serious threat in many countries such as India, Bangladesh, China, Iran, Chile, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, New Zealand, Japan, and USA, because ground water is the main source of drinking water (Pal, Mukherjee, and Sengupta 2002). The largest population at risk among the 21 countries with known ground water arsenic contamination is in Bangladesh followed by West Bengal in India. Arsenic exists in natural waters both in inorganic and organic forms. The inorganic form of arsenic is more toxic compared to its organic form. Inorganic arsenic is the predominant form in contaminated ground water. Arsenic exists in 3, 0, þ3, and þ5 oxidation states. Two forms are common in natural waters: arsenite (AsO 3 3 ) and arsenate (AsO 3 4 ), referred to as As (III) and As (V) (Pokhrel and Viraraghavan 2006). *Corresponding author. Email: alkatiwari18@yahoo.co.in ISSN 0277–2248 print/ISSN 1029–0486 online ß 2009 Taylor & Francis DOI: 10.1080/02772240802585012 http://www.informaworld.com