BACKGROUND: A study of the removal of arsenic from a sample of actual groundwater using crosslinked xanthated chitosan is described. RESULTS: RemovalofAs(III) andAs(V) wasstudiedatpH7.5underequilibriumanddynamicconditions. Theequilibriumdatawere fitted to Langmuir and Freundlich adsorption models and the various model parameters evaluated. The monolayer adsorption capacity from the Langmuirmodelfor xanthated chitosan flakes (XCF) (As(V) 20.0+/- 0.56 mg g-1; As(III) 33.0+/- 0.32 mg g-1) were lower than obtained for xanthated chitosan granules (XCB) (As(V) 36.0 +/- 0.52 mg g-1; As(III) 48.0 +/- 0.45 mg g-1). Adsorption of As (V) was unaffected by the presence of other anions while in the case of As(III) the presence of sulfate and silicate caused a 26.5-50.9% decrease in adsorption. A sample (940 bed volumes) of a groundwater spiked with 200 mu g L-1 As(V) treated with XCF in column experiments reduced the arsenic concentration to < 10 mu g L-1. The adsorbent was also successfully applied for the removal of total inorganic arsenic down to < 10 mu g L-1 from real samples of arsenic-contaminated groundwater. CONCLUSION: Xanthated chitosan was an efficient adsorbent for the removal of both forms of arsenic from groundwater under near neutral conditions. The presence of sulfur and the amino groups resulted in increased adsorption capacity of the sorbent. (C) 2012 Society of Chemical Industry