Uptake of arsenite and arsenate by clinoptilolite-rich tuffs

Clinoptilolite-containing rocks were used to study the possible uptake of arsenite (H(3)ASO(3)) and arsenate (H2AsO4) species from aqueous solution. Two samples also exhibited mordenite and erionite zeolitic phases. Batch and isotherm studies at pH 4 in the concentration range 0.1 < C < 4 mg l(-1) were performed. The experimental data were used to model Freundlich, Langmuir and Langmuir-Freundlich adsorption isotherms. Solutions were analyzed by means of ion chromatography coupled with inductively coupled plasma mass spectrometric detection (IC-ICP-MS). All zeolitic samples investigated removed more H2AsO4- than H3AsO3 at equivalent arsenic concentrations. Although the saturation capacity of the tuffs studied was inversely related to the silicium dioxide content and directly to the iron content in the acid-washed zeolite, the addition of iron did not significantly improve the removal efficiency. Up to 98% of H3AsO3 were removed from a 500 mug As l(-1) solution by three of the samples studied after a contact time of 70 days. (C) 2001 Elsevier Science B.V. All rights reserved.