. Arsenic removal from drinking water by adsorption on natural and iron modified clinoptilolite was investigated. The structure of modified and unmodified clinoptilolite samples from the Gordes-Manisa deposit was studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The elemental composition and specific surface areas of zeolitic samples were also determined. The pretreatment of clinoptilolite using NaCl and FeCl(3) solutions (0.1 and 0.01 M) resulted in 9.2 (92%) and 8.4 (84%) mu g g(-1) of arsenic uptake, whereas only 1.5 mu g g(-1) of arsenic uptake could be detected in the untreated zeolite at equilibrium time. The time required to attain equilibrium for arsenic sorption on all types of clinoptilolite was 60 min. The saturation time was independent of concentration of the initial arsenic solution. The pseudo-second-order rate equation described better the kinetics of arsenic sorption with good correlation coefficients than pseudo-first-order equation. At lower initial arsenate concentration, arsenate exhibited greater removal rates and best removed when the clinoptilolite modified by 0.1 M FeCl3 was used for adsorbent. This study showed that the amount of arsenic adsorbed on the adsorbents not only depends on the iron concentration in the clinoptilolite, but also depends on the initial arsenate concentrations. (C) 2011 Elsevier B.V. All rights reserved.