Adsorption of uranium (VI) on a natural clinoptilolite zeolite from Sweetwater County, Wyoming was investigated. Batch experiments were conducted to study the effects of pH and initial feed concentrations on uranium removal efficiency. It was found that the clinoptilolite can neutralize both acidic and low basic water solutions through its alkalinity and ion-exchange reactions with U within the solution. and adsorption of uranium (VI) species on clinoptilolite not only depends on the pH but also the initial feed concentration. The highest uranium removal efficiency (95.6%) was obtained at initial uranium concentration of 5 mg/L and pH 6.0. The Langmuir adsorption isotherm model correlates well with the uranium adsorption equilibrium data for the concentration range of 0.1-500 mg/L. From the experimental data obtained in this work, it was found that the zeolite sample investigated in this work is a mixture of clinoptilolite-Na zeolite and mineral impurities with a relatively large specific surface area (BET of 18 m(2)/g) and promising adsorption properties for uranium removal from contaminated water. (C) 2009 Elsevier B.V. All rights reserved.