This paper addresses the treatment of arsenic(III) contaminated water by adsorption technique using an unconventional adsorbent, feldspar. The removal of As(III) is dependent on contact time, concentration, pH and temperature of the solution, particle size of the feldspar and the agitation rate of the system. The maximum adsorption, i.e., 90.19%, was achieved after 100 min at the arsenic concentration 13.35 µmol L -1 , with 40 g L -1 of feldspar of particle size ≈200 µm at pH 6.5, temperature

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... ± 0.5°C and agitation rate 125 rpm. The pH of the system has played a key role in the uptake, and pH 6.5 has been determined as optimum. The process of uptake is exothermic and follows the first-order adsorption rate expression. The applicability of the Langmuir isotherm was tested for the As(III)-feldspar system at optimum conditions. The diffusion coefficients as well as thermodynamic parameters have been determined to explain the results. A model has been developed to predict the uptake capacity of the adsorbent under certain given conditions.