Adsorption of arsenic on clay surfaces is important for the natural and simulated removal of arsenic species from aqueous environments. In this investigation, two samples of clay minerals (glauconite and halloysite) in both untreated and acid activated treated forms were used for the sorption of arsenate from aqueous solution. Glauconite is mainly composed of illite/ smectite mixed layer, kaolinite and quartz. Halloysite is composed of halloysite, kaolinite, quartz, marcasite and trace amount of pyrite. Iron is existed

as separated minerals (marcasite and pyrite) in the case of halloysite or present in the structure of glauconite, which play an important role in the adsorption of arsenic. Acid activation followed by calcination enhanced the adsorption capacity compared to the untreated clay minerals due to the increased surface area and pore volume. However, the increasing of acid activation leads to dissolution of iron from sorbent clay materials which in turn lead to decrease the adsorption capacity of As (V). The effects of initial As (V) concentration, contact time and pH on the adsorption of arsenic (V) by the untreated and treated glauconite and halloysite were investigated. Maximum adsorption capacity (about 93%) was recorded for treated halloysite at equilibrium conditions pH5, 240 minute contact time, arsenate concentration 0.90 mg/L, and at temperature 25^oC. The adsorption kinetics of glauconite follow the Langmuir pseudo first-order model, while theadsorption kinetic of halloysite was neither fit with pseudo first-order kinetics model nor with pseudosecond-order kinetics model, suggesting adsorption kinetics of halloysite should be further analysis.