The chelate resin functionalized resin with dithiol group (RES resin) has been developed for the removal of dilute As (III) from the waste geothermal water. The present investigation aims to clarify the adsorption equilibrium of As (III) onto the RES rein to discuss the feasibility of this resin to apply to the geothermal water.
The adsorption equilibrium was determined by an usual batchwise method. Effects of temperature, initial concentration of As (III), pH of the solution and coexisting solutes on the equilibrium were examined. The Langmuir equation could reasonably express the adsorption data. The adsorption capacity and the equilibrium constant suggested that the RES resin was suitable for the separation of As (III) from the hot water (368K) . The effect of As (III) concentration on the isotherm was not observed. The adsorption capacity of the RES resin approximately gave a constant value at pH lower than 10, while it decreased remarkably at pH higher than 10. This result suggests that the alkaline solution (pH>10) is effectively employed as an eluent. Neither NaCl nor silica which are most commonly found as a coexisting solute in the geothermal waste water did not interfere seriously with the adsorption of As (III) . Therefore, the RES resin is promise for the selective adsorption of As (III) from the hot waste water.