Keywords: 
• arsenate /
• soil /
• adsorption /
• Zeta potential

Abstract: The effect of arsenic adsorption on Zeta potential of colloids of the three variable charge soils and the release of OH-from the soil surface during the adsorption of arsenate were investigated.Adsorption of arsenate on the variable charge soils under acidic condition made the surface charge of the soils more negative and thus decreased the Zeta potential of these soil colloids.These data suggested that the specific adsorption of arsenate occurred on the variable charge soils and adsorbed arsenate entered the stern layers of electric double layers on soil colloids.However,the adsorption of arsenite showed a little effect on the Zeta potential of the soil colloids,suggesting that arsenite was mainly adsorbed by the soils through the formation of outer-sphere complexes on soil surface.The exchange reaction between arsenate and surface hydroxyl of the soils resulted in the release of hydroxyl from soil surface to solution.The amount of OH-released increased with the increase in arsenate added and the rise of pH.The similar changing trends of arsenate adsorbed and OH-released with time were observed in kinetic experiments.The rates of arsenate adsorption and OH-release increased sharply with time at the first 20 minutes and then changed slightly.The molar ratio of OH-release to arsenate adsorption was also increased with time which suggested that the reaction of OH-release was followed the arsenate adsorption.The molar ratio in soil systems was lower than that in goethite system,thus both Fe/Al oxides and other components in the variable charge soils contributed to arsenate adsorption.