Abstract: The present study measured the adsorption and desorption isotherms of As(Ⅲ) on the ferrihydrite surface and determined the effects of ferrihydrite dosages, temperatures and pH on As(Ⅲ) adsorption and desorption. The results showed that Langmuir and Freundlich equations could well describe the relationship between adsorption amount and the original concentration of As (Ⅲ). The maximum adsorption rate of As (Ⅲ) by ferrihydrite was 99.5%. The adsorption amounts and adsorption rates at 35℃ were greater than at 25℃. The pH of the solution had great effects on the adsorption of As(Ⅲ). The maximum adsorption rate of As(Ⅲ) was obtained at pH=8．

Key words: ferrihydrite, As(Ⅲ), adsorption, temperature, pH