Anionic dyes are hazardous and toxic to living organisms. For this study, ferrihydrite was prepared to test its removal capabilities on anionic dyes. A ferrihydrite particle prepared in neutral environmental conditions is sphere-like with a diameter of 2-4 nm and its total surface area is approximately 229 m^2· g^-1. In this paper, the effects of solution pH, competitive anions, and temperature on the adsorption of acid fuchsine onto ferrihydrite and the regeneration-reutilization of ferrihydrite were investigated in detail. The results indicate that ferrihydrite is an efficient sorbent for the removal of acid fuchsine at pH 4.0. The inhibitory effect of various competing anions on the present adsorption follows the precedence relationship： NO3 〈C1- 〈SO2- 〈H2PO~. Adsorption isotherms of acid fuchsine on ferrihydrite fit the Langmuir equation well. The Gibbs free energy, enthalpy, and entropy data of adsorption indicate that this adsorption is a spontaneous, exothermic, and physical process. A ferrihydrite was regenerated and reused five times, still retaining its original adsorption capacity.
