Arsenite adsorption on gibbsite was examined as a function of pH, ionic strength (I) and contact time (tC). As(III) showed a weak affinity for gibbsite surface. The trends of pH=f(Γads) curves have showed a marked deviation from a typical anion adsorption edge showing a maximum Γads around pH∼8.2. The experimentally derived proton exchange ratio has always converged to zero when 0.26<∑[As(III)]<7 μM and 6.2<pH<8.2. The isosteric heat of adsorption, ΔHr, exhibited invariant behavior with respect to Γads. The As(III) adsorption data was quantified by charge distribution multi-site complexation (CD MUSIC) model using the surface complex postulated below: