Fig. 5. Kinetics of As adsorption on goethite at pH = 8 in the presence and absence of silicic acid, (a) As(III) and silicic acid, (b) As(V) and silicic acid. As = 0.10 mM, ionic strength (I) = 0.01 M, and goethite suspension of 1.0 g L-1.