Fig. 4. Breakthrough curves of ferrocyanide in goethite-coated sand at three pore-water velocities (a, = 0.104 cm min^-1; b, = 0.209 cm min^-1; c, = 0.305 cm min^-1). Lines result from fitting the data to the Langmuir isotherm (Eq. [6]) using MCMFIT. Fitted parameters are given in Table 3.