Mechanistic modeling of chromate adsorption onto goethite

We have investigated the adsorption of CrO42− onto goethite as a function of pH, background electrolyte and adsorbate loading. Experimental data were interpreted with a three-plane model (TPM) that accounts for spatial charge distribution of inner-sphere surface complexes. In accordance with EXAF spectroscopic data [S. Fendorf, M.J. Eick, P. Grossl, D.L. Sparks, Environ. Sci. Technol. 31 (1997) 315] >FeO0.2CrO3−1.3 and (>FeO)0.42CrO2−0.6 surface species were selected for TPM calculations. TPM simulations replicate CrO42− adsorption data well when CrO42− coverage was <2×10−7 mol m−2.