Application of the CD-MUSIC Model

As in the other surface complexation models, the chemical part consists in several adsorption reactions. In the application of the CD-MUSIC model, the choice of these reactions has been carefully based on spectroscopic evidence of course, that can be done also in other models such as TLM, BSM, and so on, but here it is rather essential for proper elucidation of the charge distribution. The original paper (Hiemstra and Van Riemsdijk 1996) applied the model to phosphate adsorption on goethite. Based on spectroscopic studies, they proposed the existence of monodentate-bound species (Reaction 12.44), an unprotonated bidentate-bound species (Reaction 12.45), and a protonated bidentate species, following  

The additional proton is bound to an external ligand thus, it does not enter in the calculation of Azq (Equation 12.47). Finally, two site types are considered regarding surface protonation singly and triply coordinated surface OH groups. 

In spite of the successful results, because of the requirement of detailed knowledge of surface species, the application of the CD-MUSIC model has been until present 

FIGURE 12.15 The adsorption of PO4 by monodomainic goethite used by Hiemstra and Van Riemsdijk (1996) and that of Bowden et aL (1980). The lines are calculated with the charge distribution model and are consistent with the surface species observed by cylindrical internal reflection-Fourier transform infrared spectroscopy. (Reprinted from Journal of Colloid and Interface Science, 179, Hiemstra, T. and Van Riemsdijk, W. H. 488-508. Copyright 1996, with permission from Elsevier.) 

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