A first step in refining traditional holistic models is to In this paper, the acid-base properties of illite/water suspenisolate and analyze the surface reaction mechanisms of difsions are examined using the constant capacitance surface comferent components in natural particles. Of particular interest plexation model. On the basis of results of potentiometric titrations are clays, since they are the dominant components in natural and solubility experiments, we conclude that the proton reactions minerals. As to what has already been done in this area, in the supernatants of illite suspensions can be successfully repre-Schindler's research group (8, 9) has modified and extended sented by proton reactions of Al(H 2 O) 3/ 6 and Si(OH) 4 in water the constant capacitance model, which has been successfully solutions. For illustrating the acidic characteristics of aqueous illite used to describe the amphoteric acid-base behaviors of inorsurfaces, two surface protonation models are proposed: (1) one ganic surface groups on oxide (10-14) and sulfide minerals site-one pK a model, GSOH S GSO 0 / H / , pK int a Å 4.12-4.23; (2) two sites-two p K a s model, GS I OH S GS I O 0 / H / , pK int a I (15-17), to interpret the surface acid-base properties of the clay minerals kaolinite (a 1:1 layer-type clay mineral) Å 4.17-4.44, and GS II OH S GS II O 0 / H / , pK int a II Å 6.35-7.74.
and montmorillonite (a 2:1 layer-type clay mineral). For the
Evaluation of these two models indicates that both of them can
give good descriptions of the experimental data of systems with study of kaolinite ( 8), in addition to the amphoteric surface different illite concentrations and ionic strengths and that the one hydroxyl group, GSOH, they postulate a second surface site-one pK a model can be considered as a simplification of the functional group, GXH, which is weakly acidic and can two sites-two pK a s model. Since both models assume only deproundergo ion exchange with cations from the background tonation reactions at the illite surfaces, they suggest that the surelectrolyte. For the study of montmorillonite (9), besides face behavior of the illite is similar to that of amorphous SiO 2 .
GSOH and GXH, another surface hydroxyl group GTOH, Model assumptions, experimental procedures, and evaluative criwhich undergoes one deprotonation reaction, is incorporated teria are detailed in the paper. ᭧ 1997 Academic Press to evaluate the surface acid-base behaviors. Wieland and