Surface groups, minerals, derivative

Premises of the treatment of Hiemstra et al. are (a) the chemistry of the surface groups can be derived from the structure of the mineral oxides using Paulings concept of bond valence [19], (b) surface oxygens are the sites for proton adsorption, they can associate with one or two protons. This leads to the following protonation reactions of a surface oxygen ... 

The objectives of this chapter are (1) to illustrate that the surface structure is important in characterizing surface reactivity and that kinetic mechanisms depend on the coordinative environment of the surface groups, (2) to derive a general rate law for the surface-controlled dissolution of oxide and silicate minerals and illustrate that such rate laws are conveniently written in terms of surface species, and (3) to illustrate a few geochemical implications of the kinetics nf oxide dissolution. 

It is important to establish the origin and magnitude of the acidity (and hence, the charge) of mineral surfaces, because the reactivity of the surface is directly related to its acidity. Several microscopic-mechanistic models have been proposed to describe the acidity of hydroxyl groups on oxide surfaces most describe the surface in terms of amphoteric weak acid groups (14-17), but recently a monoprotic weak acid model for the surface was proposed (U3). The models differ primarily in their description of the EDL and the assumptions used to describe interfacial structure. "Intrinsic" acidity constants that are derived from these models can have substantially different values because of the different assumptions employed in each model for the structure of the EDL (5). Westall (Chapter 4) reviews several different amphoteric models which describe the acidity of oxide surfaces and compares the applicability of these models with the monoprotic weak acid model. The assumptions employed by each of the models to estimate values of thermodynamic constants are critically examined. 

The adsorption of surfactant on a mineral surface is generally an exothermic process and at a constant surfactant concentration in the solution its adsorbed amount decreases with increasing temperature. Using the partial derivation 31n c/3T for a constant number of CH2 groups n of an hydrocarbon chain of a surfactant and constant values of the surface coverage a, we arrive to an equation for calculation of the total adsorption energy E. From the relation E = Ep + Ea, Richter and Schneider74 derived an equation which is valid for all isotherms ... 

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