Solute adsorption, macroscopic descriptions

Macroscopic Descriptions of Solute Adsorption and the Net Proton Coefficient. The macroscopic proton coefficient plays two important roles in our macroscopic descriptions of surface processes. First,... 

In their description of metal ion adsorption, Benjamin and Leckie used an apparent adsorption reaction which included a generic relationship between the removal of a metal ion from solution and the release of protons. The macroscopic proton coefficient was given a constant value, suggesting that x was uniform for all site types and all intensities of metal ion/oxide surface site interaction. Because the numerical value of x is a fundamental part of the determination of K, discussions of surface site heterogeneity, which are formulated in terms similar to Equation 4, cannot be decoupled from observations of the response of x to pH and adsorption density. As will be discussed later, It is not the general concept of surface-site heterogeneity which is affected by what is known of x> instead, it is the specific details of the relationship between K, pH and T which is altered. 

Elements 108 - 116 are homologues of Os through Po and are expected to be partially very noble metals. Thus it is obvious that their electrochemical deposition could be an attractive method for their separation from aqueous solutions. It is known that the potential associated with the electrochemical deposition of radionuclides in metallic form from solutions of extremely small concentration is strongly influenced by the electrode material. This is reproduced in a macroscopic model [70], in which the interaction between the microcomponent A and the electrode material B is described by the partial molar adsorption enthalpy and adsorption entropy. By combination with the thermodynamic description of the electrode process, a potential is calculated that characterizes the process at 50% deposition ... 

As mentioned in Sect. I, even the simplest electrosorption systems are extremely complicated. This complexity means that a comprehensive theoretical description that enables predictions for phenomena on macroscopic scales of time and space is still generally impossible with present-day methods and technology. (Note that MD simulations, such as those presented in Sect. II, are only possible up to times of a few himdred nanoseconds.) Therefore, it is necessary to use a variety of analytical and computational methods and to study various simplified models of the solid-hquid interface. One such class of simpHfied models are LG models, in which chemisorbed particles (solutes or solvents) can only be located at specific adsorption sites, commensurate with the substrate s crystal structure. This can often be a very good approximation, for instance, for halides on the (100) surface of Ag, for which it can be shown that the adsorbates spend the vast majority of their time near the fourfold hollow surface sites. A LG approximation to such a continuum model, appropriate for chemisorption of small molecules or ions, ° is defined by the discrete, effective grand-canonical Hamiltonian,... 

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