APPLICATIONS TO GEOCHEMICAL PROBLEMS

In this, the last major chapter of the book, we turn our attention to the applications of modern electronic structure models and eoncepts to more general geochemical problems namely, those described by Goldschmidt as being eoncerned with the distribution of elements in the geochemical spheres and the laws governing the distribution of the elements (see Preface). 

The other major realm of formation of minerals and rocks, and the most important medium of transport and redistribution of the chemical elements at the Earth s surface, is the aqueous solution. The molecular and electronic structures of aqueous solutions, their behavior at elevated temperatures, formation and stabilities of complexes in solution, and the mechanisms of reactions in solution are all considered in the second section of this chapter. 

The surfaces of minerals (or other crystalline solids) differ from the bulk material in terms of both crystal structure and electronic structure. A great variety of spectroscopic, diffraction, scanning, and other techniques are now available to study the nature of solid surfaces, and models are being developed to interpret and explain the experimental data. These approaches are discussed with reference to a few examples of oxide and sulfide minerals. Although relatively few studies have been undertaken specifically of the surfaces of minerals, many of the reaction phenomena 

In the final section, the overall geochemical distribution of the elements is considered in the light of electronic structure theories. Previous attempts to classify elements on the basis of their preferences for compound formation with oxygen or sulfur are reviewed. 

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Details of the Pitzer equations and definitions of the notations utilized in this paper and in PHRQPITZ are given in the literature (3-lOL As the focus of this report is on the capabilities and limitations of PHRQPITZ in relation to its application to geochemical problems, only selected aspects of the implementation of the Pitzer equations in PHRQPITZ are presented. 

The results of these determinations for 22 elements on 88 crude oils were subjected to factor analysis, which is a statistical technique designed to explain complex relations among many variables in terms, of a few factors which themselves represent simpler relations among fewer variables. Factor analysis only determines the relations it does not explain them. The explanation of the factors must be in the context of known information about the variables. Hitchon and Gawlak have used factor analysis in the study of aromatic hydrocarbons in gas condensates from Alberta and their paper includes pertinent background information with particular application to geochemical problems. 

Non-equilibrium thermodynamics (de Groot and Mazur, 1984 Prigogine, 1977) affords an abstract, and therefore very general, foundation for understanding pattern formation. The abstract nature of this approach makes direct application to geochemical problems difficult, but non-equilibrium thermodynamics does provide a powerful conceptual basis for thinking about pattern formation. 

Major topics include rate equations, reactor theory, transition state theory, surface reactivity, advective and diffusive transport, aggregation kinetics, nucleation kinetics, and solid-solid transformation rates. The theoretical basis and mathematical derivation of each model is presented in detail and illustrated with worked examples from real-world applications to geochemical problems. The book is also supported by online resources self-study problems put students new learning into practice and spreadsheets provide the full data used in figures and examples, enabling students to manipulate the data for themselves. 

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