Activated state theory, mineral dissolution

We have seen above that the kinetics of mineral dissolution is well explained by transition-state theory. The framework of this theory and kinetic data for minerals have shown that dissolution is initiated by the adsorption of reactants at active sites. Until now these active sites have been poorly characterized nevertheless, there is a general consensus that the most active sites consist of dislocations, edges, point defects, kinks, twin boundaries, and all positions characterized by an excess surface energy. Also these concepts have been strongly supported by the results of many SEM observations which have shown that the formation of crystallographically controlled etch pits is a ubiquitous feature of weathered silicates. 

Recent advances in applying transition state theory to geochemical kinetics (SQ, SD have emphasized the interaction of the activated complex with specific surface reaction sites. The rate of reaction is assumed to be a function of the surface reaction site density. A correspondence is also observed between surface dissolution features such as etch pits, and crystallographically controlled extended defect features such as edge and screw dislocations (S2). Based on these lines of evidence, the reactive surface area has been proposed to be proportional to the defect density within minerals... 

For the explanation of hydrolytic dissolution processes currently is widely used activated-complex theory, which is also called transition state theory or absolute reaction rate theory. According to this theory, at hydration and protonation on the surface of the mineral form functional groups X-OH, X-OH and X-0 , which have acid-alkali properties dependent on pH of the solution. However, not the entire specific surface of the mineral participates in dissolution reactions but only its effective portion, which is taken by the... 

This chapter is organized under three topical areas. First, by analyzing the dissolution and speciation data of a basalt glass and various oxides we show that the surface characteristics and the dissolution behavior of complex oxides can be modeled from the properties of their constituent oxide components. Then we examine the main features of the steady-state dissolution of multiple oxides and their implications for the application of the surface coordination theory. Finally, we discuss the problem of the nature of the active dissolution sites by analyzing recent data on the dissolution of strained minerals. 

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