Dissolution surface conditions

Berner, R. A. (1978). Rate control of mineral dissolution under earth surface conditions. Am.. Sci. 278, 1235-1252. 

Different views exist as to the reasons for selective dissolution of the asperities. According to older concepts, convection of the liquid is hindered in the solution layers filling recesses hence, reaction products will accumulate there and raise the concentration and viscosity in these layers. Both factors tend to lower a metal s anodic dissolution rate relative to that at raised points. According to other concepts, a surface condition close to passive arises during electropolishing. In this case, the conditions for passivation of the metal at raised points differ from those in recesses. 

Figure 2. Effect of various stages of corrosion on changes of glass surfaces. Conditions (b) type 2, a = 0, selective leaching (c) type 4, 0 < a < 1, selective leaching and network dissolution and (d) type 5, a = 1, network dissolution. (Reproduced, with permission, from Ref. 7. Copyright 1980, North-Holland Publishing...

Carbonate minerals are among the most chemically reactive common minerals under Earth surface conditions. Many important features of carbonate mineral behavior in sediments and during diagenesis are a result of their unique kinetics of dissolution and precipitation. Although the reaction kinetics of several carbonate minerals have been investigated, the vast majority of studies have focused on calcite and aragonite. Before examining data and models for calcium carbonate dissolution and precipitation reactions in aqueous solutions, a brief summary of the major concepts involved will be presented. Here we will not deal with the details of proposed reaction mechanisms and the associated complex rate equations. These have been examined in extensive review articles (e.g., Plummer et al., 1979 Morse, 1983) and where appropriate will be developed in later chapters. 

Factors which cause deviations from standard transport-controlled kinetics are discussed. Some of these are Surface roughness of the metal samples adsorption of reaction products a slow intermediate stage in the dissolution and conditions which cause the metal to assume a passive potential. 

Wogelius R. A. and Walther 1. V. (1992) Olivine dissolution kinetics at near-surface conditions. Chem. Geol. 97(1-2), 101-112. 

Precipitation, dissolution and reprecipitation of the various Fe oxides in the environment depend predominately on factors such as pH, Eh, temperature and water activity. For this reason, the different Fe oxides may serve as indicators of the type of environment in which they formed. Goethite and hematite are thermodynamically the most stable Fe oxides under aerobic surface conditions and they are, therefore, the most widespread Fe oxides in soils and sediments. Other Fe oxides are, however, also found in the enviroirment because, although they are thermodynamically less stable, their formation is kinetically favored and their transformation to more stable forms proceeds sluggishly. 

In this chapter, the conditions for the formation of PS, the relation between the formation conditions and PS morphology, and the mechanisms for the formation of PS and morphology are discussed. The various aspects of surface condition, nature of reactions, and reaction kinetics that are fundamentally involved in the anodic dissolution of silicon are discussed in Chapters 2-5. 

Somewhat similar measurements could be based on solid disruption [18], polymer degradation [7], or accelerated dissolution. These well-known mechanical effects of ultrasound also derive from cavitation. Thus one might measure the rate of particle size reduction under sonication of some standard solid dispersed in a given fluid. Alternatively one could measure the rate of dissolution of a standard solid in a solvent, or the reduction in molecular weight of polymer chains. Here again the initial particle size and surface conditions, together with pressure and temperature, should be carefully monitored. 

The 14 equations, sulfite rate of change in the liquid and the rates of sulfite transfer (in terms of r ) from the 13 sized particles, may be solved simultaneously for and the r s. Then the total sulfite concentration is calculated at each increment of time. In addition, to compute the proper surface conditions for the mass transfer driving force, all of the governing equations for the bulk listed in the section above on the surface conditions during dissolution must be solved at each time step. Two differences should be noted the solubility product for sulfate must now be satisfied and in the Ca2+ and sulfur balance, the effect of oxidation must be accounted for , ... 

The silicification of sediments little affected by diagenesis under surface conditions is a pronounced frequent phenomenon entailing the dissolution of silica by surface waters, as well as hydrolysis of silicates with the subsequent redeposition of the silica in the discharge zone of the surface waters (Taylor 1950 Thompson 1959 Weyl 1959 Trumit 1968). These cases of silicification are widespread under geochemical conditions favourable for the dissolution of silicates. 

Overall, the dissolution rate and solubility of minerals with diffuse-kinetic dissolution regime change within a broad range of values and depend on water acidity. These minerals are preserved for quite a long time under surface conditions even in humid climate. Their dissolution is the cause of most common on the surface carbonate karst. 

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