Kinetics of weathering

Berner RA (1983) Kinetics of weathering and diagenesis. Mineral. 8 111-134 Bolt GH, De Boodt ME, Hayes MHB, McBride MB (1991) Interactions at the soil coUoid-soil solution interface. Kluwer, Dordrecht... 

Berner, R. A. 1981. Kinetics of weathering and diagenesis. In Lasaga, A. C. Kirkpatrick, R. J. (eds) Kinetics of Geochemical Processes. Minera-logical Society of America, Washington, DC, 111-134... 

Zinder, B., G. Furrer, and W. Stumm. 1986. A coordination chemical approach to the kinetics of weathering. II. Dissolution of Fe(ni) oxide. Geochim. Cosmochim. Acta 50 1861-1869. 

Nagy, K. L. (1995). Dissolution and precipitation kinetics of sheef silicates. In "Chemical Weathering Rates of Silicate Minerals" (A. F. White and S. L. Brantley, eds), Mineralogical Society of America, Washington, DC, Reviews in Mineralogy 31, 173-233. 

Many minerals have been found to dissolve and precipitate in nature at dramatically different rates than they do in laboratory experiments. As first pointed out by Paces (1983) and confirmed by subsequent studies, for example, albite weathers in the field much more slowly than predicted on the basis of reaction rates measured in the laboratory. The discrepancy can be as large as four orders of magnitude (Brantley, 1992, and references therein). As we calculate in Chapter 26, furthermore, the measured reaction kinetics of quartz (SiC>2) suggest that water should quickly reach equilibrium with this mineral, even at low temperatures. Equilibrium between groundwater and quartz, however, is seldom observed, even in aquifers composed largely of quartz sand. 

In the next chapter (Chapter 27) we show calculations of this type can be integrated into mass transport models to produce models of weathering in soils and sediments open to groundwater flow. In later chapters, we consider redox kinetics in geochemical systems in which a mineral surface or enzyme acts as a catalyst (Chapter 28), and those in which the reactions are catalyzed by microbial populations (Chapter 33). 

In this chapter, we build on applications in the previous chapter (Chapter 26), where we considered the kinetics of mineral dissolution and precipitation. Here, we construct simple reactive transport models of the chemical weathering of minerals, as it might occur in shallow aquifers and soils. 

Stumm, W. and R. Wollast, 1990, Coordination chemistry of weathering, kinetics of the surface-controlled dissolution of oxide minerals. Reviews of Geophysics 28, 53-69. 

Frostad, S., Klein, B., Lawrence, R.W. 2002. Evaluation of laboratory kinetic test methods for measuring rates of weathering. Mine Water and the Environment, 21, 183-192. 

The Kinetics of Surface Controlled Dissolution of Oxide Minerals an Introduction to Weathering... 

Schnoor, J. L. (1990), "Kinetics of Chemical Weathering A Comparison of Laboratory and Field Weathering Rates", in W. Stumm, Ed., Aquatic Chemical Kinetics, Wiley-lnterscience, New York, pp. 475-504. 

Svendrup, H. A. (1990), The Kinetics of Base Cation Release due to Chemical Weathering, Lund University Press, Lund, Sweden. 

The morphology of weathered feldspar surfaces, and the nature of the clay products, contradicts the protective-surface-layer hypothesis. The presence of etch pits implies a surface-controlled reaction, rather than a diffusion (transport) controlled reaction. Furthermore, the clay coating could not be "protective" in the sense of limiting diffusion. Finally, Holdren and Berner (11) demonstrated that so-called "parabolic kinetics" of feldspar dissolution were largely due to enhanced dissolution of fine particles. None of these findings, however, addressed the question of the apparent non-stoichiometric release of alkalis, alkaline earths, silica, and aluminum. This question has been approached both directly (e.g., XPS) and indirectly (e.g., material balance from solution data). 

Isocyanates that are produced fi om aliphatic amines are utilized in a limited range of polyurethane products, mainly in weatherable coatings and specialty applications where the yellowing and photodegradation of the aromatic polyurethanes are undesirable [5]. The aliphatic isocyanates are not used more widely in the industry due to the remarkably slow reaction kinetics of aliphatic isocyanates compared to their aromatic counterparts [6]. Due to the slow reactivity of aliphatic isocyanates, it is not practical to use them in the preparation of flexible or rigid foams, which are the main commercial applications for polyurethane chemistry. 

The application of chemical kinetics to weathering processes of soil minerals first appeared in the work of Wollast (1967). He concluded that the rate-limiting step for weathering of feldspars was diffusion (Chapter 7). This work touched off a lively debate that is still raging today about whether weathering of feldspars and ferromagnesian minerals is controlled by chemical reaction (CR) or diffusion. 

Many of the early studies on kinetics of soil chemical processes were obviously concerned with diffusion-controlled exchange phenomena that had half-lives (r1/2) of 1 s or greater. However, we know that time scales for soil chemical processes range from days to years for some weathering processes, to milliseconds for degradation, sorption, and desorption of certain pesticides and organic pollutants, and to microseconds for surface-catalyzed like reactions. Examples of the latter include metal sorption-desorption reactions on oxides. 

In short, much future research on kinetics of soil chemical processes is needed. Areas worthy of investigation include improved methodologies, increased use of spectroscopic and rapid kinetic techniques to determine mechanisms of reactions on soils and soil constituents, kinetic modeling, kinetics of anion reactions, redox and weathering dynamics, kinetics of ternary exchange phenomena, and rates of organic pollutant reactions in soils and sediments. 

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