Weathering reaction

The final composition of stream water is the product of the weathering reactions and related processes outlined above. However, the chemical processes are influenced and controlled by an intricate combination of environmental factors that are characteristic for each drainage system. Therefore, the composition of the bedrock in an area and the residual material left at the surface as soil and subsoil exert a strong influence on the chemical composition of mnoff from the area. The reactions of water with this material are the ultimate geological control and are the source of soluble weathering products. 

Under natural conditions the rates of dissolution of most minerals are too slow to depend on mass transfer of the reactants or products in the aqueous phase. This restricts the case to one either of weathering reactions where the rate-controlling mechanism is the mass transfer of reactants and products in the soHd phase, or of reactions controlled by a surface process and the related detachment process of reactants. 

There are no unequivocal weathering reactions for the siUcate minerals. Depending on the nature of parent rocks and hydrauhc regimes, various secondary minerals like gibbsite, kaolinite, smectites, and iUites are formed as reaction products. Some important dissolution processes of siUcates are given, for example, by the following reactions (19). 

Acidolysis is a similar weathering reaction to hydrolysis in that is used to weather minerals, but in this case the source of is not water but organic or inorganic acids. Humic and fulvic acids (discussed in Section 8.3.2), carbonic acid, nitric or sulfuric acid, and low-molecular-weight organic acids such as oxalic acid can all provide H to weather minerals. All of these acids occur naturally in soils in addition nitric and sulfuric acid can be added to soil by acid pollution. The organic acids are prevalent in the... 

Overall, weathering controls the chemistry of material that is transported into the sediment and that which stays behind in the soil. As an example, consider a general weathering reaction for an aluminosilicate (Stumm and Morgan, 1995) ... 

The weathering reactions given above show the key effects of weathering the breakdown of the original rock minerals, the consumption of H, and the release of cations and silica into solution which can then be used to make new minerals or be lost from the soil into the ground-water and rivers. 

Rewrite the weathering reactions shown in Section 8.3.2.2 using HNO3 in place of H2CO3. 

This is a weathering reaction. Sillen argued that Goldschmidt s reaction could also go the other direction. The reverse reaction would be called reverse weathering. 

Carbon dioxide plays a key role in climate, in biological processes, in weathering reactions, and in marine chemistry. I shall next describe how the partial pressure of this gas in the atmosphere may be calculated. Because there is a rapid exchange of carbon dioxide between ocean and atmosphere, we must consider the fate of dissolved carbon. 

Sulfate, halide, and carbonate minerals form in mine waste as a result of chemical weathering reactions and as a by-product of mineral processing. The formation of carbonate minerals is of particular interest for its potential in offsetting greenhouse gas emissions associated with mining. We have documented secondary carbonate mineral precipitation at the Mount Keith Nickel Mine (Western Australia) and the... 

A different weathering reaction proposed by Berner et al. (1983) involves HC03" instead, but is entirely equivalent to the present equation when HC03" dissociation is taken into account. 

In Table 5.4 the contributions of the individual weathering reactions were assigned and combined in such a way as to yield the concentrations of Ca2+, Mg2+, Na+, K+, and H+ measured in these lakes the amounts of silicic acid and aluminum hydroxide produced and the hydrogen ions consumed were calculated stoichiometrically from the quantity of minerals assumed to have reacted. Corrections must be made for biological processes, such as ammonium assimilation and nitrification and the uptake of silicic acid by diatoms. Some of the H4Si04 was apparently lost by adsorption on aluminum hydroxide and Fe(III)(hydr)oxides, but the extent of these reactions was difficult to assess. 

Lake Cristallina - Weathering reactions 1 timol calcite -2 2 ... 

Most weathering reactions consume protons and produce alkalinity (Reactions (5.2) and (5.3), and Table 5.4). Here we briefly review the definitions and illustrate the value of the alkalinity-acidity concept in the context of the weathering reactions. 

Bullen TD, Kendall C (1998) Tracing of weathering reactions and water flowpaths a multi-isotope approach. Iir. Isotope Tracers in Catchment Elydrology Kendall, McDonnell JD (eds) Elsevier Science, Amsterdam, p 611-646... 

Clay minerals are important to the crustal-ocean-atmosphere fectory, not just for their abundance, but because they participate in several biogeochemical processes. For example, the chemical weathering reactions responsible for their formation are accompanied by the uptake and release of cations and, thus, have a large impact on the chemical composition of river and seawater. This includes acid/base buffering reactions, making clay minerals responsible for the long-term control of the pH of seawater and, hence, of importance in regulating atmospheric CO2 levels. 

Other examples of weathering reactions involving igneous silicates are provided in Table 14.1. In some cases, chemical weathering proceeds in a stepwise feshion in which one clay mineral can be transformed into another given fevorable environmental conditions. 

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