Weathering processes chemical

Chlorine plays a less significant role in chemical weathering processes than do sulfur and carbon. Most geochemists beHeve that much, or most, of the chloride in stream water in coastal areas is derived from sea salt that is carried landward or deposited by rainfall. Farther inland, however, a major part of the chloride loads in streams is the result of human activities. 

The spectra of the rocks in the plains are very similar to the spectra obtained on the soil (see above). The ubiquitous presence of olivine in soil suggests that physical rather than chemical weathering processes currently dominate at Gusev crater. 

A possible chemical weathering process of two primary minerals, muscovite and biotite, and their varions mineral products is presented in Fig. 2.1. 

Many technical-chemical processes take maximum benefit of similarities with ongoing processes in Nature, with increased purity or reaction speed as the most important differences. The production of carbonates is a typical example of this, and the process of C02 mineralization for carbon capture and storage (CCS) (see Section 14.4) is in fact the accelerated version of what is known as the natural weathering of minerals. This is a combination of the interacting processes of mechanical and chemical weathering, and relevant to the current discussions are the chemical weathering processes of dissolution and hydrolysis that involve C02 [6, 7]. A dissolution equilibrium reaction that proceeds in Nature with dissolved C02 in water and calcite gives a bicarbonate solution ... 

There are approximately 3000 different minerals found in rock formations however, much of the Earth s crust consists of only 50 dominant mineral forms (Degens, 1989). The primary and secondary minerals commonly found in soils are listed in table 6.1. As mentioned above, chemical weathering processes in soils are important in the transformation of primary to secondary minerals. For example, when examining the weathering of feldspars (this most abundant group of minerals in the Earth s crust), K-feldspar is transformed into kaolinite through the following reaction ... 

The key factor about physical weathering is the increase in surface area of rock that is then available for attack by various chemical-weathering processes. Chemical weathering is the reaction with natural waters, and dissolved components, resulting in partial or complete dissolution of the rock and formation of a new mineral phase. In most cases, it is the interaction of water with the minerals in the rock that is the crucial issue. 

Acid Hydrolysis. The water that enters soil as rain or snow is in equilibrium with CO2 in the atmosphere, which dissolves to form carbonic acid. Unpolluted rainwater has a pH of approximately 5.7, whereas water in soil pores may be exposed to air containing a higher partial pressure of CO2 than the free atmosphere, and hence soil water may be more acidic (see Section 5.4). It is the attack on soil minerals by this weak carbonic acid that is the major chemical weathering process in most soils. For example, acid hydrolysis of calcium carbonate yields calcium and bicarbonate ions ... 

Oxidation. For those elements that can exist in more than one valence state oxidation, and indeed reduction, may be a major reaction in the chemical-weathering process. Iron and manganese are the most important elements that behave in this way. For example, iron in the ferromagnesian minerals is in the Fe(II) state, which is oxidized to Fe(III) when released from the mineral. This can cause changes in the charge balance, requiring other ions to be lost. Formation of iron oxide can cause physical disruption to the mineral. 

Viers J., Dupre B., Deberdt S., Braun J. J., Angeletti B., Ndam Ngoupayou J., and Michard A. (2000) Major and traces elements abundances, and strontium isotopes in the Nyong basin rivers (Cameroon) constraints on chemical weathering processes and elements transport mechanisms in humid tropical environments. Chem. Geol. 169, 211-241. 

Quaternary glacial-interglacial alternations caused terrestrial alternation of physical and chemical weathering processes, and this was reflected in... 

Which three elements are most likely to undergo oxidation as part of chemical weathering process Give example reactions of each. 

The data presented suggest that the primary chemical weathering process occurs by the reaction of SO2, either in gaseous form or dissolved in rain-water, with the limestone surface. This leads to a build up of sulphur rich layer at the surface which is shown to be predominantly S04 ". A more detailed study of this reaction mechanism should allow identification of reaction intermediates such as SO3. The formation of chlorine and nitrogen compounds appears to be a secondary process for the samples studied. The data presented and the results of the experiment described in section 5 suggest that subsequent dissolution of sulphate, by rain-water, is a significant part of the weathering mechanism. 

---