Chemical weathering carbon

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. 

Weathering processes take an active part in the cycling of oxygen and carbon, but does chemical weathering affect these cycles to a significant extent Consider the following examples. 

The influence that variations of temperature and levels of atmospheric CO2 and O2 have on chemical weathering are more subtle. Temperature appears to have a direct effect on weathering rate (White and Blum, 1995). The silica concentration of rivers (Meybeck, 1979, 1987) and the alkalinity of ground waters in carbonate terrains (Harmon et al., 1975) are both positively correlated with temperature variations. It is not clear, however, whether temperature-related variations in weathering rates are largely due to variations in vegetational activity that parallel temperature variations. 

Ice ages ended quickly. Processes that promote the increase of carbon dioxide in the atmosphere are positive feedbacks in ending an ice age. Is subglacial chemical weathering a positive or a negative feedback What circumstances would allow one to give the opposite answer (Hint ... 

Chemical weathering of crustal material can both add and withdraw carbon from the atmosphere. This has been discussed in Chapter 8. The oxidation of reduced carbon releases CO2 to the atmosphere,... 

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... 

The rate of chemical weathering is related to the rate of C02 consumption. Consider first the dissolution of carbonates... 

The chemical weathering of crustal rock was discussed in Chapter 14 from the perspective of clay mineral formation. It was shown that acid attack of igneous silicates produces dissolved ions and a weathered solid residue, called a clay mineral. Examples of these weathering reactions were shown in Table 14.1 using CO2 + H2O as the acid (carbonic acid). Other minerals that undergo terrestrial weathering include the evaporites, biogenic carbonates, and sulfides. Their contributions to the major ion content of river water are shown in Table 21.1. 

The terrestrial weathering of organic matter derived from shales and soils results in the oxidation of carbon, which generates CO2. Dissolution of this CO2 in water produces carbonic acid. This weak acid serves to enhance chemical weathering reactions... 

As the rock cycle continues, the calcium silicate minerals are eventually uplifted onto land where they imdergo chemical weathering. This reaction involves acid hydrolysis driven by carbonic acid. The latter is derived from the dissolution of the magmatic CO2 in rainwater ... 

The products of chemical weathering, Ca, H4Si04, and 2HCOj, are transported by river runoff into the ocean, where they are then available to be returned to biogenic form by marine plankton. (Marine plankton have an enzyme, carbonic anhydrase, that converts bicarbonate to CO2.)... 

The biogenic soft parts that become buried in the sediments are also transformed into sedimentary rocks, predominantly shale. Geologic uplift fallowed by chemical weathering leads to the oxidation of the organic carbon, i.e.. 

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 ... 

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