Lead weathering reactions

Therefore, as an oxide mineral weathers, reactions of C02 and water at the surface lead to the formation of carbonates and bicarbonates. The presence of OH can eventually cause... 

The weathering of minerals can be understood as a continuous dissolution-precipitation process involving them. The process can be very complicated, leading to multiphase equilibria, in which more than one solid phase, solution, and gas phase may be present. For example, primary silicates transform to secondary silicate minerals via such weathering reactions (Stumm and Wollast, 1990), as in the formation of kaolinite (AljSijC OH) from anorthite (CaAl2Si208) ... 

Another useful concept is that of congruent and incongruent reactions. These terms describe reactions involving the dissolution of minerals. If all the products of a dissolution reaction are soluble, the reaction is called congruent, as in the case of the quartz dissolution reaction (1.6) described above. Because, as written, the olivine weathering reaction leads to quartz precipitation it is an incongruent reaction. 

Only sodium and potassium are moderately abundant on Earth, and are major elements of life (see Topic J3 ). They occur in many silicates, but weathering reactions at the Earth s surface lead to the dissolution of the very soluble cations, which are common in sea water and are eventually deposited in halide minerals such as NaCl and KC1 (see Topic J2). Li, Rb and Cs are of lower abundance, and obtained from silicate minerals. Francium is radioactive. Its longest-lived isotope Fr has a half-life of only 22 min and occurs in exceedingly small amounts in uranium minerals (see Topics AT,... 

More CO2 can actually be absorbed chemically into the ocean than the above reaction sequence suggests. Terrestrial weathering of rocks containing carbonate, such as limestone, and subsequent aerial or riverine transport, means that the ocean is enriched in carbonate. Keeping and Kj constant implies, through eqns. (3) and (4), that enhancing the oceanic [COj ] leads to a greater level of... 

Natural mobilization includes chemical, mechanical, and biological weathering and volcanic activity. In chemical weathering, the elements are altered to forms that are more easily transported. For example, when basic rocks are neutralized by acidic fluids (such as rainwater acidified by absorption of CO2), the minerals contained in the rocks can dissolve, releasing metals to aqueous solution. Several examples are listed below of chemical reactions that involve atmospheric gases and that lead to the mobilization of metals ... 

In the simulation, CO2 in the soil gas reacts with the feldspars, leading to the alkali leaching and separation of silica from alumina observed to result from soil weathering. Near the top of the profile, the reaction produces gibbsite and adds Na+, K+, and Si02(aq) to the migrating pore fluid, according to the reactions,... 

It is well to note at this point that the dihydroxy compound is the first identifiable compound from the photolysis and photo-oxidation reactions that actually has any color. The lack of other identifiable color compounds and also some preliminary experiments lead to a proposal [9] that the oxidation of the dihydroxy compound could actually continue on to give a quinone (Scheme 18.5, top). Given the ease of oxidation of hydroquinone compounds, this would seem to be a reasonable proposal. In this preliminary report where an orange-red solid was initially observed it was speculated that the color owed itself to a quinone compound as shown. This would add significantly to compounds that actually could be the color bodies formed upon weathering exposure. 

The weathering of siderite (reaction (2)) and ankerite (reaction (5)) in the presence of 02 can sometimes lead to dissociation of dissolved HCO3", resulting in the release of C02 to the atmosphere a significant proportion of the atmospheric 02 can also be trapped in the solid form as secondary ferric (hydr)oxide precipitates (reactions (3) and (4)). 

Figure 9 Effect of the Cr- and V-ion-implantation on the photocatalytic reactivity of TiO2 under outdoor solar beam irradiation for the photocatalytic reaction of CH3CCH with H2O leading a hydogenolysis reaction of CH3CCH with H2O at 295 K. A fine, B cloudy weather (solar intensity during fine weather 12 inW/cm amount of photocatalyst 6.0 g).

A third chemical weathering mechanism that is of importance is oxidation/ reduction that involves mainly the elements carbon, iron, manganese and, of course, oxygen. An equilibrium reaction between dissolved C02 and bicarbonate ions can lead to the precipitation of ferrous iron, giving a hematite (ferric oxide) precipitate ... 

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