2.3.2.2 Leaching and Water Contribution
Water has two unique roles as a chemical weathering agent. Firstly, water acts as a reactant in hydroxylation, i.e., hydrolysis reaction which is vital source for accumulated hydroxyl in feralitic hydroxyl oxides and layer silicates. The reaction mentioned above is exothermic in nature. Minerals hydration gives rise to enhancement in volume and hence acts as a significant factor in coarsely grained igneous rocks decaying, as reported by Rieche et al., in the year 1950 [8]. The second contribution of water is its role as leaching agent in internal drainage and flow of water allows the movement through the soil. The processes, leaching and hydroxylation, are connected to the extent that the hydrolysis products which are soluble should be eliminated for driving the reaction. Kellogg et al., in the year 1943 [16], reported that water is main agent of chemical weathering. Bayers et al., in the year 1933 [66–68], reported that the process of weathering completely expressed as hydrolysis reaction, but they also marked that the rate of process is affected by factors like specific nature of minerals, size of particles, movement of water, temperature, etc. Marbut et al., in the year 1951 [69–71], reported that rock decomposition product contains variably large quantity of combined water in comparison to materials which are not decomposed. Mineralogical analysis is the basis of hydroxyl occurrence, by direct hydroxyl determination as per Jackson and Evans et al., in the year 1952 [72–74], by weight loss as per Nutting et al., in the year 1943 [75–77], by differential thermal methods as per Rowland and Grim et al., in the year 1942 [78–80]. As per Jackson et al., in the year 1948 [37], it was reported that chemical weathering is driven by leaching which involves the elimination of few products which are formed and moreover ions leaching might be enough comprehensive that upcoming stages of weathering consists of varying elements chemically. Another important factor of leaching is calculation of solutes present in water of river. Polynov et al., in the year 1937 [5], and Smith et al., in the year 1913 [93–95], reported mobility of ions in comparative manner to describe abovementioned calculation. The order of ions in the increasing order includes HO3, SiO2, Mg, Na, and Ca. Further, by extending this study, Goldich et al., in the year 1938 [31], reported according to increasing order of loss, SiO2, I, Mg, Ca, and Na. It was considered that Al was neither lost or accumulated and combined water and iron was gained. Mohr et al., in the year 1944 [96–98], reported the significance of internal drainage due to leaching and reactions of weathering. The motion of water in the soil is controlled by drainage. As per Jackson et al., in the year 1948 [38], sediments of tourmaline, zircon, quartz, feldspar, and authigenic micas indicated reversal in a case when the ionic substances were abundantly existed in sea water.
2.3.2.3 Acidity Factor
Material pH value and water moving through it has a considerable role in the nature and rate of chemical weathering. As per Jackson et al., in the year 1948 [38], it was reported that the enhancement in acidity has a positive contribution in the rate function of weathering. Graham et al., in the year 1941b [81–83], reported feldspar faster decomposition when acidified clay is present. The procedure shows faster elimination of cations (metallic) by exchange materials and simultaneously hydrogen is released during the process of hydroxylation reaction as the product of weathering. Additionally, with acid saturation exchange, also the influence of specific acid likes sulphuric and carbonic acid should be under consideration. Truog and Attoe et al., in the year 1946 [84–86], reported release of potassium dilute acid from soil. Loss of mica and depotassication, with increment in kaolinite and vermiculite are highly enhanced with the arrival of leaching, which lowers the pH of the soil lower to 7, as reported by Jackson and Hseung in the year 1952 [87–89]. Gibbsite and kaolinite are formed because of the enhancement of the acidic condition of soil, in case of minerals containing high quantity of silica. This was explained by Hendricks and Ross et al. [90–92], in the year 1945, as high rate of elimination of silica and metallic ions due to leaching prior to recombination with sesquioxides. Even though, boehmite, gibbsite, and kaolinite are structurally hydroxyl compounds, but they act chemically like acid anhydrides or insoluble weak acids, weaker in comparison to silicic acid.
2.3.2.4 Biotic Processes Factor
Biotic processes in case of chemical weathering can be discussed in two sections. One is organic residue effects and other is ionic uptake cycles. Plants which are very tall physically affects chemical weathering by increasing the size of the cracks in rocks, as a result of which movement of water is easier and also it shades the soil, thereby affecting evaporation and soil temperature. High plants as well as microorganisms fasten the nutrients release from minerals through exchange of hydrogen ions with minerals charge and absorption. According to Bastisse and Demolon et al. in the year 1946 [1], it was reported that plants were one of responsible factors of weathering owing to the fact that soil planted with trees released higher quantity of potassium in comparison to unplanted soil. Jackson and Hseung et al., in the year 1952 [87], reported that soil acidity accumulation is followed by micas depotassication. As per Kellog et al., in the year 1943 [16], it was reported that in case of bare soil or virgin soil due to vegetation nutrients are returned as organic residue to the soil surface. Organic matter accumulation on the surface of the soil has considerable impact on the minerals weathering, either by distribution of aluminium oxide and iron present in soil or by bases leaching. As per Kanehiro and Sherman et al. in the year 1948 [99–101], it was reported that ferns present in regions of tropical humid Hawaii, below highly acidic forest floor have reactions in the pH range between 3 and 4,which is relative to the white pine forest floor the zone of cool temperate region. The organic matter mixed with soil controls the rate of chemical weathering and loss of bases. The rate of chemical weathering is faster in case of highly acidic forest floor in comparison to alkaline or neutral forest floor. Some kinds of organic matter, specifically organic acids, give rise to formation of complex with sesquioxide ions and transfer them to subsoil from the upper horizon and little amount inside the ground water. Elimination of iron out of ferromagnesian minerals is increased owing to this activity. The overall process of weathering as reported by Jackson and Hseung in the year 1952 [16] was influenced because of elimination of iron oxides from horizon A and accumulation in horizon B. As per Vagelor et al., in the year 1933 [102–104], and Mohr et al., in the year 1944 [96], it was reported that in tropical areas vegetal canopy is highly significant. According to Mohr et al., in the year 1944, it was reported that air temperature above the soil is considerably less in case of canopy forest. Similarly, soil enveloped by forest has 10°C to 15°C. The decrease in the temperature makes all the chemical reaction slower. Organic matter decomposition is slower, causing deposition of organic substances either in or at horizon surface. The condition in deciduous tropical forest and evergreen tropical forest is considerably different. Gupta and Griffith et al., in the year 1947 [105], reported that when teak is planted in laterite soil then a crust of laterite is formed due to the soil dehydration during the dormant leafless stage or drought period. The laterite soil formed hampers the tree growth. Sherman et al., in the year 1953 [106], verified these findings in case of Hawaiian Islands.
2.3.2.5 Reduction and Oxidation Factor
Reduction and oxidation reaction influences the process of chemical weathering. As per Jackson et al. in the year 1948 [37], in equation of weathering, positive sign is assigned to oxidation. Hence, iron occurrence in ferrous state or reduction favoring conditions enabled the formation of montmorin in the intermediate stage of weathering as per Wendricks and Ross in the year 1945 [107]. Moreover, occurrence of iron in ferric state or oxidation favoring conditions