Kaolinite

Kaolinite is a clay mineral that is part of the group of industrial minerals, with the chemical composition Al₂Si₂O₅(OH)₄. It is a layered silicate mineral, with a sheet of tetrahedrons linked through oxygen atoms in a sheet of alumina octahedrons. Rocks that are rich in kaolinite are known as kaolin or clay from China. The word kaolin is derived from the Chinese name for the mountain Kao-Ling shan (高岭山 / 高嶺山, pinyin Gāolǐng shān), located 50 km to the southeast of Jingdezhen town, Jiangxi province, China. The name comes from the French version of the word: kaolin, from reports by Francois Xavier d'Entrecolles of Jingdezhen. Africa, kaolin is sometimes known as kalaba (in Gabon and Cameroon).

Uses

Caolinita in the mine of Peñausende (Spain)

Caolinite

Caolin

• Agrochemicals: It is part of the components of insecticides and pesticides either as a material of accompaniment to insecticides presented in powder or only, use this today in rise for the control of certain agricultural pests, such as the olive fly especially in ecological farming.

• Civil Construction Industry: This type of clay is used in a calcined form, at temperatures between 500 and 900 °C to produce metacaolin (MK), a material of puzolenic properties within the concrete base of cement portland. Likewise, in a recent concept of ecosustainable concrete, the so-called geopolymers. Being exploited for consumption at the national level for partial and total replacement of the portland cement. Depending on the environment where it is exploited you can acquire reddish to white.

Occurrence

Red clay of Georgia.

Kaolinite is one of the most common minerals; It is mined, as kaolin, in Malaysia, Pakistan, Vietnam, Brazil, Bulgaria, Bangladesh, France, the United Kingdom, Iran, Germany, India, Australia, South Korea, the People's Republic of China, the Czech Republic, Spain, South Africa, Tanzania, and the United States. Joined.

Kaolinite mantles are common in western and northern Europe. The ages of these mantles are from the Mesozoic to the early Cenozoic.

Kaolinite clay is found in abundance in soils that have formed from the chemical weathering of rocks in hot and humid climates, for example in tropical rainforests. Comparing soils along a gradient toward progressively cooler or drier climates, the proportion of kaolinite decreases, while the proportion of other clay minerals such as illite (in cooler climates) or smectite (in drier climates) increases. These climate-related differences in clay mineral content are often used to infer climate changes in the geological past, where ancient soils have been buried and preserved.

In the classification system National Institute for Agronomic Study of the Belgian Congo (INEAC), soils in which the clayey fraction is predominantly kaolinite are called caolisol (of kaolin and soil).

In the United States, the main kaolin deposits are in central Georgia, along a stretch of the Atlantic Seaboard fall line between Augusta and Macon in Georgia. This thirteen-county area is known as the 'white gold' belt; Sandersville in Georgia is known as the "Kaolin Capital of the World" due to its abundance of kaolin. In the late 19th century, an active kaolin mining industry existed in far southeastern Pennsylvania, near the towns of Landenberg and Kaolin, and in what is now White Clay Creek Preserve. The product was transported by train to Newark, Delaware, on the Newark-Pomeroy line, along which many open pit clay mines can still be seen. The deposits formed between the late Cretaceous and early Paleogene, about 100 to 45 million years ago, in sediments derived from weathered igneous rocks and metakaolin. Kaolin production in the United States during 2011 was 5.5 million tons..

During the Thermal Maximum of the Paleocene-Eocene, the sediments deposited in the Esplugafreda area, in Spain, were enriched with kaolinite from a detrital source due to denudation.

Synthesis and genesis

Difficulties arise when trying to explain the formation of kaolinite under atmospheric conditions by extrapolating thermodynamic data from the most successful high-temperature syntheses. Church and Van Oosterwijk-Gastuche (1978) thought that the conditions under which kaolinite will nucleate can be deduced from the stability diagrams, based as they are on the dissolution data. Due to the lack of convincing results in their own experiments, La Iglesia and Van Oosterwijk-Gastuche (1978) had to conclude, however, that other factors, as yet unknown, were involved in the low-temperature nucleation of kaolinite. Due to the observed very slow crystallization rates of kaolinite from solution at room temperature, Fripiat and Herbillon (1971) postulated the existence of high activation energies in the low-temperature nucleation of kaolinite.

At high temperatures, equilibrium thermodynamic models seem to be satisfactory for describing the dissolution and nucleation of kaolinite, since the thermal energy is sufficient to overcome the energy barriers involved in the nucleation process. The importance of syntheses at room temperature and atmospheric pressure for understanding the mechanism involved in the nucleation of clay minerals lies in overcoming these energy barriers. As Caillère and Hénin (1960) indicate, the processes involved will have to be studied in well-defined experiments, because it is virtually impossible to isolate the factors involved by mere deduction from complex natural physicochemical systems such as the soil environment. Fripiat and Herbillon (1971), in a review on the formation of kaolinite, raised the fundamental question of how a disordered material (i.e., the amorphous fraction of tropical soils) can be transformed into an ordered structure. This transformation seems to take place in soils without major changes in the environment, in a relatively short period of time and at room temperature (and pressure).

The low-temperature synthesis of clay minerals (with kaolinite as an example) presents several aspects. Firstly, the silicic acid to be supplied to the growing crystal must be in monomeric form, i.e. the silica must be present in very dilute solution (Caillère et al., 1957; Caillère and Hénin, 1960; Wey and Siffert, 1962; Millot, 1970). To avoid the formation of amorphous silica gels that precipitate from supersaturated solutions without reacting with aluminum or magnesium [to form crystalline silicates, silicic acid must be present in concentrations below the maximum solubility of amorphous silica. The principle underlying this prerequisite can be found in structural chemistry: "Since polysilicate ions are not uniform in size, they cannot be arranged together with metal ions in a regular crystal lattice." (Iler, 1955, p. 182)

The second aspect of the low-temperature synthesis of kaolinite is that the aluminum cations must be hexacoordinated with respect to oxygen (Caillère and Hénin, 1947; Caillère et al. 1953; Hénin and Robichet, 1955). Gastuche et al. (1962) and Caillère and Hénin (1962) have concluded that kaolinite can only form when aluminum hydroxide is in the form of gibbsite. Otherwise, the precipitate formed will be a "mixed alumino-silicon gel" (in the words of Millot, 1970, p. 343). If it were the only requirement, large amounts of kaolinite could be obtained simply by adding gibbsite powder to a silica solution. There would undoubtedly be a marked degree of adsorption of the silica in solution by the gibbsite surfaces, but, as already stated, mere adsorption does not create the layered network typical of kaolinite crystals.

The third aspect is that these two initial components must be incorporated into a mixed crystal with a layered structure. From the following equation (given by Gastuche and DeKimpe, 1962) for the formation of kaolinite

Si2O5. Al2(OH)4 + 5H2O}}}" xmlns="http://www.w3.org/1998/Math/MathML">2Al(OH)3+2H4Yes4Δ Δ Yeah.2O5⋅ ⋅ Al2(OH)4+5H2O{displaystyle {ce {2Al(OH)3 + 2H4SiO4 - HCFC Si2O5. Al2(OH)4 + 5H2O}}} Si2O5. Al2(OH)4 + 5H2O}}}" aria-hidden="true" class="mwe-math-fallback-image-inline" src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0f28292eb8b216236fe1f4ea6e8e8f49436d850b" style="vertical-align: -1.005ex; width:53.829ex; height:3.009ex;"/>

It can be seen that five molecules of water must be removed from the reaction for every molecule of kaolinite formed. Gastuche and DeKimpe (1962) have provided field evidence illustrating the importance of removing water from the kaolinite reaction. While studying soil formation in a basalt rock in Kivu (Zaïre), they observed how the appearance of kaolinite depended on the "degree of drainage" of the area in question. A clear distinction was observed between areas with good drainage (ie areas with a marked difference between wet and dry seasons) and areas with poor drainage (ie perennial marsh areas). Kaolinite was only found in areas with a clear seasonal alternation between wet and dry. The possible importance of alternating wet and dry conditions in the transition from allophane to kaolinite has been stressed by Tamura and Jackson (1953). The role of alternating wetting and drying in kaolinite formation has also been noted by Moore (1964).

Laboratory synthesis

Kaolinite syntheses at high temperatures (above 212 °F) are relatively well known. There are, for example, the syntheses of Van Nieuwenberg and Pieters (1929); Noll (1934); Noll (1936); Norton (1939); Roy and Osborn (1954); Roy (1961); Hawkins and Roy (1962); Tomura et al. (1985); Satokawa et al. (1994) and Huertas et al. (1999). Relatively few low-temperature syntheses are known (cf. Brindley and DeKimpe (1961); DeKimpe (1969); Bogatyrev et al. (1997)).

Laboratory syntheses of kaolinite at room temperature and atmospheric pressure have been described by DeKimpe et al. (1961). From these tests, the role of periodicity becomes convincingly clear. DeKimpe et al. (1961) had used daily additions of alumina (such as AlCl
36H
2O) and silica (in ethyl silicate form) for at least two months. In addition, every day the pH was adjusted by adding hydrochloric acid or sodium hydroxide. These daily additions of Si and Al to the solution in combination with daily titrations with hydrochloric acid or sodium hydroxide for at least 60 days will have introduced the necessary element of periodicity. Only now the real role of what has been described as "aging" (Alterung) of amorphous aluminosilicates (such as Harder, 1978). As such, time is not producing any change in a closed system in equilibrium; but a series of alternations of periodically changing conditions (by definition taking place in an open system) will produce the low-temperature formation of more and more phase-stable kaolinite instead of amorphous (ill-defined) aluminum silicates.