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The soil ecosystem
Published in Stephen R. Gliessman, V. Ernesto Méndez, Victor M. Izzo, Eric W. Engles, Andrew Gerlicz, Agroecology, 2023
Stephen R. Gliessman, V. Ernesto Méndez, Victor M. Izzo, Eric W. Engles, Andrew Gerlicz
Once minerals are released from the consolidated parent material, another chemical process that is of great importance is the formation of secondary minerals, the most important being clay minerals. Clay minerals are very small particles in the soil, but they affect everything from water retention to nutrient availability. They are formed by complex processes in which silicate minerals are chemically modified and reorganized. Depending on the combination of climatic conditions and parent material, the secondary minerals that are formed are of two basic types. Silicate clays are predominantly made up of microscopic aluminum silicate “plates” with different arrangements; hydroxide clays lack a definite crystalline structure and are made up of hydrated iron and aluminum oxides in which many of the silicon ions have been replaced.
The Geosphere and Geochemistry
Published in Stanley E. Manahan, Environmental Chemistry, 2022
Clays are extremely common and important in mineralogy. Furthermore, in general, clays predominate in the inorganic components of most soils (see Chapter 15) and are very important in holding water and in plant nutrient cation exchange. All clays contain silicate and most contain aluminum and water. Physically, clays consist of very fine grains having sheet-like structures. For purposes of discussion here, clay is defined as a group of microcrystalline secondary minerals consisting of hydrous aluminum silicates that have sheet-like structures. Clay minerals are distinguished from each other by general chemical formula, structure, and chemical and physical properties. The three major groups of clay minerals are the following: Montmorillonite, Al2(OH)2Si4O10Illite, K0.2Al4(Si8-6Al0-2)O20(OH)4Kaolinite, Al2Si2O5(OH)4
Petroleum Geological Survey
Published in Muhammad Abdul Quddus, Petroleum Science and Technology, 2021
Clay minerals are secondary silicates. Clay minerals are formed from other silicates, by the action of air, water and carbonic acid. Clay silicate minerals undergo hydrolysis, in the presence of water, to produce aluminum hydroxide and silicic acid. Both aluminum hydroxide and silicic acid are reactive and produce other types of silicates. Most of the clays are hydrated minerals. The grain size of clay is very small (<0.004 mm). Clay can form gels and colloidal solutions. There are many forms of clay minerals, depending on the chemical formula and their structure. Important clay minerals that make up the sediments are kaolinite, chlorite, illite and montmorillonite. All these clay minerals are soft, white with slight tinge and with layered structures. Mud is a mixture of clays and other silt-sized minerals, namely quartz and calcite.Shale minerals are formed from the compaction of mud. The shale mineral is fissile, soft and laminated clay.Mudstone is hard. Mudstone and shale are the tertiary products of clay; they are stable in atmospheric conditions.
Effects of salt and pH on microstructure and physico-mechanical behaviors of clay sediments：A references review
Published in Marine Georesources & Geotechnology, 2023
Chang-lin Hou, Xiong-ying Ma, Xin Kang
Clay minerals are composed of aluminum-silicate crystals, which consist of sheets of silicon and aluminum in various forms. The fundamental unit of a silicon sheet is the silicon-oxygen tetrahedron, with each sheet comprising six silicon-oxygen tetrahedra (Figure 1a). Conversely, the basic unit of aluminum sheet is the aluminum-hydroxide octahedron, and each sheet is composed of four aluminum-hydroxide octahedrons (Figure 1b). Silicon sheets and aluminum sheets combine 1:1 to form the structural layer of kaolin (Figure 2a), while 2:1 to form the structural layer of montmorillonite or illite (Figure 2b). The structural layer and the interlayer domain constitute the crystalline layer. In case where the structural layer is electrically neutral, the interlayer domain can be empty or may contain water molecules, with the structural layers being interconnected through hydrogen bonds or molecular bonds. However, when the structure layer is not electrically neutral, it can be rendered electrically neutral through the interlayer material, such as cations, hydrated cations, or hydroxides. In this scenario, the structural layers are connected by either hydrogen bonds or ionic bonds. Finally, clay crystals are formed through the combination of the layers (Peng et al. 2006).
Pb contaminated soil from a lead-acid battery plant immobilized by municipal sludge and raw clay
Published in Environmental Technology, 2023
Ting Zhang, Qiang Li, Xiong Yang, Demin Zheng, Huiling Deng, Zhijia Zeng, Jiahai Yu, Qizhong Wang, Yafei Shi, Sulian Wang, Kewu Pi, Andrea R. Gerson
Clay is one of the most widely distributed components in the Earth’s crust and can be used to immobilize heavy metals and improve soil fertility [21]. In addition to ion exchange or adsorption, surface complexation, isomorphic substitution and lattice diffusion are also recognized as possible passivation mechanisms of clay for heavy metals [22]. Clay minerals can influence soil nutrient availability, stabilize soil organic matter, control the formation of soil microaggregates and populations of soil microbes, and thus affect soil fertilizer [23]. In addition, the abundance of silicates in clay minerals has been demonstrated to promote plant growth [24]. Common clay minerals, including zeolite, bentonite and montmorillonite, have been widely applied to remediate polluted soils. For instance, the application of zeolite in Pb-contaminated farmland resulted in the Pb content in the edible parts of mango trees decreases by 30% [25]. Nevertheless, little attention has been paid to soil remediation using raw clay due to its complex composition. The high content of aluminosilicates, oxides, hydroxides and oxyhydroxides in raw clay may make clays a potential choice for immobilization of heavy metals in soils [26].
Mineralogical and geochemical characterisation of kaolin deposit from Debre Tabor area northwestern, Ethiopia
Published in Applied Earth Science, 2021
Alemu Mesele, Teklay Gidey, Tilahun Weldemaryam, Wuletaw Mulualem, Tamrat Mekuria, Yahya Ali, Gizachew Mulugeta, Betelhem Tesfaye, Mulgeta Brihan
Clay minerals are the chemical weathering product of granite and feldspathic rocks (Idenyi and Nwajagu 2003) when rocks are in contact with water, air (Kabeto et al. 2012), and hydrothermal fluid (Okunlola 2008). Mostly they are found in soil, sedimentary rocks, and hydrothermal deposits (Idenyi and Nwajagu 2003; Murray 2007). The polymorphs of clay minerals are kaolinite, halloysite, nacrite, and dickite, which are characterised by the same chemistry but different structures (Baker and Uren 1982). The rate of clay minerals formation is controlled by the composition of pre-existing rock mineralogy, the nature of parent rock, the intensity of weathering, and the length of time (Murray and Kogel 2005; Akinola and Obasi 2014). According to Mosser (1980) and Mosser et al. (1991), clay minerals can preserve the geochemical fingerprint of trace elements from the source rock.