Clay Chemical Reactions

Secondary minerals. As weathering of primary minerals proceeds, ions are released into solution, and new minerals are formed. These new minerals, called secondary minerals, include layer silicate clay minerals, carbonates, phosphates, sulfates and sulfides, different hydroxides and oxyhydroxides of Al, Fe, Mn, Ti, and Si, and non-crystalline minerals such as allophane and imogolite. Secondary minerals, such as the clay minerals, may have a specific surface area in the range of 20-800 m /g and up to 1000 m /g in the case of imogolite (Wada, 1985). Surface area is very important because most chemical reactions in soil are surface reactions occurring at the interface of solids and the soil solution. Layer-silicate clays, oxides, and carbonates are the most widespread secondary minerals. 

When the temperature of a carbonate reservoir that is saturated with high-viscosity oil and water increases to 200° C or more, chemical reactions occur in the formation, resulting in the formation of considerable amounts of CO2. The generation of CO2 during thermal stimulation of a carbonate reservoir results from the dealkylation of aromatic hydrocarbons in the presence of water vapor, catalytic conversion of hydrocarbons by water vapor, and oxidation of organic materials. Clay material and metals of variable valence (e.g., nickel, cobalt, iron) in the carbonate rock can serve as the catalyst. An optimal amount of CO2 exists for which maximal oil recovery is achieved [1538]. The performance of a steamflooding process can be improved by the addition of CO2 or methane [1216]. 

The reactivity of steam can be reduced via pH control. The injection or addition of a buffer such as ammonium chloride inhibits the dissolution of certain mineral groups, controls the migration of fines, inhibits the swelling of clays, controls chemical reactions in which new clay minerals are formed, and... 

Understanding the basic hydraulic mechanisms for synthetic liners and clay liners is very important in appreciating the advantages of a composite liner. Clay liners are controlled by Darcy s law (Q = kiA). In clay liners, the factors that most influence liner performance are hydraulic head and soil permeability. Clay liners have a higher hydraulic conductivity and thickness than do synthetic liners. Additionally, leachate leaking through a clay liner will undergo chemical reactions that reduce the concentration of contaminants in the leachate. 

Five common desiccant materials are used to adsorb water vapor montmorillonite clay ([(Na,Cao.5)o.33(Al,Mg)2Si40io(OH)2 H20], silica gel, molecular sieves (synthetic zeolite), calcium sulfate (CaS04), and calcium oxide (CaO). These desiccants remove water by a variety of physical and chemical methods adsorption, a process whereby a layer or layers of water molecules adhere to the surface of the desiccant capillary condensation, a procedure whereby the small pores of the desiccant become filled with water and chemical action, a procedure whereby the desiccant undergoes a chemical reaction with water. 

Some clay minerals are excellent catalysts in important chemical reactions, even though their ability to transfer information is less than convincing. 

Racemisation is a chemical reaction, and its rate is different for each type of amino acid. An important fact is that this process is affected by many factors that influence the rate of change of the amino acids stereochemistry [106]. The main parameters affecting the racemisation process include the amino acid structure, the sequence of amino acids in peptides, the bound state versus the free state of the amino acids, the pH in the environment, the concentration of buffer compounds, the contact of the sample with clay surfaces... 

Clay minerals are structure of aluminum- and silicate-oxides. Such structures have free bond and vacancies on selective site of the mineral structure allowing them to participate in both physical adsorption and chemical reactions modifying the available concentration of the chemicals in the environment. 

Clays formed in soil by chemical reactions occurring after rock decomposition. 

Oxygen isotope data (Table VII) support conclusions drawn from the chemical data (Tables IV and VI) that clay in the high pH, WD experiments underwent significant chemical reaction, whereas clay... 

Reverse weathering Chemical reactions that are theorized to occur in the sediments. In these reactions, seawater is thought to react with clay minerals and bicarbonate producing secondary clays and consuming alkalinity and some cations. This process is approximately the reverse of chemical weathering on land that produces clay minerals. 

Almost all rocks contain some aluminum in the form of aluminum silicate minerals found in clays, feldspars, and micas. Today, bauxite is the major ore for the source of aluminum metal. Bauxite was formed eons ago by the natural chemical reaction of water, which then formed aluminum hydroxides. In addition to the United States, Jamaica and other Caribbean islands are the major sources of bauxite. Bauxite deposits are found in many countries, but not all are of high concentration. 

A.D. 79 and calcium carbonate, the stuff of seashells, chalk, and limestone. Adding water to these sets off a complex set of chemical reactions that convert the gritty pasty stuff into what is essentially artificial stone. The nineteenth-century rediscovery of Roman cement, the aforementioned Portland cement, is made from a combination of burned limestone, clay, and water. It is the single most heavily used human-made material on earth. 

A variety of solids is used as catalysts metals, alloys, clays, metal oxides, sulphides, nitrides, carbides and so on. Catalysts may be single-phase substances or multiphasic mixtures they may be crystalline, microcrystalline or even amorphous. Catalysts can be electrically insulating, semiconducting or metallic. Some examples of heterogeneously catalysed reactions are given in Table 8.1. Two aspects of catalysts are important activity and selectivity. Activity refers to the ability of catalysts to accelerate chemical reactions so that equilibrium is achieved rapidly. The degree of acceleration... 

Although gibbsite and kaolinite are important in quantity in some soils and hydrothermal deposits, they have diminishing importance in argillaceous sediments and sedimentary rocks because of their peripheral chemical position. They form the limits of any chemical framework of a clay mineral assemblage and thus rarely become functionally involved in critical clay mineral reactions. This is especially true of systems where most chemical components are inert or extensive variables of the system. More important or characteristic relations will be observed in minerals with more chemical variability which respond readily to minor changes in the thermodynamic parameters of the system in which they are found. However, as the number of chemical components which are intensive variables (perfectly mobile components) increases the aluminous phases become more important because alumina is poorly soluble in aqueous solution, and becomes the inert component and the only extensive variable. 

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