Clays calcium ions

Dispersed Non-inhibited 1. Fresh water clay based fluids. Sodium chloride less than 1%, calcium ions less than 120 ppm a. Phosphate low pH (pH to 8.5) b. Tannin—high pH (pH 8.5-11+) c. Lignite d. Chrome lignosulphonate (pH 8.5-10)... 

Species held on a surface by ion exchange (such as calcium ions on clay) are also immobile in groundwater. As with physically adsorbed species, they may be replaced by ions with a greater affinity to the solid surface. 

Increasing KC1 concentration lowers inhibition as shown in Table II. The fact that damage increased with KC1 concentration is consistant with the ionic ratio hypothesis and suggests a base exchange mechanism whereby calcium ions are more easily extracted from the clay and replaced by potassium ions as the potassium concentration increases. 

Radenti et al. reported the corrosion rate of a typical potassium chloride fluid of 247 mils/year at 212°F. In contrast, they found by substituting potassium carbonate for potassium chloride, the corrosion rate was reduced to 3 mils/year t10 . Unfortunately, potassium carbonate is not optimum as a drilling fluid additive because it can produce massive amounts of calcium precipitation, may elevate the pH to undesirable levels, and in all cases reduces the calcium ion concentration to such a low level as to promote destabililzing cation exchange with clay minerals. 

Similar observations were made for a sodium clay, with Increasing amounts of the divalent calcium or magnesium Ions (32). In the presence of calcium Ions, one can even witness a change In the sign of the deuterium quadrupolar residual splitting. A similar observation was reported recently with heavy water molecules present In and oriented by an uniaxial mesophase (33). 

As mentioned previously, because of the hydrophilic character of the clay minerals, water molecules can intrude into the interlayer spaces. The swelling of the layer leads to extremely low water permeability of layer silicates. Water permeability, however, strongly depends on the cations in the interlayer spaces. The different cations coordinate the different number of water molecules (Berend et al. 1995 Cases et al. 1997). Monovalent ions (e.g., sodium ions) decrease water permeability greater than bivalent ions (e.g., calcium ions). It can well be seen in saline soils where water permeability is unfavorable. 

Levy, R. and Francis, C.W., 1975. Demixing of sodium and calcium ions in montmorillonite crystallites. Clays Clay Miner., 23 475—476. 

Calcium ions are undesirable in alkaline flood solution, and their concentration must be kept to a very low value. This is ordinarily accomplished by using a sodium carbonate buffer, which removes calcium as it exchanges off the clay by precipitating it as insoluble calcium carbonate. In doing so, however, carbonate ions, which are the buffering agent in the system when sodium carbonate is used, are also removed. Thus, reaction with calcium on the clays also consumes the alkaline solution as it moves through the reservoir. 

Smectites, by virtue of their large surface area, are particularly sensitive to the exchangeable cation type. In nature, the most common cations are Ca and Na. Calcium ions reduce bound water layer thickness and provide some deformation resistance by cross-linking clay platelet surfaces. Sodium smectite, on the other hand, has the highest affinity for water of any common phyllosilicate, and is therefore used in water-based muds (WBM) to build viscosity and to suspend fine-grained materials used to increase the mud weight. The most geochemically sensitive shales are almost invariably smectitic with saline pore fluids. 

Smectite clays consist of 1 nm thick aluminosilicate layers separated by sodium and calcium counterions. As little as 1 to 5 wt% of these layered clays can significantly improve the mechanical properties of nylon, polyolefins, and other polymers (78). Delaminating the clay structure by replacement of the sodium or calcium ions with a polymer-compatible surfactant, a quaternary ammonium ion surfactant, for example, is essential to generate a large polymer-clay interfacial area, as shown in Figure 11.21 (79). Ammonium ion head groups of the dispersant bind to the surface of the clay by Coulombic forces, and the hydrophobic alkyl tails bind to the polymer by van der Waals forces. 

Ferreira et al. produced a high-activity metallocene catalyst (1457 kg PE/(mol Zr h atm)) by supporting Cp2ZrCl2 (II) on a pillared clay. Calcium montmorillonite was pillared with Keggin ions, [Ali304(0H)24 12H20] +, to increase its Lewis acidity. The clay was pretreated at 200°C to remove adsorbed water, then exposed to a toluene solution of MAO at 50°C to attenuate its Bronsted acidity. High activity was maintained over a period of 1 h at 50°C. The apparent absence of the usual rapid metallocenium deactivation processes was attributed to the suppression of bimolecular interactions in the supported catalyst. 

Studies have shown that high molecular weight anionic polyacrylamide polymers are most effective as soil stabUisers [76]. These polymers bind primarily to calcium ions that are in themselves bound to anionic sites on the surface of the soil crumb (a process known as calcium bridging or salt linkage). The anionic nature of the soil crumb arises due to the anionic surface charge of the clay portion within the sod. 

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