Surface electric charge

Most suspended solids in water have a surface electrical charge that provides stability to the particles. This ionic charge is usually a negative (—) charge and requires the addition of metal salts or cationic (+) polymer coagulants to destabilize the particles and permit them to agglomerate or come together. 

There are several choices for the adsorbent. Activated carbon still remains the most widely used, especially for VOCs. Activated carbon is by far the most commonly used adsorbent in odor control applications and many VOC recovery applications. Because of its relatively uniform distribution of surface electrical charge, activated carbon is not selective toward polar molecules. 

Most particles acquire a surface electric charge when in contact with a polar medium. Ions of opposite charge (counter-ions) in the medium are attracted towards the surface and ions of like charge (co-ions) are repelled, and this process, together with the mixing tendency due to thermal motion, results in the creation of an electrical double-layer which comprises the charged surface and a neutralising excess of counter-ions over co-ions distributed in... 

The existence of the strong form of chemisorption on the surface, that is, of the form in which a lattice electron or hole is localized near the chemisorbed particle, leads, among other things, to the appearance of a charge on the semiconductor surface. Denoting by [Pg.214]

The existence of surface states leads to two most important effects. First, electrons and holes may be trapped at the surface to form surface electric charge. This influences the equilibrium properties of semiconductors. Second, the surface levels may change significantly the kinetics of processes, in which electrons and holes are involved. On the one hand, they create additional... 

Adsorption of an ionic pollutant was increased by modifying the surface electric charge of Ti02 particle. P043- and nafion (anion exchange polymer) attached to Ti02 promoted the adsorption of cationic pollutant and in turn accelerated its degradation (Fig. 9.18).37)... 

The surface electrical charge densities would be proportional to the reciprocal of these areas. This, in turn, determines the surface potential, (16). The relationship between W and ip at various ionic strengths is dealt with by the DLVO theory (16). 

Most substances acquire a surface electric charge when brought into contact with a polar medium such as water. The origin of the charge can be ... 

Froth flotation is an application of foams that is used to separate mineral components from each other based on their having different surface properties, typically their wettability and surface electrical charge. For example, froth flotation is the classic process used to separate copper from lead ore. The process involves having hydrophobic particles attach to gas bubbles which rise through a turbulent suspension to create a surface foam called a froth. Figure 10.2 shows an illustration of a mechanical flotation cell. This is the classic flotation device [53,91,625], First, the flotation feed particles are well dispersed into a particle suspension. Together with chemical flotation aids, such as collectors and frothers, this constitutes what is called the flotation pulp. In a mechanical flotation cell, air is fed in the form of fine bubbles and introduced near the impeller (see Figure 10.2). In addition to mechanical flotation cells, there are also pneumatic cells and cyclone flotation cells. Pneumatic... 

Upon conlacl wilh an aqueous medium, most materials acquire a surface electric charge. A variety of processes have charging mechanisms, including ion adsorption, ionization, and ion dissolution. 

Microbial cells are surrounded by a cell wall, which retains the cell contents, and is the primary barrier between the cell surface and the environment in which it exists. The quality of the cell wall, in terms of selective permeability, maintains the necessary levels of nutrients, trace elements, and cell internal pH. The cell membrane is the site of transfer processes water is able to pass through this membrane, in or out of the cell, depending on the thrust of the osmotic pressure. The chemistry of the cell wall affects its properties in terms of surface electric charge and the availability of binding ions. 

When an alkaline solution is injected into a formation, the concentrations of OH, COs, and SiOs are increased. The increase in OH is from the injected alkaline solution. The increase in is from HCOs because high OH makes the reservoir an alkaline enviromnent and converts HCOs into COs. SiOs is a result of the reaction between the injected alkali and formation minerals. Strong alkalis dissolve the clay minerals and damage the rock surface electric charge and microstructures, which finally results in dispersion and migration of the clay minerals. If seawater is injected, S04 is increased. Ca " and Mg " are from the formation water, cation exchange, and reactions between the injected solution and rock minerals. Sometimes, there is Al. Several inorganic scales can be formed as follows ... 

In the case of two axisymmetric particles moving along the z axis toward each other with velocity = -dhidt Equation 5.255 can be integrated, and from Equation 5.256 the resistance force can be calculated. The latter turns out to be proportional to the velocity and bulk viscosity and depends on the shape in a complex way. For particles with tangentially immobile smfaces and without surface electric charge (u, = U2 = 0, O = 0), Charles and Mason have derived... 

Most substances acquire surface electrical charges when brought in contact with a polar medium, resulting from one or more of the following ... 

Clays of the montmorillonite family are lamellar aluminosificates [46] used in many industrial processes and in products such as paints, softeners, and composite materials [47]. They swell when brought into contact with water, which is due to the insertion of water molecules between the sheets. Complete exfoliation can be induced leading to dispersions of disk-like particles of 10 A thickness and 300-3000 A in diameter, depending on the variety of clay used. These clay platelets bear a rather large surface electrical charge so that electrostatic interactions between them must be considered and are actually responsible for the colloidal stability of these dispersions. These suspensions have been widely studied as model colloids and also because they form physical thixotropic gels. 

The role of the surface electrical charge is certainly crucial because the properties of the suspensions vary considerably with their ionic strength. 

Non-grafted boehmite rods experience a much more complicated interaction potential as positive surface electrical charges now play an important role. In this case, the phase diagram has to be discussed in the frame of both the Onsager model of nematic ordering and the DLVO (named after B.V. Deryagin, L. Landau, E.J.W. Verwey, and J.T.G. Overbeek) theory of colloidal stability, which describes colloidal stabihty as a balance between repulsive electrostatic and attractive van der Waals interactions [67,68]. At low ionic strength, electrostatic repulsion dominates so that the phase stability is essentially described by the... 

Heterocoagulation The coagulation of dispersed species of different types or having different states of surface electric charge. 

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