Wettability Surface electric charge

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... 

Froth flotation is an application of foams that is used to separate mineral components from each other based on their 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... 

The next four chapters provide an introduction to the concepts and techniques needed to study and understand dispersion stability. Some approaches to the characterization of emulsions, foams and suspensions, and of their dispersed species (droplets, bubbles and particles)are described in Chapter 2. The concepts of surface tension, wettability and surface activity, which are important to the stability and properties of all types of dispersion, are described in Chapter 3. To this is added the nature of electrically charged surfaces in Chapter 4. All of these aspects are brought together in Chapter 5 in an introduction to the stability of dispersions. 

The second example concerns the surface heterogeneity of clay minerals. Important problems, such as limited yield of oil recovery arising during oil exploitation, involve interaction of pore filling fluids with the minerals that form the reservoir walls. The clay minerals, due to their relatively high specific surface area and electrical charge density, are the most active for the retention of oil. Illites and kaolinites are the clay minerals that are most frequently found and their wettability properties are believed to be in relation to the heavy oil ends retention process. 

Water has a high dielectric permittivity, and it is a good solvent for most ions (cf. Chapter 4). As a result, in an aqueous environment, most electrolytes are dissociated in their individual ions. Surfaces of (solid) materials often contain ionizable groups, which in contact with water, are electrically charged. Together with the wettability, the presence of electric charge largely determines the stability of colloidal dispersions (Chapter 16) and interfacial processes as adsorption and adhesion (Chapters 14, 15, and 20), and it plays an important role in the assembly of nanostructured objects (Chapter 11). 

In addition to tailoring wettability with alkyl phosphates, one could also impart further properties of interest in the fields of biomaterials and cell -surface interactions, including electric charges (e.g., by means of terminal amine, carboxylate, or phosphate functionalities) and biologically active groups such as poly(ethylene glycol), cell-adhesive peptides, or growth factors. 

The electrostatic charges on the surface of a powder can affect the flow properties of powders. An electric detector can determine the electric field generated by the electrostatic charges on the surface of the powder. This acts as a voltmeter and allows the direct determination of both polarity and absolute value of the electrostatic field. As an example, the electrostaticity of the experimental compound ITF 296, when sieved at 200 pim, showed an electrostatic field of -60 V due to the charge on the powder surface (Dobetti et al. 1995). As a consequence, the powder formed stacked aggregates, which led to the unsieved powder being less wettable and difficult to handle. Ftihrer (1996) has reviewed interparticulate attraction mechanisms. 

In the processes under consideration, the adhesive forces of the developer powder have been increased principally by charging the contiguous bodies, i.e., as a result of electrical forces. The same sort of effect can be achieved by adjusting the wettability of the surface (see Chapter II). For this purpose, panchromat-ically sensitized zinc oxide deposited on aluminum foil is used as the photocon-... 

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