Electrokinetic measurements, flotation

Many processes involving carbonates - ubiquitous minerals in natural systems -are controlled by their surface properties. In particular, flotation studies on calcite have revealed the presence of a pH-variable charge and of a point of zero charge (Somasundaran and Agar, 1967). Furthermore, electrokinetic measurements have shown that Ca2+ is a charge (potential) determining cation of calcite. (Thompson and Pownall, 1989). 

This was shown, for example, by electrokinetic measurements of Kavanagh and Quirk177) in the system Fe203-illite at pH 2.5. Electrophoretic and cation-exchange data indicated that the net charge of clay surface became strongly positive at low pH values as a result of adsorption of polycations Fe3+. Further examples of metal ion hydrolysis in oxide and silicate flotation systems were published by Fuerstenau178) and Stumm et al.62). 

In on effort to establish the mechanism of coal flotation and thus establish the basis for an anthracite lithotype separation, some physical and chemical parameters for anthracite lithotype differentiation were determined. The electrokinetic properties were determined by streaming potential methods. Results indicated a difference in the characteristics of the lithotypes. Other physical and chemical analyses of the lithotypes were mode to establish parameters for further differentiation. Electron-microprobe x-ray, x-ray diffraction, x-ray fluorescent, infrared, and density analyses were made. Chemical analyses included proximate, ultimate, and sulfur measurements. The classification system used was a modification of the Stopes system for classifying lithotypes for humic coals. 

The structure electrical double layer at the silica-aqueous electrolyte interface was one of the earlier examined of the oxide systems. At the beginning the investigations were performed with application of electrokinetic methods next, with potentiometric titrations. The properties of this system were very important for flotation in mineral processing. Measurements proved that pHpZC and pHiep are equal to 3, but presence of some alkaline or acidic contaminants may change the position of these points on pH scale. Few examples, concerning edl parameters are shown in Table 3. Presented data concern a group of systems of different composition of the liquid phase and solid of a different origin. The latest measurements of this system takes into account the kinetics of the silica dissolution [152], and at zeta measurements, also the porosity of dispersed solid [155]. 

In many flotation systems, the electrical nature of the mineral/water interface controls the adsorption of collectors. The flotation behavior of insoluble oxide minerals, for example, is best understood in terms of electrical double-layer phenomena. A very useful tool for the study of these phenomena in mineral/water systems is the measurement of electrokinetic potential, which results from the interrelation between mechanical fluid dynamic forces and interfacial potentials. Two methods most commonly used in flotation chemistry research for evaluation of the electrokinetic potential are electrophoresis and streaming potential. 

A relatively new field is the use of flotation in wet textile processes [73]. The ( -potential of cotton fibres in aqueous solutions is negative, therefore they are effectively floated by cationics like quaternary ammonium salts, e.g. dodecyl trimethyl ammonium chloride. Sysilia et al. [74] have established, by measuring the electrokinetic potential, a clear rule between the positive surface charge of chromite and flotation efficiency. At low pH, chromite was effectively floated by fatty acid soaps, the ions of which are negatively charged under these conditions. The surfactant adsorption is reversible which is indicative of its physical nature. 

It is difTicult to find in the literature details of experiments that relate contact angle to the efficiency of the dispersion process. A correlation between contact angle and flotation rate for quartz in aqueous solutions of dodecylammonium acetate, with adsorption from solution and electrokinetic (zeta potential) data, was reported by Fuerstenau". In a later review Fuerstenau discussed the relevance of the adsorption process to flotation technology illustrating the direct relationship between the amount of surfactant adsorbed and the contact angle . Numerous values of 0 are published in the literature. Most have been measured on flat surfaces and even with these problems arise due to surface roughness" . For powders the measurement is more difficult, although a number of methods have been reported" and reviewed . 

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