Mineral interface, electrokinetic

Modifications of surface layers due to lattice substitution or adsorption of other ions present in solution may change the course of the reactions taking place at the solid/liquid interface even though the uptake may be undetectable by normal solution analytical techniques. Thus it has been shown by electrophoretic mobility measurements, (f>,7) that suspension of synthetic HAP in a solution saturated with respect to calcite displaces the isoelectric point almost 3 pH units to the value (pH = 10) found for calcite crystallites. In practice, therefore, the presence of "inert" ions may markedly influence the behavior of precipitated minerals with respect to their rates of crystallization, adsorption of foreign ions, and electrokinetic properties. 

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]. 

Sondi, I., Biscan, J., and Pravdic, V., Electrokinetics of pure clay minerals revisited, J. Colloid Interface Sci., 178, 514, 1996. 

Adsorption isotherms are habitually obtained using the solution depletion method, which consists of comparing the solute concentrations before and after the attainment of adsorption equilibrium. Electrokinetic or zeta potentials are determined by two techniques microelectrophoresis [12,14,17] and streaming potential [13,58,59]. The former is employed to measure the mobility of small particles of chemically pure adsorbents, whereas the latter is adopted to investigate the electrophoretic behaviour of less pure coarser mineral particles. A correlation between the adsorption and electrophoretic results is usually examined with the aim of sheding light on the mechanism by means of which the surfactants are adsorbed at the solution-solid interface. This implies the necessity of maintaining the same experimental conditions in both experiments. For this purpose, the same initial operational procedure is applied. 

Morris. G.E., Eomasiero. D.. and Ralston. J., Polymer depressants at the talc-water interface Adsorption isotherm, microflotation and electrokinetic studies, Int. J. Miner. Process., SI, 211. 2002. 

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. 

Electrokinetically driven iron mineralization originates when Fe(III) combines with OH" ions produced at the cathode to form insoluble ferric hydroxides [Fe(OH)3(s)], hematite ( -Fe203) andgoethite (FeOOH) (e.g., Faulkner, Hopkinson, and Cundy, 2005 Mukhopadhyay, Sundquist, and Schmitz, 2007). SEM observations of soil samples taken from the anodic zones of the experimental cells reveals a ubiquitous association between the iron minerals and subsidiary quantities of chromium. Cr(III) can substitute for Fe(III) in the FeOOH structure (Eary and Rai, 1988), and Cr(VI) reduction by Fe " leads to the development of solids at nearneutral pH showing mixed iron/chromium solid solution of the form Fe Cri x(OH)3 (Eary and Rai, 1988 Fendorf and Li, 1996). Such conditions would have been met at the interface between the acidic and alkali portions of the experimental cells (Fig. 8.5). When Fe(III) is produced solely from the stochiometric reaction with chromate, the value of x is 0.75 (Batchelor et al, 1998) ... 

Isoelectric point is a pH value, at which electrokinetic potential C on the slip plane is equal to 0, at the participation in ion exchange only of protons H% i.e., in distilled and deionized water. In Western literature it is denoted pi or lEP. Isoelectric point of a mineral is determined by the electrokinetic method, i.e., from the pH value, at which a suspension of its particles has the lowest mobility in the electric field. Isoelectric point. As opposed to the zero charge point, isoelectric point characterizes zero charge of hydrodynamic interface, i.e., conditions when 0. 

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