Zeta potential flotation

Fig. 9. Correlation of contact angle, flotation recovery, surface coverage by collector, and 2eta potential. Solid, quart2, collector reagent, 4 x 10 Af dodecylammonium acetate. = recovery, % A = zeta potential, mV Q — contact angle, degrees and = surface coverage, % of one monolayer. Ref.

Zeta Potential of Zinc-Iron Sulphide Minerals in the Presence of Flotation Reagents... 

Initially, this mechanism was proposed on the basis of results obtained for zeta potential and flotation (Fig. 29). The formation of the hydrophobic aggregates at the interface was confirmed after the advent of the fluorescence probing technique. The adsorption isotherm is determined in the presence of pyrene as the fluorescent probe and the emission spectra of pyrene in both supernatant and slurries were analyzed after adsorption. The h/h of pyrene in solutions of SDS containing 0.1 M NaCl and in the slurry are shown in Figs. 30 and 31. In solution, the ratio remains at around 0.6 till the CMC (as determined by surface tension measurement) is attained. Above CMC, the value becomes 1.0 due to the solubilization of pyrene in micelles. In... 

Flotation of Naturally Hydrophobic Minerals. Flotation response of naturally hydrophobic minerals correlates very well with elec-trokinetic measurements. Figure 3 shows that the flotation of coal correlates well with zeta potential of demineralized coal (5.). The flotation rate is maximum where the zeta potential is zero and it decreases with increase in the magnitude of the zeta potential. Similar observations were made earlier by Chander and Fuerstenau (6 ) for the flotation of molybdenite. The decrease in flotation rate with increase in zeta potential is because of the electrical double layer repulsion between the charged particle and the air bubble. 

There are many other applications of zeta potential, some of which are discussed in later sections, including mineral flotation (Section 10.3.1), bitumen flotation (Section 11.3.2), paper-making (Section 12.2), and many others. 

Figure 10.4 The correlation among collector surface coverage, contact angle, zeta potential, and flotation recovery for the flotation of quartz using dodecylammonium acetate. From Leja [91]. Copyright 1982, Plenum Press.

Figure 11.9 I llustration of the connection between hot water flotation efficiency and measured chemical and physical properties, including bitumen zeta potential From Schramm and Smith [250]. Copyright 1987, Canadian Society for Chemical Engineering.

Electioultiafiltiation (EUF) combines forced-flow electrophoresis (see Electuoseparations, electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45-47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Flotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane facilitates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

Figure 15. Plot of oil recoveries versus process aid addition level from the hot water flotation processing of an oil sand in a continuous pilot plant. Also shown is the correspondence with the zeta potentials, measured on-line, of emulsified bitumen droplets in the extraction solution. (Plotted from data in reference 50.)...

In the context of a study of foam flotation of powdered activated carbon (PAC), Zouboulis et al. [143] noted large and different pH effects when an anionic surfactant was used instead of a cationic one. For the cationic surfactant, best recovery (at low surfactant concentration) was achieved at the highest pH, in agreement with electrostatic arguments (see Section IV.B.l) for the anionic surfactant, an intermediate pH was the best. The authors also measured the zeta potential of the carbon in the presence and absence of the surfactants and concluded that the specific chemical nature and the dissociation of each surfactant. 

Graham, K. and Madeley, J.D., Relation between the zeta potential of rutile and its flotation with sodium dodecyl sulfate, 7. Appl. Chem., 12, 485, 1962. 

Hussain, S.A., Demirci, S. and Ozbayoglu, G., Zeta potential measurements on three clays from Turkey and effects of clays on coal flotation, J. Colloid Interf. Sci., 184, 535, 1996. 

Fuerstenau, D.W. and Pradip, Zeta potential in the flotation of oxide and silicate minerals, Adv. Colloid Interf. Sci., 114, 9, 2005. 

Fig. 3.14. Dependence of flotation of goethite on surface charge. Upper graph is zeta-potential as a function of pH at different concentrations of sodium chloride lower graph is flotation recovery in 1 x 10 mol/1 solutions of dodecylammonium chloride, sodium dodecyl-sulfate and sodium dodecyl-sulfonate (Iwasaki et al., 1960).

In the case of quartz flotation using primary amines and quaternary ammonium salts, as collectors, Somasundaran [24] found that the concentration (log C) of collectors at the critical flotation condition is linearly related to n values as shown in Fig. 5.7. In addition, the concentration (log C) at which the zeta-potential of quartz in alkylamine solutions is equal to zero was found to have similar linear relationship with n values (Fig. 5.8). 

In addition dissolved air flotation experiments were carried out to obtain the flotation efficiency under the same experimental conditions as the zeta potential measurement. The values of particle capture efficiency were a maximum when the absolute values of zeta potentials of the bubbles and particles were at a minimum. 

In case of using mixtures of two and more collectors, the selective hydrophobisation is accomplished simultaneously both due to chemisorption and physical adsorption. It is shown in [69] that the simultaneous use of fatty acids and hydrocarbon oils for calcium phosphate flotation from quartz different processes are observed. Fatty acid soaps form chemical compounds on the surface of the material floated, after which the hydrocarbon oil physically adsorbs. It has been experimentally established that hydrocarbon oil is transferred from quartz particles to the surface of floated phosphate. When using mixtures of anionics and nonionics, hydrophobisation of particle surfaces is also accomplished both due to the formation of chemical compounds and physical adsorption which is confirmed by measurements of the zeta-potential of the particles floated [70]. 

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 . 

The relationship between adsorption and interfacial properties such as contact angle, zeta-potential and flotation recovery is illustrated in Figure 39.2 for cationic surfactant dodecylammonium acetate/quartz system (5). The increase in adsorption due to association of surfactants adsorbed at the solid-liquid interface into two dimensional aggregates called solloids (surface colloids) or hemi-micelles occurs at about 10 M DA A. This marked increase in adsorption density is accompanied by concomitant sharp changes in contact angle, zeta-potential and flotation recovery. Thus these interfacial phenomena depend primarily on the adsorption of the surfactant at the solid-liquid interface. The surface phenomena that reflect the conditions at the solid-liquid interface (adsorption density and zeta-potential) can in many cases be correlated directly with the phenomena that reflect the... 

FIGURE 39.2 Correlation of adsorption density, contact angle, flotation response and zeta potential for quartz as a function of dodecylammonium acetate concentration at pH 6 to 7, 20 to 25°C [5]. 

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