Surfactant adsorption, minerals

Surface heterogeneity may be inferred from emission studies such as those studies by de Schrijver and co-workers on P and on R adsorbed on clay minerals [197,198]. In the case of adsorbed pyrene and its derivatives, there is considerable evidence for surface mobility (on clays, metal oxides, sulfides), as from the work of Thomas [199], de Mayo and co-workers [200], Singer [201] and Stahlberg et al. [202]. There has also been evidence for ground-state bimolecular association of adsorbed pyrene [66,203]. The sensitivity of pyrene to the polarity of its environment allows its use as a probe of surface polarity [204,205]. Pyrene or ofter emitters may be used as probes to study the structure of an adsorbate film, as in the case of Triton X-100 on silica [206], sodium dodecyl sulfate at the alumina surface [207] and hexadecyltrimethylammonium chloride adsorbed onto silver electrodes from water and dimethylformamide [208]. In all cases progressive structural changes were concluded to occur with increasing surfactant adsorption. 

Dobias B (1984) Surfactant Adsorption on Minerals Related to Flotation. 56 91-147 Doi K, Antanaitis BC, Aisen P (1988) The Binuclear Iron Centres of Uteroferrin and the Purple Acid Phosphatases. 70 1-26 Domcke W, see Bradshaw AM (1975) 24 133-170 Dophin D, see Morgan B (1987) 64 115-204... 

Dobids, B. Surfactant Adsorption on Minerals Related to Flotation. Vol. 56, pp. 91-147. 

Mutual solvents have been used to reduce surfactant adsorption on formation minerals, particularly oil-wetting surfactants (131). Ethylene glycol monobutyl ether is the most commonly used mutual solvent. 

DobidS, B. Surfactant Adsorption on Minerals Related to Rotation. Vol. 56, pp. 91-147. Doughty, M. J., Diehn, B. Flavins as Photoreceptor Pigments for Behavioral Responses. Vol. 41, pp. 45-70. 

The appeareance of maxima on the adsorption isotherms and decrease in flotability can be explained by the hypothesis that in the presence of micelles no adsorption layer of the surfactant can be formed, the character of which corresponds to the equilibrium state only with monomers (sufficiently hydrophobic adsorption layer). Due to a heterogeneity of forces acting at the surfactant ion mineral interface it can be assumed that at concentrations S CMC some of the molecules will be bound much more firmly in a three-dimensional micelle than in... 

Fig. 5. Shapes of the adsorption isotherms of surfactants on minerals, which can be described using Langmuir or Tfimkin equation for range 0 = 1...

This was shown e.g. by investigating adsorption isotherms of Na dodecylbenzene-4-sulfonate and Na 4-hexadecyloxytolyl-2-sulfonate on various mineral surfaces differing from each other by the kind of PDFs86 . The potential value in relation to the surfactant concentration reached its maximum in the region of micelle formation and confirmed thus the shape of the adsorption isotherm. The presence of adsorption maxima is explained by a decrease in surfactant adsorption resulting from a desorption effect of micelles on the adsorption film, and by setting a three-component equilibrium (adsorption film - micelle - monomer) at concentrations CMC. This happens because of different ratios of the counter ions to the surfactant ions at the micelle and on the adsorption film. 

The course of surfactant adsorption on a mineral surface as dependent on the solution temperature is controlled, in the first place, by the character of its binding with the surface species. For the free energy change of adsorption it holds ... 

The adsorption mechanism discussed in previous chapters dealt only with a monocomponent system mineral - surfactant, as a result of an adsorption equilibrium related to appropriate PDI. Since a real flotation system consists of two or more mineral components it is necessary to mention conditions of the selective surfactant adsorption in such a system. In monocomponent systems the adsorption is controlled by the character of PDI with respect to the chemical composition of the polar heads of the surfactant. However, this rule is not valid in polycomponent systems containing both kinds of PDI. Generally and under simplifying circumstances, it is possible to classify the adsorption systems according to the role played by the PDI and the kind of the mineral. 

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