Nature of Hydrophobic Entity

The results above show that the sodium sulphide-induced collectorless floatability of sulphide minerals is strong for pyrite. Galena, jamesonite and chalcopyrite have no sodium sulphide-induced collectorless floatability. Marmatite and pyrrhotite showed some sodium sulphide-induced collectorless floatability in certain conditions. 

It was established by Tolun and Kitchener (1963—1964) that a platinum electrode became hydrophobic when hydrosulphide ion (HS ) was oxidized at the electrode surface. A contribution to the hydrophobicity may be the production of sulphur. According to thermodynamics, the hydrolysis reaction of sodium sulphide is 

From the Eqs. (3-1) to (3-13), the h-pH diagram of sodium sulphide solution is constructed with element sulphxir as metastable phase considering the presence of barrier (about 300kJ/mol) or overpotential (about 3.114 mV) of sulphide oxidation to sulphate and shown in Fig. 3.7. It is obvious that the lower limit of potential of sodium sulphide-induced collectorless flotation of pyrite, pyrrhotite and arsenopyrite at various pH agree well with the potential defined respectively by reactions of Eq. (3-9) producing elemental sulphur. The initial potential 

The voltammetric behavior of pyrite at pH= 8.8 (see Fig. 3.8) shows that an anodic current commenced at about -0.25 V to give an anodic peak at about 0 V. On the reverse scan a cathodic current that appeared at the same potential could be presumed to represent the reduction of the initial oxidation products. According to the reaction (3-9), the formation of sulphur would be expected to occur at -0.26 V for the HS concentration of 10 mol/L at pH = 8.8 which is consistent with an anodic current that begins to occur. 

Heyes and Trahar (1984) further compared the floatability of pyrite with the electrochemical and contact angle result reported by Walker and Richardson. Their results are listed in Fig. 3.9. It indicates that the onset of anodic current during a 

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Abstract The sodium sulphide-induced collectorless flotation of several minerals are first introduced in this chapter. The results obtained are that sodium sulphide-induced collectorless flotation of sulphide minerals is strong for pyrite while galena, jamesonite and chalcopyrite have no sodium sulphide-induced collectorless flotability. And the nature of hydrophobic entity is then determined through J h-pH diagram and cyclic voltammogram, which is element sulphur. It is further proved widi the results of surface analysis and sulphur-extract. In the end, the self-induced and sodium sulphide-induced collectorless flotations are compared. And it is found that the order is just reverse in sodium sulphide-induced flotation to the one in self-induced collectorless flotation. 

Abstract In the beginning, the mixed potential model, which is generally used to explain the adsorption of collectors on the sulphide minerals, is illustrated. And the collector flotation of several kinds of minerals such as copper sulphide minerals, lead sulphide minerals, zinc sulphide minerals and iron sulphide minerals is discussed in the aspect of pulp potential and the nature of hydrophobic entity is concluded from the dependence of flotation on pulp potential. In the following section, the electrochemical phase diagrams for butyl xanthate/water system and chalcocite/oxygen/xanthate system are all demonstrated from which some useful information about the hydrophobic species are obtained. And some instrumental methods including UV analysis, FTIR analysis and XPS analysis can also be used to investigated sulphide mineral-thio-collector sytem. And some examples about that are listed in the last part of this chapter. 

Fuerstenau (1980) found that sulphide minerals are naturally floatable in the absence of oxygen. Yoon (1981) ever attributed the natural floatability of some sulphide minerals to their very low solubility. Finkelstein et al. (1975) considered that the natural floatability of sulphide minerals are due to the formation of elemental sulphur and related to the thickness of formation of elemental sulphur at the surface. Some authors reported that the hydrophobic entity in collectorless flotation of sulphide minerals were the metal-deficient poly sulphide (Buckley et al., 1985). No matter whichever mechanism, investigators increasingly concluded that most sulphide minerals are not naturally floatable and floated only under some suitable redox environment. Some authors considered that the natural floatability of sulphide minerals was restricted to some special sulphide minerals such as molybdenite, stibnite, orpiment etc. owing to the effects of crystal structure and the collectorless floatability of most sulphide minerals could be classified into self-induced and sulphur-induced floatability (Trahar, 1984 Heyes and Trahar, 1984 Hayes et al., 1987 Wang et al., 1991b, c Hu et al, 2000). 

Abstract This chapter first explains the natural flotability of some minerals in the aspect of the crystal structure and demonstates the collectorless flotaiton of some minerals and its dependence on the h and pH of pulp. And then the surface oxidation is analysed eletrochemically and the relations of E to the composition of the solutions are calculated in accordance with Nemst Equation. The E h-pH diagrams of several minerals are obtained. Thereafter, electrochemical determination such as linear potential sweep voltammetry (LPSV) and cyclic voltammetry (CV) and surface analysis of surface oxidation applied to the sulphide minerals are introduced. And recent researches have proved that elemental sulfur is the main hydrophobic entity which causes the collectorless flotability and also revealed the relation of the amount of sulfur formed on the mineral surfaces to the recoveries of minerals, which is always that the higher the concentration of surface sulphur, the quicker the collectorless flotation rate and thus the higher the recovery. 

Although the nature of the hydrophobic entity responsible for the self-induced flotation of sulphide minerals remains somewhat obscure, most reported results clearly show that it is only when the environment becomes slightly oxidizing that flotation is observed. The elemental sulphur and polysulphide-intermediates in the oxidation of sulphide to sulphur have ever been suggested to be of the hydrophobic species. Whatever it is, there is no doubt that sulphur can generate hydrophobicity and floatability. 

Water has been illustrated as an efficient medium for the Wittig reaction employing stabilized ylides and aldehydes.22 It has been demonstrated that solubility of the reagents and substrates is not of a paramount nature, even though pronounced hydrophobic entities are present. 

FIGURE 4.70 Nature of entities formed upon dispersal of mixtures of hydrophobed silica-liquid paraffin in aqueous 0.5 g dm sodium alkyl (Ciq i4) benzene sulfonate solution to yield the antifoam effects depicted in Figure 4.69. (a) Dispersed drops, (b) Lenses formed at air-water surface. (Reprinted from Colloids Surf. A, 85, Garrett, P.R., Davis, J., Rendall, H.M., 159. Copyright 1994, with permission from Elsevier.)... 

The products of the mitochondrial protein-synthesizing system are all found in the inner mitochondrial membrane and are hydrophobic in nature. This hydrophobic nature makes it particularly difficult to identify mitochondrial products as part of a functional entity, since on extraction they are dissociated from other proteins of the entity and are often denatured. A more productive approach has been to eliminate the mitochondrial contribution by the administration of antibiotics or by mutation of the mitochondrial DNA, and assay the function in situ for altered properties. To date, possibly four inner membrane-associated functions have been implicated as containing products of the mitochondrial synthetic systems. In all cases they are multicomponent complexes containing both mitochon-drially and cytoplasmically synthesized components. These are the cytochrome oxidase complex, the oligomycin-sensitive ATPase, the cytochrome b complex, and the mitochondrial ribosomes. All of the other inner membrane functions which have so far been studied are synthesized entirely in the cytoplasm. 

A mechanism for the long-range hydrophobic interaction is evidently hidden in the complicated matter of surface induced gas adsorption - affected by solute, electrolyte, and dissolved gas. That seems now clear from the complex behaviour of solutes on bubble coalescence, and indeed from direct force measurements and other observations mentioned above. In retrospect, that and the resulting added subtlety of molectdar forces is not a surprise. After all, nature did not put these forces to work to assemble biological entities in an aqueous environment without an atmosphere. 

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