Collectorless Flotation

Note, that the bubble surface can be covered by an adsorption layer even without the special addition of surfactant due to contaminations in natural, tap, and industrial waters. Thus, the conclusion that wetting films are stable due to the stabilising effect of molecular forces is at least doubtful for natural waters containing traces of surface active compounds which can destabilise the wetting film and can provide contactless flotation. Collectorless microflotation has been observed for example by Goldman et al. (1974). However, they did not perform any colloid-chemical investigations. 

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). 

Natural Floatability and Collectorless Flotation of Sulphide Minerals... 

Figure 1.1 Effect of pulp potential on self-induced collectorless flotation behaviors of galena and arsenopyrite at pH = 6 (Sun, 1990)...

It has been reported that although pyrite is only slightly floatable in self-induced flotation, the floatability is pronounced if sodium sulphur is added, which is called sulphur-induced collectorless flotation. As can be seen from... 

Heyes and Trahar (1984) leached pyrite with cyclohexane and compared the extract with a sulphur-containing solution of cyclohexane in a UV spectra photometer as shown in Fig. 1.4, indicating that sulphur was present at the mineral surface. Therefore, the inherent hydrophobicity and natural floatability once thought to be typical of sulphides is now thought to be restricted to sulphides such as molybdenite and other minerals or compound with special structural features. The collectorless floatability that most sulphide minerals showed came from the self-induced or sulphur-induced flotation at certain pulp potential range and certain conditions. 

This book systematically summarizes the researches on electrochemistry of sulphide flotation in our group. The various electrochemical measurements, especially electrochemical corrosive method, electrochemical equilibrium calculations, surface analysis and semiconductor energy band theory, practically, molecular orbital theory, have been used in our studies and introduced in this book. The collectorless and collector-induced flotation behavior of sulphide minerals and the mechanism in various flotation systems have been discussed. The electrochemical corrosive mechanism, mechano-electrochemical behavior and the molecular orbital approach of flotation of sulphide minerals will provide much new information to the researchers in this area. The example of electrochemical flotation separation of sulphide ores listed in this book will demonstrate the good future of flotation electrochemistry of sulphide minerals in industrial applications. 

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. 

Keywords natural flotability collectorless flotation h pH diagram linear potential sweep voltammetry cyclic voltammetry XPS UV... 

The collectorless floatability of chalcopyrite has been studied in some detail and some results are shown in Fig. 2.5 (Guy and Trahar, 1985 Wang, 1992). It has been found that there is a clear distinction between flotation and non-flotation, which appear to be pH and dependent. The upper limit and lower limit of pulp potential for collectorless flotation of chalcopyrite change with pH. 

Figure 2.5 Floatability-potential curve for chalcopyrite in collectorless flotation (Guy and Trahar, 1985 Wang, 1992)...

Figure 2.7 Effect of pulp potential on collectorless flotation behaviors of pyrite and pyrrhotite...

Figures 2.6, 2.7 and 2.8 provided the evidence that there exists the critical upper and lower limit of pulp potential for collectorless flotation at certain pH. Figure 2.9 further demonstrated the flotation recovery of jamesonite as a function of potential at different pH. It is obvious that jamesonite has very good collectorless floatability in different potential range, which much depended on different pH. The...

It appears that an oxidizing potential is usually a requirement for collectorless flotation. The surface products of oxidation will clearly have an influence on surface hydrophobicity and hence on flotation. The initial oxidation of sulphides in acid solution corresponds to a reaction of the type... 

Figure 2.14 Electrochemical phase diagram for chalcopyrite with elemental sulphur as metastable phase. Equilibrium lines (solid lines) correspond to dissolved species at 10 mol/L. Plotted points show the upper and lower limit potential of collectorless flotation of chalcopyrite reported from Sun (1990), Feng (1989) and Trahar (1984)...

The h-pH diagram of galena is constructed through the reactions (2-12) to (2-14) and (2-21) to (2-23) and presented in Fig. 2.15. It may be seen from Fig. 2.15 that the lower limit potential of collectorless flotation of galena at various pH are well defined by the conditions producing elemental sulphur. The upper limit potential of self-included collectorless flotation of galena at various pH is... 

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