Collectorless floatability

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). 

The most controversial and contradicting problem is, perhaps, the natural and collectorless floatability of sulphide minerals. Gaudin (1957) classified the natural hydrophobicity of different minerals according to their crystal structure and showed that most sulphide minerals were naturally hydrophobic to some extent, which had been fiirther proved based on van der Waals theory by Chander (1988, 1999). Lepetic (1974) revealed the natural floatability of chalcopyrite in dry grinding. Finklestein (1975, 1977) demonstrated that orpiment, realgar and molybdenite were naturally floatable, and that pyrite and chalcopyrite had natural floatability at certain conditions due to the formation of surface elemental sulphur. Buckley and Woods (1990,1996) attributed the natural floatability of chalcopyrite... 

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. 

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. 

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...

Figure 2.17 shows that although the metastable elemental sulfur maybe present at pyrite surface, pyrite does not exhibit self-induced collectorless floatability except in very strong acidic media and a narrow oxidized Eh range. Such behavior may be similar to that of arsenopyrite in alkaline solutions due to the formation of hydroxides, thiosulphate. 

The F h-pH diagram for jamesonite is given in Fig. 2.18. It may be seen from Fig. 2.18 that in acid and neutral solutions, the reactions producing elemental sulphur may render jamesonite surface hydrophobic and jamesonite shows good collectorless flotation. In alkaline solution, the hydrophilic species Fe, Pb ", HSb02, SbOj, are produced, the collectorless floatability of jamesonite becomes weaker, it may be attributed to the presence of Fe(OH)3 and Pb(OH)2 at the same time on the jamesonite surface. The relative amounts of hydrophobic sulphur and hydrophilic Fe(OH)3 and Pb(OH)2 perhaps determine the collectorless floatability of jamesonite. 

Figure 2.24 shows the voltammograms of pyrite electrode in neutral media. It follows that the potential range of flotation relates to reactions (2-24) and (2-25). The potential calculated in reaction (2-24) is 161- 180 mV, pyrite exhibit collectorless floatability due to the formation of elemental sulphur. 

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. 

Table 3.1 Rest potential for sulphide minerals in water at pH = 4 (Hayes et al., 1987) and the order of their self-induced and sulphur-induced collectorless floatability...

The type and addition of frother are found to have a pronounced effect on the collectorless floatability of chalcopyrite (Heyes and Trahar, 1977). The recovery of collectorless flotation of chalcopyrite is much higher using PPG40 than amyl alcohol. The effects of several frothers on the collectorless flotation of some minerals have been tested and the results are presented in Table 10.1. It further provides the evidence that the type of frother produces a markable influence on collectorless flotation of sulphide minerals. The frothers with lower surface tension are more effective in enhancing the recovery of collectorless flotation of sulphide minerals. 

Potential controlled flotation separation of chalcopyrite-pyrite ores has been extensively tested to be one of the most probable to obtain industrial application on the basis of the fact that chalcopyrite has strong collectorless and collector floatability whereas pyrite has poor collectorless floatability. 

In this book, a general review of the fundamental research on flotation electrochemistry of sulphide minerals is made first in Chapter 1. Chapter 2 to Chapter 9 mainly summarize the results of basic research in our group focused on the topics of collectorless floatability of sulphide minerals and hydrophobic... 

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