Sulphide minerals

P. A. Mingione, "Use of AEROPHINE 3418A Promoter for Sulphide Minerals Flotation," Proceedings of the 22nd Mnnual Meeting of the Canadian Mineral Processors, Ottawa, 1990. 

Lead The production of lead from lead sulphide minerals, principally galena, PbS, is considerably more complicated than the production of zinc because tire roasting of the sulphide to prepare the oxide for reduction produces PbO which is a relatively volatile oxide, and therefore the temperature of roasting is limited. The products of roasting also contain unoxidized galena as well as die oxide, some lead basic sulphate, and impurities such as zinc, iron, arsenic and antimony. 

The production of copper from sulphide minerals is accomplished with a preliminary partial roast of die sulphides before reaction widr air in the liquid state, known as mattes, to form copper metal (conversion). The principal sources of copper are minerals such as chalcopyrite, CuFeSa and bornite CuaFeSa, and hence the conversion process must accomplish the preferential oxidation of non, in the form of FeO, before the copper metal appears. As mentioned before, tire FeO-SiOa liquid system is practically Raoultian, and so it is relatively easy to calculate the amount of iron oxidation which can be canned out to form this liquid slag as a function of the FeO/SiOa ratio before copper oxidation occurs. The liquid slag has a maximum mole fraction of FeO at the matte blowing temperatures of about 0.3, at solid silica saturation. 

The colour is the most obvious and conspicuous external property of a large number of minerals. Minerals are distinguished by an extraordinary variety of colours and shades of varying richness and intensity. Some mineral species are characterised by a constant colour, which enables one to detect them almost unerroneously. Just as an example, mention may be made of a sulphidic mineral of copper, bomite (Cu5FeS4). The best identifying feature of this mineral is its purplish-blue tarnish over a bronze colour ( peacock ore). 

The Cretaceous sedimentary rocks of the Western Canada Sedimentary Basin (WCSB), renowned for their hydrocarbon resources, are seldom considered to have potential to host base metal sulphide mineralization. These sedimentary rocks have also discouraged those who presumed that the Precambrian rocks of the Canadian Shield to the east and north are more favourable hosts of base metal mineralization (ctMacqueen 1997). 

Most of the current commercial operations that treat PGM from sulphide-dominated deposits are located in South Africa (Morensky Reef), Stillwater mines (Montana, USA) and Lac des Hies (Ontario, Canada). From a processing point of view, most of these ore types contain hydrophobic gangue minerals, including talc, which has a negative effect on PGM recoveries. Other major factor that affects flotation recovery of PGM is the presence of a variety of sulphide minerals, including pyrrhotite, pentlandite, chalcopyrite, violarite and pyrite, where... 

In general, the flotation properties of PGM from sulphide-dominated deposits are very dependent on the ratio of the individual sulphide minerals present in the ore and the nature and occurrence of hydrophobic gangue minerals present in the ore. 

Each of the sulphide minerals, which are PGM carriers (i.e. pyrrhotite, pyrite, pentlan-dite, etc.) have different flotation properties under some flotation conditions. The selectivity between sulphide minerals and gangue minerals is relatively poor in principle, and in the majority of cases, a hydrophobic gangue depressant has to be used. 

The flotation behaviour of the individual sulphide minerals contained in PGM sulphide-dominated ores can be described as follows ... 

Ekmekci, Z., Bradshaw, D.J., Harris, P.J., and Buswel, A.M., Interactive Effect of Milling Media and CuS04 Additions on the Flotation Performance of Sulphide Minerals from the Morensky ore, Part II Froth Stability, International Journal of Mineral Processing, Vol. T8, pp. 164-174, 2006. 

In general, the calceous-dolomitic rocks from the Cambrian age are affected by their upper beds, by sulphide mineralization of lead, zinc and iron contemporaneous with sedimentation. The oxide lead and zinc minerals are disseminated through dolomitic limestone. As a consequence of the action of the descending process, these formations may assume different types of mineralization. According to the intensity of the oxidation process, which is associated with the different characteristics of the country rock, this country rock may be (a) principally calceous, (b) calceous with dolomitized zones and (c) primarily dolomitized. 

Occurrence. Arsenic is associated with sulphide minerals (As4S4 realgar, As2S3 orpiment, FeAsS arsenopyrite, Cu3AsS4, enargite, etc.). Occasionally arsenic is found as free element, usually in ore containing cobalt, antimony, nickel. 

Occurrence. Native sulphur occurs in deposits around volcanoes and hot springs. It occurs in numerous sulphides minerals, in sulphates, in crude oils, in coal and as H2S in natural gas. 

Arsenic occurs primarily in sulphide minerals associated with copper ores, and to a lesser extent with zinc, lead and gold ores. Arsenic is produced as a by-product of the smelting of these metals. Primary arsenic production has now ceased in the USA and Europe, and most arsenic is now imported from China and Mexico. The volatility of arsenic represents a significant concern, and there is at present no known natural mechanism by which arsenic is immobilized in the environment. Anthropogenic activities account for an input of some 19000 tonnes into the atmosphere, compared with 12000 tonnes from natural processes, such as volcanism and forest fires (Ayres and Ayres, 1996). 

Chapter 1 General Review of Electrochemistry of Flotation of Sulphide Minerals... 

Abstract This chapter reviews the development of froth flotation achieved in the past one hundred years and accounts for the achievements of the theory of flotation of sulphide minerals in four aspects, which are the natural flotahility of sulphide minerals, the role of oxygen in the flotation of sulphide minerals, the interaction of collectors with sulphide minerals, the effect of the semi-conductor property of sulphide minerals and electrochemical behaviors in the grinding system. Furthermore, the purpose of this book is revealed in the end. 

The one hundred year history of froth flotation may be classified into three periods. The earliest stage is from the end of the 19 century to the early 20 century, i.e. surface flotation or bulk oil flotation. The natural hydrophobic sulphide minerals can be collected by the addition of oil. Froth flotation came into practice in 1909 with the use of pine oil, mechanical flotation machine in 1912, and xanthate and aerofloat as collectors in 1924—1925 (Gaudin, 1932 Sutherland and Wark, 1955). 

In the 2nd period ranging from the 1930s to the 1950s, basic research on flotation was conducted widely in order to understand the principles of the flotation process. Taggart and co-workers (1930, 1945) proposed a chemical reaction hypothesis, based on which the flotation of sulphide minerals was explained by the solubility product of the metal-collector salts involved. It was plausible at that time that the floatability of copper, lead, and zinc sulphide minerals using xanthate as a collector decreased in the order of increase of the solubility product of their metal xanthate (Karkovsky, 1957). Sutherland and Wark (1955) paid attention to the fact that this model was not always consistent with the established values of the solubility products of the species involved. They believed that the interaction of thio-collectors with sulphides should be considered as adsorption and proposed a mechanism of competitive adsorption between xanthate and hydroxide ions, which explained the Barsky empirical relationship between the upper pH limit of flotation and collector concentration. Gaudin (1957) concurred with Wark s explanation of this phenomenon. Du Rietz... 

Since the 1960s , various electrochemical methods such as linear potential sweep voltammetry, cyclic voltammetry etc. and various surface analysis apparatuses such as infrared spectra, X-ray photoelecfron spectroscopy etc. have been developed to investigate the electrochemical reaction mechanism involved in the flotation of sulphide minerals (Fuerstenau et al., 1968 Woods, 1976 Ahmed, 1978 Stm, 1990 Feng, 1989 Buckley, 1995 Arce and Gonzalez, 2002 Bulut and Atak, 2002 Costa et al., 2002). 

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 inherent hydrophobicity once thought to be typical of sulphides (Ravitz and Porter, 1933) is now thought to be restricted to sulphides such as molybdenite (Chander et al., 1975) and other minerals or compound with special structural feature (Gaudin et al, 1957b). Common commercial sulphide minerals, which are needed to recover in flotation, are normally composed of anion (S ) and heavy metal ions such as Cu, Cu, Pb, Zn, Hg, Sb, Bi transitive metal ion such as Fe, Co, Ni and noble and rare metal ions such as Ag, Au, Mo. On the basis of structural pattern or mode of linkage of the atoms or polyhedral imits in space, Povarennyk (1972) introduced a crystallochemical classification of sulphide minerals, which have six major patterns as shown in Table 1.1. 

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... 

Many authors indicated that self-induced flotation of sulphide minerals can occur only under moderately oxidizing environments. It is obvious that the... 

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. 

Role of Oxygen and Oxidation of Sulphide Minerals in Flotation... 

Therefore, it has been concluded that the reduction of oxygen as a cathodic process was essential for the electrochemical reaction on sulphide surface and was different for various sulphide minerals. The reduction of oxygen affected the oxidation of sulphide minerals and the interactions with collectors, which had a pronounced influence on flotation behavior of sulphide minerals (Ahmed, 1978 Buckley et al., 1985, 1995 Woods, 1984,1994 Hu et al., 2004 Yu et al., 2004a Zhang et al., 2004a, d). 

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