Sulphur pyrite

A liquid/solid separation yields a residue and a solution. The solution is cooled to produce crystalline PbCl2 which is later electrolyzed to lead metal and chlorine in a fused salt cell. The residue consists of elemental sulphur, pyrite and gangue. 

Though Finland lacked deposits of coal, oil and many minerals, it did possess natural resources suitable for chemical production. In the 1910s, a new, rich copper mine at Outokumpu was opened its ore contained sulphur pyrites, among other things. However, the most valuable resources for the chemical industry were timber and water power. Processing staple wood products gave the forest industries opportunities to extract various chemicals as byproducts. Hydroelectricity was a new energy source for the electrochemical industries at the time. 

Year Acid production Sulphur Pyrites Acid prodn. % Spent oxide Acid prodn. % Anhydrite Acid prodn. % Zinc concentrates Acid prodn. % ... 

The first crystal structure to be detennined that had an adjustable position parameter was that of pyrite, FeS2 In this structure the iron atoms are at the comers and the face centres, but the sulphur atoms are further away than in zincblende along a different tln-eefold synnnetry axis for each of the four iron atoms, which makes the unit cell primitive. 

Large deposits of free sulphur occur in America, Sicily and Japan. Combined sulphur occurs as sulphides, for example galena, PbS, zinc blende, ZnS, and iron pyrites, FeSj, and as sulphates, notably as gypsum or anhydrite, CaS04. 

Many of these sulphides occur naturally, for example iron(ll) sulphide, FeS (magnetic pyrites), and antimony(III) sulphide, Sb S, (stibnite). They can usually be prepared by the direct combination of the elements, effected by heating, but this rarely produces a pure stoichiometric compound and the product often contains a slight excess of the metal, or of sulphur. 

It can be readily calculated that pyrite will exert a sulphur dissociation pressure of 1 atmos only at 1512K. However, when the sulphide reacts with air the main gaseous product is SO2, and the reaction is then... 

Calculate the volume of 5 per cent barium chloride solution which must be added from the approximate sulphur content of the iron pyrites FeS2 or of the mineral sulphide. 

On heating with sulphur, MS2 result. PtS2 has the 6-coordinate Cdl2 structure whereas PtS2 is Pd2+(S2 ) in a distorted pyrite structure (4-coordinate PdPd—S 2.30 A) confirming the preference for the divalent state for... 

Alonso-Vante N, Chatzitheodorou G, Fiechter S, Mgoduka N, PouHos 1, Tributsch H (1988) Interfacial behavior of hydrogen-treated sulphur deficient pyrite (FeS2 x). Sol Energy Mater 18 9-21... 

In the early 1980s, Nobel (a reagent manufacturing company) developed selective apatite collectors (Lilaflot series) based on modified fatty acids, which were capable of removing apatite without any loss of ilmenite. The pH in the ilmenite circuit was controlled with the use of sulphuric acid. In 1980, the tall oil used in the pyrite circuit was replaced with Lilaflot 100 (modified fatty acid). 

Sulphuric acid is the largest volume chemical in the world with an annual production of about 180 mill, t/year which is used primarily for phosphate fertilizers, petroleum alkylation, copper ore leaching and in smaller quantities for a number of other purposes (pulp and paper, other acids, aluminium, titanium dioxide, plastics, synthetic fibres, dyestuffs, sulphonation etc.). The major sulphur sources for sulphuric acid production are sulphur recovered from hydrocarbon processing in the refineries and from desulphurisation of natural gas, SO2 from metallurgical smelter operations, spent alkylation acid, and to a minor extent mined elemental sulphur and pyrites. A simplified flow sheet of a modem double-absorption plant for sulphuric acid production from sulphur is shown in Fig. 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... 

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... 

Fig. 1.3, sulphur-induced flotation of pyrite was observed at pH = 8 if the concentration of the sulphur during conditioning was 10" mol/L or greater, but there was no significant flotation when the concentration of the sulphur was below this level (Trahar, 1984). 

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. 

Figure 1.3 Recovery-time data for sulphur-induced flotation of pyrite at pH = 8...

Figure 1.4 Comparison of UV spectrum of cyclohexane extract of sulphidized pyrite after flotation with that of cyclohexane solution of sulphur (Heyes and Trahar, 1984)...

The h-pH diagrams of surface oxidation of arsenopyrite and pyrite are shown in Fig. 2.16 and Fig. 2.17, respectively. Figure 2.16 shows that jBh-pH area of self-induced collectorless flotation of arsenopyrite is close to the area forming sulphur. The reactions producing elemental sulphur determine the lower limit potential of flotation. The reactions producing thiosulphate and other hydrophilic species define the upper limit of potential. In acid solutions arsenopyrite demonstrates wider potential region for collectorless flotation, but almost non-floatable in alkaline environment. It suggests that the hydrophobic entity is metastable elemental sulphur. However, in alkaline solutions, the presence of... 

Figure 2.17 h-pH diagram for pyrite in aqueous solutions with elemental sulphur as metastable phase. Equilibrium lines correspond to dissolved species at lO" mol/L. Plotted points show the upper and lower limit potential of collectorless flotation of pyrite reported from Sun (1990,1992)... 

Pyrite and arsenopyrite have similar oxidation and self-induced collectorless flotation behavior. It is generally suggested that anodic oxidation of pyrite occurs according to reactions (2-24) in acidic solutions (Lowson, 1982 Heyes and Trahar, 1984 Trahar, 1984 Stm et al., 1991 Chander et al., 1993). The oxidation of pyrite in basic solutions takes place according to reactions (2-25). Since pyrite is flotable only in strong acidic solutions, it seems reasonable to assume that reaction (2-24) is the dominant oxidation at acidic solutions. Whereas pyrite oxidizes to oxy-sulfur species with minor sulphur in basic solutions. 

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. 

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. 

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. 

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