Pyrite behavior

Arico AS, Antonucci V, Giordano N, Crea F, Antonucci PL (1991) Photoelectrochemical behavior of thermally activated natural pyrite-based photoelectrodes. Mater Chem Phys 28 75-87... 

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... 

It is found that the dissolution of zinc sulfides occurs more rapidly when they are in contact with copper sulfide or iron sulfide than when the sulfides of these types are absent. This enhancement is brought about by the formation of a galvanic cell. When two sulfide minerals are in contact, the condition for dissolution in acidic medium of one of the sulfides is that it should be anodic to the other sulfide in contact. This is illustrated schematically in Figure 5.3 (A). Thus, pyrite behaves cathodically towards several other sulfide minerals such as zinc sulfide, lead sulfide and copper sulfide. Consequently, pyrite enhances the dissolution of the other sulfide minerals while these minerals themselves understandably retard the dissolution of pyrite. This explains generally the different leaching behavior of an ore from different locations. The ore may have different mineralogical composition. A particle of sphalerite (ZnS) in contact with a pyrite particle in an aerated acid solution is the right system combination for the sphalerite to dissolve anodically. The situation is presented below ... 

Figure 1.2 Effect of pulp potential on self-induced collectorless flotation behaviors of pyrrhotite and pyrite (Heyes and Trahar, 1984)...

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

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. 

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. 

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. 

Janetski et al. (1977) used voltanunetric method to study the electrochemical behavior of a pyrite electrode in ethyl xanthate solution containing various concentration of sodium sulphide. They observed an additional anodic wave due to the oxidation of the dissolved sulphide species present and that the wave appeared at potential cathodic to xanthate oxidation. Therefore, they concluded that the presence of sulphide in solution introduced an anodic process which occurred in preference to xanthate oxidation and hence dixanthogen would not be formed and the pyrite would not be rendered floatable. 

Janetski et al. (1977) also studied the behavior of a pyrite electrode in a solution of cyanide concentration in the absence and presence of xanthate using voltammetric technique. They reported that on increasing the concentration of cyanide at constant pH and xanthate concentration, the oxidation wave of xanthate is shifted to more anodic potential indicating that the presence of cyanide, which may react with the mineral surface to form an insoluble iron cyanide complex will result in the inhibition of the electrochemical oxidation of xanthate and the depression of pyrite. 

Keywords mechano-electrochemical behavior pyrite sphalerite galena... 

Mechano-Electrochemical Behavior of Pyrite in Different Grinding Media... 

This work has demonstrated that organically bound sulfur forms can be distinguished and in some manner quantified directly in model compound mixtures, and in petroleum and coal. The use of third derivatives of the XANES spectra was the critical factor in allowing this analysis. The tentative quantitative identifications of sulfur forms appear to be consistent with the chemical behavior of the petroleum and coal samples. XANES and XPS analyses of the same samples show the same trends in relative levels of sulfide and thiophenic forms, but with significant numerical differences. This reflects the fact that use of both XPS and XANES methods for quantitative determinations of sulfur forms are in an early development stage. Work is currently in progress to resolve issues of thickness effects for XANES spectra and to define the possible interferences from pyritic sulfur in both approaches. In addition these techniques are being extended to other nonvolatile and solid hydrocarbon materials. 

Cobalt disulfide has a cubic pyrite structure, a0 = 5.5362(5)A. It is ferromagnetic with a Tc of 124 K and shows metallic behavior from 4 K to room temperature. 

In any development of advanced physical coal-cleaning (PCC) techniques, an important consideration is the heterogeneous nature of coal and, in particular, the variable manner in which pyrite occurs in coal. This variability influences the behavior of coal with regard to cleaning (26). In some coals, pyrite is distributed throughout the coal matrix as particles only microns in size. Thus, to separate pyrite from these coals, the coal must be crushed to very fine size in order to "liberate the pyrite from the coal particles. However, conventional commercial PCC techniques cannot... 

The flocculation results on the individual mineral suspensions are shown in Figure 2 (A B). These graphs show the effect of polyacrylic acid dispersant before (PAA) Figure 2A, and after xanthation (PAAX) Figure 2B, on the flocculation-dispersion behavior of individual suspensions of coal and pyrite with Purifloc-A22 flocculant. 

The iron sulfide used in the experiment was obtained from the thermal decomposition of pyrite(FeS2). The particles were extremely porous, with pores sizes of several tens of microns. In contrast, the reaction behavior obtained with natural pyrrhotite or synthetic FeS composed of fine particles, gave much worse results. Thus, the influence of the specific surface area of a solid on the formation behavior was thought to be important. 

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