Sphalerite formation

Faser-asbest, m. fibrous asbestos, -asche, /. fiber ash. -bildung, /. fiber formation, fibra-tion. -blende, /. fibrous sphalerite. Faserchen, n. little fiber, fibril, filament. Faserfarbung, /. coloration of the fiber, faserfdrmig, a. fibrous, filiform. 

In order to obtain reliable formation temperatures based on electrum-sphalerite geothermometer, the following conditions have to be satisfied. 

Because natural stannite contains a considerable amount of zinc, sphalerite contains a considerable amount of iron, and these contents can be easily analyzed using an electron microprobe, a stannite-sphalerite pair is expected to be a useful indicator of formation temperature and sulfur fugacity. 

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 ... 

Several reviews on ore processing by flotation are available.17-21 In addition to providing details of the chemistry of collectors they describe the use of activators and depressants. The former usually convert the surfaces of an ore particle which does not bind strongly to conventional collectors to one that does. The addition of Cu2+ ions to enhance the flotability of minerals such as sphalerite, a zinc sulfide, has been exploited for some time.4 Formation of a surface layer of CuS has been assumed to account for this, but the mechanisms and selectivities of such processes continue to be investigated.18,22,23... 

It is necessary to use statistical procedures to assess chemical dynamics. The amount of Zn, As and SO42" that are removed were compared using linear correlation analyses. Examining the output from each cell for removal of these metals shows a marked correlation between Zn and S042" in the 2nd plant cell and Typha cell (r2= 0.8), before decreasing to 0.6 in the pond. This high positive correlation supports that the formation of ZnS (sphalerite) is an important aspect. Values for As are not as high. 

Considering the formation of 8203" needing 0.5 V over-potential, assuming the concentration of all dissolved species to be 10 mol/L, the reaction potential are 0.28 V and 0.37 V respectively, corresponding to reactions (2-57) and (2-58), the upper limit potential of flotation of sphalerite depends on reaction (2-57). 

From the study of Kainthla et al. [48], XRD of the films showed clearly that solid solution formation occurred the (predominantly sphalerite) diffraction peaks shifted with change in composition. For compositions with S concentration < 60%, only zincblende structure formed the amount of wurtzite increased with increasing S content but was always low. The concentration of S in the films was somewhat greater than that in the deposition solution i.e., S deposited preferentially. This is not surprising since CdS deposition is normally faster than that of CdSe. The concentration of ammonia was increased as the thiourea selenosulphate ratio increased, ostensibly to slow down the rate of formation of CdS through decreased Cd concentration (although the rate of CdSe formation is also dependent on this same factor). 

Many mineral species are known to be selectively crystallized by the presence of bacteria. Carbonate minerals, such as calcite, aragonite, hydroxycalcite, and siderite oxide minerals, such as magnetite and todorokite oxalate minerals, such as whewellite and weddellite sulfide minerals, such as pyrite, sphalerite, wurtzite, greigite, and mackinawite and other minerals, such as jarosite, iron-jarosite, and g3q>sum, are known to precipitate in the presence of bacteria. Therefore, investigations have been developed to analyze the formation of banded iron ore by the action of bacteria, and to analyze the ancient environmental conditions of the Earth through the study of fossilized bacteria. 

The most widely applied activation procedure is that involving the use of copper(II) ions to enhance the floatability of some sulfide minerals, notably the common zinc sulfide mineral sphalerite.2 Sphalerite does not react readily with the common thiol collectors, but after being treated with small amounts of copper it floats readily owing to the formation of a surface layer of CuS." A similar procedure is often adopted in the flotation of pyrrhotite (FeS), pyrite (FeS2), galena (PbS) and stibnite (Sb2S3). In the context of coordination chemistry, the major contribution has been to the understanding of the chemistry involved in the deactivation of these minerals, a procedure often adopted in the sequential flotation of several minerals from a complex ore. 

Fig. 20a and b. a) Radiolarian test enclosed in pyrite from the Devonian shale of Meggen (FRG). Silica of the testis replaced by sphalerite (ZnS) b) Marcasite containing budding structures interpreted as pseudomorphs after Pyrodictium. From sulfide formation of the East Pacific rise (Tufar et al., 1984) 92>... 

Three primary reactions were observed between aqueous chlorine and the base-metal sulfides. Elemental sulfur was produced during the reaction with chalcocite, bornite, and covellite. A rapid oxidation of the pyrrhotite, pyrite, and arsenopyrite to the sulfate form was observed. The formation of sulfur monochloride was indicated with sphalerite, galena (under most conditions), and chalcopyrite. The ratio of sulfur to sulfate was close to what could be expected if the sulfur monochloride hydrolyzed to form sulfur. Thermodynamic considerations indicated sulfate formation as the primary product. 

Figure 7 Replacement driven by force-of-crystal-Uzation is characterized by authigenic phases that develop euhedral faces that are not plausibly constmed as crystal growth within pore spaces (a) sphalerite replaces albitized detrital feldspar and adjacent portions of clay-rich matrix, Frio Formation, Oligocene, South Texas and (b) siderite crystal (s) attacks a detrital K-feldspar (K) in sandstone, Breathitt Formation, Pennsylvanian, eastern Kentucky.

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