Sulfur native

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

Production of Frasch and native sulfur probably peaked in the CIS at about 3.2 million metric tons. It has declined since and was reported as 400,000 metric tons in 1995. About 200,000 metric tons was produced in the Ukraine, with the remainder from Turkmenistan and Russia. 

Sulfur can be produced direcdy via Frasch mining or conventional mining methods, or it can be recovered as a by-product from sulfur removal and recovery processes. Production of recovered sulfur has become more significant as increasingly sour feedstocks are utilized and environmental regulations concerning emissions and waste streams have continued to tighten worldwide. Whereas recovered sulfur represented only 5% of the total sulfur production ia 1950, as of 1996 recovered sulfur represented approximately two-thirds of total sulfur production (1). Recovered sulfur could completely replace native sulfur production ia the twenty-first century (2). 

Frasch process The process used to extract native sulfur from underground deposits, 558... 

Important metallic ore deposits include Besshi (Kieslager)-type (strata-bound cupriferous pyritic deposits), strata-bound Mn-Fe-type, skam-type, Kuroko-type and vein-type. Dominant non-metallic deposits are limestone, clay, native sulfur, zeolite, silica and gypsum deposits. The deposits are divisible into three groups, based on their ages of formation Carboniferous-Jurassic, Cretaceous-Paleogene and Tertiary-present. 

Figure 1.93. /02-pH diagram with the stability fields of aqueous species in Na-K-H-S-Se-0 system for the conditions SS = 10 mol/kg H2O, ESe = 10 mol/kg H2O, ionic strength = 1, and temperature = 150°C. Dashed lines are the ratio ho-a i- /a i- in logarithmic units. Stability fields for native sulfur and native selenium and the boundaries between predominance regions of oxidized and reduced selenium species are omitted for clarity (Shikazono, 1978b). 

In the siliceous body, electrum and Cu minerals (enargite, luzonite, covelline), and native sulfur occur. The Ag content of electrum is lower (0.0-5.3 wt%) than that from epithermal Au-Ag vein-type deposits (Fig. 1.194) (Shikazono and Shimizu, 1987). Low Ag content of electrum and sulfide mineral assemblage (enargite, native sulfur, covellite, pyrite) indicate high fs2 condition (Fig. 1.194). 

Eastern Manus Basin Desmos cauldron (3 42 S, 151°52 E) 2000 Caldera of basalt/basaltic andesite at an intersection of a spreading center and a transform fault Sulfide ores were not recovered. Megaplume-like methane anomalies in water column over the caldera. Ferruginous oxide deposits. Pyrite and native sulfur disseminated in basaltic andesite. 

The difference in mineralogy of the Kuroko and present-day back-arc deposits are (1) metastable phases such as native sulfur, wurtzite, and amorphous silica are poor in the Kuroko deposits (2) arsenic minerals such as jordanite, tetrahedrite-tennantite, native arsenic, and realgar are common in the present day back-arc deposits (Okinawa Myojinsho Knoll Caldera), but rare in Kuroko deposits except tetrahedrite-tennantite (3) secondary minerals such as cerussite and covellite are common in present day back-arc deposits (e.g., Okinawa, Myojinsho Knoll Caldera) (4) Dendritic texture is common in the present day back-arc deposits. 

A second complication is that we would like to decouple zero-valent sulfur from the element s other redox states, since Reaction 17.28 produces native sulfur, but the database does not include such a coupling reaction. Situations of this nature are not uncommon, occurring when an element in a certain oxidation state is stable as a solid, but no corresponding aqueous species occurs under geochemical conditions. To work the problem, we invent a ficticious zero-valent species S(aq) with an arbitrarily low stability. Setting log K for the reaction... 

The sulfate —> sulfide reduction requires quite low Eh conditions (figure 8.21D). The process takes place through enzymatic mediation (enzymes oxidize organic matter at the Eh of interest). At low pH, the reducing process may result in the formation of native sulfur, as an intermediate step of the process... 

As already mentioned, the Eh-pH extension of the field of native sulfur depends on the total sulfur concentration in the system. With solute molality lower than approximately 10 moles/kg, the field of native sulfur disappears. 

Equilibria 9.93 and 9.94 are similar to those proposed by Fincham and Richardson (1954) for native sulfur. According to these equilibria, the solute states of sulfur compounds depend on oxygen fugacity the total concentration of sulfur dissolved in the melt initially decreases with increasing /q, based on equation 9.93, and then increases again when equilibrium 9.94 becomes dominant. 

Let us now consider equilibrium 9.117. The formation of HjS obviously implies the presence of sulfur in the system (but not necessarily native sulfur). The main crystalhne sulfur compound in geothermal fields is always pyrite FeS2. Equilibrium 9.117 can thus be rewritten as follows ... 

Sulfur occurs widely in nature as the element and was thus easily obtainable by the ancients. The Chinese had rich natural deposits, and the substance is readily purified by sublimation, a process in which the native sulfur is heated and the evolved vapour collected directly as a pure solid. 

Sulfur, one of the most important industrial raw materials, is distributed throughout the world in both elemental and combined forms. Sulfur has been used by mankind since antiquity and its consumption has increased at an annual growth of 4-4.5 percent More than half of the world s sulfur output is in elemental form, nearly all of which is obtained from native sulfur deposits and natural gas. Fertilizer manufacture accounts for approximately 60 percent of all sulfur consumed, followed by chemicals, pig-... 

Sulfur is present in several oxidation states, usually as sulfide and sulfate. Locally native sulfur may occur in significant quantities. Sulfate is present in large concentrations in seawater and is probably the most important oxidizer in the water of anoxic basins such as the Black Sea, Kaoe Bay, and many fjords. 

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