Pyritization with sulfur

Mercuric Sulfate. Mercuric s Af2iX.e.[7783-35-9] HgSO, is a colorless compound soluble ia acidic solutions, but decomposed by water to form the yellow water-iasoluble basic sulfate, HgSO 2HgO. Mercuric sulfate is prepared by reaction of a freshly prepared and washed wet filter cake of yellow mercuric oxide with sulfuric acid ia glass or glass-lined vessels. The product is used as a catalyst and with sodium chloride as an extractant of gold and silver from roasted pyrites. 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

The lower explosive limit and minimum explosive concentrations of flax, wool, cotton, jute, hemp and sisal fibres are of the same order of magnitude as those of highly explosive dusts [15], The explosibility of pyrites dusts with sulfur contents above 20% was evaluated experimentally. Dusts of 30% sulfur content gave explosion pressures of 3 bar at pressure rise rates of 16 bar/sec. Mixtures of 60% pyrites and 40% powdered limestone still showed significant pressure effects, and the proportion of limestone actually needed to suppress explosions was considerably above the values currently accepted by mining industries [16], Effects of mixtures of particle sizes in combustible dusts upon minimum ignition temperature (T ") and upon presence or absence of explosion were studied. Presence of 30% of fines in a coarse dust lowers Tf significantly [17], Experimental explosions of polyethylene,... 

Arsenic sulfide is prepared commercially by heating a mixture of iron pyrites and arsenopyrite or by heating arsenic trioxide with sulfur. The com-... 

The pyrite sulfur is generally considered to be sulfur associated with iron pyrite, FeS2 In most cases only the second sulfur of the pyrite molecule can be considered to be in this class. This sulfur can be expelled from iron pyrite with moderate heating (approximately 500°C) to form iron sulfide, FeS, and elemental sulfur condensate in the cooler vapor space above the sample. 

The degree of pyritization of iron (DOP) or the fraction of reactive iron that is bound with sulfur appears to increase rapidly with increasing S Fe ratios and may approach an asymptotic value of about 75% at S Fe ratios of 3 (Figure 6). 

Figure 6. The degree of pyritization, defined as the fraction of reactive iron present as pyrite, is a measure of the extent to which available iron has reacted with sulfur (226). In lake sediments, iron monosulfides frequently are as abundant as pyrite and hence were included with pyrite in the values calculated for surface sediments from 13 lakes and presented here. Even this correction neglects Fe(II) that may have been reduced by sulfide but may be present as siderite. Availability of iron appears to be more important than bottom-water oxygenation in determining the degree of pyritization. In the right-hand graph, darkened squares represent sediments known to experience seasonal anoxia only the uppermost point experiences permanent anoxia. (Data are from references 30, 34, 56, and 61.)...

Guerrot, 2000 Pokrovski, Kara and Roux, 2002, 2361). Arsenian pyrite is also common in hydrothermal deposits at temperatures as low as 150 °C and as high as 250-300 °C (Kesler, Riciputi and Ye, 2005, 132 Reich et al., 2005, 2788 Pokrovski, Kara and Roux, 2002, 2375, 2361). Most pyrites contain only 0.02-0.5 wt % arsenic (Welch et al., 2000, 597). However, arsenian pyrites may host up to 6 wt % arsenic as a solid solution with sulfur (Reich and Becker, 2006). Although pyrites from Nevada, USA, contain as much as 19.76 wt%, much of this arsenic exists as nanoscale arsenopyrite or other mineral inclusions rather than as a true solid solution (Reich et al., 2005 Reich and Becker, 2006, 2784-2786). 

Earlier work on the isotopic compositions of pyrite, elemental sulfur, and organic sulfur in coals from Japan, Australia, and Germany (107-110) was summarized by Nielsen (102). Smith and Batts (110) showed that organic sulfur in Australian coals ranging in age from Permian to Tertiary has a large isotopic variation (+2.9 to +24%c) in coals with more than % sulfur, whereas organic sulfur in low-sulfur coals (less than 1% sulfur) has a narrow isotopic composition between +4.6 and +7.3%o. The relatively uniform isotopic... 

Further developments of the work include a more accurate study of the mechanisms of desulfurization processes using instrumental improvements. This will enable an easy quantitation of gas yield and a thermochemical approach of elemental processes. We also have been using model polymers to better study the interactions of pyrite and sulfur with the organic matrix during coal pyrolysis, oxidation and combustion (34 and to examine more accurately the specific role of organic sulfur in thermal degradation processes. 

Sulfur dioxide is produced by burning either sulfur or a sulfide such as pyrite in the furnace. The dioxide is then mixed with the catalyst, NO, which may be prepared in either of two ways. In the older method, nitric acid vapor is formed in the niter pot, and when this vapor comes into contact with sulfur dioxide, nitric oxide is formed in accordance with the following equation ... 

Clean Kentucky Coal and Clean Kentucky Coal with Sulfur-Containing Additives. In Figure 14 are presented values tor the clean Kentucky coal with synthesis gas, and clean Kentucky coal with additives containing sulfur. The additives were present in amounts calculated to contain the same relative amount of sulfur. All of the autoclave times were one hour. The point for clean Kentucky coal (which still contains some pyrite and some magnetite (as an artifact of the cleaning process) in about a 2 1 mole ratio) and the point for thiophene lie on the pyrite-pyrrhotite equilbrium line. The... 

At atmospheric pressure, Ir combines with sulfur to yield IrS2, which has an orthorhombic structure it is isostructural with lrSe2. If the ratio of S Ir is raised to 3 I, the sulfide formed has a pyrite structure with cation vacancies balancing the charge of the Ir + ions. At 60 kbar and 1500 °C and with... 

Other less common elements recorded in these analyses are tin, chromium, and nickel. The tin is found among some of the opaque constituents (minerals) and is thought to be present as the mineral cas-siterite (Sn02), which is reportedly (17) associated with sulfide mineralization. Less is known about the location of the chromium, which may be a minor element in more than one mineral, e.g., pyrite and calcite. Nickel, on the other hand, is associated with sulfur, as can be shown in the X-ray spectra (Figure 10) obtained from a diamond-shaped mineral fragment. The analysis was obtained in the reflection (SEM) mode on the STEM, which excluded the recording of an electron diffraction pattern. The mineral tentatively is identified as millerite, a nickel sulfide (NiS) with no iron and a 1 1 ratio of nickel to sulfur. However, these conclusions must be considered as tentative until positive identification of the nickel sulfide is possible. 

Table II. ulfate-to-Sulfur Ratio for Extraction of Coal and Mineral Pyrite with Ferric Chloride Solution...

Zinc blende, galena and copper pyrites are important raw material sources in the Federal Republic of Germany. These ores are utilized in the extraction of metals with sulfuric acid being produced as a byproduct, so-called metal acid. As a result of increased efforts in environmental protection, the proportion of recycled sulfuric acid e.g. from nitration reactions or oil refineries, has increased significantly in the last 20 years. 

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