Sulfur From Pyrite

Heating iron pyrites to ca. 1200°C in the absence of air (Outokumpu process) yields sulfur and liquid iron(II) sulfide. 

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Noranda Process. When pyrites are heated to about 540°C in the absence of oxygen, about half of the sulfur content in the pyrites evolves in the elemental form. Noranda Mines Ltd. and BatteUe Memorial Institute developed a process based on this property to recover elemental sulfur from pyrite (27). The first commercial plant was built at Welland, Ontario, in 1954 but operated on an experimental basis for only a few years before being closed for economic reasons. 

Mineral matter may also contribute to the volatile matter by virtue of the loss of water from the clays, the loss of carbon dioxide from carbonate minerals, the loss of sulfur from pyrite (FeS2), and the generation of hydrogen chloride from chloride minerals as well as various reactions that occur within the minerals, thereby influencing the analytical data (Given and Yarzab, 1978). 

Orkla A complex process for recovering sulfur from pyrite. The ore was smelted with coke, limestone, and quartz, with very little air at 1,600°C, and the iron was removed as a slag. The copper and other nonferrous metals formed a matte with the sulfur. Pyrolysis of this matte removed half of the sulfur. An air blast removed the other half without oxidizing it. Developed by the Orkla Mining Company, Norway, between 1919 and 1927. First commercialized at Thamshavn, Norway, in 1931, but the plant closed in 1962. The process was used for many years in Spain, Portugal, and Hungary. 

Elemental sulfur, also called brimstone," is the preferred raw material for sulfuric acid production whenever it is available at a reasonable cost. Elemental sulfur may be mined by the well-known Frasch process or recovered from volcanic ores, sour" natural gas, or oil. It is also possible and sometimes commercially feasible to produce elemental sulfur from pyrites, other sulfide ores, and coal. 

It is also understood and agreed that in the event of any material increase in the present production of elementary sulfur from pyrites this agreement shall be cancelled and become null and void three months after commencement of such increased production. 

At the beginning of the twentieth century, the world s sulfur demand of about two million metric tons was met by sulfur produced from elemental deposits in Sicily, Italy, and from pyrite mined on the Iberian Peninsula. By 1995, sulfur was recovered in more than 78 countries. 

Burning Pyrites. The burning of pyrite is considerably more difficult to control than the burning of sulfur, although many of the difficulties have been overcome ia mechanical pyrite burners. The pyrite is burned on multiple trays which are subject to mechanical raking. The theoretical maximum SO2 content is 16.2 wt %, and levels of 10—14 wt % are generally attained. As much as 13 wt % of the sulfur content of the pyrite can be converted to sulfur trioxide ia these burners. In most appHcations, the separation of dust is necessary when sulfur dioxide is made from pyrite. Several methods can be employed for this, but for many purposes the use of water-spray towers is the most satisfactory. The latter method also removes some of the sulfur... 

In both reactions, Fe is produced as a consequence of the oxidation of sulfur from the — 1 oxidation state of pyritic sulfur to the +6 state of sulfate. 

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). 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

The developed process aimed for the removal of iron and sulfur from coal. While several patents for microbial removal of pyrite from coal exist, this one is unique because of the microbial mixture developed by the group for this purpose, which is partially... 

By this reaction, sulfur from the pyrite oxidizes to form sulfate ions, liberating protons that acidify the solution. 

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. 

It is generally assumed that metamorphism reduces the isotopic variations in a sulfide ore deposit. RecrystaUization, liberation of sulfur from fluid and vapor phases, such as the breakdown of pyrite into pyrrhotite and sulfur, and diffusion at elevated temperatures should tend to reduce initial isotopic heterogeneities. 

The goal of beneficiation is to remove as much sulfur from a fuel as possible before it is ever burned. When burned, fuel with lower sulfur content will produce less sulfur dioxide. Beneficiation is usually accomplished by a physical process that separates one form of sulfur, pyritic sulfur, from coal. Pyritic sulfur consists of sulfur minerals (primarily sulfides) that are not chemically bonded to coal in any way. The name is taken from the most common form of mineral sulfur usually found in coal, pyrite, or iron sulfide (FeS2). 

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