Pyrite effect

Many of these sulphides occur naturally, for example iron(ll) sulphide, FeS (magnetic pyrites), and antimony(III) sulphide, Sb S, (stibnite). They can usually be prepared by the direct combination of the elements, effected by heating, but this rarely produces a pure stoichiometric compound and the product often contains a slight excess of the metal, or of sulphur. 

Reactions of Goal Ash. Mineral matter impurities have an important effect on the utili2ation of a coal. One of the constituents of greatest concern is pyrite because of the potential for sulfur oxide generation on combustion. The highest concentrations of pyrite are associated with coal deposition under marine environments, as typified by the Illinois Basin, including parts of Illinois, Indiana, and Kentucky. Additionally, the mineral matter... 

Biological processes are also being studied to investigate abiHty to remove sulfur species in order to remove potential contributors to acid rain (see Air pollution). These species include benzothiophene-type materials, which are the most difficult to remove chemically, as weU as pyritic material. The pyrite may be treated to enhance the abiHty of flotation processes to separate the mineral from the combustible parts of the coal. Genetic engineering (qv) techniques are being appHed to develop more effective species. 

Figure 4-469 shows the effect on corrosion rates of 1020 steel in different water systems with dissolved hydrogen sulfide. The difference in corrosion rates is due to different corrosion products formed in different solutions. In solution I, kansite forms. Kansite is widely protective as the pyrrhotite coats the surface giving slightly more protection until a very protective pyrite scale is formed. In solution II, only kansite scale forms, resulting in continued increase in the corrosion rate. Finally, in solution 111, pyrite scale is formed as in solution I however, continued corrosion may be due to the presence of carbon dioxide. 

In an extensive study by Read et al. [93], 10 anionic surfactants were evaluated for their ability to remove pyritic sulfur and ash from ultrafine Illinois no. 5 coal by flotation processes. The authors observed that of the commercially available surfactants, sodium dodecyl sulfate was the most effective on either a weight or a molar basis, followed by a linear AOS (average molweight 272) and alkylpolyethoxylated sulfonates. Of the noncommercial surfactants tested, -(E -b-dodecene-b-suIfonate (f0) was the most effective and better than any commercial surfactant on a dosage/recovery basis. 

Binary systems of ruthenium sulfide or selenide nanoparticles (RujcSy, RujcSey) are considered as the state-of-the-art ORR electrocatalysts in the class of non-Chevrel amorphous transition metal chalcogenides. Notably, in contrast to pyrite-type MS2 varieties (typically RUS2) utilized in industrial catalysis as effective cathodes for the molecular oxygen reduction in acid medium, these Ru-based cluster materials exhibit a fairly robust activity even in high methanol content environments of fuel cells. 

Iron in the feed concentrate is rejected either as unreacted pyrite mixed with elemental sulfur or as jarosites in the leach residue. The pyrite/sulfur mixtures said to be suitable for indefinite storage, but the well known environment effects caused by pyrite weathering are likely to make storage of this material a less than straightforward problem. Besides this, there are problems associated with the disposal of the leach residues from the pressure leach process. 

The bacterial leaching of uranium minerals is complex. This is because of the fact that uranium minerals are not sulfides and are not, therefore, directly attacked by the bacteria. However, the uranium sources usually have a substantial pyrite content which can be bac-terially oxidized to give an acidic ferric sulfate solution which is an effective leaching medium for uranium minerals. The reactions involved in the system can be shown in a simplified form as ... 

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. 

Table V Analyses of Unwashed Coals Used to Determine the Effect of Pyrites...

The iron sulphide in South African coals is a mixture of pyrite and marcasite (18). Although marcasite is known to transform into pyrite at elevated temperatures, separate spiking experiments were performed to see if pyrite or marcasite would show a preferential catalytic effect. The addition of pyrite and marcasite minerals (-200 mesh), to the coal showed equivalent total conversions, and yields of oil and asphaltene. 

The Effect of Mineral Matters on the Decomposition Ethers. Recently, the effect of mineral matters of coal on the coal liquefaction has received much attention. It was shown that small amounts of FeS or pyrite are responsible for the hydro-genative liquefaction of coal. Therefore, it is interesting to elucidate the effect of mineral matters of coal on the decomposition rate and products of aromatic ethers, and so three diaryl ethers were thermally treated in the presence of coal ash obtained by low temperature combustion of Illinois No.6 coal at about 200°C with ozone containing oxygen. 

Cruz R., Bertrand, V., Monroy, M., GonzAlez, I. 2001. Effect of sulphide impurities on the reactivity of pyrite and pyritic concentrates a multi-tool approach. Applied Geochemistry, 16, 803-819. 

Figure 17.3 Effect of pyrite content of the ore on gold recovery in the copper-gold concentrate at 30% Cu concentrate grade (1 ore from Peru 2 ore from Indonesia).

This method is highly sensitive to temperature. Figure 17.5 shows the effect of temperature on pyrite/arsenopyrite separation. In this particular case, most of the gold was associated with pyrite. Successful pyrite/arsenopyrite separation can also be achieved with the use of potassium peroxy disulphide as the arsenopyrite depressant. 

Figure 17.5 Effect of temperature on separation of pyrite and arsenopyrite from a bulk pyrite/ arsenopyrite concentrate.

Most of the current commercial operations that treat PGM from sulphide-dominated deposits are located in South Africa (Morensky Reef), Stillwater mines (Montana, USA) and Lac des Hies (Ontario, Canada). From a processing point of view, most of these ore types contain hydrophobic gangue minerals, including talc, which has a negative effect on PGM recoveries. Other major factor that affects flotation recovery of PGM is the presence of a variety of sulphide minerals, including pyrrhotite, pentlandite, chalcopyrite, violarite and pyrite, where... 

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,... 

Unfortunately, pyrite sulfur makes up only half the sulfur content of coal, while the other half is organically bound. Coal gasification is the only means by which this sulfur mode can be removed. Of course, it is always possible to eliminate the deleterious effects of sulfur by removing the major product oxide S02 by absorption processes. These processes impose large initial capital investments. 

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

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