Pyrite from coal

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... 

Esposito, M. C., Chander, S., Apian, F. F., 1987. Characterization of pyrite from coal source. In Process Metallurgy, VE, Transaction of Metallurgical Society/American Institute of Mining Engineers, 475 - 493... 

Rudimentary investigations of microbial desulfurization have received little attention in the literature at this time (2). One successful example of desulfurization is the removal of pyrite from coal by Thiobacillus sp. and Ferrobaccus sp. (3). While studies of the complex hydrocarbon-sulfur systems are of great value, being closer to in situ reality, investigation of a defined system should form the foundation of these more detailed studies. 

For flotation to be most effective, reagents such as oil (collector) and surfactant (frother) must be added to the aqueous coal slurry. The collector adsorbs on the coal surface and makes it more hydrophobic, while the surfactant facilitates production of a stable froth. According to Leonard (26), the optimum coal sizes for froth flotation are between 50 and 140 mesh (0.3 and 0.106 mm). While conventional froth flotation will successfully remove minerals from coal, it has limited effect on the pyrite content, as pyrite tends to float almost as well as coal. Because of this, researchers have been looking for better ways to remove pyrite from coal. In addition, as previously mentioned, it is necessary to grind coal to very fine sizes in order to sufficiently liberate the mineral matter and pyritic sulfur. But, at these very fine sizes,... 

It is believed, therefore, that the separation-removal of pyrite from coal prior to its combustion would greatly reduce the sulfur dioxide emission and render many coal deposits within the new source performance standards. 

For separation of coal from relatively coarse shale and pyrite, gravity-based techniques have been effectively utilized. For sizes below 300 micrometers to about 100 micrometers, froth flotation has been used satisfactorily for separating coal from shales (3.). Even separation of pyrite from coal has been achieved by flotation (k). However, most of these processes become less effective when the particle size of the coal suspension is significantly below 100 micrometers. 

Hoffman, M.R., Faust, B.C., Panda, F.A. and Koo H.H., Tsuchiya, H.M. 1981, Kinetics of the Removal of Iron Pyrite from Coal by Microbial Catalysis. Applied Environ. Microbiology. 42 259-271. 

Andrews, G.F., Maczuga, J. 1984. Bacterial Removal of Pyrite From Coal, Fuel 63, 297-301. 

Hoffmann, M. R., B. C. Faust, F. A. Panda, H. H. Koo, and H. M. Tsuchiya. 1981. Kinetics of the removal of iron pyrite from coal by microbial catalysis. Appl. Environ. Microbiol. 42 259-271. 

SABA [Spherical Agglomeration-Bacterial Adsorption] A microbiological process for leaching iron pyrite from coal. The bacterium Thiobacillus ferrooxidans adsorbs on the surface of the pyrite crystals, oxidizing them with the formation of soluble ferrous sulfate. Developed by the Canadian Center for Mineral and Energy Technology, Ottawa. In 1990, the process had been developed only on the laboratory scale, using coal from eastern Canada. 

The concept of chemically removing pyrites from coal has not previously been advanced as a solution to the sulfur oxide air pollution problem because iron pyrites are not soluble in any known liquids. For example, the acids hydrochloric, hydrofluoric, sulfuric, or combinations of... 

An economically viable process for the chemical removal of pyrites from coal would require an oxidizing agent (most likely aqueous) which is (a) selective to pyrite, (b) regenerable, and (c) highly soluble in both oxidizing and reduced forms. Ferric sulfate and ferric chloride meet the above combination of requirements, and these reagents form the basis of the process chemistry described here. 

The use of iron-oxidizing autotrophs in the removal of pyrite from coal (Ashmead, 1955 Zarubina et al., 1959) and in the secondary recovery of copper and molybdenum from their sulfide minerals has already been reported (Bryner et al., 1954 Bryner and Anderson, 1957 Bryner and... 

The iron(III) produced may be used for further pyrite beaching these reactions are the basis of a process for the removal of pyrite from coal. 

Hessley, R.K. 1990. In Fuel Science and Technology Handbook, J.G. Speight (Ed.). Marcel Dekker, Inc., New York. Hessley, R.K., Reasoner, J.W., and Riley, J.T. 1986. Coal Science. John Wiley Sons, Inc., New York. Hoffmann, M.R., Faust, B.C., Panda, F.A., Koo, H.H., and Tsuchiya, H.M. 1981. Kinetics of the removal of iron pyrite from coal by microbial catalysis. Applied and Environmental Microbiology, 42(2) 259-271. Honda, H., Hirose, Y., and Yamakawa, T. 1959. Proceedings of the Symposium on the Nature of Coal. Central Fuel Research Institute, Jealgora, India, p. 238. 

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