Coal washing

The KDF filter was first tested in prototype on a coal mine in northern Germany. It was installed in parallel with existing vacuum filters and it produced filter cakes consistendy lower in moisture content by 5 to 7% than the vacuum filters. Two production models have been installed and operated on a coal mine in Belgium. The filter is controlled by a specially developed computer system this consists of two computers, one monitoring the function of the filter and all of the detection devices installed, and the other controlling the filtration process. The system allows optimization of the performance, automatic start-up or shut-down, and can be integrated into the control system of the whole coal washing plant. 

De-watering of coal, tin, copper or gold mines, coal washing and sludge pumping Pumping industrial effluents... 

Amongst the products made by polymerisation casting are propellers for small marine craft, conveyor buckets used in the mining industry, liners for coal washing equipment and main drive gears for use in the textile and papermaking industries. 

Figure 8. Relations between benzene solubility and total (pyridine) solubility 273 g ZnCl2, 50 g coal Wash (M)> benzene ( 7), HzO (%), HCl...

In the froth flotation cell used for coal washing, illustrated in Figure 1.48, the suspension contains about 10 per cent of solids, together with the necessary reagents. The liquid flows along the cell bank and passes over a weir, and directly enters the unit via a feed pipe and feed hood. Liquor is discharged radially from the impeller, through the diffuser, and... 

Figure 1.48. A Denver flotation cell for coal washing...

In removal of sulphur from coal gas In nonferrous smelting industries In mineral separations (e.g. coal-washing)... 

Preliminary studies have shown that it is possible to remove over half of the potentially toxic trace elements present in coal when the mineral matter is reduced by coal washing. When coal is burned in a power plant, about 13% of the mercury and about 50% of the lead and cadmium may remain with the fly ash. Analytical chemical techniques have been developed to determine Hg, Cu, Cr, Mn, Ni, Cd, Pb, and F in coal and fly ash. These techniques produce accurate and precise results despite the fact that there are no coals with established trace element content, except for mercury. 

Two trace element studies are being done to answer some of these questions. The first study, funded by the Environmental Protection Agency, concerns coal washing and is designed to determine the distribution of certain trace elements in coal. The various specific gravity fractions of coal are separated by a sink-float procedure. Commercially available organic fluids are used as the separation media. 

Material balances are done where possible to check overall precision and accuracy. In the coal-washing study, material balances are always possible. In cases where enough data for statistical calculations has not been accumulated, an arbitrary limit of 15% for acceptable material balances has been set. 

Fluorine. Tables X, XI, and XII show the results obtained for fluorine in the coal-washing study with coals from Pennsylvania, Iowa, and West Virginia. In all three coals, the fluorine appears to be associated with the mineral matter in the coal. Therefore, removal of the higher specific gravity fractions would lower the fluoride content of the remaining coal. 

Lead and Cadmium. Table XV shows the results obtained in the coal-washing study for cadmium and lead in a Hazard No. 4 coal from... 

Coal washing is a process by which mineral matter is removed from coal by the use of any one of several washing processes to leave the coal as near mineral-free... 

Examples of the kinds of fine solids that have been separated from suspension in the form of floes or spherical agglomerates include phosphate ore particles from water, calcium phosphate from phosphoric acid, soot from various aqueous process streams, coal particles from coal-washing slurry, and iron ore from aqueous tailings [324-326],... 

For the alkali-treated coal washed subsequently with HC1, levels of Mn, Pb, Rb, Sr, and Zn were reduced by 75% or more, while levels of Ba, Cd, Cr, Ni, and Se, were reduced by 30-60%. The coal that had been pretreated showed reductions of 75% or more for Mn, Pb, and Zn, while Cd and Ni were reduced by 60% or more. It is interesting to note that every alkali and alkaline earth metal determined was enriched in the pretreated coal relative to the coal that was leached with no pretreatment. Some of these, such as Ba and Ca, were more concentrated in the pretreated coal than in the raw coal. The high Cu concentration in the coal which was pretreated is a result of contamination from the stirrer used in the autoclave. The relatively high Cu levels in this sample caused an interference in the Zn determination. A different autoclave and stirrer was used for the non-oxidative treatments. 

---