Graduate Thesis Or Dissertation
 

Bioleaching of coal in a fluidized bed

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/g158bk80b

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  • Illinois coal ground to 80-200 mesh was leached with a low phosphate, high nitrogen medium containing a mixture of Thiobacillus ferrooxidans and thiooxidans in a fluidized bed. Coal slurries of 20-160 g/L were treated in a 5 cm ID, 9.5 m high continuous loop bioreactor with crossovers at top and bottom, and a volume of 41.3 L (11 gal). Air introduced into the bottom of one side at 1500 cm³/min oxygenated the system and caused a rapid continuous circulation. Fresh medium was added to the top of the reactor at the same place air was vented, while coal-free leachate was continuously removed from the bottom of the reactor; the flowrate being 1.9 cm³/min with a liquid residence time of 15.2 days. This produced about 20 gal of drained leachate plus what was still in the column at the end of a 28 day run. Temperature, pH and dissolved oxygen concentration were monitored. Atomic absorption spectrophotometer (AAS) analyses of the leachate (drained and in column) plus leached and unleached coal indicated significant leaching of sulfur, iron, calcium, lead, magnesium, sodium, chromium, nickel and gold (0.4 ppm in leachate). AAS readings for silicon, titanium, platinum and arsenic (column samples only) suffered from high detection limits due to noise or other difficulties with the atomic absorption unit used and, consequently were not detected. A significant level of Arsenic was detected in the concentrated coal extracts, which indicated that leaching had occurred; however, data scatter was large. A small amount of aluminum was also leached. Shake flask experiments were also carried out to compare surfactant levels, coal type, the effect of a filtered inoculum (ferric sulfate but no bacterium), and the controls,. These results were related to the reactor data to develope parameters describing the effect on leaching of variation in coal type and slurry concentration for various elements. The efficiency of the reactor compared to shake flask work was also determined.
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