Laboratory Investigation Of Bio-Heap Leaching To Remove Sulfur From Kiln Feed Materials

The west central Upper Peninsula of Michigan contains a large resource of graphitic slate. The slate has potential industrial use as a substitute for shale currently used in the production of portland cement. Some of the unweathered slate, however, has a high concentration of pyritic sulfur that can create emission problems when processed in a kiln. A low-cost method to reduce the sulfur content of the slate through the optimization of pyrite oxidation in a bio-heap leaching operation was investigated. In this study, optimal conditions for the bacterium Thiobacillus ferrooxidans were created to promote pyrite oxidation and, therefore, sulfur removal from the slate. Preliminary lab scale flask tests using crushed and sized slate (-40 + 100 mesh) and T. ferrooxidans bacteria in a sulfuric acid medium resulted in 70% oxidation of pyrite over a one-month period. Subsequent column leaching tests on coarser materials (-3/8+1/4 in.) operated for six months resulted in a maximum reduction of total sum of 75%. These data suggest that bio-heap leaching to remove sulfur from the slate for use as a kiln feed material is viable.