The impact of indigenous microorganisms on coal flotation: A new perspective on water consumption

Abstract

Coal preparation plants are devoted to finding new strategies for reducing fresh water consumption, however, rarely taking consideration on slurry microorganisms. The impact of the abundant microorganisms on coal flotation, especially the isolated indigenous bacteria Bacillus sp. QX4 was systematically investigated in this study. Orthogonal experiments involved in parameters of concentration of microorganisms, collector and frother were conducted. The response surface analysis showed that the concentration of microorganisms was the main factor affecting flotation recovery and water consumption. With the amount of microorganisms increased from 105 to 108 cells/ml, clean coal yield decreased by 15 %, and water consumption increased by as high as 30 %. The characterization of the coal showed that the attachment of microorganisms increased the number of oxygen-containing functional groups onto the coal surface, and the contact angle of coal decreased from 79.5°to 56.6°. In addition, the net negative zeta potential decreased after microorganism addition, which improved the froth stability and weakened the coal’s attachment to the collector molecules. Further evaluation showed that the transfer of water reduced the calorific value of the clean coal by about 500 kcal/kg while increasing the carbon emission during combustion by about 5.9 %. This study provides a new perspective on the reverse impact of indigenous microorganisms on fresh water consumption and flotation product in coal flotation, which can potentially help efficient operation involved in optimizing water management of coal preparation plants.