Flocculation and flotation of coal by adhesion of hydrophobic Mycobacterium phlei

Separation of fine coal particles from the associated mineral matter is achieved either by flotation or flocculation. Such a separation process relies on the surface modification of the components involved. Flotation is mainly accomplished with the addition of a suitable collector molecule to the coal slurry and flocculation makes use of synthetic flocculants such as polyacrylamide and polyethylene oxides. In the latter case, the interaction between coal particles and the polymer flocculant is considered to be non-specific and often results in inefficient flocculation. In the present study a microorganism, Mycobacterium phlei, has been used as a bioflocculant in the separation of combustibles from Illinois #6 and Kentucky #9 coals. This bacterium was reported to be negatively charged and highly hydrophobic. The flocculation phenomenon was explained based on the interactions between the coal particles and the bacteria. The results suggested that the hydrophobic interactions play a dominant role. The aggregated coal flocs were found to contain some pyrite and mineral matter due to similar settling velocities. However, improved separation of combustibles was accomplished by column flotation using a frother and nitrogen gas.