Ultrafine Coal Cleaning using Selective Hydrophobic Coagulation

ABSTRACT

Studies have shown that ultrafine hydrophobic materials such as coal and graphite can be selectively coagulated and separated from hydrophilic impurities without using oily agglomerants, flocculants, or electrolytes. This process, which is referred to as Selective Hydrophobic Coagulation (SHC), has been used in laboratory tests to significantly reduce the ash and sulfur contents of several ultrafine, run-of-mine coal samples. The selective coagulation occurs at ζ-potentials significantly higher than those predicted by the classical DLVO theory due to the presence of an attractive interaction energy between hydrophobic particles such as coal. To account for this additional attraction, the interaction energies for the coal-mineral system have been calculated using an extended DLVO theory that incorporates the hydrophobic interaction energy in addition to the traditional dispersion and the electrostatic energies. The results of these theoretical calculations correlate well with separation response obtained using the SHC process.

Keywords:

• Ultrafine coal cleaning
• Selective coagulation
• Hydrophobic interaction
• DLVO theory

Acknowledgments

The authors acknowledge the financial support of the U.S. Department of Energy (Contract No. DE-AC22–90PC90174) and technical discussions with Dr. Z. Xu of the University of Alberta.