Enhanced column flotation performance for fine coal cleaning

Past studies have found that the froth flotation process is efficient in recovering heavy middling particles, which negatively affects the recovery-grade curve achieved for fine coal recovery. Experimental and theoretical results indicate that the recovery of middling particles can be reduced from 25% to 10% using flotation columns in a multi-stage cleaning approach, thereby improving the overall separation performance. Tests conducted on a -48 mesh coal sample found a 7% improvement in mass yield using a rougher-cleaner column circuit while producing a flotation concentrate containing 8% ash. Similar findings were obtained from the treatment of a -65 mesh coal sample using a different flotation column technology. To fundamentally evaluate the use of multi-stage cleaning, a continuous column model has been developed which incorporates selective and non-selective froth drop-back, and feed component flotation kinetics. For kinetic rate limiting conditions, separation performance was found to substantially improve with the use of multi-stage cleaning, which agrees with the experimental findings. Under carrying capacity conditions, the improvement is a function of the degree of selectivity in the detachment process. Economic justification of the use of multi-stage column treatment must be based on enhancements in product grade and/or mass yield.