Analysis of flotation of unburned carbon from bottom ashes

Bottom ash from power plants contains unburned carbon (UC) as a waste, which is a potential contaminant for the environment unless recycled as a source of energy. In the present study, separation of the UC (3.1%) from the bottom ash of a power plant has been studied. The overall grade of combustible matter for the concentrates ranged from 20.6% to 28.8 while the recovery levels varied from 45.7 % to 84.0%. A statistical analysis of the combustible recoveries according to a 3-variable 2-level (2(3)) factorial experimental design, examined the influence of dosages collector (kerosene) and frother (AF65) and also impeller speed. The main effects of all three factors on the recovery are positive. The most important factor is collector dosage, while the frother has a secondary significance. The effect of impeller (conditioning) speed is also statistically significant. Two of the 2-way interaction effects are significant. Recovery of combustible matter increases with an increase in the dosages of kerosene and AF65. The main and interaction effects involving kerosene consistently point out the selectivity of the flotation process for carbonaceous particles, which have been discussed in relation to dispersion and attachment of collector droplets to the particles, interfacial area and probable collecting properties of the frother used.