An Experimental Investigation of the Flotation of Residue Solids from Liquefied Coal

A semibatch flotation column has been used to investigate the feasibility of separating the mineral ash components from liquefied coal without the addition of a surfactant. The variables studied included the type of foaming gas and its flow rate, the ash concentration, the diffuser pore size, the length of foaming time, and the temperature profile along the column. For a suspension containing 4.6% ash, a separation up to 60% was achieved with a bulk liquid temperature of 110°C and a foam temperature of 65 °C. A temperature gradient between the foam and liquid was essential if separation was to be achieved. The best separation was obtained with a 50-μm average pore size diffuser. Separation using smaller pore size diffusers was more erratic but statistically in the same range. Very poor separation resulted from a 150-μm diffuser.