<p>A method comprising: a step in which unburned carbon contained in coal ash is mechanically separated with a classifier; a step in which the coal ash from which part of the unburned carbon has been removed with the classifier is pulverized or disaggregated with a pulverizer; a step in which water is added to the coal ash pulverized or disaggregated with the pulverizer to obtain a slurry; a step in which a scavenger is added to the slurried coal ash; a step in which a shear force is applied to the slurry containing the scavenger to cause the scavenger to selectively adhere to the unburned carbon contained in the coal ash; a step in which a foaming agent is added to the slurry in which the scavenger has adhered to the unburned carbon; and a step in which the unburned carbon is floated on the slurry containing the foaming agent together with bubbles and is separated.</p>
