Abstract: Fuel briquettes on the basis of solid organic combustible material, notably biomass material such as straw or other agricultural, horticultural and silvicultural waste or organic household waste, or fine particle industrial waste obtain a satisfactory storing and transporting quality when the binder therein is 3-50% by weight of fly ash coke. Fly ash coke is the carbon rich fraction separated from the mineral components of fly ash, preferably by flotation under specified conditions. The briquettes are otherwise prepared in briquette presses according to the teachings of the art. Preferably there is used a nozzle pressure for the extrusion of 70-100 kg/cm.sup.2 and it is advantageous to preheat the raw materials to 50.degree.-70.degree. C. before conveying them to the briquette press.

Abstract: Flotation of fly ash to recover coal contained therein is carried out in at least two steps, pH of the flotation slurry in the first step being 6-8, and in the last step lower than in the first step and below 6.5, preferably in the range of 3-5. The temperature may be ambient but is preferably 30.degree.-60.degree. C. As collector and frother several of those commonly employed are usable, preferably gas oil and pine oil, respectively. Desired pH is preferably achieved by sulphuric acid if desired in part by acidic flue gases. There is obtained separation into an almost carbon-free ash fraction and a carbonaceous fraction of low ash content.