A German process that cleans the coal and also reduces the moisture content to about 10%. Heavy oil is added to a coal slurry containing 50% to 60% water. On mixing, the coal particles become coated with oil and hence resistant to water, whereas the shale particles remain uncoated and easily wetted. By high-speed centrifuging the coal-oil mixture is retained in the centrifuge while the shale particles pass out with the water. The process is not as efficient as froth flotation.