A method has been developed which permits mineral oils, mineral oil-like substances or mineral oil-containing substances (eg waste oil) to be separated in powder form, even when these substance are present in a continuous phase with water (for example, oil slurries). A compound (eg. line) which forms a hydroxide with water is added, the formed hydroxide then acts as carrier substance. Prerequisite for obtaining the end-product in powdered form is that the homogeneous mixing of the oil-containing substance and hydroxide-forming substance takes place at a faster rate than the necessary auxilliary reaction, namely hydroxide formation, and further that water in present in at least stoichiometric quantities. The powdered end-product finds numerous applications eg. road construction, soil conditioning and compacting, recultivation measures in cement manufacture, and others.