Abstract: A high yield active carbon is obtained from brown coal, lignite and similar carbonaceous materials. The brown coal is converted into a potassium-coal by reaction with an aqueous solution containing potassium ions; the potassium-coal is carbonized (pyrolysed) and the char so produced is leached to remove the bound potassium ions. The potassium-coal can be tabletted or extruded prior to the carbonization. Surface areas of up to 1500 m.sup.2 /g have been observed in the product. Additional activity can be achieved by subjecting the product to a conventional activation process.