Treating solid fuel

A method of treating fine particles of solid carbonaceous fuel of the coal or coke type comprising

• (i) mixing the fuel particles with a liquid aqueous solution comprising essentially (a) sodium, potassium, or lithium hydroxide together with (b) calcium, magnesium, or barium hydroxide or carbonate, or a plurality thereof, with a ratio of (a) to the fuel of about 0.04 to 0.07 by weight, a ratio of (b) to the fuel of about 0.02 to 0.30 by weight, and a ratio of water to the fuel of about 1 to 10 by weight;
• (ii) heating the resulting mixture, at an elevated pressure, to a temperature of about 150.degree. to 375.degree. C in such a manner as to leach sulfur and ash from the fuel particles into the solution and to incorporate within the volume of the particles a significant amount of calcium, magnesium, or barium, or a plurality thereof;
• (iii) separating the fuel particles, as a solid phase, from the easily removable liquid phase of the solution;
• and
• (iv) washing the separated fuel particles;
• in such manner as to produce a clean, solid fuel having a lowered sulfur and sodium, potassium, or lithium content while containing calcium, magnesium, or barium, or a plurality thereof, to combine with sulfur remaining in the fuel particles during combustion, pyrolysis, or gasification thereof, whereby the combined sulfur can be retained in the char or the ash of the fuel.