To obtain a coke which is hard to react with CO2 gas of not less than 1,000°C and can be burned in a hearth.

To make a coke less reactive with CO2 gas at a high temperature of not less than 1,000°C, preferably the surface of the coke is coated with a nonreactive material. As the material to coat the coke surface with, an inorganic material powder such as minerals and the like is used. By sprinkling it on the coke, coating the coke with a slurry of the inorganic material powder and water, a solvent or the like, or coating the coke with cement or the like, the pores of the coke are filled and the surface area of exposed carbon is significantly reduced to control the reaction. The resolution loss reaction at a high temperature area in a burning or melting furnace can be suppressed and the thermal energy which a fuel contains can be used with the maximum efficiency. The fuel consumption to burn, melt and solidify industrial waste or to melt various metals or the like is reduced as well as the emission of carbon dioxide. The dust generation is remarkably reduced by coating the coke surface and the working place environment is improved.