Abstract: Disclosed is a process to effect a reduction to a desired, constant degree as exactly as possible and to achieve a low surplus of carbon. The reduction by treatment with carbonaceous reducing agents is effected in such a manner that fine-grained solids, which contain higher metal oxides, are calcined at 800.degree. to 1100.degree. C. with hot gases in which the solids are suspended. The calcined solids are reduced at a temperature in the range of from 800.degree. to 1100.degree. C. to form low metal oxides in a stationary fluidized bed, which is supplied with carbonaceous reducing agents and oxygen-containing gases. The carbonaceous reducing agents are supplied to the stationary fluidized bed at such a rate so as to reduce the higher metal oxides to low metal oxides, while maintaining the reduction temperature in the stationary fluidized bed and insuring that the discharged matter has the desired carbon content.

Abstract: A process for the calcining of limestone or hydrated lime by thermal treatment thereof with hot gases in an oxidizing atmosphere in a rotary kiln through which the kiln atmosphere and the charge are countercurrently passed, which kiln is fed with fuel from shell burners, is described. The invention resides in the use of different fuels which release different quantities of SO.sub.2 and SO.sub.3 per unit of calorific heat. The fuel which releases the larger quantity of SO.sub.2 or SO.sub.3 per unit value of calorific heat is supplied to the upper portion of the rotary kiln, and the fuel which releases the smaller quantity of SO.sub.2 and SO.sub.3 per unit of calorific heat is supplied to the lower portion of the rotary kiln.