The invention relates to a process for the hygienization of carbonation sludges. For this purpose, these are mixed with wastes having a high calorific value and containing organic substances and are decomposed by pyrolysis, in the absence of air, at a temperature from 200.degree. C. to 800.degree. C., preferably 250.degree. C. to 720.degree. C.
The fuel gases obtained in the decomposition by pyrolysis can be utilized for external heating of the thermal reactor, autothermic operation, that is to say self-sustaining operation, becoming possible when wastes of high calorific value are added to the carbonation sludge in such a quantity that the calorific value of the waste mixture is more than 1,000 kcal/kg.