Abstract: The process consists essentially of injecting into slags and cinders derived from the manufacture and various treatments of irons, cast irons, steels, and non-ferrous metals while they are molten and before or during cooling thereof, dry pulverulent mineral compounds capable of releasing non-polluting gases by thermal dissociation (metallic carbonates in particular). The easily fragmented slags and cinders obtained are usable in many fields such as: building and construction, ground coverings, abrasives, water filtering, fertilizers for agriculture, etc.