In a process for the treatment of at least one mixture of solid and liquid waste substances which contains at least one metal such as Fe and/or compounds thereof, for example oxides, the mixture occurring in a condition in which it can be used at least only with difficulty, the mixture is at least extensively homogenized and mixed with at least one very fine-grain dry substance containing fly ash and/or coke. The resulting mixture is of such a nature, for example being at least predominantly in the form of agglomerates, that it can be fed to a thermal procedure, possibly after a grading operation.