In the future, waste incineration will become increasingly important, and so will the recycling of the resulting residues. This work is part of the K1-MET Project 1.3 "Resource Efficient Copper Refining Process" and primarily focuses on the enrichment of copper and copper-containing metals from residues of waste incineration plants. To make the sorting of waste incineration slags with sensor-based sorting systems possible, a sufficient breakdown of the sample surface must be achieved beforehand. The term "sufficient" indicates that the necessary breakdown for efficient separation can vary depending on the downstream sorting system. To achieve this sufficient breakdown, the slag surface must be treated before the sorting step, and the achieved breakdown must also be described. The aim of this work is to develop a surface treatment procedure and a methodology to assess the degree of liberation achieved. Various surface cleaning methods are tested on a laboratory scale. Methods for evaluating the efficiency of the achieved liberation are developed and compared. In addition to the test work at the Chair of Mineral Processing, a pilot scale test is conducted in cooperation with industry using a LIBS sorting system to implement the findings from the laboratory trials on an industrial scale. In the course of this work, a liberation procedure was developed. A procedure based on digital image processing proved to be an objectifiable description of the breakdown and breakdown rate, alongside the measurement of the mass loss of the slag granules. Initial results with the sensors of industrial sorting systems demonstrate the improved detection of copper.