The control of non-metallic inclusions is inevitable for the quality of cleanness-sensitive steels. As alkali oxides have already been used in mold fluxes to achieve lower melting temperatures, it is suggested that there could be a positive effect on the inclusion removal in secondary metallurgical slags. In this work, the dissolution of synthetic particles in multiple alkali oxide containing slags is studied on a laboratory scale using High-Temperature Confocal Scanning Laser Microscopy. This method enables the in-situ observation of inclusion behavior at steelmaking temperatures. Thermodynamic calculations using FactSage are additionally applied. In the experiments, Al2O3, MgO∙Al2O3 and SiO2 particles interact with slags containing different amounts of Li2O, Na2O and K2O. Significant differences in dissolution time for the specific particle types are observed. Moreover, the dissolution mechanisms are investigated.