Acidic decontamination sludges are currently unsuitable for final disposal due to their low pH and high concentrations of organic and complexing species, which hinder their direct stabilization and long-term management. In this work, an acidic liquid waste is immobilized using two types of alkali-activated slag binders, namely BFS-C and BFS-S, and the performance of these systems is compared with that of a reference Portland cement binder (R). In parallel, three stainless steel grades are evaluated as candidate materials for waste-conditioning drums intended for the containment of the immobilized waste. Electrochemical corrosion parameters are determined in order to assess the corrosion behaviour of the metallic materials when exposed to the different binder matrices. The results indicate that the duplex stainless steels 1.4482 and 1.4462, together with the austenitic stainless steel 1.4404, exhibit a moderate apparent tendency to corrode in the alkali-activated slag environment. However, surface examinations show that sulfide phases inherently present in the slag significantly influence the electrochemical response of the system. This effect leads to an overestimation of the actual corrosion activity derived from electrochemical measurements. Once this interference is taken into account, the results demonstrate that all three stainless steel grades are compatible with alkali-activated slag matrices and can be considered suitable materials for the confinement and conditioning of acidic liquid wastes.