The heavy-metal elements (HMEs) in the slags severely restrict their reuse in the building materials. However, little is known about their leaching risks yet. In this study, three typical HMEs-containing metallurgical slags were collected, namely electrolytic manganese residue (EMR), lead–zinc slag (LZS) and electric-furnace ferronickel slag (EFS). Distributions of the HMEs in them were observed, and then the leaching behaviors and risks were investigated by experiments and modelling. The results show that Mn in EMR mainly exists as a soluble phase, while HMEs in LZS and EFS primarily exist as insoluble phases. Therefore, Mn is easy to leach from EMR in neutral solutions, while HMEs in LZS and EFS can hardly leach until the pH value drops to approximately 4. When HMEs that leached in acid solutions encounter neutral or alkaline environments, the leached HMEs will mainly be controlled by the complexation and precipitation according to the modelling.