The environmental performance, and particularly the leaching behavior, of a slag is a function of its chemical composition, crystalline phases’ assemblage and particle size distribution (thereby specific surface area), for a given environment. Although slags from different smelters differ in characteristics, the majority of non-ferrous metal production slags consists of similar phases that differ in proportions. Understanding the relative leachability of these different phases would allow to adjust the operating process parameters so as to promote formation of leaching-resistant phases which facilitates downstream slag applications.