Slag Posted on 21st December 20157th May 2021 by ThePD (The Project Definition) Slag is waste material separated from metals during the smelting or refining of ore. Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window) Related Posted in Technology and tagged metallurgy. ThePD (The Project Definition) ThePD has been developing the Preferred Project Definitions based on the actual project execution and operation experiences and knowledge with the Project Language, and sharing with you daily basis.