Mill debris is a term used to describe the waste material that is produced during the milling process. SLAG is a type of mill debris that is composed of non-metallic materials such as ash, cinders, and clinkers. It is created when metal ore is heated and melted in a furnace, and the molten material is then poured into a SLAG pit. SLAG is often used in construction and road building projects, and can also be used as an aggregate in concrete.