Smelting refuse is the process of melting down and purifying metals from their impurities. The four crossword solutions for this term are DROSS (5 letters), SCORIA (6 letters), SLAG (4 letters), and SCUM (4 letters). DROSS is a waste material that forms on the surface of molten metal, SCORIA is a type of volcanic rock that is a by-product of smelting, SLAG is a glass-like by-product of smelting that contains metal oxides and other impurities, and SCUM is a foam-like material that forms on the surface of molten metal.