Synergistic utilization of diverse industrial wastes for reutilization in steel production and their geopolymerization potential.

Recycling wastes back into a manufacturing process, or into a separate product, is an important challenge. The primary aim of this work was to combine wastes from the steel industry, the galvanizing industry and the pulp and paper industry to form two new useful products. The steel industry generates the wastes red dust, mill scale, blast oxygen furnace slag and iron ore fines. Galvanizing industrial facilities dispose of sulfuric acid contaminated with iron. The pulp and paper industry produces the byproduct black liquor, which is high in lignin. Inserting these wastes as resources into the steel industry, or as stand-alone products, could reduce the need for virgin materials. The main methodology of the work was three-fold. First, spent sulfuric acid was used to precipitate the lignin from black liquor. Second, this lignin was combined with steel industry wastes and geopolymeric materials to make briquettes, a sustainable reducing material for steelmaking furnaces. Briquettes contained red dust, mill scale, blast oxygen furnace slag, iron ore fines and lignin precipitated from black liquor with spent sulfuric acid. Key research findings of compressive strength and weight loss testing showed the briquettes to be feasible for steel-making furnace use. Third, these steel industry wastes were investigated as a partial fly ash replacement in geopolymers. Main research findings were that compared to the control geopolymer, these geopolymer samples improved compressive strength and gave similar workability. Thus, the investigated wastes have the potential to both increase recycling in the steel industry and to improve geopolymeric products.