Development and evaluation of in-line disposal technology for chromium-containing solid wastes in the iron and steel industry

Chromium-containing metallurgical dust, slag and sludge represent solid waste in the iron and steel industry. Due to the complex characteristics, high heavy metal content, and large stock, they are tricky to be disposed of. This situation leads to an urgent need to establish a targeted categorization system for chromium-containing solid waste and to provide a corresponding disposal route. This study established a classification system for the disposal of chromium-containing solid waste and developed an online disposal process route for zero solid waste regeneration. This process used stainless steel slag, stainless steel dust, and pickling sludge as raw materials for blast furnace slag bath, AOD slag bath, and iron bath melt disposal technologies. The results show that in terms of heat balance, the AOD slag bath required the slightest total heat of 117.2 kJ/kg, while the iron bath needed the most significant total heat of 2 056 kJ/kg. In terms of material balance, the main product from the blast furnace using slag bath process was granular glass slag, achieving a vitrification rate of 99%. The residue substitution was 50%, and the amount of Cr leached after the preparation of cementitious materials was 0.017 mg/L. The AOD slag bath process mainly produced Fe-Cr-C alloy and low-Cr residue. When the residue substitution was 30%, the amount of Cr leached after the preparation of cementitious materials was virtually undetectable, and its compressive strength was 37.5 MPa. The main products of the iron bath process were Fe-Cr alloy and low Cr residue. When the residue substitution was 70%, the amount of Cr leached after the preparation of cast stone was 0.013 mg/L, and the flexural strength was 135.5 MPa. Finally, a new comprehensive economic index, CBI, was defined. The iron bath had the most considerable CBI value, indicating a competitive advantage. All three embedded online disposal processes can achieve low-carbon, energy-saving, safe, and zero-solid disposal of hazardous solid waste. The alloy products can be used in the steelmaking process, and the residue can be safely used as an alternative raw material for building materials.