Phase evolution of stainless-steel pickling sludge and blast-furnace gravity dust during high-temperature process

Abstract

Stainless-steel pickling sludge (SSPS) and blast-furnace gravity dust (BFGD) are solid wastes and hazardous materials produced during iron- and steel-making processes and are important secondary metallurgical resources. The comprehensive use of these two materials shows important environmental significance and economic value. Herein, the elemental content, phase composition, and microstructure of SSPS and BFGD samples were then analyzed. Then, a high-temperature process for SSPS, BFGD, and their mixtures (mass ratio of 1:1) in air and N2 was analyzed by thermogravimetry and differential scanning calorimetry, and the high-temperature calcination products were identified and analyzed using X-ray diffraction. In air, the mixture of SSPS and BFGD can generate SFCA after roasting at 1200 °C. In N2, the carbon in the BFGD reduced the CaSO4 in SSPS to CaS. Based on the high-temperature phase-transformation behavior of the SSPS and BFGD mixture under aerobic and anaerobic conditions, a novel process flow of mixture pelletizing‒sintering agglomeration–blast furnace smelting was proposed for the synergistic treatment of SSPS and BFGD. This process is expected to provide innovation for stainless steel production enterprises to realize the closed circuit recycling of solid waste without leaving the factory.