Progress and trend of bulk utilization technology of metallurgical solid wastes in China

In China, the annual discharge of steel slag, red mud, copper slag, and most ferroalloy slag has reached 10–100 million tons; these slags are difficult to be resued due to poor utilization in the fields of cement, concrete, or road pavement. The difficult reusing of these wastes requires new theory and technology, particularly due to the huge scale and concentration in their distribution in China. This study analyzed the current situation of the bulk utilization of the abovementioned typical metallurgical solid wastes and summarized the causes of the problems hindering the utilization, including harmful components, low cementitious reactivity, fine particle size, instability in composition, and huge discharge amount in China, distribution concentrated in several areas for a kind of metallurgical solid waste. Owing to a huge market of 100 million tons or even 10 billion tons per year in China, aggregates, ceramic materials, and artificial stones are suitable for the bulk utilization of solid wastes. Relative research progresses in the low-cost preparation of sintered ceramsite from metallurgical slags, slag-based ceramic tiles and fired bricks, modification of molten slags for producing aggregates, and artificial stones directly converted from molten slags were reviewed. During these researches, an experiment on the industrial production of sintered ceramsite with mass fraction of 50%–65% red mud in its raw materials was conducted in a new 100-thousand tons production line. Ceramic tiles and sintered bricks with mass fraction of 40%–60% red mud or 30%–50% steel slag, or 50%–80% copper slag were respectively produced in the pilot-scale experiment and industry line. The direct conversion of molten slag into building materials is an energy-saving and carbon-reducing technology. An industrial experiment for modification of a molten electric arc furnace slag with mass fraction of 12.96% sand added during its discharge process without any energy supply was completed, and the modified slag was further converted into an artificial aggregate with qualified volume stability properties. A casting stone with low production cost was prepared directly from the modified molten slag in small-scale experiments using the “Petrurgic” heat treatment method. Finally, main trends of the utilization technology for the metallurgical slag were further put forward, including the large-scale utilization technologies, synergistic utilization technology for different solid wastes, energy-saving or recovery and carbon reduction technologies during the utilization process, and intelligent technologies integrated into the resource’s utilization process. Besides these four aspects, the change and improvement of approach toward solid wastes, management of solid wastes, and promotion of new technology applications for people in the production, treatment, and management departments in the metallurgical industry are especially important.