Abstract:

Steel slag contains metallic iron and its oxide, which are high value‐added renewable resources, and it can be utilized as a mineral admixture in the building materials industry. After different cooling treatment processes, the phase of steel slag evolves, thus affecting the recovery of iron in steel slag and the cementitious activity of tailings. In order to improve the recycling of iron resources in steel slag and the effective utilization of tailings, this paper studied the steel slag of three different treatment processes, namely, hot splash, roller crushing‐pressurized hot stewing and roller crushing‐hot splash. It used petrography analysis, XRD, SEM‐EDS, and chemical phase‐selective dissolution, and other methods to analyze the distribution of the iron phases and the state of enrichment of steel slags, and to determine the rate of magnetic separation powder and iron grade, and the cementitious activity of tailings. The results show that: the metal iron is easier to be enriched and deposited under the hot splash process, and the iron phase is mainly in the form of FeO uniformly distributed in the RO phase and the ferrite phase, with less Fe in the phase, and the yield of magnetic separation powder is higher, but the grade is poorer, which is 32.22% and 33.43%, respectively. After roll crushing‐pressurized hot stewing, no obvious metal iron particles can be seen in the slag; Fe in the phase accounts for more, and the yield of the magnetic separation powder is low but the grade is higher, which is 28.37% and 37.12%, respectively; after roll crushing‐hot splashing, the iron phase mainly exists in calcium ferrite phase and silicate phase in the form of Fe₂O₃, Fe in the phase accounts for more and contains Fe₃O₄, and the magnetic separation powder has high yield and high iron grade, which is 37.60% and 39.69%, respectively. Under roll crushing‐pressurized hot stewing, the C₂S content in steel slag is relatively more and better developed, and has high cementitious activity, 7 d and 28 d activity index of tailings is 78% and 92%, respectively; the 7 d activity index of the roll crushed‐hot splash slag is low at 66%, but the 28 d activity index grows to 92%; the cementitious activity of the hot splash slag is in the middle.

Key words: steel slag treatment process, iron occurrence state, mineral composition, magnetic separation, cementitious activity