Iron ore tailings (IOTs) are a form of solid waste produced during the beneficiation process of iron ore concentrate. In this paper, iron recovery from IOTs was studied at different points during a process involving pre-concentration followed by direct reduction and magnetic separation. Then, slag-tailing concrete composite admixtures were prepared from high-silica residues. Based on the analyses of the chemical composition and crystalline phases, a pre-concentration test was developed, and a pre-concentrated concentrate (PC) with an iron grade of 36.58 wt % and a total iron recovery of 83.86 wt % was obtained from a feed iron grade of 12.61 wt %. Furthermore, the influences of various parameters on iron recovery from PC through direct reduction and magnetic separation were investigated. The optimal parameters were found to be as follows: A roasting temperature of 1250 °C, a roasting time of 50 min, and a 17.5:7.5:12.5:100 ratio of bitumite/sodium carbonate/lime/PC. Under these conditions, the iron grade of the reduced iron powder was 92.30 wt %, and the iron recovery rate was 93.96 wt %. With respect to the original IOTs, the iron recovery was 78.79 wt %. Then, highly active slag-tailing concrete composite admixtures were prepared using the high-silica residues and S75 blast furnace slag powder. When the amount of high-silica residues replacing slag was 20%, the strength of cement mortar blocks at 7 days and 28 days was 33.11 MPa and 50 MPa, respectively, whereas the activity indices were 89 and 108, respectively. Meanwhile, the fluidity rate was appropriately 109. When the content of high-silica residues replacing slag was not more than 30%, the quality of mineral admixtures was not reduced. Last but not least, reusing the high-silica residues during iron recovery enabled the complete utilization of the IOTs.

Steel slag CO₂ sequestration helps mitigate global warming and decrease the stockpile of steel slag (SS). Through orthogonal design tests and single-factor tests, this paper evaluated the effects of the water/solid mass ratio (w/s), gypsum ratio (G/SS), molding pressure, and curing duration on uniaxial compressive strength (UCS) and CO₂ uptake of the compacts. The results indicated that high w/s enhanced both strength and CO₂ capture ability. The proper addition of gypsum helps promote UCS increase and CO₂ uptake of steel slag. In addition, increasing the molding pressure can significantly improve UCS without reducing CO₂ uptake. The optimum conditions in the study were a w/s of 0.20, G/SS of 1/16, and molding pressure of 27 MPa, under which conditions 1 d UCS and CO₂ uptake were 55.30 MPa and 12.36%, respectively. Microanalyses showed that gypsum activates mainly mayenite in steel slag. An increase in water addition also increased the hydration and carbonation products greatly, and the strengthened molding pressure had a significant densification effect on micro-pore structures. The study gives guidance in the application of steel slag in CO₂ capture and manufacturing green construction material.