Recovering Iron from Iron Ore Tailings and Preparing Concrete Composite Admixtures

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.