Abstract: Improving the utilization rate of iron tailings is of great significance to promote the sustainable development of
iron ore mines. Sulfate-activated composite filling cementitious materials were prepared by co-combustion of iron tailings and
calcium oxide with slag. The effects of slag content on the fluidity,mechanical properties and microstructure of filling slurry
were systematically studied under fixed cement-sand ratio and mass concentration. The results show that the slurry expansion
decreases slightly with the increase of slag content. The strength of the filling body is significantly improved,but the strength increase
slows down after the content exceeds 50% . The microscopic analysis shows that abundant hydration products are formed
in the coexistence system of modified iron tailings and slag,and the hydration product network formed by the interweaving of CS-
H gel and ettringite significantly improves the compactness of the microstructure of the filling body. The synergistic mechanism
of the two is that the gel product generated by the rapid hydration of slag constructs the early strength skeleton,and the
modified iron tailings particles effectively fill the internal pores through the micro-aggregate effect,and its active components also
participate in the hydration reaction. The coupling effect of physical filling and chemical reaction significantly improves the
overall strength of the filling body. The scheme of modified iron tailings with 30%-50% slag content can achieve the balance
between performance and economic benefits,which provides new ideas and technical support for the resource utilization of iron
tailings.