Return fines of sinter (return fines) are used to prepare cold‐bonded briquettes (CBBs). The reduction disintegration index (RDI) of RDI+3.15 and compressive strength after RDI experiment of CBB are higher than that of the sinter. For microscopic morphologies after RDI experiment, cracks initiate in the area of the return fines but do not propagate through the whole matrix of CBB. The reduction index (RI) of CBB is lower than that of the sinter; conversely, the compressive strength of CBB after RI experiment is higher than that of the sinter. For phase composition after RI experiment, there are phases of metallic iron, wüstite, and silicate in the periphery part, whereas there are calcium ferrite, wüstite, and silicate in the core part. The reduction behavior of CBB can be improved by decreasing the volume of CBB and adding coke in the CBB. The return fines are bonded by the compound binder in two ways: forming a mutually interlaced reticular structure and a dense and acicular solid connecting bridge. For the phase change of the compound binder with temperature, the total content of bredigite is above 63% at 300 to 1100 °C; moreover, the phases of melilite, Ca2(Al, Fe)2O5, and Ca(Al, Fe)2O4 appear respectively at different temperatures as new bonding phases.
Return fines of sinter is now being utilized in blast furnaces straight after cold briquetting, a novel method of return fines utilization. [1][2][3][4] This technique can prevent return fines from being repeatedly sintered at high temperatures. On the one hand, it can lower the amount of energy used by the sinter plant, and on the other, it can increase the output of the sintering process. The compressive strength, reduction degradation index, and reducibility index of coldbonded briquette prepared from return fines are close to those of the sinter, which is acceptable for use in a large blast furnace. Cold-bonded briquette prepared from return fines has successfully substituted 5-10% of the sinter in a 2800 m 3 blast furnace in Gansu Province, China. [1,4] However, the lack of knowledge regarding the cold-bonded briquette prepared from return fines' reduction kinetics in the blast furnace prevents further advancements in the cold-bonded briquette prepared from return fines' utilization ratio.Numerous studies have investigated the reduction kinetics of sinter under varying conditions. The sinter's porosity, particle size, and chemical composition affect its reduction kinetics. [5] For instance, sinter with greater porosity or with a large number of microscopic pores is usually reduced more quickly because the pores enable the reducing gas to reach the reaction's interface. However, macropores (>0.125 mm) are more crucial than micropores for the increased reduction rate of sinter because the reduction front of fine pores (<0.125 mm) is complex and irregular. [6] The reduction rate usually increases with the decreasing particle size of the sinter, and varied iron
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