Study on Properties of Cold-Bonded Briquettes Prepared from Return Fines of Sinter

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, wustite, and silicate in the periphery part, whereas there are calcium ferrite, wustite, 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 degrees C; moreover, the phases of melilite, Ca-2(Al, Fe)(2)O-5, and Ca(Al, Fe)(2)O-4 appear respectively at different temperatures as new bonding phases.