Recrystallization of Fe2O3 During the Induration of Iron Ore Oxidation Pellets
Magnetite and hematite concentrates are the two main raw materials for oxidized pellet production. Magnetite concentrates have more predominance due to the heat release by oxidation during roasting and may reduce energy consumption (Jiang et al., 2008; Li et al., 2009). However, with the continuous consumption of iron resources driven by the rapid development of iron and steel industry, magnetite resources are becoming scarce and so the development of pellet production is restricted to some extent. Thus, it is imperative to make better use of hematite resources to meet the raw material supply for pellet production (Xu, 2001).
Induration mechanisms of oxidised pellets prepared from mixed magnetite–haematite concentrates
Abstract The crystallisation behaviour of Fe2O3 during preheating and roasting of pellets made from mixed magnetite–haematite (M–H) concentrates has been studied. The results indicate that the strength of pellets is mainly provided by the crystalline connections between Fe2O3 particles during preheating. This occurs because the activity of Fe2O3 from secondary haematite (SH) (oxidised from magnetite concentrate, SH) is higher than from original haematite (OH). In the roasting process, when temperature is lower than 1250°C, the strength is mainly provided by the development, connection and growth of Fe2O3 crystalline grains from SH. Only if the temperature exceeds 1280°C does Fe2O3 recrystallisation in OH grains develop well with the iron ore particles in the pellets fully connected, so increasing pellet strength.
ROOM- AND HIGH-TEMPERATURE MAGNETIC PROPERTIES OF Sm(CobalFexCu0.088Zr0.025)7.5 (x=0.30) SINTERED MAGNETS
The effect of Fe content on room- and high-temperature magnetic properties of Sm(CobalFexCu0.088Zr0.025)7.5 (x=0-0.30) sintered magnets, prepared by the conventional powder metallurgy method, has been systematically studied. With increasing Fe content, the remanences BT and maximum energy products (BH)max at room temperature gradually increase and reach optimal values of 1.055 T with x=0.27 for BT, and 205 kJ/m3 with x=0.21 for (BH)max, respectively, and then drop sharply with further Fe increase. An excessive addition of Fe (x≥0.24) results in rapid deterioration of permanent magnetic properties due to the formation of a considerable amount of FeCo soft magnetic phase. It was found that the effect of Fe content on high temperature stability is huge. The lower the Fe content, the smaller the temperature coefficient of coercivity. When x=0.07, a temperature coefficient of coercivity of -0.14%/K (293-723 K) can be achieved, as compared with -0.23%/K for x=0.21. BT of 0.725 T, bHc of 517 kA/m, iHc of 764 kA/m, and (BH)max of 95 kJ/m3 at 723 K were obtained, and the B-H demagnetization curve remains a straight line.