A Study of the Effect of Aluminium on the Mechanochemical Reduction of Hematite by Graphite

Abstract

The effect of addition of small amounts of aluminium on mechano‐chemical reduction of hematite by graphite was studied. Various amounts of aluminium (0 to 10%) were added to a hematite‐graphite mixture, in which C/O ratio was 1:1. The hematite‐graphite‐aluminium mixtures were then subjected to ball milling followed by heating up reduction. The heating up reduction was carried out in Ar atmosphere, using TG‐DTA device. In TG‐DTA experiments, samples were heated by a constant heating rate of 10 °C/min from room temperature up to 1100 °C and maintained for 30 minutes at this temperature. To clarify the reactions which took place during milling and heating up reduction, the samples were subjected to XRD examinations. It was found that the heat generated during exothermic reaction of aluminothermic reduction of hematite promoted the endothermic reaction of carbothermic reduction. In the course of heating up reduction, the carbothermic reaction occurred just after aluminothermic reaction. Increasing of aluminum content from 0 to 10% in 2 hours ball milled samples decreased the temperature of carbothermic reaction from 1020 °C to about 860 °C. The further ball milling of the samples up to 5 and 10 hours, for the samples containing 10 and 5% aluminium respectively, caused the decrease of the temperature of aluminothermic and carbothermic reactions to around the melting point of aluminium.

Effect of iron on mechanical activation and structural evolution of hematite–graphite mixture

“…Although the reduction of iron oxides during milling of the H-G mixture has been reported, it has been always emphasized that H could not be completely reduced to metallic iron by carbon due to mechanical milling [8,[10][11][12][13]. It is because the stored energy in the H-G mixture due to milling (even in extended milling times) could not provide the sufficient energy for highly endothermic reduction reactions of iron oxides by carbon to produce metallic iron.…”

“…Since, the stored energy in the mixture is significantly affected by the physical, chemical and mechanical properties of the powder mixture, the total amount of stored energy meaningfully varies in the presence of different components [1][2][3]8]. The considerable influence of the presence of aluminum on increasing the stored energy in the H-G mixture due to mechanical milling and consequently on its subsequent reduction process has been reported [8].…”

“…Because of the importance of the reduction of iron oxides by carbonaceous materials as well as present difficulties in this subject, a great deal of studies have been carried out on mechanical activation (MA) of iron oxides and their mixtures with reductant materials and its effect on increasing the rate of the reduction reaction [5][6][7][8][9][10][22][23][24][25]. Grohn et al [26] in 1966, for the first time, investigated the mechanochemical reduction of hematite (H) by carbon at ambient temperature.…”

“…Thus, the most significant feature of the mechanochemical processes is that they intensely affect the structural conditions of the mixture by which they activate the powder mixture and extremely influence the kinetics of chemical reactions between particles. The intensity of the induced changes in the microscopic characteristics of the mixture highly depends on the physical, chemical and mechanical properties of the materials as well as the milling parameters such as the type of the mill, rotation speed, the milling time and the milling atmosphere [1][2][3][4][5][6][7][8][11][12][13]. In fact, mentioned factors affect the structural conditions through their influential role in the transferred energy to the mixture due to milling.…”

Lead immobilization in mechanochemical fly ash recycling

“…These results clearly indicate that PbO was reduced to Pb during MC treatment, probably in a process similar to the MC reduction of metal oxides reported in previous research. [17][18][19][20] Because the solubility constant of PbO (0.107 g/l) in water is much higher than that of Pb (3.1 × 10 −4 g/l), the immobilization of Pb by MC treatment may result from the reduction of the PbO.…”