Lowering Reduction Temperature of Iron Ore and Carbon Composite by Using Ores with High Combined Water Content

Abstract

The steel industry is facing two difficult and urgent tasks to reduce CO 2 emissions and to use low-grade iron resources effectively. The utilization of an iron ore-carbon composite is one of the promising methods to solve the former. The latter is concerning to goethite ores such as Australian Marra Mamba and pisolite ores, which contain high concentration of combined water. In this study, the effect of combined water on the reduction behavior of the iron ore-coal composites at elevating temperature was examined under inert gas flow.Below 1 200 K, the reduction of iron oxide in Marra Mamba ore-coal and pisolite ore-coal composites proceeded faster than that in hematite ore-coal composite. It can be attributed to the larger specific surface area of the ores after decomposition of the combined water. Metallic iron also formed at lower temperature in the composites containing Marra Mamba and pisolite ores. The generation rate of CO gas from these composites showed the maximum value at approximately 1 170 K; however, that from the hematite-coal composite gave no peak, because formed metallic iron could act as a catalyst for the gasification of carbon. These results indicate that the reduction of ores with high combined water concentration can proceed at lower temperature. Above 1 373 K, however, the reduction rate of these ores in the composite significantly decreased due to a drastic decrease in the specific surface area of the ores and the formation of slag.KEY WORDS: ironmaking; iron ore-coal composite; reduction degree; combined water. centration of combined water and gangue minerals in different iron ores on the reduction and gasification behaviors of various composites were systematically evaluated at a constant heating rate. Experimental ProcedureFive types of iron ores: one hematite (H1), two Marra Mamba (M1 and M2) and two pisolite (P1 and P2) ores with particle sizes from 105 to 250 mm were used to prepare the composites. The chemical composition and loss on ignition (LOI) of these ores are shown in Table 1. The weight change in these ores was measured by TG-DTA (20 K/min, Ar: 1.66ϫ10Ϫ6 Nm 3 /s) to understand the dehydration behavior. The ores were heat-treated for 1.8 ks under Ar atmosphere at 673 K and for 3.6 ks in air at 1 073 K. And, the specific surface area of these ores was measured. Noncoking coal (VM: 36 %, fixed carbon: 56 %, ash: 8 %) having size of Ͻ44 mm and graphite reagent (average particle size: 20 mm) were used as a carbonaceous reductant.The ratio, C/O, which was defined as the molar ratio of fixed carbon in coal to oxygen in iron oxide, was 0.8. Powders of ore and coal were well mixed without reducing the particle size. Then, the mixed powder was press-shaped under a pressure of 9.8ϫ10 7 Pa. A composite sample with 10 mm in diameter and 10 mm in height was obtained. Figure 1 shows a schematic diagram of the a) sample holder and b) experimental system used for the reduction of the composite. The holder consisted of an alumina tube coated by platinum paste. Fifty alumina balls with 2 mm ...

Reduction Mechanism of Composite Consisted of Coal and Hematite Ore by Volatile Matter at 700–1100 K

“…It indicates that iron oxide acts as a catalyst for the cracking reaction. Similar result was obtained from previous study 15) and H 2 gas and carbon generated by decomposition of CH 4 gas have strong effect on reduction of iron oxide compared to CH 4 gas. 17) In the same temperature range, the amount of H 2 O gas generated increases due to reduction of Fe 2 O 3 by H 2 gas that is generated from decomposition of CH 4 gas, as shown in Eq.…”

Utilization of Ores with High Combined Water Content for Ore–carbon Composite and Iron Coke

“…These results suggest that the reduction reaction of iron oxide by carbon and hydrogen, which were produced from the volatile matter present in coal, proceeded below 1 100 K. 8) The generation rate of CO gas from the M-coal composite shows the local maximum value at approximately 1 160 K; however, the generation rate of CO gas from the H-coal composite remained constant up to this temperature. 8) The peak value of the generation rate increases with a decrease in the particle size of the iron ore. However, the peak value of the CO gas generation rate obtained above 1 300 K decreases with decreasing the ore particle size.…”

“…However, when C/O is higher than 1.3, this trend is reversed, and this temperature becomes lower than 1 400 K. The reason for this is that the slag, which has a low reducing ability, started to form at approximately 1 373 K because the FeO formed by the reduction of Fe3O4 reacts with the gangue in the ore, thus decreasing the reduction rate. 8) These results indicate that to lower the reduction temperature of the composite using high combined water content ore, it is desirable to complete the reduction reaction at a temperature below 1 373 K.…”

“…(6). Despite the physical property of ore 8) and its particle size, these temperatures corresponded with each other. Accordingly, this second increase in the gasification rate is caused by the increase in the reaction rate of Eq.…”

“…These ores contain higher amounts of gangue minerals as well as combined water since their major component is goethite, FeOOH. 7) In a previous study, 8) our group evaluated the effect of combined water content on the reduction behavior of iron ore-coal composites at elevated temperatures under an inert gas flow. However, the effects of the ore particle size and the mixture ratio of carbonaceous materials to iron ore were not clarified.…”