Characteristics of Calcium-Aluminate Slags and Pig Iron Produced from Smelting-Reduction of Low-Grade Bauxites

Abstract

Low-grade bauxite ores are not favorable in the conventional Bayer process for alumina production, as they are producing more bauxite residue (red mud) and accompanying lower alumina yield than high-grade ores. In the current study, the thermodynamics and characterization of calcium-aluminate slags and pig iron produced from smelting reduction of high iron-and silica-containing bauxites are studied. Coke and limestone are used to reduce the iron oxide and adjust the basicity of slag during smelting. There is evidence that complete iron separation from bauxite is feasible through smelting-reduction process, and up to 99.9 pct of iron can be eliminated. Moreover, it is shown that the partial separation of silicon, titanium, and other elements from the Al 2 O 3 -containing slag occurs. The phase compositions and the distribution of elements between the metal and slag phases provide information about the high-temperature behavior of the bauxite components during smelting reduction. Employing electron microscopy analysis, it is indicated that the morphologies of CaOAEAl 2 O 3 , 12CaOAE7Al 2 O 3 , 2CaOAEAl 2 O 3 AESiO 2 , and CaOAEAl 2 O 3 AESiO 2 phases in the slag, as well as the complex oxides of Ca-Al-Si-Ti in the slag behave differently as the mass ratio of Al 2 O 3 / (Fe 2 O 3 + SiO 2 ) in the bauxite changes. It is also shown that the phases of slag produced from smelting-reduction below 5 K s À1 of cooling rate are proper for further leaching process.

Semi-Smelting Reduction and Magnetic Separation for the Recovery of Iron and Alumina Slag from Iron Rich Bauxite

“…The optimal anthracite ratio is 11.92 wt % at the w(CaO)/w(SiO 2 ) ratio, reduction time, and temperature, of 1.25, 15 min, and 1425 • C, respectively. Compared with the smelting reduction of the low-grade bauxites and red mud, the utilization rate of the pulverized coal of the semi-molten reduction process is very high, and the unreacted carbon content in the slag is only about 0.6 wt %-1.2 wt %, which is much lower than that of the unreacted coke of the smelting reduction process [23,26].…”

“…In addition, the pig iron nugget is excellent for its ease of shipping, handling, and storage. Imanasa et al [23] studied the characteristics of calcium aluminate slags and pig iron produced from the smelting reduction of low-grade bauxites. The studied results show that the recovery rate of iron can reach from 94.8 wt % to 99.9 wt %, the amount of slag reached 70%-85%, and the unreacted coke particles can float over the molten slag phase at elevated temperatures.…”

Reductive Smelting of Neutralized Red Mud for Iron Recovery and Produced Pig Iron for Heat-Resistant Castings

“…Gehlenite and perovskite are not present in slag at 1750 °С, and the main slag phase is di-calcium silicate (γ-Ca2SiO4). This may be explained by the shifting of the slag composition to the larnite primary phase field [48]. At 1700 • C, as the SiO 2 content in slag decreases due to silicon reduction into the metal, and the slag composition shifts from the gehlenite primary phase field towards the larnite primary phase field, which leads to an increase of its content in the slag.…”

“…Gehlenite and perovskite are not present in slag at 1750 • C, and the main slag phase is di-calcium silicate (γ-Ca 2 SiO 4 ). This may be explained by the shifting of the slag composition to the larnite primary phase field [48].…”

On the Direct Reduction Phenomena of Bauxite Ore Using H2 Gas in a Fixed Bed Reactor

“…Significant research efforts on the Pedersen Process at NTNU [9,10] recently have basis in earlier unpublished work. The results and conditions are sufficiently promising to revive it in a modernized form considering the importance of sustainable approaches in the metallurgical industries.…”