Feasibility of improving the quality of dirty manganese ores in furnaces used for the liquid-phase reduction of iron

Abstract

The known reserves of manganese ores in Russia are presently estimated to be 150 million tons. The deposits located on the eastern flank of the North Ural Mountains (Polunochnoe and Marsyatskoe), in the Kemerovo Region (Usinskoe), and the Krasnoyarsk Province (Mazul'skoe) are sedimentary carbonate deposits and were formed in the Cenozoic and Paleozoic eras.Most of these deposits are composed of such minerals as calcium rhodochrosite (CaMn)CO3, oligonite (FeIMn)CO 3, psilomelane MnO2.MnO-nH20 , and pyrolusite MnO 2.Based on the chemical composition of their minerals, these ores (Table 1) can be classified as dirty low-grade manganese ores with a very low value of the ratio Mn:Fe (1:6). This precludes their use tor making ferromanganese in blast furnaces.As is known, the indicated ratio should be greater than 10 in order to make the higher grades of ferromanganese (Mn > 75%). Such a value is necessary due to the significant difference in the coefficients that characterize the transfer of Mn and Fe to pig iron (in a blast furnace, these coefficients are equal to 0.6--0.8 and 0.996, respectively). For example, the consumption of an ore with a Mn content of 50% will be as follows in the production of ferromanganese (82% Mn, 2% Si, 10% Fe, and 8% C): 82/50 x 0.8 = 2.05 tons/ton alloy. Then the maximum allowable iron content of the ore will be: 10:2.05 = 4.87.Thus, the value of the ratio Mn:Fe in the given case cannot be less than 50:4.87 = 10.3.The ratio of Mn to Fe is almost never improved by the beneficiation of ore, since iron enters the crystalline lattice of the manganese-bearing ore minerals and is transferred completely to the concentrate. The only way to increase the value of this index by an order of magnitude or more is liquid-phase reduction of the iron, such as in a Romelt furnace (invented by V. A. Romenets, A. V. Vanyukov, and E. E Vegman in 1979). The process yields synthetic high-quality fused manganese ore for blast furnaces.In the Romelt furnace (useful volume 140 m 3, hearth area 20 m 2, capacity up to 700 tons of conversion pig iron a day) built at the Novolipetsk Metallurgical Combine, about 50,000 tons of pig iron containing 0.1-0.3% Si, 0.1-0.2% Mn, 0.03-0.05% S, 0.1% P, and 4.4% C have been obtained thus l:ar in trial heats [1, 2]. Since there is no coke column in this furnace, the manganese and silicon undergo almost no reduction during the refining operation and the oxides of these metals remain in the slag; the coefficient characterizing the transfer of iron to the pig iron is 0.98. Thus, a real possibility has arisen for the almost complete separation of manganese from iron and the production of a fused manganese slag with a very low iron content and an extremely high Mn:Fe ratio (200 or more).Two trial heats were conducted in the furnace in 1988 to obtain ferromanganese with the use of sinter produced from high-quality Nikopol' manganese ore (Mn:Fe = 10.85). In both cases, the pig iron contained only 0.25-2.85% Mn. Changing the basicity of the slag within a broad range of values (CaO:SiO 2 ...