Aspects of the High-Temperature Reduction of Manganese Ores by Coal

Abstract

The existing technology for producing ferroalloys based on manganese is quite energy-intensive and entails relatively large losses of the main element. The use of ore-coal briquets makes it possible to speed up the reduction of manganese oxides and improve on the performance characteristics of traditional ferroalloy production methods [1]. Ore-coal briquets or pellets are particularly effective if used in a new type of process unit ‐ the oxygen reactor developed by the Moscow State Institute of Steel and Alloys [2]. The technology involves the introduction of a charge containing ore-based materials, fluxes, and a carbon fuel, injecting oxygen or air into the fuel column through lances located in the lower part of the reactor, and injecting gas with an oxygen content in the range 5‐95% through top (auxiliary) lances located above the stockline. The ore-based materials are charged in agglomerated or pulverized form. Coke and/or coal is used as the carbon-bearing fuel. The main feature of the process is complete use of the calorific value of the coal and coke inside the reactor as a result of combustion of carbon monoxide above the column of carbon-bearing solid material. In addition, the use of green ore-coal pellets causes the reduction zone to be localized mainly on the surface of the coke column ‐ in the space where most of the heat used in the process is concentrated. The technology reduces the total consumption of carbon-bearing fuel, allows much of the coke to be replaced by coal in the green ore-coal pellets or briquets, and speeds up the smelting of pig iron and ferroalloys. The consumption of carbon fuel is as follows: for smelting pig iron ‐ 500 kg/ton (coke ‐ 200 kg/ton, coal in the briquets ‐ 300 kg/ton), instead of 600 kg of coke per ton of pig iron in blast furnaces; in the production of ferroalloys based on manganese, chromium, or silicon ‐ roughly 700 kg/ton (coke ‐ 300 kg/ton, coal in the briquets ‐ 400 kg/ton), instead of 2000 kg/ton in blast furnaces. Unlike blast furnaces, the reactor has no shaft, stoves, or complex charging equipment. This article reports the results of our determination of the optimum conditions for the rapid and complete reduction of manganese ores by coal under smelting conditions in the oxygen reactor in order to obtain carbon-bearing ferromanganese and silicomanganese. We studied the reduction of different manganese ores: oxide and carbonate Polynochnyi ores (Russia); Zhairemsk ore (Kazakhstan); Groote Eyland (Australia); Comilog (Gabon); Wessels High Grade (South Africa). The reducing agent used was gas coal of grade G containing 10‐15% ash and 15‐20% volatile matter (Table 1). The amount of reducing agent (carbon) needed was determined on the basis of the criterion of achieving complete reduction of the oxides of iron and manganese (Fe 3 O 4 and Mn 3 O 4 ). A prepared mixture with a mass of 2‐3 g was placed in an alundum crucible, covered with a tungsten cover, and lowered into a graphite-heater-equipped furnace that had been preheated to the test temperature (1600°C). The mixture was kept in the furnace for 3‐7 min. We measured the amount of mass lost by the specimen as a function of time under isothermal conditions. The degree of reduction of the charge was calculated as follows: α = {[(16/28)⌉M]/(M 0 Fe + M 0 Mn )}·100, %,