To determine the general possibility of the refined ferromanganese smelting using alumosilicomanganese alloy (AlSiMn) as a reducing agent, experiments were carried out in the laboratory conditions.
During the tests, as the charge material, primary manganese ore from the “Ushkatyn III” deposit (Central Kazakhstan) was used and the reducing agent was the complex alloy AlSiMn, the chemical composition of which is given in Table 1.
|Manganese ore, %||AlSiMn, %|
|Mn||Fe||SiO||Al O||CaO||P||loss on burning||Mn||Si||Al||C||Fe|
The goal of briquetting was the intelligent use of manganese ore and the effective use of elements, involved in the reduction processes during the metallothermic obtaining process for refined ferromanganese. Considering the slaking behavior in the air of the AlSiMn alloy due to the appearance of the unstable compound of aluminum carbide Al C , which interacts with the atmospheric moisture and forms aluminum hydroxide Al(OH) with the release of hydrocarbons , it was proposed to briquette it with the commercial manganese ore (fraction 0-5 mm) using a determined ratio. In this case, it is necessary to proceed from the consideration of the recovery process intensification by increasing the contact surface of the reacting phases.
Briquetting was carried out as follows. Initial materials, first in the dry state, and then with the binder were thoroughly mixed. Liquid glass was used as a binder in the amount of 10% of the charge dry mass. The liquid glass density is 1.41 g/cm , the silicate module SiO /Na O = 2.64-2.84. The composition of the monocharged briquettes was as follows:
After mixing, the compound was processed on the “HYDROPRESS 50” installation, where under a pressure of 210 Bar briquettes in the form of cylinders with a diameter of 50 mm and a height of 15–20 mm were obtained at a temperature of 200 C and a duration of 50 minutes (Figure 1). The chemical composition of the briquettes is given in Table 2.
As the fluxing material used the lime with CaO content 90%.
After all the above operations, the charge materials were loaded into coreless induction furnace (furnace power is 25 kW, inductor voltage is 380-480 V, the inductor current is 200-1800 A) which prevented the alloy pollution with carbon. After the loading of the charge, the furnace was turned on. The temperature was measured with a WRe 5-20 thermocouple. When the temperature reached 900 C, all the experimental melting had a gas emission with the specific white deposit on the walls of the furnace body. At a temperature of 1350 C, the beginning of charge melting was noted, and at a temperature range of 1430-1450 C, a liquid melt appeared, as evidenced by the presence of an alloy adhered to the molybdenum wire. At a temperature of 1500 C, in the bath of the furnace, gases were formed and released in the form of bubbles, resembling boiling water. The duration of melting from the start of loading of the first charge portion to the metal and slag tapping for the current melting was 100 minutes. After the melting, the furnace was turned off, then with the aid of a manual drive, the furnace was gently tilted and at the same time, the metal and slag were poured into cast-iron molds. The metal was separated well from the slag. The slag was a stone-like mass of bright green color. The basicity and the ratio of the slag/metal were: 1.75 and 2.0, respectively. The obtained alloy in chemical composition meets the requirements of the standard. The results are presented in Table 3.
During laboratory experiments, it was noted that the reduction process in the furnace was very intensive with throat welding of the entire charge and with a clear separation of metal and slag. The achievement of this effect is provided by the small fraction of the mixture components. The fine fraction of the AlSiMn alloy increases the efficiency of the alloy as a reducing agent due to the more developed surface of the material itself, as well as due to the uniform distribution throughout the volume of briquettes. From Table 3 it can be seen that the use of silicoaluminum reducing agent AlSiMn in the refined ferromanganese metallothermic process leads to the formation of clay-containing slags. The concentration of alumina in them is 6-10%, while according to standard technology it is 2-3% . However, in order to determine the actual technical and economic indices of production for refined ferromanganese grades, it is necessary to conduct further research in the large-scale laboratory and semi-industrial conditions.
• It was established that it is possible in principle to obtain briquettes from primary manganese ore and AlSiMn alloy with a fractional composition of 0-5 mm;
• The use of primary manganese ores from the “Ushkatyn III” deposit for the smelting of the refined ferromanganese makes it possible to reduce lime consumption up to 40% due to the high content of calcium oxide in the ore;
• The possibility of the refined ferromanganese smelting using a briquetted monocharge has been proven, and the resulting alloy is of high quality, since the carbon content ranges from 0.4 to 0.65%.
• An improvement in the technological indicators of the process has been achieved: the degree of manganese extraction in the metal increased to 70%, instead of 55%, the slag/metal ratio was reduced to 2.0, instead of 2.5. The recommended values of slag basicity are 1.75. Laboratory melting slags were obtained in a stony state with no signs of breaking.