Electromelted corundum of Northern Onega bauxites and refractories based on it

Abstract

White electrocorundum melted from commercial alumina is used in the refractory industry for production of corundum and particularly high-alumina refractory parts and compounds. In addition to white electrocorundum the abrasive industry also produces normal electrocortmdum (types 13A-15A to OST MT 71-5-84) produced by melting of bauxites. It is frequently called black because of the dark color caused by the presence of about 5 % impurities, including titanium dioxide and iron oxides. Such corundum, containing 94-96% A1203, is little used in the refractory industry primarily because of the increased content of fluxes and to some extent because of lack of production of it in the industry.Taking into consideration the shortage and very high cost of commercial alumina, the production from bauxites of electrocorundum for production of refractories, the requirements for which differ from the requirements for abrasive corundum, is a pressing problem. The latter must contain a minimum of calcium oxide as the most harmful, impurity and 1.5-2%* titanium dioxide. For refractory corundum, calcium oxide is less harmful, while titanium dioxide is very undesirable. Therefore in melting of black electrocorundum the abrasive industry uses (or used) primarily imported bauxites with a low CaP content. Domestic bauxites, particularly of the Northern Ortega group of deposits of Arkhangel Oblast, contain from 0.25-0.35 to 0.5-1.0% CaP. At present, in this group Iksinsk deposit is the raw material base of the Northern Onega Bauxite Mine and is characterized by the presence of bauxites with a comparatively low iron oxide content (an average of 6-8 %) with a significant alumina content (60-70%).Taking into consideration these differences in the requirements for corundum, independent tests have been made of production of electrocorundum from bauxites for the refractory industry. The principle of reduction melting of bauxite used in the abrasive industry remains common. To the bauxite is added coke (anthracite, etc.) to reduce the oxides of silicon, iron, titanium, etc. Arc furnaces with powers of 9-10 and 16.5 MW with two tap holes for separate tapping of the upper layer of molten material -corundum -and the lower -ferroatloy (ferrosilicon) -are used. The energy consumption per ton of corundum is about 3000 kWh and increases with an increase in the weight portion of silica in the bauxite. The capacity of the 10.5 MW furnace is about 70 tons per day. The temperature of the molten corundum reaches 2400-2500 K and it is tapped into metal molds lined with chromite-periclase refractories.In melting, reduction and removal into the metal alloy of oxides of silicon, iron, titanium, etc. occurs. There exist data [1] on obtaining etetrocorundum with 98.9% A1203 from bauxite. The degree of reduction is determined by the thermodynamic stability of the oxides, the process temperature, the heating rate, the concentrations of carbon and oxides in the charge, the composition of the ferroally incidentally obtained, and other factors. Under the action of CO...

The Way of Utilization of Fused Corundum Dust Waste for the High-Alumina Chamotte Production

“…High-alumina refractories have high resistance to deformation, high chemical resistance and thermal stability. With an increase in the Al2O3 content in refractories of this type, all indicators improve [9][10][11][12][13][14][15][16].…”