Molybdenum News Center

Background of Thermite Smelting of Ferromolybdenum

Ferromolybdenum is in widespread commercial use as an alloying addition agent in steelmaking and other metallurgical operations. Ferro-alloys of molybdenum conventionally contain from about 60% up to about 75% by weight molybdenum and are commercially produced employing batch-type operations, either by a thermite process or by an electric furnace reduction process. Both of these techniques are labor and energy intensive and various alternative techniques have heretofore been proposed for use to increase the efficiency of such processes in order to reduce the costs of the ferro alloy produced.

Ferromolybdenum alloys are principally produced commercially by the so-called thermite process by which ingots or buttons of the alloy can be produced in sizes up to about 2,000 pounds. Typically, a thermite reaction mixture is comprised of about 1,300 pounds of contained molybdenum in the form of the oxide, 116 pounds of 98% aluminum, 1,122 pounds of 50% ferrosilicon, 618 pounds of a high-grade iron ore, 160 pounds of limestone and 50 pounds of high-grade fluorspar. The particulated reaction mixture is placed in a refractory lined steel-backed crucible positioned over a shallow pit of sand, over which a dust hood is placed and the reaction is started by igniting the charge with a starting fuse. This so-called top-fired thermite smelting reaction is rapid and the fumes and dust are withdrawn from the dust hood through a bag filter for recovery of fines and for post-treatment of the fumes in order that they can harmlessly be discharged to the atmosphere. The thermite reaction is usually complete in about 20 minutes, whereupon the crucible is lifted and the mass of molten ferromolybdenum alloy and overlying molten slag layer are allowed to solidify, whereafter the slag layer is removed and the so-called ferro-alloy button crushed and thereafter screened to the desired particle size range consistent with its intended end use.

Problems associated with the aforementioned prior art top-fired thermite smelting process include the limitation on the quantity of ferro-alloy that can be produced during each heat and the relatively high percentage of valuable molybdenum constituents entrapped in the lower and upper layers of the slag as a function of the total surface area of the slag layer which usually necessitates a post-treatment of the slag to recover the molybdenum values therein. The necessity of producing such ingots or buttons within a relatively narrow range of thicknesses to avoid undesirable variations in composition and to enable subsequent crushing into a particulate product using commercially available crushing equipment has also handicapped the quantity of ferromolybdenum alloy that can be produced in a crucible.

The present process overcomes many of the disadvantages associated with prior art techniques by increasing the proportionate yield of ferro-alloy for a given volume of crucible, by reducing the magnitude of molybdenum values entrapped in the slag layer and by proportionately decreasing the labor and energy requirements per unit weight of ferro-alloy produced.

 

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