US2280041A - Production of ferromanganese - Google Patents

Description

. Patented Apr 14, 1942 UNITED STATES PATENT O FICE PRODUCTION OF WMANGANEBE James C. Vignos, Canton, Ohio, asslgnor to Ohio Form-All poration of Ohio No Drawing.

= 3 Claim.

In the blast furnace productionof ferromanganese there is used a charge comprising manganese ore, carbon, usually coke, as the reducing agent, and limestone as the fiuxing material. In such operations there is substantial loss of manganese contained in the ore, and this is so irrespective of the type of ore, the composition of the furnace charge, the method of furnace operation, and the analysis of the slag and of the ferromanganese produced. The greatest loss of manganese occurs in the slag, the composition of which varies with that of the ore and with the furnace charge and its operation. As ordinarily produced, however, such slags contain from about 20 to 25 per cent'of lime, about ya Corporation, Philo, Ohio, a cor- Application November 1, 1940, Serial No. 364,665

10 to 15 per cent of alumina, about 1 to 20 per 1 cent of magnesia," about 20 to per cent of. silica, and about 3 to 25 per cent of manganese.

The loss of manganese to the slag represents, on an average, about 10 to 15 per cent of that charged into the furnace. Manganese is lost also in the stack gases, and this stack loss may, and commonly does, constitute about 5 to 15 per cent of the total manganese charged. Ac-

cordingly, of the total manganese charged into the furnace only 70 to 80 per cent is recovered in the ferromanganese, the balance being lost in the slag and in the stack. 4

In the production of ferromanganese in the blast furnace it is considered desirable that the slag have a ratio of lime-plus-magnesia to silica of at least 1.2 to 1. As this ratio is increased to about 2.5 to 1 the manganese pick-up by the slag decreases, but the volume of slag increases, and more lime and. fuel are required. Within this ratio of 1.2 to 2.5 less than 6 percent of the silica is reduced to silicon. Also, if the amount of carbon is increased the loss of manganese to the slag decreases, but the stack losses increase. It has been considered not economically feasible to produce ferroma'nganese in the blast furnace from low grade ores, particularly those high in silica, such as some of the manganese ores found in the United States. Consequently, low silica ores have been demanded, and in the past penalties have been placed on ores carrying more than 8 per cent of S102.

It is among the objects of this invention to reduce the manganese losses in producing ferromanganese in the blast furnace, and "thereby to improve the efliciency of such operations.

A further object is to provide a'novel process of producing ferromanganese in the blast furnace which makes practical the production of ferromanganese in such a furnace from high silica manganese'ores, which is simple, easily practiced, and economical, in which lossesof manganese are reduced relative to prior .practice, and which produces ferromanganese of improved utility.

fore in the blast furnace, whichcontains from Q about to per cent of manganese and 3 to 12 per cent of silicon, and which in its preferred embodiment has a ratio of manganese to silicon ofat least 6:1, and advantageously 7:1.

Other objects description:

This invention'is predicated upon my discovery that in making ferromanganese in the blast furnace manganese losses can be lowered, high silica ores can be utilized, and a ferromanganese of peculiarly advantageous character is produced by providing silica in excess of the ratio limeplus-magnesia to silica of 1.2 to 1, whereby silica is available for reduction by carbon. In other words, the burden is made up so that the ratio bon to elemental silicon over the ratio of CaO-H fl to SiOz (between 1.2 to 1 and 2.5 to 1) which has been standard in the art.

The reduction of silica with carbon to produce elemental silicon reduces the amount of limestone required to maintain the said ratio of bases to acids from 2 to 5 pounds, and the total slag volume 2 to 5 pounds for each pound of will appear from the following ganese lost in the slag is the product of its contentof manganese and the weight of the slag,

" any change which leaves the percentage of manganese in the slag unchanged but which decreases the amount of slag improves the recovery of manganese. In view of the substantial reduction of slag volume which follows the practice of the invention, it will be evident that through its practice the recovery of manganese is improved decidedly. Also, in lowering the limestone charged, by reduction of silica with carbon, the total amount of carbon required remains about the same because less carbon is required for melting, and by maintaining the carbon charge as usual'there is thus provided substantially the amount required for reduction of the silica.

To illustrate the benefit derivable from the: invention, reference may be made to the production of ferromanganese from an ore containing 41 per cent of manganese and 9 per cent of silica. A charge of 6000 pounds of such ore made up in accordance with modern practice would require .2400 pounds of limestone containing approximately 55 per cent of lime-plus-mag'nesia, and 6000 pounds of coke. In ordinary blast furnace operation such. a burden, in which the ratio CaO+MgO EiO, is about 1.59, will yield about 3200 pounds of slag containing 28 per cent of silica and 11.5 per V cent of manganese. Of vthe total manganese charged about 2460 pounds, or approximately 72 per cent, is recovered'as ferromanganese, while about 15 per cent is lost in the slag and 13 per cent in thestack. Using the same ore in the practice of this invention, the limestone charge would be reduced 800 pounds, thus making available for reduction about 400 pounds of silica, and the coke and manganese ore charge would re-- main the same. Such a burden would havea CaO-l-MgO i0.

,ratio of about 1106 and would produce about 2500 pounds of ferromanganese containing about 76 per cent of manganese, 2 per cent of silicon, and 4.5 per cent of carbon, and for each ton of metal produced there would result about 2200 pounds of slag of approximately the same comticehas been to block the heat with an addition of a silicon material, such as ferrosilicon, and subsequently to provide the desired manganese content by the further addition of ferromanganese. By blocking and adding manganese through a single addition of an alloy such as provided by this invention the time required for making a heat of steel is reduced, and the operations are simplified and made more certain. For such purposes I prefer that the ratio of manganese to silicon in the alloy be at least 6 to 1, and suitably at least 7 to 1. Such alloys are especially suited to the production of steels containing more than about 0.5 per cent of manganese. Ferromanganese of such silicon content is not made in the electric furnace, and it is characteristic of blast furnace operation that the silicon content of ferromanganese does not exceed about 12 per cent.

In addition to the important advantage of improved manganese recovery which flows from the invention it will be realized also that the invention is meritorious in that it permits the use of low grade domestic manganese ores, those high in silica being fully suited to the ends of the invention. These ores can be used directly, or

they may be blended with foreign ores, thus reducing the requirements of the latter materials.

According to the provisions of the patent statutes, I have explained the principle and method -of practicing my invention and have described 'what I now consider to represent its best embodiments. However, I desire to have it understood that, within the scope of the appended claims,

position-as .in standard practice, but through reduction in the volume of slag the manganese loss would be decreased about 115 pounds.

In the practice of the invention the furnace burden is preferably balanced so as to provide 'suflicient silica that there will be produced a ferromanganese containing from about to about per cent of manganese with from about 4 to about 10 per cent of silicon. I have found that such alloys are especially well adapted for use in themanufacture of steel because their high content of silicon permits blocking of a charge and simultaneous addition of desired manganese content. In other words, by the use of such an alloy a single addition suflices both to block'the heat and to provide desiredimanganese content except in the case of' very high manganese steels. This is advantageous, as will be realized, inasmuch as heretofore the usual practhe invention may be practiced otherwise than as specifically described.

I claim: i

1. In a method of producing ferromanganese in the blast furnace from a burden-comprising manganese ore, limestone, and carbon, the improvement which consists in compounding said burden to contain silica in excess of the ratio lime plus magnesia to silica equals 1.2 to 1. whereby to produce a substantially decreased amount of slag of about the same proportion of manganese as is produced when the said ratio is 1.2 to 1 or greater, charging blast furnace with said burden, and operating said furnace to produce ferromanganese containing 'about.60 to 80 tains more than 3 to about 12 per cent of silicon.

2. A process according to claim 1, the ratio of manganese to silicon in said ferromanganese being at least 7 to 1.

3. Ina method of producing ferromanganese in the blast furnace from a burden comprising manganese ore, limestone, and carbon, in which the burden is so compounded that the ratio of lime plus magnesia to silica is at least 1.2 to 1, the improvement which consists in reducing the amount of lime charged, whereby said ratio is less than 1.2 to 1 and the slag produced is less in amount but contains substantially-the same proportion .of manganese as is produced when said ratio is greater than 1.2 to 1, and operating said furnace to cause reduction of silica and produce ferromanganese containing about 60 to 80 per cent of manganese and mare than to'about 0 12 per cent of silicon.