US3099554A - Process for producing metals - Google Patents

Description

United States Patent 3,099,554 PRQCESS FOR PRODUCHNG METALS James H. Downing, Bufialo, and Benjamin J. Wilson,

Kenmore, N31 assignors to Union Carbide (Iorporation, a corporation of New York No Drawing. Filed Feb. 21, 1961, Ser. No. 90,625 2 Claims. (Cl. 75-80) The present invention relates to a process for producing metals'from oxidic source materials, and in particular, relates to a process for producing substantially pure metal by vaporization of the metal from the metal borides.

It has been known for some period of time that nu merous metals can be volatized from mixtures of different metals. Since the rate of evaporation of these metals depends upon the temperature to some extent, it is commonly known that higher temperatures will increase the rate of vaporization. However, the extent the ternperature can be increased is limited by the melting point of the metals themselves when high yield and high vaporization rates are desired. When the melting point is reached a drastic reduction in the vaporization surface occurs and yield and vaporization rates decrease.

It is known to distill manganese from its carbon-containing alloys such as ferromanganese and silicomanganese. According to the prior art processes, these alloys are heated in a retort at reduced pressure where the easily vaporized manganese evaporates. One of the disadvantages of the prior art methods is the necessity of advancing the temperature in multiple stages to avoid melting the charge and thus greatly reducing the rate of evaporation owing to the formation of the liquid phase and the subsequent reduction in evaporating surface. By advancing the temperature in several stages, a porous graphitic residue is formed which functions as a wick and thus preserves the maximum evaporating surface.

It is an object of the present invention to provide a process for producing substantially pure metal from their oxides via a vaporization process.

It is another object to provide a process for producing substantially pure metals from borides of the metals.

It is a further object to provide a process for the va porization of metals from their borides at increased rates of metal production and at high metal yields.

It is a still further object of the present invention to provide a process for vaporizing metals directly from the solid state at temperatures Well in excess of the melting point without fusion of the metal in the boride and consequently at increased rates of production.

Other objects are apparent from the remaining disclosure and appended claims.

The process which satisfies the above mentioned objects comprises charging in the solid state at least one metallic boride into a vacuum furnace, the metal of said boride being selected from the group consisting of manganese, and chromium; evacuating substantially all the gas from the vacuum furnace which is reactive with the boride and the selected metal; heating the boride in vacuo to a temperature sufficiently high to produce metal vapor at least at a vapor pressure in excess of the ambient pressure within the vacuum furnace and maintaining the temperature sufliciently high to maintain the metal vapor at least at a vapor pressure in excess of the ambient pressure within the vacuum furnace; and conducting at least a portion of the metal vapor to a condensing zone to be condensed to recover substantially pure metal.

The metals amenable for treatment as borides in the present process are manganese, and chromium. All these Patented July 30, 1963 metals are capable of forming borides which are substantially stable :at elevated temperatures. The borides of these metals will not detrimeutally break down at elevated temperatures before the metal itself can be vaporized and essentially will not break down at temperatures lower than the melting point of the selected metals in the borides themselves. That is, the borides are essentially stable at least up to the melting point of the metals in the boride and preferably are substantially stable at temperatures considerably in excess of the melting point of the metal contained therein.

The borides of the above metals can be produced by a variety of known metallurgical processes. For example, when treating oxidic manganese sources such as ore or slag, a co-reduction of oxidic manganese material and boron oxide by a carbonaceous reducing agent may be conducted in electric are or induction furnaces. The reaction may be represented as follows:

The present novel process may then be utilized to treat the boride of manganese to produce manganese metal.

The particle size of the charge is maintained within the range of from approximately A3 to /2 inch, the preferred size being inch. These particles of the charge may be either solid pieces or pellets composed of compacted fines. The fines may be any size substantially less than inch but it is to be understood that when finely divided material is used it is to be compacted into pellets approximately A; to /2 inch diameter.

Any suitable vacuum furnace may be utilized in the present process.

Substantially all the gas which is reactive with the metal boride being treated and/ or the metal vapor to be produced must be evacuated from the vacuum furnace in practicing the present process. This is accomplished in particular to avoid production of contaminated metal and/ or to prevent consumption of the borides as well as to obtain the required vacuum conditions. It is to be noted that the terms vacuum and the phrase in vacuo are utilized throughout this disclosure and in the claims to indicate pressure below one standard atmosphere. Specific vacuum pressures will be denoted by millimeters of mercury-(cg. mm. of Hg).

One of the major advantages of the present process is the ability to heat the boride to temperatures considerably in excess of the melting point of the metal constituent in the boride without formation of the liquid phase of the metal. In this manner maximum vaporization rates are maintained without loss of rate or yield due to the formation of substantial amounts of liquid. It is generally found that the boride in its solid state is heated at as fast a rate of temperature rise as possible, without causing fusion due to thermal shock, to temperatures sufliciently high to produce vaporization of the metal in the boride. The temperature is maintained at a sufiiciently high level to maintain a vapor of the metal at a vapor pressure in excess of the ambient pressure in the vacuum furnace. Note that the metal vapor pressure must be in excess of the ambient pressure of the furnace to enable an artisan to secure high rates and yields of the metal sought. The highest possible temperatures are. preferred up to the temperature immediately below that level which may cause conversion of the metal and/ or boride to the liquid phase.

It is readily apparent that the rate of metal production and to some extent the yield of the metal sought is largely governed by the difference in the ambient pressure of the atmosphere within the furnace and the vapor pressure of the metal being volatized. Consequently, extremely low vacuums are most desirable in the present process and, indeed, as low an ambient pressure within the furnace as can be maintained 'by the equipment should be utilized.

Though the present process is desirably conducted in the above manner, substantial rates and yields of metal can be achieved Where less divergent metal vapor and ambient pressures are utilized. This is largely due to the amenability of the borides of the present process to treatment at temperatures far in excess of the melting point of the particular metallic constituent sought to be recovered from the boride. In the production of manganese from manganese boride a temperature of about 1750" C. and an ambient pressure of about 0.05 to 0.07 mm. Hg have been found to be satisfactory.

Condensation may be carried out in any one of a variety of known condensers. Condensation may be conducted in vacuum or in inert gas atmospheres.

Boron is produced as a byproduct of the present process in the form of a residue upon vaporization of the metal. The boron may be recycled in the process to provide additional borides for treatment.

In the following example an induction heated carbon type vacuum furnace was utilized.

Manganese boride comprising 76.1 weight percent manganese, 16.9 weight percent boron, 2.8 Weight percent iron, 2.0 weight percent carbon, 0.05 weight percent aluminum and 0.69 weight percent silicon was pelletized to form compacts approximately /8 to /2 inch in diameter and placed in a graphite crucible and heated in vacuo in a furnace from which substantially all the air had been removed. The rate of temperature rise was about 300 to 400 C. per hour. The heating was continued until a temperature of 1750 C. and a vacuum of about .045 to .090 mm. Hg was obtained. This temperature was maintained for a period of about 025' hour. The vapors were conducted to a condensing zone and condensed to form manganese metal comprising 98.5 Weight percent manganese. The residue was comprised of 65 weight percent boron, 2.87 weight percent manganese and 9.84 weight percent carbon.

The following example illustrates the production of chromium by the present process.

Chromium boride comprising 17.32 weight percent boron was pelletized, placed in graphite crucibles and heated in vacuo at a starting pressure of about 0.05 micron in a furnace from which substantially all the air had been removed. The following table is a compilation of the temperature, time, average pressure during the process and an analysis of the resulting product.

What is claimed is:

1. A process for producing at least one of the metals selected from the group consisting of manganese and chromium from solid state borides of said metals comprising charging at least one of said borides ofs said selected metals in particulate form ranging from about 0.125 to about 0.5 inch in diameter into a vacuum furnace; evacuating substantially all the gas reactive with said boride and said selected metal from said vacuum furnace; heating said boride of said selected metal in vacuo to a temperature sufiiciently high to produce metal vapor of said selected metal at least at a vapor pressure in excess of the ambient pressure within said vacuum furnace; maintaining a temperature sufiiciently high to maintain a metal vapor of said selected metal at least at a vapor pressure in excess of the ambient pressure within said vacuum furnace while essentally maintaining said boride in said solid state; conducting at least a portion of said metal vapor to a condensing zone and condensing said metal vapor to form at least one of said selected metals in substantially pure metallic form.

2. A process for producing manganese from manganese boride comprising charging manganese boride in the solid state in particulate form ranging from about 0.125 to about 0.5' inch in diameter into a vacuum furnace, evacuating substantially all the gas reactive with said manganese boride and said manganese; heating said manganese boride in said solid state in vacuo to within the range of about 1500 C. to 1750 C. to produce manganese vapor; maintaining said temperature within said range to maintain a metal vapor of said selected metal; conducting at least a portion of said manganese vapor to a condensing zone and condensing said metal vapor to form manganese metal in substantially pure form; and recycling at least the boron remaining in the residue to produce additional borides.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR PRODUCING AT LEAST ONE OF THE METALS SELECTED FROM THE GROUP CONSISTING OF MANGANESE AND CHROMIUM FROM SOLID STATE BORIDES OF SAID METALS COMPRISING CHARGING AT LEAST ONE OF SAID BORIDES OF SAID SELECTED METALS IN PARTICULATE FROM RANGING FROM ABOUT 0.125 TO ABOUT 0.5 INCH IN DIAMETER INTO A VACUUM FURNACE; EVACUATING SUBSTANTIALLY ALL THE GAS REACTIVE WITH SAID BORIDE AND SAID SELECTED METAL FROM SAID VACUUM FURNACE; HEATING SAID BORIDE OF SAID SELECTED METAL IN VACUO TO A TEMPRATURE SUFFICIENTLY HIGH TO PRODUCE METAL VAPOR OF SAID SELECTED METAL AT LEAST A VAPOR PRESSURE IN EXCESS OF THE AMBIENT PRESSURE WITHIN SAID VACUUM FURNACE; MAINTAINING A TEMPERATURE SUFFICIENTLY HIGH TO MAINTAIN A METAL VAPOR OF SAID SELECTED METAL AT LEAST AT A VAPOR PRESSURE IN EXCESS OF THE AMBIENT PRESSURE WITHIN SAID VACUUM FURNACE WHILE ESSENTIALLY MAINTAINING SAID BORIDE IN SAID SOLID STATE; CONDUCTING AT LEAST A PORTION OF SAID METAL VAPOR TO A CONDENSING ZONE AND CONDENSING SAID METAL VAPOR TO FORM AT LEAST ONE OF SAID SELECTED METALS IN SUBSTANTIALLY PURE METALLIC FORM.