US3729544A - Separation of iron by chlorination of a ferro-alloy - Google Patents

Abstract

D R A W I N G
IRON IS SEPARATED BY HALOGENATION FROM A MATERIAL, E.G. AN ALLOY, CONTAINING AT LEAST ONE OTHER METAL SELECTED FROM THE GROUP CONSISTING OF ZR, TI, HF, V, NB, TA, MO, W, AND RE WHEREIN THE MATERIAL IS CHLORINATED TO FORM A GASEOUS MIXTURE CONTAINING FERROUS CHLORIDE AND AT LEAST ONE OTHER METAL CHLORIDE, FOLLOWING WHICH THE ONE OTHER METAL CHLORIDE IS SEPARATED FROM THE FERROUS CHLORIDE BY CONDENSING OUT THE LATTER AT A TEMPERATURE AT WHICH THE AT LEAST ONE OTHER METAL CHLORIDE IS VOLATILE.

Description

P? 24, 1973 E. K. A. SVANSTROM 3,729,544

SEPARATION OF IRON BY CHLORINATION OF A FERRO-ALLOY 2 Sheets-Sheet 1 FIG.I

Original Filed June 18, 1970 FIG. 2

April 1973 E. K. A. SVANSTROM 3,

SEPARATION OF IRON BY CHLORINATION OF A FERRO-ALLOY Original Filed June 18, 1970 2 Sheets-Sheet 2 Chlorino'ring Agent Condenser 23 Volofile Chlorides Reactor Reactor FeClz United States Patent US. Cl. 423149 7 Claims ABSTRACT OF THE DISCLOSURE Iron is separated by halogenation from a material, e.g. an alloy, containing at least one other metal selected from the group consisting of Zr, Ti, Hf, V, Nb, Ta, Mo, W, and Re wherein the material is chlorinated to form a gaseous mixture containing ferrous chloride and at least one other metal chloride, following which the one other metal chloride is separated from the ferrous chloride by condensing out the latter at a temperature at which the at least one other metal chloride is volatile.

This application is a continuation of US. application Ser. No. 47,366, filed June 18, 1970, now abandoned.

This invention relates to a method of separating by halogenation iron from materials, e.g. alloys, containing at least one other metal selected from the group consisting of the refractory metals Zr, Ti, Hf, V, Nb, Ta, M0, W, and Re.

It is known to produce halides of metals selected from the Groups 412, 5b, 6b and 7b of the Periodic System of the elements (i.e. the refractory metals Zr, Ti, Hf, V, Nb, Ta, Mo, W and Re) by reacting the metal with a halogenating agent, e.g. chlorine or other gaseous halogens. Chlorine is the most commercially interesting of the halogenating agents. Thus, while the invention will be described from the viewpoint of using chlorine as the agent, it will be understood that other halogenating agents can be used in the same manner and, for purposes of this invention, the other halogenating agents shall be deemed to be equivalent to chlorine.

According to the prior art, it is possible to treat ores, oxides, sulfides, etc. of the foregoing metals with chlorine at elevated temperatures. Generally, a reducing agent is necessary for the chlorination reaction to take place. However, such kinds of technical starting materials often contain substantial quantities of other components that cannot be chlorinated. Such materials have their disadvantages in that the residues remaining after the chlorination is completed must be removed from the apparatus during operation which presents practical problems; for example, it is difiicult to extract the desired metal component with acceptable yields.

Different methods for increasing the yields have been described in literature. However, at present there is no satisfactory solution to this problem. Because several of the foregoing metals are very expensive (e.g. tungsten), high yields are very necessary if the method is to be practical. Where such expensive metals as Nb, Ta, W, Mo and V are to be recovered, it is preferred to start with metallic raw materials, such as alloys, the impure metals and carbides. The somewhat higher price for these starting materials is not too important in view of the recoveries achieved with the process.

The advantage of starting with metallic materials is that they can be easily chlorinated, the amount of chlorination residues being insignificant and of no practical importance. By starting with metallic materials, the re- 3,729,544 Patented Apr. 24, 1973 covery of metal is almost percent. The chlorination operation is fairly simple and quite economical. However, a technical difiiculty connected with chlorination of metal alloys is the problem of separating the chlorination products formed.

This is particularly the case with ferrous alloys of, for instance, W, Nb, Ta, which are well established products in the marketplace. The metallurgical production of these alloys is quite economical and has been used for quite some time. In spite of the availability of these alloys, they have not been used as starting materials due to the difficulties of separating the ferric chloride formed during chlorination from the final product. lHeated beds of sodium chloride are used, through which metal chloride vapors are passed, whereby the ferric chloride combines with the sodium chloride and is retained on the bed this way while chlorides of, for instance, W, Nb and Ta pass through. The combination of sodium chloride and ferric chloride is drained off at the bottom of the bed while fresh sodium chloride is added to the top of the bed. The use of the bed is inconvenient in that plugging occurs and also the efficiency is poor due to excessive amounts of liquid salt remaining in the bed. In US. Pat. No. 3,407,031, a method for separating iron chloride is disclosed wherein chlorination in a salt melt is employed. However, this method has its disadvantages, owing to unacceptably low yields which makes the method unsuitable for commercial.

use.

In US. Pat. No. 3,261,664, the separation of FeClfrom a mixture of TiCl FeCl and FeCl is disclosed. According to the conditions described therein, a balance occurs such that FeCl is formed only in very small quantities, due mainly to the formation of the dimer, Fegcla.

As far as is known, a satisfactory method has not been proposed for efficiently recovering metal halides from ion-containing metallic materials.

*It is thus the object of the invention to provide an economical method for recovering refractory metals from iron-containing materials, e.g. ferro alloys, by halogenation wherein the iron is efficiently separated from the other metals.

The foregoing and other objects will more clearly appear from the following disclosure and the accompanying drawing, wherein:

FIGS. 1 to 3 are schematics of apparatus embodiments which may be employed in carrying out the invention.

Stating it broadly, a method is. provided for separating iron by halogenation from material containing at least one other refractory metal selected from the group consisting of Zr, Ti, Hf, V, Ta, Mo, W and Re comprising, forming a particulate bed of said material of suitable depth in a reactor, subjecting the bed to chlorination by passing a chlorinating agent through the bed from one end of the bed to the other at a chlorinating temperature sutficient to form gaseous chlorides containing ferrous chloride, passing the gaseous chloride through a condensing zone maintained at a temperature at which the ferrous chloride condenses while the remaining at least one metal chloride is volatile, and then separating the at least one volatile chloride from the condensed ferrous chloride.

According to the invention, the chlorination is carried out such that the iron in the material is converted into ferrous chloride and the formation of ferric chloride avoided. In using other halogenating agents in place of chlorine, the process is similarly carried out to form ferrous halide.

Generally speaking, chlorination reactions of this type are carried out in a fixed bed by adding chlorine gas at an elevated temperature. The chlorination gas is added under such conditions that the chlorine reacts completely with the charge before leaving the bed. This can be effected by means of a suitable control of the bed temperature, feed velocity of chlorination gas, and grain size of the charge, etc. The temperature of the chlorination should exceed about 670 C., for example, 1000 C. By controlling the reaction in this manner, the ferric chloride initially formed in the first reaction, as the gas enters the bed will, before it leaves the bed, reacts with the remaining charge to form ferrous chloride.

However, it is not necessary that the conversion into ferrous chloride take place in the same bed. It may be advantageous, for example, for the conversion to be effected in a separate step, where the gaseous chlorides are reacted again with the same material and where the reaction conditions, i.e. with respect to particle size and reaction temperature, can be the same or can be different. The gases from the first reactor can alternatively be reacted with any suitable material with good affinity for chlorine, for instance, silicon or certain ferrous alloys.

In the chlorination of ferro-tungsten, an added circumstance contributes to the formation of iron chloride in bivalent form. Normally the chlorination is carried out at a temperature exceeding 670 C. Tungsten is then converted to WCl which is the thermodynamically stable chloride at higher temperatures. If the chlorination conditions are favorable, the iron is simultaneously converted to FeCl A less complete conversion of the chlorine in the reaction zone results, to start with, in the formation of FeCl and, when essentially all iron is obtained as FeCl free C1 will occur in the chlorination products if the chlorination rate is still lower.

[When the temperature of the gaseous chlorination products is lowered to make possible the separation of FeCl in solid form, WCl will take one chlorine from Fe Cl to form WCl and FeCl according to the equation:

A requirement for the reaction to proceed to the right to an essential degree is that the temperature does not exceed about 400 C., which temperature is also suitable from the standpoint of separating out the ferrous chloride.

As ferrous chloride has a very high boiling point compared with ferric chloride and the refractory metal chlorides produced in the pure state herein, ferrous chloride can be completely separated at temperatures over the boiling point of the chlorides to be produced, such as tungsten chloride, niobium chloride, tantalum chloride, etc. This means that the temperature of the gas mixture can be maintained at the range of about 350-400 C. in the separation step. The ferrous chloride Will then separate in solid form from the gas mixture. On account of the very low vapor pressure of the ferrous chloride at the temperatures used, its separation will be practically 100 percent. The separation is preferably carried out in a separate vessel (e.g. a condenser), where the ferrous chloride can be deposited out. In order to insure that the fine granular ferrous chloride condensed is not transported further, the gas is preferably filtered before the other chlorides are condensed out. As will be appreciated, this method gives a simple and very effective method for the separation of iron.

In carrying out the invention, the apparatus of either FIGS. 1 or 2 may be employed, among others. Referring to FIG. 1, a hopper 1 is shown from which the raw material to be chlorinated is charged into reactor 4 via valve or gate 3. A chlorinating gas, e.g. C1 is fed via tube 2 into reactor 4 containing a particulate charge 4A of a ferro-tungsten alloy. The reactor comprises a ceramic lining 5 which converges to a smaller cross section at 5A to leave a reduced opening at 11 at which a bridging element 12 is provided across it to insure support of bed 4A while allowing chlorinating gas to pass through the charge from the top through the bottom thereof and through opening 11. The reaction being exothermic is carried out at above 670 C., e.g. at about 1000 C. or 1050 C.

The reactor communicates with a large condensing chamber 13 which is maintained at a lower temperature, eg. 350 C. to 400 C. via electric heating elements 6 embedded in insulation 7 surrounding the outer surface of the chamber. The ferrous chloride condenses to a solid 8 at the bottom of the chamber as shown and at regular intervals is removed from it by opening closure element 14. Coupled to the condensing chamber is an enclosed filter 9 and an exit port 10 through which the volatile metal chlorides to be recovered are withdrawn for subsequent separation by condensation. The filter 9 separates finely suspended solid ferrous chloride particles from the volatile metal chlorides. As will be noted from FIG. 1, the gaseous chlorinating agent passes from the top of the charge through the bottom thereof.

FIG. 2 is similar to FIG. 1 and similar elements are identified by the same numerals, except that the chlorinating agent enters through tube 2 in the bottom of the charge and out through the top thereof. The particulate charge 4A is fed via hopper 1 by way of valve or gate 3 with reactor 4 similarly insulated by ceramic 5, a bridging element 12 being provided at the reduced end or bottom of the reactor for assuring support of the charge bed. As the chlorinating agent passes through the charge from the bottom thereof, the volatile chlorides formed are led off through conduit 15 into condensing chamber similarly maintained at a lower temperature (e.g. 350 C. to 400 C.) by means of heating elements 6 embedded in insulation 7. Solids of ferrous chloride 8 are condensed out in chamber 13 as shown in FIG. 2, the solids being removed at regular intervals by opening closure element 14. As in FIG. 1, a filter 9 and exit port 10 is coupled to the coudenser through which the volatile chlorides are removed after filtering out any suspended solids of ferrous chloride.

As stated hereinbefore, as the chlorinating agent enters the charge, whether through the top or the bottom thereof, ferric chloride is first formed which is reduced to ferrous chloride as it passes through the remainder of the charge. An alternative approach is to have two beds in tandem series connected so that the volatile chlorides formed in the first bed are comprised of ferric chloride in addition to the other metal chlorides which chlorides are then passed through the second bed containing the same charge or other material for reducing the ferric chloride. The beds may both be at about 1000 C.

A schematic flow sheet of the foregoing is shown in FIG. 3 comprising first and second reactors 20 and 21, respectively, series connected so that the chlorinating agent 22 (e.g. chlorine) passing through the first bed of, for example, ferro-tungsten, from the top through the bottom thereof results in volatile chloride gases containing ferric chloride and tungsten chloride. The volatile gases are then fed through the second bed (reactor 21) where the ferric chloride is reduced to ferrous chloride which is thereafter condensed out in condenser 23, the volatile tungsten chloride being thereafter removed at 24.

As illustrative of the invention, the following examples are given:

EXAMPLE 1 A ferro-tungsten alloy having the composition of 70% W, 25% Fe and 4% Si and some incidentals was chlorinated in a heat insulated quartz tube. The reaction was started by heating the lower part of the charge to about 500 C., Whereafter chlorine was added. The weight of the charge at the start of the chlorination with 4.4 kgs. During the course of the chlorination, a further addition of 6.0 kgs. of alloy was made. At the end of the test, 4.9 kgs. of unreacted material remained in the bed. Chlorine was added at a rate of 60 g./min. The temperature in the reaction zone during the chlorination was about 1050" C. The volatile reaction products were transported from the reactor into a container which was kept at a temperature of about 400 C. and where the ferrous chloride was separated by condensation in the solid state from the gaseous tungsten chloride. The uncondensed chlorides were passed further through a filter and through a heated tube to a condenser where the tungsten chloride was separated. About 8.2 kgs. of tungsten chloride and 3.2 kgs. of ferrous chloride were collected in the respective receiving containers. Analysis of the tungsten chloride showed a content of 50 mg. iron per kg. of tungsten or a very low iron content of only 0.005%.

EXAMPLE 2 Niobium and tantalum are recovered from a ferroniobium alloy containing about 68% niobium, 7% tantalum and 25% iron by forming a first and second particulate bed of the alloy using the flow sheet of FIG. 3. About 10 kgs. of the alloy are placed in each of the reactors 20 and 21. The first reactor is maintained at a temperature of about 800 C., the second one at about 1000 C. Chlorine is passed through reactor 20 at a rate of 50 g./min. to provide volatile chlorides containing ferric chloride, niobium chloride and tantalum chloride, the volatile chlorides being then passed through the second bed where the ferric chloride is reduced to ferrous chloride, following which the ferrous chloride is removed from the niobium and tantalum chlorides by condensation in a condenser 23 maintained at a temperature of approximately 400 C.

EXAMPLE 3 Perm-molybdenum containing about 73% molybdenum, 25 iron and 2% Si is treated similarly as in Example l. The reaction is carried out with about 8 kgs. of the particulate alloy at a temperature of about 950 C., the chlorine being fed at a rate of about 60 grams per minute to provide a volatile chloride mixture of ferrous chloride and molybdenum chloride. The ferrous chloride is condensed out as described in Example 1 and the mlybdenum chloride thereafter separated out from the condensed ferrous chloride.

EXAMPLE 4 Ferro-titanium comprising about 65% titanium and 35% iron is treated similarly as in Example 1. The reaction is carried out with about 5 kgs. of particulate alloy at a temperature of about 975 C., the chlorine being fed at a rate of about 75 grams per minute to provide a volatile chloride mixture of ferrous chloride and titanium tetrachloride. The ferrous chloride is condensed out as described in Example 1 at a temperature of about 400 C. and the titanium tetrachloride then recovered as a gas.

As is apparent from the foregoing, by converting the iron in the alloy to ferrous chloride, it makes it relatively easy to separate the iron from the other volatile chlorides. This will be apparent by comparing the properties of FeCl with certain of refractory metal chlorides as follows (Handbook of Chemistry and Physics, 28th edition, 1944):

Metal chloride Sublimes.

Examples of materials (e.g. alloys) which may be treated in accordance with the invention are the fol lowing:

5 Material: Typical analysis (1) Ferro-tungsten 83% W, 16% Fe, 1% C. (2) Iron-silicon tungsten alloy. 80% W, Fe, 10% Si. (3) Ferro-niobium 68% Nb, 7% Ta, 25% Fe. (4) Ferro-vanadium 56% V, 41% Fe, 3% Si. (5) Ferro-molyb- 71% Mo, 28% Fe, 1% 'Si.

den-um.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variatio s may be resorted to without departing from the spirit" and scope of the invention as those skilled in the art will readily 2O understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

\Vhat is claimed is:

1. A method of separating iron by halogenation from a ferro-tungsten alloy which comprises:

forming a particulate bed of said alloy of suitable depth in a reactor,

subjecting said bed to chlorination by passing gaseous chlorine in the absence of a reducing agent from one end of the bed through said depth to the other end thereof at a temperature of at least about 670 C. to form gaseous chlorides such that any ferric chloride formed initially as the gas enters the bed reacts with the remainder of the bed to form ferrous chloride,

passing said gaseous chlorides containing tungsten chloride and said ferrous chloride essentially free of any ferric chloride through a cooling zone maintained at a temperature at which said ferrous chloride condenses in solid form whi.e at least the tungsten chloride is volatile,

and then separating the tungsten chloride from the solid ferrous -chloride.

2. The method of claim 1, wherein the temperature of the condensing zone is about 350 C. to 400 C.

3. A method of separating iron by halogenation of a ferro-alloy containing a substantial proportion of at least one metal selected from the group consisting of Zr, Ti, Hf, V, Nb, Ta, Mo, W and Re, which comprises:

treating a first particulate bed of said ferro-alloy with gaseous chlorine in the absence of a reducing agent to provide a gaseous chloride mixture containing ferric chloride and at least one of said other metal chlorides,

passing the gaseous chloride mixture containing the ferric chloride through a second particulate bed formed of a material selected from the group consisting of ferro-alloys and silicon, whereby to reduce said ferric chloride to ferrous chloride in the mixture,

passing the thus formed gaseous chloride mixture through a cooling zone maintained at a temperature at which the ferrous chloride condenses in solid form while the remaining at least one metal chloride is volatile,

and then separating the at least one volatile metal chloride from the solid ferrous chloride.

4. The method of claim 3, wherein the material in the second particulate bed is substantially the material of the first particulate bed.

5. The method of claim 3, wherein the material of the second particulate bed comprises silicon.

6. The method of claim 3, wherein the material chlorinated is a ferro-tungsten alloy which is chlorinated at a temperature exceeding 670 C., and wherein tungsten chloride formed by reaction is subsequently separated from the condensed ferrous chloride.

7. The method of claim 6, wherein the temperature of the condensing zone is about 350 C. to 400 C.

References Cited UNITED 8 Mayer 423-67 Sutherland 423-62 Cairns et a1. 423-149 X Peterson et a1. 423-491 UX OTHER REFERENCES Extraction and Refining of the 'Rarer Metals, 21 Symposium book, 1957, pp. 274 and 287. The Institution of Mining and Metallurgy, London.

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