US2752301A - Recovery of chromium and iron values from chromium-iron ores - Google Patents

Description

June 26, 1956 H. s, COOPER RECOVERY OF CHROMIUM AND IRON VALVES FROM CHROMIUM-IRON ORES Filed March 7, 1951 2 Sheets-Sheet l PREHEA TER HOT ORE HOPPER NON-CONDENSED 5 A G L 3 E u 8 6 h 1 C c w H 1 N 7 L 9 Z 1 K 5 h 2 F g Y Z R A, H a 1 A M M R M C L W w n m m .D. M H C Ufi N H5 l A 0L 5 E c R P R L M 0 A R e 0 P T E 0 C M ii R T 0 F Z O H a 8 5 BEL E Z w k H 2 G 5 A #4 a 6 Z 7 2 H |NVENTOR Hugh S. Coorer PM ATTORNEY RECOVERY OF CHROMIUM AND IRON VALVES FROM CHROMIUM-IRON ORES 2 Sheets-Sheet 2 Filed March 7, 1951 ORE STORAGE NON CONDENSED GASES 6 m 4 4 4 l M 6 R GE 5 0 5 aw m 2 4 w w "Hl l'lfl m ,2 C 5 E q 5 5 )1 J. 3 MW 5 w L T C 5 Y z Y z M m W 5/ M N E J 6 Z R H R .T 55 EE H TE 2 F om R 2 EE 5 /1 cc 4/ R 6 5/ R u 6 E a A Y FF D L H N RN m 00 L e E Ry m Fc R 1v m 0 5 m m H a 5 A G 8 I -N MI E 3 cu m a v 8 N Uh eR V w 5 w z Fm m w c 5 9 H. .H. U w 3 ML R L 4 U 5 W M 3 5 F Hugh 5. co o aer ATTORNEYS United States Patent RECOVERY OF CHROMIUM AND IRON VALUES FROM CHROMIUM-IRON ORES Hugh S. Cooper, Shaker Heights, Ohio, assignor to Walter M. Weil, Cleveland, Ohio Application March 7, 1951, Serial No. 214,247

22 Claims. (Cl. 204-) This application relates to the treatment of chromium ores and particularly to the treatment of chromite ores for selectively separating desired constituents therefrom.

A major portion of the chromium used by industry today goes into steels as an alloying element, though there is also a large demand for chromium metal in a pure form for other purposes, and also for pure chromium salts for use in the chemical industries. The principal source of chromium is the ore known as chromite, which consists principally of chromium and iron oxides in admixture with various other minerals. Though much of the chromium oxide and iron oxide contents of chromite ores are combined in the form of ferrous chromite (CrzOs-FeO), for most purposes the chromium and iron may be considered as being practically all in the form of C1203 and FeO, respectively. Depending on their source, chromite ores generally contain about 30 to 55% chromic oxide, about 10 to 25% ferrous oxide, with widely varying chromium-iron ratios calculated on a metallic basis, and other minerals consisting largely of oxides of magnesium, aluminum, silicon, and calcium in various proportions and combinations. When used to produce pure chromium metal or pure chromium salts, chromite ore has been handled in various ways, but the principal problem has always been the elimination of the iron oxide and other mineral impurities at some stage in the process.

When used for the production of chromium steels, the chromite ores are generally first concentrated and smelted to eliminate most of the components other than chrominum and iron and to produce a ferro-chromium master alloy of one of the following two commercial grades;

1. High carbon-66 to 70% Cr, 4.5 to 7% c, balance largely Fe 2. Low carbon66 to 70% Cr, 0.03 to 2% C, balance largely Fe The high carbon master alloy is made by smelting the chromium.

Because the iron in the ferro-chromium master alloy also forms a part of the final product, the ratio of chromium to iron in the master alloy is important. The presence of too much iron in the master alloy requires the use of excessive amounts to obtain the desired chromium content in the final product, thus exerting a deleterious chilling effect on the melt. Moreover, the use of such high-iron master alloys would be uneconomical.

-Depending on their source, the chromite ores generally contain about 30 to 55% chromic oxide and about 10 to 25 ferrous oxide with widely varying chromiumiron ratios. Most of the ores fall roughly into one of the following three commercial classes:

1. Refractory grade30 to 40% CrzOa and 13 to 25% FeO 2. Chemical or intermediate grade40 to 45% CrzOs and 18 to 25% FeO 3. Metallurgical grade45 to 55% CrzOa and 10 to 15% FeO Thus, for practically all metallurgical uses, only the metallurgical grades of chromite contain a sufficiently high chromium-iron ratio to produce a practically useful ferro-chromium master alloy. To be used for producing a satisfactory ferro-chromium master alloy, the leaner grades of chromite must be treated in some manner to increase the chromium-iron ratio by eliminating a portion of the iron. This has heretofore been so difiicult and expensive as to effectively preclude any significant metallurgical use of either of the two leaner grades of chromite.

Unfortunately, many of the deposits of chromite throughout the world are of the low grade (refractory or chemical) varieties which have been economically unsuitable for metallurgical uses. Many countries, including the U. S., depend almost entirely on foreign sources for their supplies of the metallurgical grades of chromite which are in such great demand, though many of these same countries, again including the U. 8., have extensive deposits of lower grade chromite ores. As a consequence, there has been an important, widespread, and long recognized need for a practical and economical process for vbeneficiating the lower grades of chromite ore to increase .solution of the chromite beneficiation problem even more urgent.

While this problem has been the subject of extensive investigation, particularly during the last two decades, and various types of ore treatment have been tried, the most promising processes have involved some kind of chloridizing of the ore with removal of volatile metal chlorides as gases or vapors. In some cases fractional condensation of the gases or vapors has been employed to efiect further separation of the various volatilized chlorides.

Numerous patents have been granted on processes of this general character and on apparatus for carrying out such processes. In some cases the inventions have been directed to the formation and vapor phase removal of only the chlorides of iron and chromium, followed by fractional condensation. In other cases, chlorides of other metals have also been formed and vaporized in substantial quantity, requiring more complex fractional condensation operations. In still other cases, efforts have been made to vaporize and condense chlorides of the iron only. In spite of the great need for practical processes of this character, however, their general use on a commercial scale has heretofore been found to be impractical.

One of the major objections to the prior art processes has been that the chlorination and vaporization operations have not been sufliciently selective or complete, and sufficiently selective fractional condensation has been accomplished only at prohibitive costs.

Another major objection to the prior art processes has been the difliculty of obtaining efficient chloridization Where the temperatures, apparatus, and reactants employed have been chosen to render the chloridization more selective. The less volatile chlorides of calcium and magnesium vaporize only at excessively high temperatures andnormally remain in the reactor in a fused or 'semifused condition, coating the ore and choking the reactor with a gas impervious mass. This both slows down the reaction and makes it ditficult to carry it to completion. The chloridizing agents most frequently mentioned in the prior art as equivalent chloridizing agents have included chlorine gas, hydrochloric acid, phosgene, sulfur tetrachloride, and ferric chloride. The ore has generally been mixed with various amounts of carbon to aid in the reduction of the metal oxides to render them more readily or more selectively attacked by the chloridizing agents. Various temperatures have been maintained by various expedients for controlling the reactions. Special forms of reactors have been employed to facilitate the reactions. And numerous vapor collection and condensation devices and procedures have been employed to improve the selectivity of the fractional condensation. However, none of these devices or expedients has been sufficiently successful to permit the large scale treatment of low grade chromite ores for general use in place of the naturally occurring, but rel'atively scarce, ores of metallurgical grade.

Accordingly, the principal object of the present invention is to provide a process for chloridizing low grade chromite ores that is sufficiently selective to effect the separation of iron and chromium values without fractional condensation.

Arelated and more specific object of the invention is to provide a ehloridizing process that selectively chloridizes and removes only the iron component of chromite ores.

A further object of the invention is to provide a process for treating chromite ores to selectively remove all or any desired part of the iron component.

Another related and more specific object of the invention is to provide a chloridizing process for producing from chromite ores a pure, anhydrous, ferrous chloride suitable for direct electrolysis to produce pure iron powder.

A further object of the invention is to provide a chloridizing process for producing from chromite ores a substantially pure, anhydrous chromium chloride suitable for direct electrolysis to produce pure chromium powder.

A further object of the invention is to provide a chloridi'zing process for producing from chromite ores a substantially pure, anhydrous mixture of ferric and chrornic chlorides in selected proportions suitable for direct electrolysis to produce a pure ferro-chromium alloy.

Still another object of the invention is to provide a system for treating chromite that may be readily controlled to selectively separate all or any desired proportion of the iron component and all or any desired proportion'o'f the chromium component.

Still another object of the invention is to provide a system for chloridizing chromite to produce in substantially pure, anhydrous form, ferrous chloride and either chromic chloride or a mixture of ferric and chromic chlorides suitable for direct electrolysis to produce substantially p'ure metallic iron and metallic chromium or a ferro-chromium alloy.

Still another object of the invention is to provide a system for chloridizing chromite ores, that includes suitable electrolytic cells for respectively producing metallic iron and metallic chromium or a ferro-chromium alloy by the fused bath electrolysis of chlorides formed in the system, with the recovery of gases from the electrolytic cells for use in chloridizing additional ore.

A general object is to accomplish the foregoing objectives in a simple and economical manner suitable for the large scale treatment of chromite ores, particularly those of the lower grade.

One important feature of the invention involves the use of dry, substantially pure, hydrogen chloride gas as a first chloridi'zing agent in the presence of less than the customary amount of carbon or, preferably, no carbon at all. At temperatures above about 850 C., up to and including temperatures as high as 1100 C., or more, in the absence of carbon, 'dry hydrogen chloride attacks only the iron oxide component of chromite ores, converting the ironto ferrous chloride which volatilizes rapidly abovev about 900 C. The reaction is represented by the formula So long as any carbon present does not exceed a roughly critical limit that is related to the amount of ferrous oxide present, as more fully explained hereinafter, it has no appreciable effect on the reaction and, at most, only insignificant amounts of chlorides of metals other than iron are formed.

The completeness of removal of the iron is controllable by varying the conditions of the dry hydrogen chloride treatment, leaving as the residue a beneficiated chromite containing any desired chromium-iron ratio, including a substantially completely iron-free residue wnen desired. By reason of the high selectivity and the high temperature of the treatment, the condensed FeClz is substantially pure and anhydrous, which renders it ideally suited for fused bath electrolysis to produce high purity iron powder.

Another important feature of the invention involves the fused bath electrolysis of the FeClz in a bath of alkali metal chloride permeated with hydrogen gas, depositing elemental iron on the cathode and releasing chlorine from the anode. The chlorine combines in the bath with the hydrogen to produce dry hydrogen chloride suitable for return to the first chloridizing reactor for use as the chloridizing agent.

Another optional, but important feature of the invention involves carrying out the first chloridizing reaction in the complete absence of carbon until the iron is substantially completely removed, then subjecting the iron-free residue to a second chloridizing treatment with straight chlorine gas above about 850 (3., up to and including temperatures as high as 1100 C., in the presence of an amount of carbon just sufiicient to react with the oxygen of the CrzOs component to form carbon monoxide. This treatment chloridizes the chromium, which is removable as chromium chloride vapor, with substantially no contamination by chlorides of any of the undesired gangue material. A substantially pure and anhydrous chromium chloride results from condensation of the removed vapors. The reaction is represented by the formula When employing this optional operation to produce chromium chloride, another important feature of the invention involves electrolysis of the chromium chloride in a fused alkali metal chloride bath of the same type employed for FeClz and with hydrogen gas permeating the bath to produce elemental chromium of high purity and additional dry hydrogen chloride for return to the first chloridizing reactor.

Still another optional and important feature of the invention involves carrying out the first chloridizing reaction to remove sufiicient iron to produce a residue having a predetermined chromium: iron ratio, then subjecting the residue with a reduced iron content to a second chloridizing treatment above about 850 C., up to and including temperatures as high as 1100 C., in the presence of an amount of carbon just sufiicient to react with the oxygen of the oxides in both iron and chromium in the residue to form carbon monoxide. This treatment chloridizes both the chromium and the remaining iron which are removed as chromic and ferric chloride vapors substantially free from contamination by chlorides of any of the undesired gangue materials. Upon condensation of these vapors, a substantially pure, carbon-free, anhydrous mixture of solid chromic and ferric chlorides in the same proportions (based on metallic content) as the proportions of the metals in the iron impoverished residue from the first chloridizing treatment is obtained. When the mixed chlorides are electrolyzed in a fused alkali metal chloride bath of the same type mentioned above and with hydrogen gas permeating the bath, a substantially carbon-free ferro-chromium alloy is recovered from the cathode in line crystalline form and dry hydrogen chloride is recovered for return to the first chloridizing reactor.

The first chloridizing reaction and the fused bath electrolysis of FeClz are thus carried out in a closed system as a result of the reconversion of chlorine to HCl and return of the HCl to the chloridizing reaction. Employment of the second chloridizing reaction and the fused bath electrolysis of CrCls or mixed chromic and ferric chlorides contributes additional dry HCl for use in the first chloridizing reaction, thus further improving the economy of the entire process.

The foregoing and various additional objects, features, and advantages of the invention will be more fully understood from the following detailed description of two alternative ore treatment systems and from the accompanying drawings in which Figure l is a flow diagram of a system for treating ore to remove a portion of the iron content, producing an iron impoverished ore residue and substantially pure metallic iron powder as the final products; and

Figure 2 is a flow diagram of a system for treating ore in which the iron content of the ore is first substantially completely removed in the form of ferrous chloride, and the chromium content of the ore is then substantially completely removed in the form of CrCls, the iron and chromium chlorides then being separately disassociated in electrolytic cells for the production of substantially pure elemental iron powder in one cell and substantially pure elemental chromium powder in the other cell.

In both Fig. l and Fig. 2 of the drawings, the individual pieces of apparatus are represented diagrammatically, only sufiicient structural detail being shown in a few instances to indicate the general nature of preferred types of apparatus.

Referring first to Figure 1, the system shown therein for illustrative purposes comprises any suitable furnace for preheating the ore to be treated in the system; a conveyor 11, which may be of the rotating screw type for feeding preheated ore from the furnace 10 to a hot ore storage hopper 12; a conduit or suitable conveyor 13 for feeding ore at a desired rate from the hopper 12 to a reactor 14, which may be in the form of an inclined, rotatable, tube-type kiln externally heated by a gas burner 15 or the like; a suitable conduit 16 for removing gaseous reaction products from the reactor 14 and transporting them to a condenser 17; a suitable conduit or conveyor 13 for transporting solid material from the condenser 17 to a temporary storage hopper 19; a conduit or suitable conveyor 20 for feeding solid material from the storage hopper 19 into a closed electrolytic cell 21; a hydrogen gas supply conduit 22 for supplying hydrogen gas to the electrolytic cell 21, preferably through a hollow graphite anode 23 and into the cell adjacent the bottom thereof; a valve-controlled blow-off conduit 24 for diverting gases emerging from the electrolytic cell during a preliminary scavenging operation; a valve-controlled conduit 25 for removing gases released within the electrolytic cell during electrolysis and conveying them back to the reactor 14; a source 26 of hydrogen chloride connected to the conduit 25 through a branch-conduit 27 for supplying additional hydrogen chloride to the system as needed; and, if desired, a source 28 of chlorine connected to the conduit 25 through a branch conduit 29 for supplying sufiicient chlorine to react with at least part of the excess hydrogen normally exhausted from the electrolytic cell 21 in admixture with hydrogen chloride.

The hot ore hopper 12 in the type of system illustrated in Fig. l is intended merely to provide a temporary storage for receiving preheated ore continuously or intermittently at any desired rate from the furnace 10 and supplying it continuously or intermittently at a desired rate to the reactor 14, the hopper being suitably insulated to perform this function with a minimum of heat loss.

The reactor 14 may be ofany suitable design for receiving solid, granular material at its upper end and tumbling slowly through the reactor and out the opposite lower end, while a gas reagent, admitted adjacent the lower end of the reactor, flows counter-current therethrough and reacts with the granular material to produce gaseous reaction products withdrawn adjacent the upper end of the reactor through the conduit 16.

The condenser 17 may be of any conventional type commercially employed in the art, and is preferably so located as to receive the gaseous products from the reactor 14 after a minimum travel through the conduit 16. As nearly as physically possible, the reactor 14 should exhaust gaseous products directly into the condenser 17, where heat is extracted therefrom to condense them to solid form. The noncondensed gases, including excess HCl, water vapor, and, in some cases, substantial amounts of H2, are drawn off as indicated by the arrow 17a.

The storage hopper 19, like the hopper 12, merely serves to receive solid material continuously or intermittently at a desired rate from one piece of apparatus (the condenser 17) and to feed the solid material continuously or intermittently at a desired rate to another piece of apparatus (the electrolytic cell 21).

The electrolytic cell 21 is preferably of the general character disclosed in my copending applications Serial No. 144,410, filed February 16, 1950 (now abandoned), Serial No. 201,089, filed December 16, 1950 (now abandoned), and Serial No, 453,898, filed September 2, 1954. In such a cell, a closed metal pot forms the cathode, and the anode 23 is a hollow rod or tube, preferably of graphite, that extends downwardly to adjacent the bottom of the pot and serves as a conduit for conducting hydrogen gas into the pot and discharging it into the contents of the pot adjacent the bottom thereof, whereby the gas is dispersed and diffused throughout the contents of the pot for reaction with chlorine released from the anode during electrolysis. The hydrogen chloride resulting from direct combination of hydrogen and chlorine in the electrolytic cell, together with the excess hydrogen desirably supplied to the cell, are exhausted through the top of the cell and carried off by the conduit 25, as pointed out above.

In accordance with the invention, a finely granulated ore containing chromium and iron oxides, such as chromite, is introduced into the furnace; heated to a temperature preferably in the range of about 1200 to 1300" C.; collected in the hopper 12; and discharged as needed through the conduit or conveyor 13 into the upper end of the reactor 14 at a temperature not greatly below that at which it emerged from the furnace 10 and preferably above about 1000 C. During passage of the ore through the reactor 14 it is maintained at a temperature of at least 850 C. and preferably between about 900 and 1050 C., and the gas burner 15 is used for supplying additional heat for this purpose as required.

During passage of the ore in a state of agitation through the reactor 14, it is intimately contacted by dry hydrogen chloride supplied at the lower end of the reactor and flowing upwardly and counter-current to the direction of the movement of the ore. The dry HCl readily reacts with the ferrous oxide in the ore; converting it to ferrous chloride, which is removed from the upper end of the reactor through the conduit 16 along with the excess HCl that is preferably supplied to the reactor. In the absence of an excessive amount of carbon, the dry HCl is highly selective in its action and does not attack the oxides of chromium, magnesium, aluminum, calcium, and silicon that, along with ferrous oxide, constitute practically all of most chromite ores. Therefore, the ore residue exhausted from the lower end of the reactor may contain a readily controllable fraction only of the original iron content of the ore, depending upon (a) The rate at which the ore is supplied to the reactor, (1)) The fineness of the ore particles (c) The rate at which dry HCl, is supplied to the reactor,

(d) The time interval during which the ore travels from one end of the reactor to the other,

(e) The violence of the agitation of the ore during its travel through the reactor, and

(f) The temperature maintained in the reactor.

By a-proper control of the variables mentioned, the percentage of iron removed may be regulated over a wide range from a relatively small percentage to a figure closely approaching 100% of the iron in the ore.

The amount of free carbon that may be tolerated with the ore during the treatment with hydrogen chloride, for reasons not fully understood, may be related roughly to the amount of oxygenpresent in the form of iron oxide in the ore residue. So long as the free carbon present at anystage during the HCl treatment does not materially exceed that'amount which, if combined with the oxygen of the residual iron oxide, would form carbon monoxide, none of the chromium appears to be affected by the HCl. In the presence of a materially greater quantity of free carbon, chromic chloride is formed and vaporized in greater and greater amounts as the carbonziron oxide ratio in the residual ore is raised by removal of iron oxide. In the presence of an original amount of carbon less than the limiting equivalency indicated, only ferrous chloride is formed and sublimed and the carbon, which does not enter into this reaction, also seems to remain unaffected. When the amount of iron oxide in the residual ore has been reduced in this manner, the carbonziron oxide ratio is correspondingly increased. When this ratio materially exceeds the limiting equivalency indicated, chromic chloride begins to be formed and sublimes with the ferrous chloride.

Thus, to avoid contamination of the ferrous chloride sublimate with chromic chloride, the amount of carbon originally present should be sufficiently small so that the carbonziron oxide ratio in the sublimate at the end of the HCl treatment is not substantially greater than the limiting ratio explained above. If all of the iron is to be removed as ferrous chloride, the carbonziron oxide ratio in the original charge must be substantially zero. If a portion of the iron oxide is to be left in the residual ore, an amount of carbon based on that amount of iron oxide may be tolerated in the original charge.

The ferrous chloride removed from the reactor through the conduit 16 is readily condensed in the condenser 17 at a temperature in the range of about 350 to 650 C without condensing the water vapor formed with the FeClz in the reactor. The water vapor, along with the excess HCl introduced into the reactor, are removed from the condenser 17 as indicated at 17a. The intense afiinity of HCl for E20 apparently assists in preventing hydration of the FeClz and insuring substantially complete removal of the H20 from the system. This HCl and H20 mixture must'be carefully and thoroughly dehydrated if the HCl is to be reused for the treatment of additional ore. This requires the use of special apparatus and techniques forming no part of the present invention and, therefore, not shown or described herein. By reason of the highly selective action of the dry HCl in the reactor 14, the gaseous FeClz removed from the reactor is normally better than 99% pure, and solid FeClz of substantially the same purity is recovered from the condenser and temporarily stored in the hopper 19 for use as needed in the electrolytic cell 21. Because of the nature of the process by which the FeClz is made and condensed, it is substantially completely anhydrous and, therefore, ideally adapted to be used as a source of iron in a fused bath electrolysis process. It is also highly significant that the sublimate is in the form of FeClz rather than FeCla, since less power is required in the electrolytic cell to reduce the iron from its lower state of oxidation.

The electrolysis process, as carried out in the electrolyticcell 21, involves essentially the following operations: a fused bath ofsodium chloride, potassium chloride,-or a mixturethereof in any desired proportion, is

first prepared and brought to a temperature between about 650 and 1000" C., the preferred temperature being between 750 and 900 C. After forcing hydrogen gas downwardly through the fused alkali metal chloride bath for a suificient time to saturate the bath with hydrogen and to scavenge all air from the space above the bath and blowing it ofi through the branch conduit 25, a charge of FeClg is introduced into the bath through the hydrogen atmosphere to protect it from oxidation. The FCClz dissolves quickly in the bath without turning or foaming, and electrolysis is then begun by connecting the terminals of the cell to a source of direct current power. The introduction of hydrogen gas into the bath is continued throughout the electrolytic process to keep the bath saturated with an excess of hydrogen, whereby the chlorine of the FeClz, released at the anode, is quickly converted to l-lCl and is exhausted in that form through the conduit 25 for return to the reactor 14. The hydrogen also seems to have a tendency to reduce part or" the FeClz chemically, thus improving the apparent electrical efficiency of the process.

At the conclusion of the electrolysis operation, which may be carried substantially to completion, the flow of hydrogen gas through the conduit 22 is stopped, the anode 23 and the cover of the pot are removed, and the depleted bath is decanted off by tilting the pot. Iron powder deposited on the walls of the potmay then be readily removed.

The above described electrolysis procedure and apparatus therefor are the subject of my copending applications Serial No. 214,988, filed March 10, 1951 (now abandoned) and Serial No. 453,898, filed September 2, 1954.

While continuous operation of the electrolytic cell 21 is possible with certain modifications, the advantages to be obtained thereby are not suflicient to justify the complications involved in most instances. By using a plurality of cells and shutting down only one cell at a time for recovery of the iron powder, a fairly uniform supply of dry HCl may be maintained in the conduit 25 leading back to the reactor 14.

Because of inherent losses of HCl from the condenser 17 in the system as shown, additional HCl must be continuously supplied and, optionally, an amount of chlorine only sufficient to combine with excess'hydrogen from the electrolytic cell, at some convenient point. Thus, the C12 and HCl make up tanks 26 and 28 are shown connected to the conduit 25 for use as needed.

The reactor employed in the system of Fig. l, as shown in the drawing, is externally heated. However, combustible fuel gases may be introduced into the reactor with the HCl and burned therein to supply additional heat as needed. At least in the absence of any substantial amount of added carbon, any carbon resulting from improper combustion of the fuel is insufiicient to affect the selectivity of the process.

The presence of free chlorine in the first chloridizing reactor 14 is to be carefully avoided, for C12 readily chloridizes the chromium, even in the absence of carbon, and its presence in any appreciable amount would seriously upset the selectivity of the chloridizing operation and contaminate the sublimate with chromium chloride and ferric chloride. This not only would result in loss of chromium but would also impair the value of the desired ferrous chloride for the production of iron powder.

The system shown in Fig. 1 ofthe drawing and described above is ideally suited for the treatment of low grade refractory type chromite ore, of which there are huge deposits in the U. S. and other countries. The system is particularly suitable for treatment of these ores to remove only a suflicient portion of the iron to produce a treated ore residue having a chromium content and a chromium-iron ratio equivalent or superior to the metallurgical-grades of ore which are available only from a relatively few sources in the world. Thus, the invention makes useful to the metals industry for the first time cheap low grade ores available in huge quantities from local sources at low cost. In addition, the system is well suited to the treatment of other types and grades of ores containing iron and chromium oxides, including metallurgical grades of chromite, to increase the chromium-iron ratio and produce substantially pure iron powder as a by-prodnet.

The combination of the chloridizing reaction to produce a beneficiated chromite ore, as one product, with the electrolysis of the sublimate to produce iron powder, as a second product, and the recovery of HCl from the electrolytic cell for use in chloridizing additional ore, results in a unitary process of particularly great economic significance. The value of the iron powder, under present market conditions, is alone suflicient to substantially cover the cost of operating the entire process, whereby the enhancement of the value of the ore by raising its chromiumiron ratio at least to that of a metallurgical grade of ore may be viewed as having been achieved at very little or no cost. Conversely, the enhanced value of the treated ore residue is sufficient to more than cover the cost of operating the entire process, and the iron powder may be viewed as a valuable by-product obtained without cost.

Referring next to Figure 2, the system shown therein for illustrative purposes is particularly suited for the treatment of chromite ores to produce, as the final products, substantially pure elemental iron powder and substantially pure elemental chromium powder. The system may comprise a hopper or storage bin 30.;from which ore to be treated may be drawn as needed; a conduit or suitable conveyor 31 for feeding ore from the hopper 30 to a rotary kiln 32;-a conduit 33=for removing gaseous reaction products from the kiln 32 and transporting them to a condenser 34; a suitable conduit or conveyor 35 for transporting solid material from'the condenser 34 to a temporary storage hopper 36; a conduit or suitable conveyor 37 for feeding solid material from the storage hopper 36 into a closed electrolytic cell 38; a hydrogen gas supply conduit 39 for supplying hydrogen gas to the electrolytic cell 38, preferably through a hollow graphite anode 40 and into the cell adjacent the bottom thereof; a valve-controlled blow-off conduit 41 for diverting gases emerging from the electrolytic cell during a preliminary scavenging operation; a valve-controlled conduit 42 for removing the gases released within the electrolytic cell during electrolysis and conveying them back to the kiln 32; a source of hydrochloric acid gas 43 connected to the conduit 42 through a branch conduit 44 for supplying additional gas to the system as needed; and, if desired, a source 45 of chlorine connected to the conduit 43 through a branch conduit 46 for supplying sufi'icient chlorine to react with at least a part of the excess hydrogen normally exhausted from the electrolytic cell 38 (and the electrolytic cell 58 hereinafter mentioned) in admixture with hydrogen chloride. In addition to the foregoing pieces of apparatus, connected together to form a closed circuit similar to that in Fig. 1, the system of Fig. 2 may include a hopper or storage bin 50 for receiving and temporarily storing the substantially iron-free ore residue discharged from the kiln 32; a conduit or suitable conveyor 51 for feeding the ore residue from the hopper 50 to a second rotary kiln 52; a conduit 53 for removing gaseous reaction products from the kiln 52 and transporting them to a condenser 54; a suitable conduit or conveyor S for transporting solid material from the condenser 54 to a temporary storage hopper 56; a conduit or suitable conveyor 57 for feeding solid material from the storage hopper 56 into a closed electrolytic cell 58; a hydrogen gas supply conduit 59 for supplying hydrogen gas to the electrolytic cell 58, preferably through a hollow graphite anode 60 and into the cell adjacent the bottom thereof; a conduit 61 for removing gases released within the electrolytic cell 58'and conveying them into 10 the conduit 41 leading from the electrolytic cell 38 back to the first rotary kiln 32; and any'suitable form of receptacle 62 for receiving the substantially iron-free and chromium-free'ore residue from the second rotary kiln 52.

In this system also the rotary kilns 32 and 52 may be of either the internally or externally fired variety, preferably mounted for rotation about a horizontal axis and tiltable to discharge the solid contents thereof at intervals as desired. The detailed construction of the kilns forms no part of the present invention and any form of kiln employed in the art for similar purposes may be used.

The condensers 34 and 54 and the electrolytic cells 38 and 58 may be identical with the condenser 17 and electrolytic cell 21 of Fig. 1. Also, as in the system of Fig. 1, a plurality of electrolytic cells may be employed to maintain continuous operation and insure a fairly constant flow of dry HCl back to the reactor 14.

When operating the system shown in Fig. 2, finely granulated ore from the ore storage hopper 30, preferably containing no free carbon, is charged into the first rotary kiln 32 and is heated therein to a temperature in the range from about 900 to about 1400 C. While maintaining the ore in the kiln 32 within this temperature range, and in a state of agitation as a result of rotation of the kiln, the ore is intimately contacted by a stream of dry hydrogen chloride introduced into the kiln from the conduit 42. To insure complete removal of iron, this kiln is preferably operated on a batch basis. As in the system shown in Fig. 1, the dry hydrogen chloride reacts with ferrous oxide in the ore, converting it to ferrous chloride, which is removed from the kiln in gaseous form as it accumulates therein. In the absence of free carbon, the iron in the original ore may be substantially completely recovered as substantially pure gaseous ferrous chloride, the chromium and other metal oxides remaining in the reactor unaffected by the hydrogen chloride.

After being condensed in the condenser 34 and transported to the electrolytic cell 38 as before, the ferrous chloride is electrolyzed in the electrolytic cell in the presence of hydrogen to produce elemental iron powder in the same manner as in the system shown in Figure l, the dry HCl gas from the electrolytic cell, along with the excess hydrogen, being routed back through the conduit 42 to the rotary kiln 32, with or without the addition of a limited amount of chlorine to convert some of the excess hydrogen to HCl.

When the material charged into the rotary kiln 32 has been substantially completely depleted of its original iron oxide content, the ore residue is dumped into the hopper 50, from which it may be charged as desired into the second rotary kiln 52 for a second roasting operation. An amount of carbon as nearly as possible equal to that which will convert to CO, all of the oxygen of the CrzOs present in the substantially iron-free ore residue is mixed therewith in the storage hopper 50, or is charged therewith into the second kiln 52. Upon bringing the charge of ore residue and carbon to a temperature in the range of about 850 C. to 1100" C. in the second kiln 52, a stream of straight chlorine gas is introduced into the kiln and brought into intimate contact with the heated and agitated ore and carbon for converting the chromic oxide to gaseous chromic chloride. By limiting the amount of carbon to the quantity that will combine with all of the oxygen of the CrzOs component of the ore residue being treated, to form carbon monoxide, substantially only the chromium oxide is attacked, and the oxides of calcium, magnesium, aluminum, and silicon again remain substantially unaffected.

The chlorine treatment of the iron-free ore residue in the second kiln 52 is continued until substantially all of the chromium content has been removed as gaseous chromic chloride, at which point the kiln is emptied into the hopper 62 and is ready to receive a second charge from the storage hopper 50.

If desired, of course, appropriate changes may readily be made in the system shown in Fig. 2 of the drawing whereby the residue from the HCl treatment may be left in the kiln 32, the necessary carbon added, and chlorine gas introduced to perform the chlorine treatment in the same kiln. While one kiln may thus be eliminated, the separate condenser 54 will generally be required to avoid contamination of one sublimate with the other in the condenser.

The gaseous chromic chloride from the second kiln 52 is condensed in the condenser 54, transported into the temporary storage hopper 56, and charged as needed into the second electrolytic cell 58. Again the electrolysis is carried out by dissolving the material to be electrolyzed in a bath of alkali metal chloride while hydrogen is passed into the cell through the anode 50, and electrolysis is carried out with a continuous stream of hydrogen being diffused through the bath to react with and remove chloline gas released at the anode. This electrolysis operation and apparatus therefor are subjects of my above mentioned copending application Serial No. 201,089.

The dry HCl gas recovered from the second electrolytic cell 58 is conducted into the conduit 41 and returned to the first rotary kiln 32 for use in the treatment of additional ore. The chromium metal deposited in the cell is recovered by tilting the cell to decant the exhausted alkali metal chloride bath, whereby the chromium may readily be raked and scraped from the cell for purification in accordance with the process described in my application Serial No. 201,089.

Since the iron content of the original ore is substantially completely removed in the first rotary kiln 32, the chromic chloride recovered from the second rotary kiln 52 is substantially iron-free. By careful control of the amount of carbon charged into the second kiln 52, the chromic chloride withdrawn therefrom is also substantially free of contamination with chlorides of any of the other metals commonly present in the original ore. The chromic chloride may readily be produced with a purity at least as high as 99%, and chromium metal of a corresponding purity is obtainable with substantially 100% yield from the second electrolytic cell 58.

The system of Fig. 2 may also be advantageously employed to produce a carbon free ferro-chromium alloy in the electrolytic cell 58, instead of pure chromium. In this case, the HCl treatment in the first kiln 32 is terminated before all of the iron has been converted to gaseous ferrous chloride, leaving any desired amount of iron oxide in the ore residue to be charged to the second kiln 52. When a selected amount of iron oxide is to be left in the ore residue from the HCl treatment, a corresponding amount of carbon may be tolerated in the original charge without danger of contaminating the FeClz sublimate with CICls. However, no advantage is obtained by having carbon present at this stage in the process, and it is preferable that none be employed.

The ore residue discharged from the kiln 32, after having its chromium:iron ratio reduced to any desired degree, may be mixed in the container 50 with enough carbon to react with all of the oxygen of both the chromium oxide and iron oxide. Alternatively the required amount of carbon may be added directly to the second kiln 52 with the ore residue from the container 50. Upon treatment of this mixture with chlorine in the kiln 52 at a temperature between about 850 and 1100 (1., all of the chromium and iron may be converted to CrCls and FeCls, sublimed together, and condensed together in the condenser 57. Again, the sublimate is substantially free from contamination with any of the gangue metals or compounds thereof, and a substantially pure mixture of CrCla and FeCl-s is recovered from the condenser 56.

As disclosed in my above mentioned application Serial No. 453,898, filed September 2, 1954, for Fused Bath Electrolysis of Metal Chlorides, electrolysis of such amixture of chromium and iron chlorides in a fused alkali metal chloride bath, with excess hydrogen diffused through the bath, results in :deposition of a carbon-free term-chromium alloy on the cathode of the cell. The proportions of chromium and iron in theldeposited alloy substantially correspond to the proportions of the chromium and iron chlorides in the bath, and excellent yields .of a high purity alloy are obtained. Thus, when charging the mixed chlorides from the condenser 54 into the second electrolytic cell 58, and operating it in the same manner as when straight CrCla is to be electrolyzed, the finalproducts of the system are iron powder from the first electrolytic cell 38 and ferro-chromium powder from the second electrolytic cell 58, both products being produced in a state of high purity with recovery in these .two commercially valuable forms of substantially all of both the iron and chromium of the original ore.

EXAMPLE 1 'A. High grade Philippine ore Temperature C ,900 Time -..hours 1 Analysis beforetreatment:

Per cent C1'203 49.80 FeO 10.22 (Cr:Fe=='4.3 1)

Analysis of residue:

Per cent CrzOs 65.0 'FeO 3.86

(Cr:Fe=l4.7:l) Sublimate: 99% FeClz, 0.65% CrCla B. Low grade Philippine ore Temperature .C 950 Time hours '2 Analysis beforetreatment:

Per cent CrzOa 32.63 FeO 12.78 (Cr:Fe=2.26:'l)

Analysis of residue:

Per cent CrzOs 42.34 FeO 3. 68

(Cr:Fe=l0.-1 :15

Sublimate: 99+% FeClz, trace of CrCla C. Low grade Philippine are (same as B) (Crz-Fe=4."3 6: 1)

Sublimate 99 FeGlz,.trace of CrCls E. South African are (same as D) Temperature C 900 Time hours 2 Analysis of residue:

Per cent Cr203 65.30 FeO 1.70 (Cr:Fe=33.8:1)

Sublimate: 99+ FeClz, trace of CrCla F. Rhodesia are Temperature C 950 Time hours Analysis before treatment:

Per cent CrzOa 44.00 FeO 9.09 (Cr:Fe=4.25:1) Analysis of residue:

Per cent CI'203 45.35 FeO 7.61 (Cr:Fe=';23:1)

Sublimate: 99+% FeClz, trace of CrCla G. Rhodesia are (same as F) Temperature C 950 Time hours 2 Analysis of residue:

Per cent C1'203 5 1.10 FeO 1.56 (Cr:Fe=28.8:1) Sublimate: 99+ FeClz, trace of CrCla H. Montana ore (Mouat) Temperature C 950 Time hours 1 Analysis before treatment:

Per cent CraOa 37.20 FeO 12.49

(Cr:Fe=2.62:1)

Analysis of residue:

Per cent CraOa 39.56 FeO 9.93 (Cr:Fe=3.50:1)

Sublimate: 99+ FeClz, trace of CrCls I. Montana ore (same as H) Temperature C. 950-1050 Time hours 3 Analysis of residue:

Per cent FeO 6.57

(Cr:Fe=6.18: 1) Sublimate: 99+% FeClz, trace of CrCls J. Montana ore (M0uat'-difierent sample) 14 Analysis of residue:

Per cent C1203 49.98 FeO 4.19 (Cr:Fe=10.5:1) Sublimate: 99+% FeClz, trace of CrCla K. Montana ore (Benbow) Temperature C. 950 Time hours 5 Analysis before treatment:

Per cent C1'203 44.60 FeO 21.41 (Cr:Fe=1.83:1)

Analysis of residue:

' Per cent CI'203 56.07 FeO 0.77

- (Cr:Fe=64.0:1) Sublimate: 99+% FeClz, trace of CrCls L. Montana are (same as K) Temperature C. 1000 Time hours 5 Analysis of residue:

Per cent CrzOg 56.30 FeO 0.65

(Cr:Fe=75.0:1) Sublimate: 99+% FeClz, trace CrCla From the foregoing tests of representative ores of different grades, it is apparent that the chr0rnium:ir0n ratio may be raised at will until substantially all the iron is eliminated while recovering a sublimate of better than 99% FeClz. From a comparison of the last two tests K and L, it will also be observed that substantially optimum results may be obtained at about 950 to 1000 C.

EXAMPLE 2 To illustrate the effectiveness of the C12 treatment of a substantially iron-free residue to produce CrCla, the residue from Test L of Example 1 was mixed with just enough carbon to react with the oxygen of the CrzOs and form CO. The mixture was then heated in straight Clz at a temperature of about 950 C. for 2 hours. The sublimate from this treatment was collected, condensed, and analyzed with the following results:

Per cent CrCls 99+ FeClz and/or FeCla 0.40

Another treatmentof the high grade Philippine ore of Example 1A with dry HCl yielded a residue analyzing 60.40% CrzOs and 2.75% FeO. When this residue was treated first with chlorine gas in the absence of carbon, there was an impractically slow reaction at temperatures up to as high as 1050 C. However, when the residue was mixed with just the amount of carbon which would react with the oxygen of the C1'203 to produce CO, and the mixture was treated at 1000 C., the removal of chromium and iron" was substantially complete in less than 1 hour. Analysis of the sublimate showed no EXAMPLE 4 A Montana Mouat ore analyzing 37.20% CrzOs and 12.4% FeO (Cr:Fe=2.60:l) was first treated with HCl for one hour at 900 C. to produce ferrous chloride and a residue designated residue A. A second sample of the same ore was treated for three hours with HCl at 950 C. to produce ferrous chloride and a residue designated residue B. The residues A and B analyzed as follows:

Residue A Residue B 9.50% FeO 6.57% FeO 39.56% .CrgOa z a (Gr:Fe=3.9:1) (Cr:Fe=6.2:l)

Residues A and B were then mixed with just sufficient carbon to convert all of the oxygen of the chromium and iron oxides to carbon monoxide, and the mixtures were treated with chlorine gas at 950 C. for one hour. The sublimates from these two treatments, respectively designated sublimates A and B, analyzed as follows:

Sublimate A Sublimate B 19.50% FeCla Balance CrCla (Cr: Fe=4.09: 1)

11.34 FeCls Balance CrCl; (Cr: Fe=7.70 l) The foregoing examples 2, 3 and 4 illustrate the practicality of producing either substantially pure CrCls or substantially pure mixtures of CrCls and FeCls, depending upon the amount of iron oxide in the residue treated, by gassing the residue with C12 in the presence of the theoretically required amount of carbon. The carbon apparently reacts preferentially with the chromium and iron oxides and leaves the gangue materials substantially unaifected in the final residue. At most, only mere traces of the gangue metals, aluminum, silicon, magnesium, and calcium, are detectable in the sublimate, and the proportion of iron in the sublimate is substantially the same as in the residue treated with chromium.

The two chloridizing reactions are sufficiently selective, when controlled as described, so that iron and chromium powders, or iron and ferro-chromium powders, of better than 99% purity can be produced by electrolysis of the two sublimates.

The particular chloridizing agents and the chlorodizing conditions employed in accordance with the invention are highly critical in obtaining commercially useful results. For example, during the HCl treatment of a chromite ore, the presence of more carbon than the limiting quantity mentioned above causes the HCl to chloridize chromium as well as iron, though more slowly. Within the preferred temperature range (900 to 1050 C.),. given sufiicient carbon with the ore, iron chloride begins to come off first, then a mixture of iron and chromium chlorides comes off, and gradually the sublimate becomes richer in chromium chloride and leaner in iron chloride until the former is present in a great preponderance over the iron. While the sublimation temperature of iron chloride is somewhat below that of chromium chloride, vaporization of the former at a practical rate is not feasible below the sublimation point of the latter. Also, depending upon various factors, the temperature of formation of the chlorides is often above their sublimation temperatures. Accordingly, when chlorides of both iron and chromium 16 are formed together, selective sublimation of the iron chloride alone at a practical rate is substantially impossible.

Since the HCl treatment for removal of iron chlorides does not require the presence of any carbon, there is no reason for purposely adding any carbon to the first rec or or kiln 1 (Figur .1) or 3.2, (figure 2)- It i inere g n e, ho that the limited m n f carbon specified above may be tolerated during the HCl treatment. Why suchan amount of carbon, which is apparently not actually used by the iron oxide, has no effect, whereas a larger amount causes the chromium to react and produce CrCla is not at all clear. As a result, the tolerable amount of carbon is dependent upon presently unknown factors, and it may be sheer coincidence that such limit can be related to the amount of oxygen in the iron oxide to be left in the first ore residue.

The fact that the presence of some carbon may be tolerated permits greater freedom in the selection and use of fuels to be burned in contact with the ore where internal heating of the kiln is desired. Substantially complete freedom from carbon during the HCl treatment is preferred and is the best guarantee that the maximum tolerable amount will not be exceeded.

If chlorine gas is substituted in whole or even in a small part for the dry HCl gas in the initial chloridization of an ore containing a substantial amount of FeO, even in the presence of limited amounts of carbon or no carbon at all, the selective formation and/or volatilization of iron chloride alone is apparently not feasible at a commercially practical rate, for .the chlorine attacks both the chrominum and the iron with the production of chromium chloride in the sublimate. While the presence of a substantial amount of carbon is necessary to effect the rapid chloridization of CrzOa with chlorine when little or no FeO is present, the presence of a substantial amount of FeO seems to render the CrzOs more susceptible to attack by chlorine in the absence of carbon, and a chloridizing agent containing appreciable free chlorine is wholly unsuited for selectively chloridizing only the iron component of an w Mor over, chlor ne con e ts R0 to FeCla, rather h n FeC z, hich i es suited o e ectrolysis because of the greater amount of power required for its reduction.

Phosgene and carbon tetrachloride, both being more active than chlorine, are even more objectionable than chlorine as a possible substitute for dry HCl for they attack the other oxides of the ore as well as the chromium and iron oxides, and do so at relativelymuch lower temperatures. As a result, the sublimate is contaminated with chlorides of aluminum and silicon, and, sometimes, also with the chlorides of magnesiumand calcium.

The presence of any appreciable amount of water vapor during the 'HCl treatment seriously retards the chloridization of the iron oxide and renders the process commercially impractical, if not totally inoperative. Thus, completely dry HCl gas is preferred for the first chloridization treatment, and only very minor amounts of water vapor can be tolerated in commercial operations.

Attempts to use vapors from concentrated hydrochloric acid in the HCl treatment have resulted not only in extremely slow reaction, but have also resulted in the absorption of so much water by the small amounts of iron chloride formed that the iron chloride is saturated and may even become an aqueous solution.

In various prior art patents, reference is made to the introduction of substantial amounts of oxygen with the chloridizing reagents employed. While this may perform some useful function where lower temperatures and appropriate chloridizing reagents are employed to form chlorides without volatilizing them, it is tobe carefully avoided at temperatures of 850 C. or higher. At such temperatures the presence of oxygen in any material am un nv rt bot chr mium and 1 79. ch or de t0 oxy-chlorides and may even carry thegpcgalsbacl; to the '17 oxide stage, thus working directly at cross-purposes with the primary objects of the invention.

While dry HCl gas, in the presence of sufiicient carbon, will attack the chromium oxide as noted above, this chloridizing reagent is impractical for use in treating the ironfree residue in the second chloridizing reacton because it is not sufliciently active, and excessive times and temperatures are required, as shown in Example 3. The use of phosgene or sulphur tetrachloride in the second chloridizing reaction, on the other hand, is impractical because these reagents attack the other oxides of the residue and result in contamination of the chromium chloride with chlorides of aluminum and silicon and, in some cases, with the chlorides of magnesium and calcium as well. Thus, chlorine gas is by far the most satisfactory chloridizing agent yet found for treatment of the iron-free residue to produce pure chromium chloride.

From the foregoing, it will be appreciated that I have provided a method and system by which all of the various objects of the invention may be accomplished. By means of the invention, low grade chromite ores are, for the first time, rendered practically and economically suitable for numerous uses that formerly required metallurgical grades of ores or were not feasible by any known process. In addition, an economical process has been provided for producing from the low grade ores, as Well as from the high grade ores, substantially pure iron, chromium, and ferro-chromium in powdered form.

Having described my invention, I claim:

1. A process for beneficiating chromite to increase the chromium-to-iron ratio by selectively forming and subliming ferrous chloride, comprising contacting the ore in a chamber at a temperature above about 850 C. under anhydrous conditions with a gaseous reagent consisting essentially of dry hydrogen chloride, and removing gaseous ferrous chloride from said chamber as it is formed; free chlorine and active oxidizing gases and active reducing gases being excluded from said chamber during the reaction, and any free carbon in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide left in the ore residue at the end of the reaction, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue.

2. The process of claim 1 in which said elevated temperature is between about 900 and 1050 C.

3. A process for producing anhydrous ferrous chloride from chromite by treating the chromite to selectively form and sublime ferrous chloride, comprising contacting the ore in a chamber at a temperature above about 850 C. under anhydrous conditions with a gaseous reagent consisting. essentially of dry hydrogen chloride, and removing gaseous ferrous chloride from said chamber as it is formed and condensing it under anhydrous conditions; free chlorine and active oxidizing gases and active reducing gases being excluded from said chamber during the reaction, and any free carbon in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide left in the ore residue at the end of the reaction, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue.

4. The process of claim 3 in which said elevated temperature is between about 900 and 1050 C.

5. The process of claim 3 in which said gaseous ferrous chloride removed from said chamber is condensed at a temperature between about 350 and 650 C. while removing, in vapor form, any water entrained with the gaseous ferrous chloride.

6. A process for producing ferrous chloride from ore containing oxides of iron and chromium by treating the ore to selectively form and sublime ferrous chloride, comprising contacting the ore in a chamber at a temperature above about 850 C. under anhydrous conditions with a gaseous reagent consisting essentially of dry hydrogen v chloride, and removing gaseous ferrous chloride from said chamber as it is formed; free chlorine, active oxidizing gases, and active reducing gases being excluded from said chamber during the reaction, and any free carbon in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide left in the ore residue at the end of the reaction, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue.

7. The process of claim 6 in which the gaseous ferrous chloride removed from said chamber is condensed to an anhydrous powder at a temperature between about 350 and 650 C. while removing, in vapor form, any water entrained with the gaseous ferrous chloride.

8. A process for producing ferrous chloride from ore containing oxides of iron and chromium by treating the ore to selectively form and sublime ferrous chloride, comprising continuously feeding said ore preheated above about 1000 C. into a reaction chamber, continuously contacting the ore in said chamber under anhydrous conditions with a gaseous reagent consisting essentially of dry hydrogen chloride while maintaining the temperature of the ore above about 850 C., continuously removing from said chamber gaseous ferrous chloride as it is formed, and continuously removing an iron-impoverished ore residue from said chamber; free chlorine, active oxidizing gases, and active reducing gases being excluded from said chamber during the reaction, and any free carbon in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide left in the ore residue as it is discharged from said chamber, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue.

9. The process of claim 8 in which the gaseous ferrous chloride removed from said chamber is condensed to an anhydrous powder at a temperature between about 35 0 and 650 C. while removing, in vapor form, any water entrained with the gaseous ferrous chloride.

10. A process for recovering iron and chromium values from ore containing oxides of iron and chromium, comprising contacting the ore in a chamber at a temperature above about 850 C. under anhydrous conditions with a gaseous reagent consisting essentially of dry hydrogen chloride, and removing gaseous ferrous chloride from said chamber as it is formed and condensing it under anhydrous conditions; free chlorine, active oxidizing gases, and active reducing gases being excluded from said chamber during the reaction, and any free carbon in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide left in the ore residue at the end of the reaction, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue; contacting the ore residue with chlorine gas at a temperature above about 850 C. in the presence of carbon in an amount suflicient to react with the oxygen of the remaining iron and chromium oxides, to convert the chromium and remaining iron, if any, to gaseous chromic and ferric chlorides, and removing the resulting gaseous chromic chloride and any gaseous ferric chloride as they are formed and condensing them under anhydrous conditions.

11. The process of claim 10 in which said elevated temperatures are between about 900 and 1050 C.

12. A process for producing iron powder from chromium-iron ores and leaving a beneficiated, high-chromium, iron-impoverished ore residue, comprising contacting the ore in a chamber at a temperature above about 850 C. under anhydrous conditions with a gaseous reagent consisting essentially of dry hydrogen chloride, and removing gaseous ferrous chloride from said chamber as it is formed; free chlorine, active oxidizing gases, and active reducing gases being excluded from said chamber during the reaction, and any free carbon in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide-left in the 19 ore residue at the end of the reaction, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue; condensing the removed gaseous ferrous chloride at a temperature above about 350 C. while separating entrained water vapor formed therewith to produce anhydrous ferrous chloride in powder form, electrolytically disassociating the anhydrous ferrous chloride in a fused bath consisting essentially of alkali metal chloride in an electrolytic cell while diffusing hydrogen gas through the bath, to deposit elemental iron on the cathode of the cell and produce dry hydrogen chloride; and returning the dry hydrogen chloride to said chamber for contacting additional ore.

13. The process of claim 12 in which the temperature in said chamber is between about 900 and 1050 C.

14. A process for producing iron powder from chromium-iron ores and recovering a beneficiated, high-chromium, iron-impoverished ore residue, comprising contacting the ore in a chamber at a temperature between about 850 and 1100 C. under anhydrous conditions with a gaseous reagent consisting essentially of dry hydrogen chloride, and removing gaseous ferrous chloride from said chamber as it is formed; free chlorine, active oxidizing gases, and active reducing gases being excluded from said chamber during the reaction, and any free carbum in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide left in the ore residue at the end of the reaction, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue with a reduced amount of iron; condensing the removed gaseous ferrous chloride at a temperature sufiiciently above the boiling point of water, while separating entrained water in vapor form, to produce anhydrous ferrous chloride in powder form, melting the anhydrousferrous chloride in a fused bath consisting essentially of alkali metal chloride in an electrolytic cell, electrolyzing the ferrous chloride in said bath while difliusing hydrogen gas therethrough to deposit elemental iron powder on the cathode and release chlorine at the anode for reaction with the diffused hydrogen, and withdrawing dry hydrogen chloride so formed and returning it to said chamber for contacting additional ore; recovering a high-chromium, ironimpoverished ore residue from said chamber; and recovering elemental iron powder from said electrolytic cell.

15. The process of claim 14 in which the temperature in said chamber is between about 900 and 1050 C., and the gaseous ferrous chloride removed from said chamber is condensed at a temperature between about 350 and 650 C.

16. The process of claim 14 in which ore preheated to above about 1000 C. is continuously fed into said chamber, said gaseous reagent is continuously fed into said chamber counter-current to the feed of the ore, and said high-chromium, iron-impoverished ore residue is continuously removed from said chamber.

17. The process of claim 14 in which ore preheated to above about 1000 C., is continuously fed into said chamher, said gaseous reagent is continuously fed into said chamber counter-current to the feed of the ore, said highchromium, iron-impoverished ore residue is continuously removed from said chamber, and gaseous ferrous chloride is continuously removed from said chamber together with entrained water vapor formed therewith and passed into a condenser maintained at a temperature between about 350 and 650 C., said water vapor being continuously withdrawn uncondensed from said condenser, and the ferrous chloride being deposited in the condenser as a substantially anhyrous powder.

18. A process for recovering iron and chromium from chromium-iron ores, comprising contacting the ore in a chamber at a temperature above about 850 C. under anhydrous conditions with a gaseous reagent consisting essentially of dry hydrogen chloride, and removing gaseous ferrous chloride from said chamber as it is formed and condensing it under anhydrous conditions; free chlorine, active oxidizing gases, and active reducing gases being excluded from said chamber during the reaction, and any free carbon in the chamber during the reaction being limited to an amount not exceeding one part to six parts by weight of any iron oxide left in the ore residue at the end of the reaction, whereby substantially the entire chromium content of the ore remains as oxide in the ore residue; electrolyzing the condensed ferrous chloride in a fused bath of alkali metal chloride in a first electrolytic cell while diffusing hydrogen through the bath to deposit iron powder on the cathode and release chlorine for reaction with said hydrogen to produce dry hydrogen chloride; contacting said ore residue with chlorine gas at'a temperature above about 850 C. in the presence of carbon in an amount suflicient to react with the oxygen of the remaining iron and chromium oxides, to convert the chromium and remaining iron, if any, to gaseous chromic and ferric chlorides, and removing the resulting gaseous chromic chloride and any gaseous ferric chloride as they are formed and condensing them under anhydrous conditions; electrolyzing the condensed chromic chloride and any ferric chloride condensed therewith in a fused bath consisting essentially of alkali metal chloride in a second electrolytic cell while diifusing hydrogen therethrough to deposit the chromium and any iron present as a powder on the cathode and release chlorine for reaction with said hydrogen to produce dry hydrogen chloride; removing dry hydrogen chloride from said cells and feeding it into said chamber for contacting additional ore; and recovering elemental iron powder from said first electrolytic cell; and recovering elemental chromium, alloyed with any iron present, from said second electrolytic cell.

19. The process of claim 18 in which the contacting of said ore with dry hydrogen chloride and the contacting of said ore residue with chlorine are both carried out between about 850 and 1100 C.

20. The process of claim 18 in which the gaseous ferrous chloride, and the gaseous chromic chloride together with any ferric chloride formed therewith, are condensed at a temperature between about 350 and 650 C. while removing in vapor form any Water entrained therewith.

21. The process of claim 18 in which the contacting of said ore with dry hydrogen chloride and the contacting of said ore residue with chlorine are both carried out between about 850 and 1100 C., the contacting of the ore with dry hydrogen chloride and the removal of ferrous chloride being continued until a substantially ironfree residue remains, whereby the metal powder recovered from said second electrolytic cell is substantially pure chromium.

22. The process of claim 18 in which ore preheated to above about 1000 C. is continuously fed into said chamber, said gaseous reagent is continuously fed into said chamber counter-current to the feed of said ore, said ore residue is continuously withdrawn from said chamber and continuously fed into a second chamber for reaction with chlorine, the chromic chloride and any ferric chloride formed therewith are continuously removed from said second chamber, a substantially iron-free and chromiumfree ore residue is continuously withdrawn from said second chamber, and dry hydrogen chloride from at least one of said electrolytic cells is continuously fed to the first mentioned chamber for contacting additional ore.

References Cited in the file of this patent UNITED STATES PATENTS 1,434,485 DAndriam Nov. 7, 1922 1,571,502 Venn-Brown Feb. 2, 1922 1,805,567 Cooper May 19, 1931 2,240,345 Muskat Apr. 29, 1941 2,349,747 Muskat May 23, 1944 2,355,367 Cooper Aug. 8, 1944 2,665,191 Graham et al Jan. 5, 1954 (Other references on following page) 21 FOREIGN PATENTS Great Britain 1913 Great Britain Feb. 28, 1922 Great Britain 1925 Germany Aug. 26, 1941 Great Britain Feb. 11, 1929 22 OTHER REFERENCES I. W. Mellors Inorganic and Theoretical Chemistry, vol. 14, pp. 10, 11, 20-22. Longrnans, Green & C0., N. Y.

Transactions of The Electrochemical Society, vol. 87 (1945), pages 551 thru 567, article by Kroll.

Claims (1)

1. A PROCESS FOR BENEFICIATING CHROMITE TO INCREASE THE CHROMIUM TO-IRON RATIO BY SELECTIVELY FORMING AND SUBLIMING FERROUS CHLORIDE, COMPRISING CONTACTING THE ORE IN A CHAMBER AT A TEMPERATURE ABOVE ABOUT 850* C. UNDER ANHYDROUS CONDITIONS WITH A GASEOUS REAGENT CONSISTING ESSENTIALLY OF DRY HYDROGEN CHLORIDE, AND REMOVING GASEOUS FERROUS CHLORIDE FROM SAID CHAMBER AS IT IS FORMED; FREE CHLORIDE AND ACTIVE OXIDIZING GASES AND ACTIVE REDUCING GASES BEING EXCLUDED FROM SAID CHAMBER DURING THE REACTION, AND ANY FREE CARBON IN THE CHAMBER DURING THE REACTION BEING LIMITED TO AN AMOUNT NOT EXCEEDING ONE PART TO SIX PARTS BY WEIGHT OF ANY IRON OXIDE LEFT IN THE ORE RESIDUE AT THE END OF THE REACTION, WHEREBY SUBSTANTIALLY THE ENTIRE CHROMIUM CONTENT OF THE ORE REMAINS AS OXIDE IN THE ORE RESIDUE.

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