US2277220A - Ore treatment - Google Patents

Description

lMarhzl, 1942. A -JQGAILEY 2,277,220

ORE TREATMENTv Filed Dec. 28, 1939 INVYENTOR BYANDREW J. GAILEY ATTORNEY Patented Mar. 24, 1942 e UNITED STATES PATENT OFFICE GRE TREATMENT Andrew J. Galley, Niagara Falls, N. Y., assignor to Electro Metallurgical Company, a corporation of West Virginia Application December 28, 1939, Serial No, 311,369

Claims.

This invention relates to methods of treating materials containing oxides of iron and chro-` mium, for instance chromite, for the principal purpose of raising the ratio lof chromium to iron in such material.

There exist large deposits of chromite-bearing ore in which the ratio of chromium to iron is so low that the ore is considered to be of an inferior grade. In general, if the ratio of chromium to iron is less than three to one, the ore is ill suited to important uses now made of high grade ores, for instance the manufacture of ferrochromium containing 65% to 72% chromium. It is important to the producer and consumer alike that there be available an economical method of treating the low grade ore to raise the ratio of chromium to iron toat least three to one, and it is a specific object of this invention to provide such a method. l

A more general object of lthe invention is to provide a method of raising the ratio of chromium to iron in a Wide variety of materials containing oxides of both chromium and iron.

A further object is to remove, from materials containing oxides of both chromium and iron, substantial amounts of iron but only insignificant amounts of chromium.

Other objects will be apparent from the following description and the accompanying drawing in which the single figure is a diagrammatic s representation in cross-section of a suitable furnace for use in practicing the invention.

In accordance with the invention, material containing oxides of both chromium and iron is treated with carbon'monoxide and an agent selected from the groupconsisting Vof chlorine, sulfur chloride, and mixtures of chlorine with sulfur chloride, at an elevated temperature above about 600 C. The temperature employed should not be so high that any substantial amounts of chromium chlorides are formed; ordinarily this temis beest to dryer emmene material before treating it. The calcination will drive oi water and will harden the briquets if the material is used in that form.

stance equal volumes of chlorine and carbon monoxide. Other gases, such as nitrogen and'carbon dioxide, may be present with the chlorine and carbon monoxide. Carbonmonoxide containing a substantial proportion of nitrogen may be prepared by the combustion of coke with air in a gas generating chamber. The use of carbon monoxide generated in this way is preferred.

Any by-product or industrial gas containing an appreciable proportion of carbon monoxide may be usedsin the process of this invention, although it should be noted that hydrogen or hydrogen compounds detrimentally aiect the emciency of the operation by contributing to the formation of hydrogen chloride. Nitrogen and carbon dioxide are not harmful to thev reaction and may even be benecial when functioning as diluents.

The treatment may be carried out in any suitable vessel/ for-examplel a retort, sagger, tube or shaft furnace. If a shaft furnace or a similartype of apparatus is used, the treatment of sucperature will be be1ow 850 c., but .the upper temperature limit varies with different conditions, for

example, of gas velocity, gas concentration. and pressure, and in some instances may be 900 C. or higher. At the proper temperatures, iron oxide in the ore is converted to iron chloride, most of which is volatilized, but no substantial part of the chromium is converted to the chloride. T

The material to be treated, chromite ore for example, is-crushed, for instance to pass through an 8 mesh screen (2.4 mm. openings). v finely ground, for instance to such a particle size that most of the material will pass through a 100 mesh screen (0.15 mm. openings). In either case, the crushed or ground material may be pressed into the form of pellets or briquets, using water or other suitable binder, or the ore may be treated in the loose, unbonded condition. -It

Itmay be cessive charges of ore may be made continuous. In such case, the eliiuent gases may be readjusted as to composition after the removal of at least the major part of the ferric chloride and then recycled. Preferably, the reaction vessel is well insulated to prevent loss of heat by radiation. The reaction is self-sustaining, and after the vessel is brought to the necessary temperature no heat need be added unless there are substantial losses of heat.

The single gure of the drawing diagrammatically illustrates a furnace suitable for use in practicing the invention. A vertical tube T in which the charge I0 is held is provided with a refractory lining L. A double bell charging dev ice'B adapted to charge the furnacewithout opening it to the atmosphere is mounted on.top of 'the tube T, and a device D into which treated material -is discharged through a. valve 20 is provided at the bottom of the tube T. A carbon monoxide inlet H and a chlorine inlet l2 are provided for admitting gases to the interior of the tube T. From the top of the tube T a iiue I3 leads into a condenser C provided with a "clean out I4, an exhaust gas outlet I5, a shaft I6 driven by a driving mechanism I'I and provided with a helical scraping means I8 for removing condensed ferric chloride from the condenser C. Ferric chloride is condensed from the gas emanating from the tube T in the condenser C and is discharged into a container V through a valve I9.

In using this type of furnace, the reaction is initiated by the combustion of fuel gas in the charged furnace. When the proper temperature is reached, chlorine is admitted to the furnace through the chlorine inlet I2, and a mixture of carbon monoxide and nitrogen is admitted justed as to composition and recycled in known manner or may be wasted. The treated material is collected in the device D. The furnace may be operated continuously, or the operations may be of the batch type.

If desired, external heating means, for example a muilie' equipped with a gas burner, may be used to heat the furnaceinitially.

The principles of the invention are illustrated in the following specific examples. A low grade chrome ore containing 30.2% chromium and 18.5% iron (ratio `Cr:le=l.6:1) was ground .to pass a 100 mesh screen, and formed into briquets, using water as a binder. In a test running 2.8 days, 2,796 pounds o f dried briquets were fed,

portionwise, into the top of a. vertical tube furnace eight feet in height, and fourteen inches in diameter. The furnace was maintained at an average temperature of approximately 715 C. in the reaction zone. Into the bottom of the tube was fed a mixture of 650 pounds of chlorine, 375 pounds of carbon monoxide, and 945 pounds of nitrogen. (CO and N2 obtained from the combustion of coke in air.) From the bottom of the tube were withdrawn 1,837 pounds of briquets containing 32.9% chromium and 8.9% iron (ratio Cr:Fe=3.7:l) and 643 pounds of briquets containing 16.5% iron. 'I'he total weightl of briquets recovered was 2,480 pounds, having an average composition of 32.7% chromium and 10.6% iron (ratio Cr:Fe=3.1:1). 533 pounds of crude ferric chloride containing 0.13% vchromium were condensed and recovered. The chlorine emciency (based on FeCla removed) was 75.7%.

In another test using the same kind of ore, 150 pounds of briquets were calcined and fed asa batch into the top of a. well-insulated vertical tube furnace of the type shown in the drawing.

.'Ihe reaction was started by burning carbon monoxide and air within the furnace in such manner that thecombustion occurred within the charge. After obtaining a temperature of about 800 C. the -air was shut oil', and chlorine was fed into the furnace at a rate of about one-half cubic j foot per minute, together with a carbon monoxidenitrogen mixture which was fed at a rate of about three cubic feet per minute. The carbon monoxide-nitrogen mixture contained 25.9% carbon monoxide, 68.4% nitrogen, the remainder principally carbon dioxide. The temperature remained at about 800 C. to 850 C. for about 81/2 hours. A total of 32 pounds of chlorine, 26 pounds of carbon monoxide and 70 pounds of nitrogen was fed into the furnace. A representative portion of the treated material contained 36.2% chromium and 4.4% iron (ratio Cr:Fe=8.2:1). The ferric chloride formed in the reaction was condensed from the exit gases. No chlorine was detectable in the exit gases by the usual tests, and very little carbon monoxide was present. The chromium Vrecovery based upon an aggregate sample of the entire mass discharged was 100%.

I claim:

l. Method of removing iron from a material containing oxides of both chromium and iron which comprises subjecting such material, at a temperature above about 600 C., but below the temperature at which 4substantial amounts of chromium chlorides are formed. to the action of a gaseous mixture consisting essentially of carbon monoxide, a chlorinating Vagent selected from the vgroup consisting of chlorine, sulfur chloride, and mixtures thereof, and a diluent gas substantially free from hydrogen, whereby iron oxide is converted to iron chloride but no substantial proportion of chromium oxide is attacked; and volatilizing and removing at least the major portion of the iron chloride so formed.

2. Method as claimed in claim 1 in which the chlorinating agent employed isI chlorine `and the diluent gas is carbon monoxide in excess of that which will react with said material.

3. Method of removing iron from a chromite ore which comprises subjecting finely ground ore, at a temperature between 600 C. and 900 C., to the action of a stream of gas consisting essentially of chlorine, carbon monoxide, and a diluent gas substantially free from hydrogen, whereby to form iron chloride without attacking any substantial proportion of chromium oxide; volatilizing and removing at least the major portion of the iron chloride so formed; and continuing the treatment until the ratio of chromium to iron of said ore has been raised substantially.

4. Method of removing iron from a chromite ore containing chromium and iron in a ratio lower than 3 to 1 which comprises passing through the ore, ground sulciently fine to pass a 100 mesh screen (0.15 mm. openings) and at a temperature between 600 C. and 900 C., a stream of gas essentially comprising chlorine, carbon monoxide,- and a. diluent gas substantially free from hydrogen. whereby to form iron chloride but no substantial proportion of chromium chloride; volatilizing and removingy in said stream the iron chloride so formed; and continuing the treatment until the ratio of chromium to iron of said ore is at least 3 to l.

5. Method of removing iron from a chromite ore which comprises finely grinding such ore;

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