US2939784A

US2939784A - Process for elimination of sulfur from metals

Info

Publication number: US2939784A
Application number: US763426A
Authority: US
Inventors: Joseph H Brennan; Cecil G Chadwick
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1958-09-26
Filing date: 1958-09-26
Publication date: 1960-06-07
Anticipated expiration: 1977-06-07

Description

United States Fatent O PROCESS FOR ELHVIINATION OF SULFUR FROM METALS Joseph H. Brennan, Niagara Falls, and Cecil G. Chadwick,

Lewiston, N.Y., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Sept. 26, 1958, Ser. No. 763,426

14 Claims. (Cl. 75-1305) This invention relates to an improved process for the removal of sulfur from metals.

vOne of the important problems involved in the making of commercial alloys, such as terrochromium, is the production of suitable low-sulfur alloys. In the present state of the art, low-carbon, low-sulfur ferrochromium may be produced by reacting high carbon ferrochromium with silica according to the method disclosed by H. deW. Erasmus in US. Patent No. 2,473,019. While this method is eiiective in substantially eliminating the sulfur content, it produces a low-carbon, ferrochromium alloy containing large amounts of silicon. When the high carbon 'ferrochromium is decarburized with oxides other than silica, only a small part of the sulfur content is removed.

It is, therefore, an important object of the present invention to provide a simple, inexpensive and effective method of substantially eliminating the sulfur of sulfurbearing metals and alloys without the introduction of undesirable elements.

Another object of the present invention is to provide an improved and simplified method of removing sulfurous contaminants from metals and alloys during the vacuum-heating thereof.

Another object of the present invention is to provide a novel mixture capable of employment with the novel method of the invention to produce a low-sulfur ferrochromium alloy of improved quality, which is substantially free from the effects of silicon.

According to the broad aspects of the invention, a sulfur-containing metal or alloy, such as ferrochromium, is intimately mixed with tin or other metals capable of forming a volatile sulfide compound. Under vacuum heating conditions, the tin reacts with sulfur in the solid state at temperatures well below the melting point of the alloy, to form a readily removable, volatile, stannous sulfide. Having a low boiling point, tin is especially suitable in the practice of the invention, since the excess or uncombined tin may be readily volatilized at temperatures well below the temperatures normally encountered in vacuum heating.

The sulfur-bearing metal or alloy to be treated ac cording to the method of the invention may have a high or a low carbon content and may contain any desired constituents, as for example, metals such as chromium or nickel. For simplicity, the invention will be described in connection with the decarburization of high carbon ferrochromium, using tin as the addition agent, although it is to be understood that the invention is not limited thereto, but is susceptible of application in other sulfurbearing metals and alloys with various suitable metal additions other than tin.

The tin to be used in the method of the invention may be used in its elemental form, as a constituent of the chromium alloy, or as a separate alloy or ferroalloy, or even as the common ore of tin cassiterite, depending upon the specific conditions desired. For example, a ferrotin alloy may be used in conjunction with the high ICC carbon sulfur-bearing ferrochromium to constitute the respective sources of tin and ferrochromium material in the method of the invention.

According to the present invention, improved sulfur removal in the vacuum heating of high carbon, sulfurbearing ferrochromium may be attained by reacting the sulfur with tin in the solid state to form a volatile sulfide of tin. To this end, the high carbon ferrochromium and tin are proportioned within certain prescribed limits, so that the tin reacts with substantially all of the sulfur contaminants in the ferrochromium.

For efliciently utilizing the reactivity between the tin and the sulfur, the amount of tin present in the ferrochromium should be at least equal to that required for complete stoichiometric reaction with the contained sulfur. Preferably, an excess quantity of tin may be employed, over and above the stoichiometric amount required, the excess being readily volatilized at the decarburization temperatures used in the practice of the invention.

In a preferred practice of the invention, the high carbon ferrochromium and the tin or a grindable alloy of tin may be finely comminuted to 325 mesh (0.044 mm. openingslor smaller, and mixed with chrome ore or other suitable oxide until a substantially homogeneous dry mixture is attained. A compact of this mix may then be suitably bonded, using, for example, a cereal binder such as Mogul and water in an amount suflicient to moisten and plasticizethe mix. The moistened ingredients may be compacted into pellet form and dried by mildly heating at about 200 C. Thereafter, the pelletized material may be decarburized by vacuum heating at a pressure of about 2 mm. Hg. absolute and a temperature sufiicient to provide a reaction in the solid state but below the fusion point of any of the charge, preferably at about between 1100 C. and 1450 C.

As an alternative, the tin may be alloyed with high carbon ferrochromium, either by simple addition to the pots receiving ferrochromium from the smelting furnace, or as an alloying addition during the smelting of the high carbon ferrochromium charge. If added during smelting, the tin additive material may be in the form of metallic tin, 'ferrotin, or the mineral cassiterite.

The following examples are illustrative of the practice of the invention, and more fully indicates the extent of the desulfurization effect of tin on high carbon ferrochromium during vacuum heating decarburization treatment.

EXAMPLE I Lbs. Ferrochromium 1800 Tiebaghi chrome ore 700 Mogul 40 The chrome ore had the following approximate analysis:

Percent Or O 54 FeO 14 A1 0 10 Si0 3 MgO 16 CaO 1 Sufficient water was added to Slightly moisten the mixture Table 1 LC. Ferrochromium Product Produced in Accordance with the Invention H.C. Ferroehromium V Charge Percent Percent Sn c Fe and Incidental Impurities balance EXAMPLE II In a series of tests similar to the test conducted in Example I, varyihgadditions of tin were made in the form of cassiterite concentrates containing 71.88 percent tin. In these tests the tin was less than the stoichiometric amount (0.23 percent by weight) required to react with balance horizontal vacuum furnace at a temperature below the fusion point of any of the charge. The furnaced pellets all the sulfur in the ferroc'hromium. Before treatment the highcarbon ferr'ochromiuin contained 0.064 percent sulfur. The analyses of the products obtained are indicated in Table II. v

Table II Preduclt Constituent,

Tin Addttlonf Percent wt. of 11. 0. FeCr ercent Top The above test results indicate that the combination of tin and high carbon ferrochromium is admirably suited in substantially lowering the sulfur content during the decarburization of high carbon ferrochromium, without any significant carryover of the tin addition in the resultant low carbon ferrochromium product. Because of the reactivity of tin and sulfur in the solid state under 'vacuum heating conditions, and the low boiling tempera- To illustrate the procedure wherein tin compounds are were then analyzed for sulfur, carbon, and tin. The results are shown in Table III.

Table 111 Product Constituent, percent Desulturlzlng Tln Compound Top Bottom.

0- 0.007 0.005 Stannous chloride, 51101221120 S I 0.020 0.028 Sn 0.001 0. 001 C 0.009 0.005 Stannic Oxide, S 8 0.025 0.013 sn 0.001 0.001 C 0.012 0.012 Stannous chromate, Sn(CrO4) S 0.012 0.015

s 0. 001 0,001 C 0.008 0.003 'Iln concentrates, 70% Sn as SnOLn, S 0. 035 0.017 Sn 0.001 0.001

From these data it may be seen that tin may be added inthe form of tin compounds as well as, in the form of alloys and elemental metal for the removal of sulfur from the low ferrochrome product provided that the compound, ore, alloy or elemental metal does not contain sulfur, i I

It 'will be understood that modifications and. variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

This application is a continuation-in-part of United States patent application Serial No. 605,925, filed August 2.4, 1956, now abandoned.

What is claimed is:

1. In the art of manufacturing a low-carbon sulfurfree ferrochromium alloy from a high-carbon sulfurbearing ferrochromium alloy, the improvement which comprises comminuting said high-carbon ferrochromium to a particle size of less than 325 mesh, mixing therewith at least one similarly sized sulfur-free material selected from the group consisting of elemental tin, tin alloys, tin compounds, and tin-containing ores, in an amount suflicient to react with all of the sulfur in said highcarbon ferroch-romium, pelletizing the admixture of said high-carbon'ferrochromium and said selected material, and decarburizing the said pelletized material under vacuum heating conditions for a time sufficient to react in "the solid state the tin of said selected material with sub stantially all of the sulfur in said high-carbon ferrochromium to form a volatile sulfur compound and to vaporize any excess contained tin.

2. In the method of desulphurizing a sulfur-c0ntain ing ferrochromium wherein said ferrochromium is comminuted and mixed with a comminuted oxidant, and the mixture so formed is heated under subatmospheric pressure, the improvement comprising admixing, prior .to heating under subatmospheric pressure, at least one oomminuted sulfur-free material selected from the group consisting of elemental tin, tin alloys, tin compounds, and tin-containing ores, in an amount approximately required to react with all of the sulfur in the solid state during said heating to form a volatile sulfurstin compound.

3. In the solid state, vacuum' heating of sulfur-Icontaining materials selected from the group consisting of metals and alloys to effect'desulphurization. thereof, the improvement which comprises providing, in a corn- .minuted mixture containing said selected groupmember, an amount of atleast one sulfur-free material selected from the group'co nsisting of elemental tin, tin alloys,'

tin compounds, and tinrcontaining ores capable ofreacting, during said-heating, with. substantially all ofsaid contained sulfur to form a volatile sulfur-tin compound without causing a substantial amount of tin to remain in the resultant product. v

4. In the manufacture of a sulfur-free metal from; a

sulfur-containing metal, the improvement which comprises incorporating with said metal at least one sulfurfree material selected from the group consisting of elemental tin, tin alloys, tin compounds, and tin-containing ores, containing an amount of tin approximately sufficient to react with all of the contained sulfur, and heating said metal and selected group material at a pressure and a temperature, below the fusion points of said metal and tin, suflicient to react said contained tin and said sulfur in the solid state to form a volatile tin sulphide compound and to vaporize any excess contained tin.

5. An improved process in accordance with claim 2 wherein said comminuted sulfur-free material is ferrotin.

6. An improved process in accordance with claim 2 wherein said comminuted sulfur-free material is tin oxide.

7. An improved process in accordance with claim 2 wherein said comminuted sulfur-free material is elemental tin.

8. An improved process in accordance with claim 2 wherein said comminuted sulfur-free material is stannous chloride.

9. An improved process in accordance with claim 2 wherein said comminuted sulfur-free material is stannous chromate.

10. An improved process in accordance with claim 4 wherein said comminuted sulfur-free material is ferrotin.

11. An improved process in accordance with claim 4 wherein said comminuted sulfur-free material is tin oxide.

12. An improved process in accordance with claim 4 wherein said comminuted sulfur-free material is elemental tin.

13. An improved process in accordance with claim 4 wherein said comminuted sulfur-free material is stannous chloride.

14. An improved process in accordance with claim 4 wherein said comminuted sulfur-free material is stannous chromate.

References Cited in the file of this patent UNITED STATES PATENTS 2,238,194 Tainton Apr. 15, 1941 2,473,019 Erasmus June 14, 1949 2,626,863 Erasmus Jan. 27, 1953 FOREIGN PATENTS 729,177 Great Britain May 4, 1955

Claims

1. IN THE ART OF MANUFACTURING A LOW-CARBON SULFURFREE FERROCHROMIUM ALLOY FROM A HIGH-CARBON SULFURBEARING FERROCHROMIUM ALLOY, THE IMPROVEMENT WHICH COMPRISES COMMINUTING SAID HIGH-CARBON FERROCHROMIUM TO A PARTICLE SIZE OF LESS THAN 325 MESH, MIXING THEREWITH AT LEAST ONE SIMILARLY SIZED SULFUR-FREE MATERIAL SELECTED FROM THE GROUP CONSISTING OF ELEMENTAL TIN, TIN ALLOYS, TIN COMPOUNDS, AND TIN-CONTAINING ORES, IN AN AMOUNT SUFFICIENT TO REACT WITH ALL OF THE SULFUR IN SAID HIGHCARBON FERROCHROMIUM, PELLETIZING THE ADMIXTURE OF SAID HIGH-CARBON FERROCHROMIUM AND SAID SELECTED MATERIAL, AND DECARBURIZING THE SAID PELLETIZED MATERIAL UNDER VACUUM HEATING CONDITIONS FOR A TIME SUFFICIENT TO REACT IN THE SOLID STATE THE TIN OF SAID SELECTED MATERIAL WITH SUBSTANTIALLY ALL OF THE SULFUR IN SAID HIGH-CARBON FERROCHROMIUM TO FORM A VOLATILE SULFUR COMPOUND AND TO VAPORIZE ANY EXCESS CONTAINED TIN.