US2035454A - Production of antimony oxide - Google Patents

Description

M rch 31, 1936'. J. o. BETTERTON PRODUCTION OF ANTIMONY OXIDE I Original Filed Jan. 30, 1933 Patented Mar. 31, 1936 UNITED STATES PATENT OFFICE? Signor to American Smelting and Refining Company, New York, N. Y., a Corporation of New Jersey Application January 30, 1933, Serial No. 654,'176 Renewed July 10, 1935 10 Claims.

This invention relates to the production of antimony oxide from alloys of antimony and lead, and particularly concerns a new process for treating such alloys to obtain antimony oxide in a high state o'f purity and possessing an excellent white color tone.

In its broad aspects the invention is an improvement of that described and claimed by Burt C. Stannard and Calvin W. Haffey in United States Letters Patent No. 1,535,743, issued April 28, 1925.

By the present invention white antimony oxide, free from lead or at most containing only insignificant or permissible amounts of that element, is volatilized directly from antimony-lead alloys having a lead content within the range of appreciable quantities to approximately In general, the invention contemplates establishing an active, thin, molten, mobile slag film, oil-like in appearance, upon the surface of a molten antimony-lead bath in the presence of a suitable oxidizing atmosphere and so stabilizing the system that practically pure white, lead-free antimony oxide is volatilized from the Supernatant slag film regardless of the concentration of lead in the bath within the limits heretofore specified.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which Fig. 1 is an elevation of one type of apparatus suitable for practising the method of the invention; and

Fig. 2 is an elevation taken along the line 2-2 and at right angles to the elevation of Fig. 1.

Like reference characters denote like parts in the several figures of the drawing.

Referring now to the drawing, one suitable form of furnaceassembly is shown c'omprising a steel casing l lined with suitable refractory material 2' with beams 3 supporting a cast-iron melting and fuming pot 4. The furnace is mounted on trunnions 5 and may be tilted by suitable manipula- 'tion of the worm gear 6. A burner 1 opening into heating chamber 8 is provided for heating the antimony-lead bath 9 in fuming pot 4 while flue provides an exit for waste 'combustion gases. A hood ll adapted to fitsnugly over'fuming pot 4 is' provided with adjstable `v`entilators z and' an inner cylinder l3. The cylinder [3 is capable of adjustment both in respect to hood l l and the surface of the bath 9 by suitable means (not shown) attached to chains 14. A fiue !5 leads from hood ll to suitable fume recovery apparatus (not shown).

Employing the above-described apparatus, the process may be practiced as follows: the furnace is brought to the upright position and suitable antimony-hearing material, for example, anti-'- mony dross containing over 40% antimony and the balance substantially lead, charged to the pot 4. The metal may be melted and brought to a suitable temperature by heat derived from burner l and any dross formed during the melting down operation removed from the molten bath. Hood H may then be lowered over the furning pot and the inner cylinder l3 adjusted so that the lower edge is a suitable distance, for instance, approximately nine inches, above the surface of the bath and the desired distance may be maintained by suitable readjustment as the metal level falls during the operation of the process due to depletion of the antimony content of the bath by volatilization of antimony oxide.

Upon removal of the melting-down dross and exposure of the clean molten metal to the atmosphere,'a very thin, oil-like, mobile slag film forms on the surface of the bath 9 and antimony oxide, white in color and practically free from lead, rapidly volatilizes. As a thin hard crust appears on the slag film after a time which will depress the volatilization of antimony oxide if the crust is allowed to accumulate, the slag film is gently worked from time to time, for example, by an iron tool, in order to maintain the thin, molten, mobile slag film and to prevent and break up crust formation, When necessary, the surface should be skimmed with a perforated iron skimming tool or other suitable device to remove accumulated crust from the system. The metal should be maintained -within a controlled temperature range, for instance, approximately 1375 F. to 1500 F., and air admitted in required and regulated Volume through vents l2 in hood Il, care being taken to prevent rupturing the surface of the slag film or' appreciable cooling thereof by the incoming air.

By thus maintaining conditions of equilibrium between the molten bath, the thin slag film and the oxidizing atmosphere, fuming of practically pure antimony oxide may be efiected until the antimony content of the bath is depleted to approximately 40% antimony. The fume as it arises from the kettle may be conducted out through the inner cylinder !3 of hood ll to suitable recovery apparatus, for example, a baghouse, a fan (not shown) preferably being utilized in this operation.

When the fuming operation is completed, for example, when the antimony content of the bath falls below 40%, the heat may be turned ofi, the burner moved out of the way, the hood raised and the kettle emptied by suitably Operating the worm gear to tilt the furnace. Thereafter the fu'nace may be brought back to its original position, additional antimony-hearing material charged to the pot 4 and. the operation repeated.

It is to be clearly understood that the preceding specific example is given merely for purposes of illustration and is in no sense to be construed as limiting the broad scope of the invention.

In practising the invention various sources of antimony may be employed. For example, antimony-lead alloys, drosses or materials of similar composition containing approximately 40% oimore of antimony are suitable for the production of antimony oxide by the improved process, although an antimony content of 15% or more is preerred. The antimony content of antimonial lead compositions containing less than 40% antimony may be increased by adding bars of antimony metal thereto. Also, the source of antimony may contain ordinary impurities, such as arsenic, tin, copper, sulphur, nickel, bismuth, iron, etc. without special limitation except as follows: tin, if present to the extent of more than a few tenths percent, seriously retards the volatilization of the `antimony until it has oxidized and is removed by skimming the slag. Hence, tinfree base metal is preferred. Arsenic, while not affecting the color of the antimony oxide produced, will oxidize and volatilize as arsenious oxide along with the antimony oxide and, therefore, should not be present if a Strictly arsem'c-free antimony oxide is desired. Non-Volatile impurities, such ,as copper, bismuth, nickel, iron, etc. have little if any detrimental efiect and may be present in considerable amounts. Sulphur, if present, is easily oxidized and volatilized as sulphur dioxide gas or remains in the slag as sulphates.

Temperatura control is important if antimony oxide of the desired purity is to be obtained. It has been found that temperatures of 1425 F, to 1450 F. are preferable from an Operating standpoint, although the desired product may be obtained within a temperature range of approximately 1375 F. to approximately 1500 F. However, if the temperature is materially lowered below 1375 F. the thin, active slag film becomes less fluid and decreased volatilization results. On the other hand, when the Operating temperature is substantially increased above 1500 F., the color of the antimony oxide is detrimentally afiected within a very short time. If, however, the temperature does fall materially below 1375 'F., the fiuidity may be promptly restored by decreasing the Volume of air coming in contact with the film surface and by frequent gentle working of the slag film to break up any crust formation.

As has .already been pointed out, suitable means must be employed to gently work the slag film and prevent and/or remove crust formation and thus impart stability to the system. This is important because the formation of any considerable quantity of crust results in lead being volatilized which imparts a yellowish or brownish tinge to the fume. This is true even though the volatilization of antimony oxide may not appear to be visibly diminished. Due care should be exercised both in working the slag film and in admitting air into contact with the surface thereof in order not to rupture the slag film and thereby efiect volatilization of lead.

It is also important to note that the moving atmosphere in contact with the slag film should always be of an oxidizng character, as a reducing atmosphere destroys the film and allows lead to contaminate the antimony oxide. Also, the oxdizing atmosphere must be of uniform composition and free from contaminants which would, if present, discolor the volatilized oxide. Hence, air is preferably used although other oxid'zing gases which will meet the requirements specified may be utilized.

It will thus be appreciated that the present invention makes possible the volatilization of pure, white antimony oxide from alloys of antimony and lead, which phenomenon is remarkable in view of the large amount of lead which may be contained in the molten bath.

By reason of its high purity, antimony oxide produced in accordance with the principles of the present invention may be utilized in various industries demanding antimony oxide possessing a high quality, white color tone. Among other uses, it is particularly adapted for use as a pigment in white paints and as an opacifying agent in the enameling art.

The following explanation and Chemical equations are believed to explain, in part at least, the phenomenal volatilization of pure, white antimony oxide, from antimony alloys containing substantial amounts of lead, in accordance with the principles of the present invention. This explanation, however, is advanced merely as a hypothesis and is not to be considered as binding upon the applicant or in any way affecting the validity of the invention.

Vhen the thin slag film first forms on the molten metal, it is believed that the following two simple Chemical reactions take place:

and that probably the respective amounts of PbO and Sb203 in the slag film bear a definite relationship to the ratio of lead to antimony in the metal bath.

As the moving oxidizing atmosphere comes in contact with this slag film and enter into reaction therewith, oxidation probably results as follows:

It would appear that the thin, fluid slag film is highly active as an oxygen carrier due to rapid convection currents therein, thus providing effective contact between the oxidized lead and antimony compounds and the antimony in the bath, which results in converting the latter' to antimony oxide which volatilizes.

If the hypothesis and the explanations advanced are correct, there is probably little lead oxide existing as such in the active slag film by the time conditions of stabilization and equilbrium are established between the molten bath, the slag film and the moving oxidizing atmosphere. It appears probable that antimony oxide is rapidly entering the slag film, but under normal conditions of operation, it does not accumulate but is eliminated from the system practically as fast as it is formed.

While certain novel features of the invention have been disclosed and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. The process for treating antimony lead alloys containing less than 60% of the latter element which comprises forming a molten bath of such an alloy within a temperature range of approximately 1375 F. to 1500 F., introducing a moving oxidizing atmosphere into contact with the surface of said bath whereby pure, white antimony oxide is volatilized and gently working the surface of the bath at intervals to maintain stability of the system.

2. The process for treating lead-antimony alloys containing more than 40% of the latter element which consists in heating a bath of such an alloy to a temperature of approximately 1375 F. to approximately 1500 F. and gently sweeping the surface of the bath with air thereby volatilizing antimony oxide of high grade both as to purity and whiteness of color.

3. The process for treating antimony lead alloys containing less than 60% of the latter element which comprises forming a molten bath of such an alloy within a temperature range of approximately 1375 F. to 1500 F., introducing a moving oxidizing atmosphere into contact with the surface of said bath whereby pure, white antimony oxide is volatilized from a thin, fluid, mobile slag film covering the surface of the molten bath, gently working said slag film without rupturing same thereby stabilizing the volatilization of antimony oxide and recovering the volatilized antimony oxide.

4. The method of directly volatilizing white antimony oxide from an antimony-lead alloy containing more than 40% of antimony which comprises establishing and maintaining, within an approximate temperature range of 1375 F. to 1500 F., a thin, fluid slag film upon the surface of a molten bath of such alloy in the presence of a moving oxidizing atmosphere.

5. The method of directly volatilizing white antimony oxide from an antimony-lead alloy containing more than 40% of antimony which comprises establishing and maintaim'ng, within a temperature range of 1425 F. to 1450 F., a thin, fluid slag film upon the surface of a molten bath of such alloy in the presence of a moving oxidizing atmosphere.

6. In the direct volatilization of antimony oxide from a bath composed substantially of lead and antimony, the latter forming more than 40% of the total weight of the bath, the improvement which comprises gently sweeping the bath with air and periodically breaking the crust formed on the surface of the bath during the volatilization operation.

7. In the direct volatilization 'of antimony oxide from a bath composed substantially of lead and antimony, the latter forming more than 40% of the total weight of the bath, the improvement which comprises gently sweeping the bath with air and periodically skimming the crust formed on the surface of the bath during the volatilization operation.

8. The process of extracting substantially pure,

white antimony oxide from antimony contaminated with lead, which comprises maintaining a molten bath of the impure metal at a temperature sufficient to form and maintain a thin, fluid film on the surface of the bath, subjecting said filmcovered surface to the action of a gaseous oxidizing agent in predetermined Volume without rupturing the film thereby volatilizing the antimony as antimony oxide without volatilizing the lead in appreciable amount and recovering the volatilized antimony oxide.

9. The process of extracting antimony oxide from molten antimony contaminated with Volatile impurities, such as lead which consists in forming a thin, fluid, mobile film on the surface of the molten metal, subjecting said film at an appropriate temperature to the action of a controlled moving stream of air and maintaining conditions of equilibrium between the molten metal, film and stream of air by gently working the film at intervals and periodically breaking the crust formed thereon whereby antimony is withdrawn from the bath and substantially pure antimony oxide is continuously Volatilized from the film.

10. The process for preparing pure, white antimony oxide which comprises establishing an active, fluid, mobile slag film on the surface of a molten bath of a lead alloy containing in excess of 40% antimony and contacting the slag film with a moving, oxidizing atmosphere without rupturing said film thereby volatilizing' pure, white antimony oxide.

JESSE OATMAN BETTERTON.

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