US1678607A - Metallurgy of zinc - Google Patents

Description

July 24, i928.

METALLURGY OF ZINC Filed May 5,` 1925 f Il., llll .IIIIII I n l l IIIIIIIIU Patenteduuiy 24, 192s.

UNITED y STATES PATENT OFFICE.

JAMES A. SINGMASTER, OF BRONX'VILLE, NEW YORK, AND FRANK G. BREYER AND EARL H. BUNCE, F PALMERTON, PENNSYLVANIA, ASSIGNORS T0 THE NEW JER- SEY ZINC COMPANY, OF NEW YORK, N. Y., A CORPORATION 0F NEW JERSEY.

METALLURGY 0F ZINC.

Application filed May 5, 1925. Serial No. 28,058.

This invention relates to the metallurgy of zinc, and has for its object the provision of an improved method of reducing zinciferous materials. The resulting zinc vapors i may be suitably treated for the production of zinc, zinc dust, zinc oxide, etc.

Metallic zinc or spelter, when produced by the reduction of oxidized zinc ores at high temperatures, is almost universally l0 made at the present time in zinc distillation or spelter furnaces having a number of relatively small retorts to the outer ends of which condensers are attached. The retorts are usually mounted at a slight inclination,

l usually inclined downward from the butt or closed end towards the open or outer end. The condenser is in effect an extension or elongation of the retort, although usually mounted in a substantially horizontal position, and hence not in exact alignment with the elongated axis of the retort. The zinc vapor and other gases pass in a substantially horizontal line from the retort through the condenser, and the exhaust gases escape through the open end of the condenser. The efficiency of this present customary condensing apparatus is far from satisfactory7 only about 60 to 65% of the metallic zinc vapor passing out of the retort being condensed as metallic zinc or spelter, the remainder being condensed as blue powder or burning at the mouth of the condenser to zinc oxide and lost. y

The complete operation, in this heretofore customary practice of producing metallic zinc. usually takes a full day of 24 hours.

'lhe spent residues are removed from the retorts with considerable difficulty, and sometimes have to be manually pulled or scraped from the retort with a specially constructed tool.' These spent residues are frequently slaggezl and form very undesirable adhesions to the walls of the retorts. In addition to the labor difficulty of chargingand discharging the retorts and the long time element, Q4 hours for the complete working off of a retort charge, this heretofore customary practice effects far from complete elimination of the available zinc from the '/.iuciferous material of the charge. A comparatively large 'amount of this uneliminated zinc remains behind with the spent residues and is lost.

Our improved method of reducing` zinciferous materials involves externally heatmg an agglomerated or briquetted charge of mixed zinciferous material and carbonaceous reducing agent in an appropriate chamber, under substantially complete reducing conditions, to a sufficiently high temperature to reduce the compounds of zinc and volatilize the resulting zinc, and then sultably treating the zinc vapor so formed for the production of zinc, zine dust, zinc oxide, etc.

In our preferred practice, we employ a vertical retort made of appropriate heatresisting and heat-conducting material. The

retort is mounted within an appropriate' furnace structure and is surrounded by a heating chamber or laboratory. The laboratory may be heated in any appropriate manner` as, for example, by the products of combustion from burning fuel, such as coal, oil or gas, or by electric energy.

In carrying out our invention, the agglomerated or briquetted charge of mixed zinciferous material and carbonaceous reducing agent is fed into the vertical retort at the top and the spent residue or worked.- od charge is withdrawn from the bottom. The retort may be operated intermittently or continuously. Appropriate openings are provided for regularly ascertaining the temperature throughout the laboratory or heating chamber for enabling the proper temperature control of the operation. The temperatures within the laboratory are usually maintained at from 1200o C. to 1300o C. depending, in some measure, upon the nature of the particular charge being worked.

We prefer to agglomerate the mixed zincalthough it is to be understood that briquettes of other forms and dimensions may be used.

The working4 of an agglomerated or briquetted charge in a vertical retort or shaft furnace, in accordance with the principles of our present invention, has many advantages. In the case of a loose or unagglomerated charge of mixed zinc ore and coal, the heat conducted through the wall of the retort very quickly reduces the zinc ore and consumes the coal in that part of the mixed charge adjacent or in immediate proximity to the heated wall of. the retort. The exhausted coal ash, which is very loose and porous as a consequence of the carbon being burned out of it, and the exhausted zinc ore, which is also very loose and porous as a consequence of the zinc being volatilized out of it, then constitute a most eiiicient heat insulator and the temperature of the retort wall must consequently be raised very high in order to drive the heat necessary to reduce the ore in the core of the retort into this core in a given time. In the case of the ordinary zinc or spelter retortv (8 to 9 inches in diameter) operating with a loose or unagglomerated charge, this is a days (approximately 24 hours) operation. But even with this length of time allowed for the 'penetration of the heat, the temperature of the retort wall necessary to drive the hea-t into the core of the charge is so high that the exhausted ore and coal ash in the outer ring next to the retort wall fuse and slag to the wall of the retort, thus causing bridging and hanging up of the charge and make the removal of the exhausted charge dicult.

On the other hand, where the charge of .mixed zinc ore and carbonaceous reducing `the heat-absorbing agglomerates or briquettes themselves, convection currents are set up in the spaces between the agglomerates or briquettes and heat is conducted quite efficiently from the hot wall of the retort to the cooler agglomerates or briquettes forming the core of the charge. The same gas, inasmuch as it only serves in this particular case as a heat carrier, circulates round and round or backand forth carrying heat to the core of the charge.

Furthermore, each individual agglomeratie or briquette, due to its increased density as a consequence of having' been agglomerated or briquetted, has very much greater heat conducitivity than the same volume of loose charge. 'lhe operation of the agglomerating or bri netting not only facilitates the transfer of eat from the hot wall of the retort to an agglomerate or briquette in the core of the charge in consequence of the free gas passages between the agglomerate or briquettes, but each agglomerate or briquette in the core of the charge is much more capable of conveying heat from its surface into its center than an equivalent volume of loose charge in consequence of the densifying operation involved in' agglomerating or briquetting. The long carry of heat, say 4 or 5 inches or more, is hastened by providing free play for convection or heat-conduct1ng currents of gas. The short carry of heat, say one-half to one inch, in an individual unit of the charge (an agglomerate or briquette) at the core of the retort is hastened by increasing the conductivity of this unit volume of charge by densifying it. Thus, the improved method of our resent invention involves a combination ot these two efficient modes of securing heat transfer.

ln practicing our present invention under4 the controlled conditions characteristic thereof, the agglomerated or briquetted units maintain their form until practically all of the zinc in the ore has been reduced and volatilized. The spent agglomerates or briquettes then crumble to a tine ash residue which is easily removed from the bottom of the retort, intermittently or continuously, as desired.

The volatilized zinc flows upwardly through the retort and out the top or mouth thereof. It may be suitably treated for thc manufacture of the desired zinc product In the case of zinc or spelter, which will now be more particularly described, the zinc va por is conducted into an appropriate condenser where the zinc vapor is condensed to metallic zinc or liquid spelter. l,Ve prefer to employ a vertical condenser having substantially upright condensing walls and a condensing ceiling of the character described in the copending application of Messrs. Mahler, Handwerk and Bunce, Serial No. 28,056, filed May 5, 1925.

lIn the accompanying drawings, we have illustrated a furnace of the vertical retort type for practicing the improved method of our invention in the manufacture of zinc or spelter. In these drawings Fig. 1 is a front sectional elevation of the furnace;

Fig. 2 is a side sectional elevation of the furnace,

Fig. 3 is a section on the line 3 3 of Fig. 2, and

llo

Fig. 4 is a detail modification of the lower ing drawings comprises a vertically disposed cylindrical retort of `fire clay or other appropriate material. This retort may, if desired, be built up of a plurality of superosed sections. The retort 10 is surrounded ibi' the greater part of its length, b a laboratory or heating chamber 11. T e heating chamber 11 is built within a furnace structure comprising an outer steel shell or casing 12, an intermediate la er 13 of heat insulating material and a re ractory lining made u of tire brick 14 covered with graphite bloc rs or plates 15. Appropriate openings 16 are provided through the wall of the furnace structure for permitting the insertion of pyrometers within the laboratory or heating chamber 11, for ascertaining and appropriately controlling the temperature throughout the length of this chamber.

The furnace structure is mounted on an appropriate foundation 17. In Figs. 1 and '2 of the drawings the bottom of the retort 10 opens into a closed chamber or pit 18 having a cleanout door 19.

Any a propriate means may be employed for heating the retort 10. Thus, for example, the products of combustion rom burning fuel, such as coal, oil or gas, may be conducted through the laboratory 11, around the retort 10 and to an appropriate stack. In the apparatus illustrated in the accompanying drawings, the heating of the retort 10 is effected by electric energy. The electric heating or resistance element vcomprises two graphite rods or resistors 20 extending through the top of the furnace structure and resting on graphite blocks 21 slightly below the center of the chamber 11. The lower portion of the rods 2() are hollow and have a spiral slot so as to provide a helical resistance path for the flow of the electric current. One terminal of the source of electric energy is connected to one of the graphite rods 20 and the other terminal of the source of electric energy is connected to the other graphite rod 20, the electric circuit between the lower ends of the two rods 20 being completed through the graphite blocks 21 and the graphite lining 15. Either direct or alternating current may be used for supplying electric energy to the graphite rods 20.

The bottom ot the chamber 11 is provided with two graphite resistance rods or elements 22, of the same general construction as the resistors 20. The rods 22 extend horizontally through the furnace structure and rest on graphite blocks 23 which serve to electrically connect in parallel the intermediate spiraled portions of the two rods 22. This lower heating element may often be dispensed with, and is provided as an auxiliary or additional source of heat when desired or necessary. The two terminals of the source of electric energy are connected respectively to the outer ends of the two rods 22, and either alternating or direct current miy be use feed tube 28 may be provided near the top of the retort 10 for introducing the briuetted charge into the retort. Such a fee tube is of particular advantage when the retort is continuously operated.

In Fig. 4 of the accompanying dra an automatic dischar 'ng device is provided for continuously an automatically remov. ing the finely divided worked-off charge or residue, at a predetermined rate, from the bottom of the retort 10. A cylindrical extension 29 is bolted, or otherwise ap ropriately secured, to the underside of the ttom steel plate ofthe furnace structure. A lindrical sleeve 30 is loosely threaded on ille lower part of the extension 29. The exten sion 29 and sleeve 30 register with the retort 10 and constitute, in effect, a continuation of theretort below the furnace structure pro r. A rotatable disk or table 31 is mounte in proximity to the lower end of the sleeve 30, and the distance between the sleeve and the table can be adjusted by turning the sleeve on its threaded connection with the extension 29. The table 31 is rotated from any suitable source of power. A horizontally and vertically adjustable arm or rake 32 extends over the top of the table 31, and serves, during the rotation of the table, to scrape off a predetermined amountof the fine residue accumulating on the table. By this discharge mechanism, a continuous and uniform discharge of the fine residues from the bottom of the retort may be readily effected.

An appropriate condenser is vertically mounted on top of the furnace structure and axially in alignment with the retort 10. The condenser illustrated in the accompanying drawings comprises a c lindrical, vertically disposed wall 24. flat, circular ceiling 25 covers the top of the cylinder 24 and an annular plate 26 partially closes the bottom of the cylinder. The cylinder 24 and plates 26 and 27 are made of heat reractory material, such as fire clay, carborundum, mixtures of the same, or the like. These three elements may be integrally united or separately formed and joined together to constitute a plug-hat con` denser.

A nozzle 33 is attached to the bottom plate 26. The diameter of the central opening in the plate 26 and the internal diameter1 of the nozzle 33 are less than the diameter of the retort 10 and these three elements are axially in alignment. The nozzle 33 extends upwardly to about mid-way of the condensing chamber provided Within the cylinder 24.

The ceiling 25 has a central opening 34 loosely covered by a. plate 35. The exterior of the condenser (cylinder 24 and ceiling 25) is covered with an appropriate layer 36 of heat insulating material. In practice, we have found coal dust admirably adapted as a heat insulating covering for the condenser. From the loosely packed insulating material (coal) around the plate 35, the carbon monoxide gas escapes from the open1ng 34 of the condensing chamber and burns in the air.

The annulai` space between the nozzle 33 and the cylinder 24 provides a well for collecting molten zinc, and molten zinc is tapped from this well, from time to time, through a tap hole 37.

The mixture of zinc vapor and carboi monoxide gas (resulting from the reduction of the oxidized zinc ore in the retort 10) passes out of the top of the retort into the nozzle 33. An upwardly flowing stream or current of zinc vapor thus passes through the bottom of the condenser and into the condensing chamber. This stream of zinc Vapor impinges against and fans out over the ceiling 25 and is uniformly deflected down the side of the upright Wall 24.

The inner surface of the cylindrical Wall 24 and the entire ceiling 25 are covered with a film of molten zinc. The zinc vapors entering the condenser are drafted across this constantly renewed fresh lilm of molten zinc and condensed thereon. Thus, the film of molten zinc provides a nucleus on which condll densation of the zinc vapor readily takes place. The exhaust gases, for the most part carbon monoxide, escape through the opening 34, passing underneath the loose plate and through the loose heat insulating material thereon. By properly regulating the temperature of the condensing walls (24 and 25) substantially all of the zinc vapor will condense as metallic zinc or liquid spelter.

The metallic zinc condensing on the wall of the cylinder 24 flows down this Wall into the molten metal well at the bottom of the condensing chamber. The molten zinc ac* cumulates in this Well and is periodically removed therefrom through the tap hole 37.

It is important that the temperature of the Walls of the condensing chamber (24 and 25) be carefully controlled. If the temperature of these walls is too high, the gases es. caping through the opening 34 will carry toc much zinc vapor, and if the temperature of these walls is too low, an excessive amount of blue powder Will be formed. We have found a temperature of from 500 to 850 C. satisfactory, and when the condensing walls are maintained Within this temperature range, very etlicient 'condensation of zinc vapor to metallic zine or liquid spelter results.

The control of the temperature of the wall 24 and ceiling 25 is conveniently effected by regulating the amount of external heat insulation around these elements. In prac tice, a. pyrometer (thermo-couple) is periodically inserted into the condensing chamber (preferably through the top opening 34) and when the temperature within the chamber is too high, the amount of external heat insulation is decreased, and when the temperature is too low, the amount of this external heat insulation is increased. This external heat insulation may advantageously consist of a layer of dust coal or other appropriate heat insulating material, loosely packed around the outside of the condenser.

In practicing our improved method of making metallic zinc in the apparatus illustra-ted in the accompanying drawings, the agglomerated or briquetted charge of mixed zinciferous material and carbonaceous reducing agent is charged into the retort l0, intermittently or continuously as desired. and the retort is heated to a temperature of approximately 12004300o C. At this temperature reduction of the compounds of zinc in the zinciferous material takes place, and Athe reduced zinc is volatilized and passes upwardly and out of the top of the retort 10. The zinc vapor, together with the carbon monoxide gas resulting from the reaction, flow into the condenser, where the zinc vapor is condensed, the resulting molten zinc collectcd and periodically tapped from the condenser, as hereinbefore described.

`We have found that the metallic zinc can be reduced and volatilized from the zinciferous material of the charge Without fusion or slagging by agglomerating or briquet-ting the charge as hereinbefore described. The temperature to which the agglomerated or briquetted charge is heated is at no time much above the temperature which is necessary to reduce the compounds of zinc in the charge. The proper control of the temperature of the charge is important. The temperature is never so high thatJ the exhausted or worked-oil agglomerates or briquettes fuse or sinter, but on the contrary the exhausted or worked-oli2 charge is dry and pulverulent, in which condition the residues cause no gradual reduction in the capacity of the retort and gradual reduction in the heat-conductivity of the charge due to the ever thickening layer of slag residues, but in this condition the Worked-off charge is most easily removed from the retort and constituted its own seal at the bottom of the retort. Vhen worked-olf, the charge is completely pulverulent and readily flows out of the bottom of the retort.

The mixed charge of zineiferous material and carbonaceous reducing agent may be agglomerated in any appropriate manner. The individual agglomerates should possess suilicient strength to withstand any normal weight of charge imposed thereon in the retort. We prefer to agglomerate the charge lill A retort was filled with by briquettin in the course of which the material is su jected to a pressure of from 1000 to 2000 pounds to the uare inch. Briquettes made under the conditions herein partlcularly described possess lsuiiicient--mechanical'strength for the purposes of the invent-ion, and retain their form in the vertical retort until the greater part of the zinc and carbon have been removed or consumed, the agglomeratin of thel charge may be satisfactoril eifecte by extrusion.

The fo lowing specific example will serve to further illustrate th* principles of the invention although it is to be understood that this example is illustrative and inno manner restrictive of the invention.

The charge was made u of 7 5-50 parts by weight of Iinely divided) zinc silicate ore (containing from -50% of zinc) and 25-50 parts by' weight of anthracite dust coal. Approximately 80% of the zinc ore passed through a 20 mesh screen. The dust coal, together with about 3% by weight of concentrated sulite waste liquor (equivalent to about 1.5% by weight of solids), was placed in a revolving mixer of the kind employed for the mixing of concrete and, after a short iod of mixing, the zinc silicate ore was added, and the maxing operation then continued for a further period. From the revolving mixer, the material was dumped directly into a dry pan Chilean mill and subj ected to the mixing and comminuting action of the mill for several minutes. From the Chilean mill, thesmaterial was taken to a briquetting press and formed into briquettes by a compressive -force of approximately 2,000 pounds to the square inch. The briquettes were of the over-stuled pillow block type, approximately 2 inches square and one and one-half inches thick. The briquettes ywere dried at a temperature of approximately 200 C. and were then ready to be charged into the vertical retort furnace.

The retort was about 10 feet long and 8 inches internal diameter. The bottom of the ulverulent residuum for'about 2 feet of its ength. This residuum was finely divided and was an appropriate portion of the material left in the retort from the previous charge. The retort was filled to the top with the briquettes and the working of the charge begun. The heating of the retort was controlled so as not to overheat the charge, and no slag was formed and no fusion of the briquettes took place. The temperature within the laboratory or heating chamber was maintained at about 1200- 1250 C. There was a difference of about 20 C. between the temperature at the top and bottom of the heating chamber surrounding the retort. The charge was completely worked-olf in approximately 8 hours. The worked-olf charge was removed (except for about two feet at the bottom of the rein the externally tort) by shoveling the residues from the pit 18 throu h the cleanout door 19, the exhausted c arge falling freely through the irtorttas fast as material lwas removed from T e gaseous products of the reaction, for the most part zinc va or and carbon monoxide gas, pass out of t e topf'of the retort 10 into the condenser where the zinc vapor is condensed and collected as hereinbefore described.

In the working of the briquetted charge heated vertical retort, the zinc in the ore 1s reduced to metallic vapor when the carbon in the carbonaceous reducing agent combines with the oxygen of zinc compounds in the ore. In order that the optimum result may be obtained, it is important that there issue from the top of the retort a relatively pure carbon monoxide gas and zinc vapor in order that other impurities may be left lbehind in the charge. Hence, astrictly, reducing atmosphere is at all times maintained within the retort.

Various charge mixtures may be employed in the practiceof the invention. Thus, we have secured satisfactory results with mixtures of from 10 to 50% by weight of carbonaceous reducing agent and 90 to 50% by weight of zinciferous material.

Assuming that a substantially pure mixture of carbon monoxide gas and zinc vapor issue from the mouth of the retort 10, the two factors that play the greatest part in the eiciency of condensation of the zinc vapor are the temperature of the condensing walls and the pressure within the condensing chamber. Both of these factors are controlled by the size and the construction of the condenser. If' the temperature in the condenser is too great, zinc vapor will escape and be lost. If the temperature is to low, the zinc will be condensed and collected in the form of blue powder, rather than molten metal. If the pressure in the condensing chamber becomes too great, it will have a deadening effect on the velocity of the reaction and, therefore, adversely aiect recoveries. If the pressure in the condenser becomes to low, the zinc will condense as blue powder rather than molten metal.

In operating a vertical retort furnace on batch or intermittent charging rather than Continous charging, the question of condensation of the zinc vapor Lbecomes more difficult. With continuous charging the ratio of zinc and carbon monoxide in the gas mixture and the amount of zinc vapor therein may be held fairly constant,l and the conditions of condensation are accordingly uniform.

In the case of batch charging, however, consideringJ an 8 hour period to represent one batch, the greater portion of the zinc is liberated from the charge in the first four hours of the operation. In addition, in the first four hours of the operation the percenta of zinc in the .mixed .gases is less than 1n the second four hours of the o eration. During the first four hours o the operation, the condenser, therefore, should have a relatively large radiating surface and a relatively large volume in order to keep the temperature and pressure down to within the limits for efficient condensation. Durin vthe latter four hours -of the operation, tie ratio of zinc in the mixed gases increases while the quantity decreases so that it is necessary to insulate the condenser in order to maintain a high enou h temperature for efficient condensation. t is impossible to change the volume of the condenser, and, therefore, during this stage of the operation the pressure in the condenser is too low for efficient condensation, and some of the zinc is necessarily condensed as blue powder.

In constructing a condenser for batch operation, it is preferable to compromise between the two extremes, rather than to provide a condenser suitable for one or the other extreme.

In batch or intermittent chargin it is difficult to prevent the formation o a certain amount of blue powder. In order to completely prevent the formation of blue powder it is necessary to have absolute control of the tem erature and pressure of the condenser. 'Io do this requires a constant and uniform stream of mixed carbon monoxide gas and zinc vapor, constant not only in the ratio between the zinc and the carbon monoxide, but also in the amount of vapor that the condenser has to handle. This constant supply of carbon monoxide gas and zinc vapor is best obtained by continuous charging. Where it is impossible or infeasible to charge continuously, the nearer continuous charging is approximated, the more nearly ideal will be the operating conditions; and the larger the size of the retort in batch charging, the more nearly ideal will be the conditions.

While the above illustration of the practice of the invention is confined for the most part to the manufacture of zinc or spelter, the invention may also be utilized in the manufacture of other zinc products, such as zinc dust, zinc oxide, etc.

Zinc dust is finely divided metallic zinc. The zinc dust products of commerce usually contain small percentages of zinc oxide, rarely as much as 10% and usually less than 10%. The value of the zinc dust is dependent, to some extent, at least upon its metallic zinc content and is, for certain purposes, deteriorated by the presence of zinc oxide.

Zinc dust has heretofore been incidentally and unavoidably made in the manufacture method of makingl. 1

of spelter. Zinc dust has also been prepared by appropriatel tallic zinc vapor obtaine by melting and volatilizing metallic zinc. The specially prepared zinc dust is of higher grade and commercially more valuable than the product'unavoidably made in spelter manufacture. However, the costs of operation frequently make this special method of preparing zinc dust uneconomical.

Our present invention contemplates an economical and metallurgically simple zinc dust of high grade,-that is, of gh metallic zinc content. In accordance with our invention, metallic zinc vapor suitable for condensation into zinc dust is produced b the reduction ofl zinciferous materials. 'Ilie zinc vapors are thus produced directly from ore or other ap ropriate zinc-bearing material under su stantially non-oxidizing conditions, and are appropriately condensed with little, if any, oxidation. In addition to an economical and metallurgically simple method of making zinc dust, our invention permits varying the quality of the zinc dust product, such, for example, as high or low metallic content, and large or small particle s1ze.

The volatilized zinc vapor is conducted from the retort into an appropriate condensing or dust-forming environment. We prefer to promote the zinc dust formations by directing the vapor into a completely non-oxidizing atmosphere. To this end a suitable canister may be substituted for the condensers above described in the manufacture of zinc or spelter. An outlet is provided in the canister for the escape of gases, while the zinc dust particles settle within the canister. Collected zinc dust may be withdrawn from time to time.

specially condensing me- Heretofore it has been customary to make 4 zinc oxide in two fundamentally different ways, namely, by the American or Wetherill process and by the French or retort volatilization rocess.

In the merican or Wetherill process, the zinc oxide is made direct from the zinc ore or other appropriate zinciferous material. In the production of zinc oxide by this process, a charge of zinciferous material mixed with a reducing agent and spread on an ignited bed of fuel is subjected to a combustion supporting blast or draft and brought to a sufficiently hi h temperature to reduce the compounds o zinc and volatilize the reduced metal, the zinc vapors burnin above the top of the charge and in the o take pipes or lues to zinc oxide which is collected in an appropriate manner. In this practice, the necessary heat is furnished by the combustion of the coal mixed with or sup 'orting the zinciferous material, and muc of the impurities in the heat-producing coal may pass over with the zinc oxide and thus contaminate the product. The

Wetherill furnace practice is frequently described as a compound reducing and oxidizoperation.

n the French process of producingI zinc' oxides metallic zinc is melt-ed and volatilized in appropriate receptacles or retorts, under non-oxidizing conditions, and the resulting metallic zinc vapor burns in "an appropriate oxidizing environment, thereby 'forming zinc oxide which is collected in an appropriate manner. This practice is, in effect, a twostage process, since it is first necessary to roduce metallic zinc, and this metallic zinc 1s then remelted volatilized and oxidized for the production of zinc oxide.

In accordance with the practice of the present invention the volatilizedzinc vapor coming from the agglomerated or briquetted charge of zinciferous material and carbonaceous reducin agent may be oxidized to form zinc exige. In our present preferred practice, the zinc vapor is conducted from the retort to an oxidizing environment. If it is desired to obtain a zinc oxide product of relatively small particle size, the issuing stream of zinc vapor may, for example, be subjected to a blast of relatively cool oxidizing gas, such as air.

We claim:

1. The method of reducing zinciferous materials which comprises confining an agglomerated charge of mixed zincifcrous material and carbonaceous reducing agent in an upright retort, and subjecting the agglomerated charge in the retort to a sufficiently high temperature to reduce compounds of zinc and Volatilize the resulting metallic zinc.

2. The method of reducing zinciferous materials which comprises confining a briquetted charge of mixed zinciferous material and carbonaceous reducing agent in an upright retort, subjecting the briquetted charge in the retort to a sufficiently high temperature to reduce the compounds of zinc and volatilize the resulting metallic zinc, and conducting the metallic zinc vapor in the form of a flowing stream from the retort.

3. The method of reducing zinc'ferous materials which comprises progressively passing an agglomerated charge of mixed zinciferous lmaterial and carbonaceous reducing agent through an upright retort heated to a sufiiciently high temperature to reduce the compounds of zinc and volatilize the resulting metallic zinc.

4. The method of reducing zinciferous materials which comprises progressively passing by gravity an agglomerated charge of vmixed zinciferous material and carbonaceous reducing agent through a vertical retort ex-` ternally heated to a sufiic'ently high tenmperature to reduce the compounds of zinc and volatilize the resulting metallic zinc.

5. The method of reducing zinciferous materials which comprises confining an agglomerated charge ofmixed zinciferous material and a carbonaceous reducing agent in an upright retort in contact with a Wall of said retort, subjecting the agglomerated charge in the retort to a sufficiently high temperature to reduce compounds of zinc and volatilize the 'resulting metallic zinc, and conducting the metallic zinc vapor so formed from the retort.

6. The method of reducing zinciferous ma terlals which comprises confining an agglomerat-ed charge of mixed zincierous material and carbonaceous reducing agent in an externally heated upright retort, subjecting the agglomerated charge in the retort to a sufliciently high temperature to reduce compounds of zinc and volatilize the resulting metallic zinc, and conducting the metallic vapor so formed from the retort.

7. The method of reducing zinciferous materials which comprises progressively passing an agglomerated charge of mixed zinciferous material and carbonaceous reducing agent through an externally heated upright retort heated to a sufficiently high temperature to reduce the compounds of zinc and volatilize the resulting metallic zinc.

8. The method of reducing zincierous materials which comprises subjecting an agglomerated charge of mixed zinciferous material and carbonaceous reducing agent in an upright retort to a sufficiently high temperature to reduce compounds ofezinc and volatilize the resulting metallic Zinc, the minimum cross-sectional dimension of the retort being several times greater than any crosssectional dimension of the agglomerates and the agglomerates being of such shape that spaces exist between contacting agglomerates whereby the agglomerates near the center of the charge are heated lin large part by convection of the gases filling the spaces between the agglomerates, and conducting the metallic zinc vapor so formed from the retort.

9. The method of reducing zinciferous materials which comprises subjecting an agglomerated charge of zincif'erous material and carbonaceous reducing agent within and in contact with an externally heated upright retort to a sufficiently high temperature to reduce compounds of zinc and to volatilize the resulting zinc metal, the core of said charge being heated in large part by currents of retort gases rising through the spaces provided between adjacent agglomerates and zig-zagging alternately between the heated retort walls and the core of the charge, and conducting the metallic zinc vapor so formed from the retort.

10. The method of reducing zinciferous material which com rises confining an agglomerated charge o mixed zinciferous material and carbonaceous reducing agent in an upright retort, and heating the agglomerated charge in the retort to a sufficiently high temperature to reduce compounds of zinc and volatilize the resulting metallic zinc without fusing or sintering the charge.

11. The method of reducing zinciferous material which comprises progressively passing an agglomerated charge of mixed zinciferous material and carbonaceous reducing agent through a vertical retort externally heated to a sufficiently high temperature to reduce the compounds of zinc and volatilize the resulting metallic zinc without fusing or sintering the charge.

12. The method of reducing zinciferous material according to claim 8 ,1n which the zinc compounds are reduced and the resulting metallic zinc is volatilized without usililg or sintering the charge and the Worked o agglomerates dislntegrate into pulverulent material.

In testimonywhereof We affix our signatures.

JAMES A. SINGMASTER. FRANK G. BREYER. EARL H. BUNCE.

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