US1749126A - Reducing zinciferous materials - Google Patents

Description

Patented Mar. 4, 193D PATENT OFFICE EARL H. BUNCE AND GEORGE T. MAHLER,

OF PALMERTON, PENNSYLVANIA, ASSIGN- 038 TO THE NEW JERSEY ZINC'COMPANY, OF NEW YORK, N. Y., A CORPORATION OI'NEWJ'EBSEY Io mm;

- but commonly found in zinc ores such as germanium and hallium, boil at temperatures above the boilin temperature of Z1110, nevertheless apprecia le amounts thereof find their way into the gaseous product of the zinc smelting operation and thereby1 contaminate the zinc product obtained t erefrom. Lead is one of the most common contaminants of zinc ores and their concentrates, and when present in relatively small amounts prevents the production by pyrometallurgical methods of high grade zinc products, such as zinc metal, zinc. oxide, zinc dust, etc., substantially free of lead. A relatively large tonnage of zinc concentrates containing from 0.05 to b 5% of lead are available for zinc smelting,

but no entirely satisfactory pyrometallurgical method has heretofore existed for producing substantially lead-free zinc products therefrom. Similarly, tin, antlmony, b1smuth, germanium and probably thalhum aluminum and magnesium when present in title zinc smelting charge, will, to some extent a least, contaminate the Z1110 product obtained from the smelting operation, and while such contaminating metals are ordinarily present in relatively small percentages, frequently amounting to mere traces, they very often deleteriously influence the properties of the ultimate zinc product.

The object of our present invention is to provide a pyrometallurgical treatment for zinciferous materials containing one or more of the aforementionedcontaminating metals in the course of which a substantial removal of the contaminating metals is effected, there- I,

mncme zmomnnons mn'rnnmns" Application filed January 4, 1928. Serial No. 244,401.

by making possible the recovery of a purer and more desirable zinc product than can be obtained by the heretofore customary methods of zinc smelting. Since, in the practice of the invention, all of the contaminating metals appear to behave similarly, we will herein more particularly describe the invention with respect to the elimination of lead. The invention may be practiced solely for the elimination of lead without special regard to the elimination of other metals, or it may be practiced for the elimination of any one or more of the contaminating metals. In general the elimination of substantially all of the lead by the practice of the invention will at the same t1me effect a substantial elimination of such others of the contaminating metals as may be present in the zinc smeltin charge. Throughout the specification an the appended claims, we intend the terms contaminating metals and more particularly lead to include both the metallic form of these metals and com ounds thereof. On the other hand, such lea -content figures as are given in the specification are percentages of lead calculated as metallic lead.

The present invention is based on our discovery that under appropriate conditions lead can be almost completely removed from the gaseous product of the zinc smelting operation by passing the gaseous product through a body of appropriate aggregates maintained at an appropriate elevated temperature in a reducing environment. We have also discovered that other metals whose boiling temperatures are above that of zinc but which accompany the gaseous product of the zinc smelting operation can be similar- 1y removed, in large part at least, from the gaseous product. We have found that the aggregates may be any material which will withstand the prevailing temperature and not react with zinc so as to affect its subsequent recovery by condensation or otherwise.

While the principles of these discoveries appear to be of general application, we have found that practical considerations make it desirable that the gaseous product be supplied in a substantially continuous stream of practically constant volume and composition and relatively free of oxidizing gases.

Based on these discoveries, our present invention involves smelting zinciferous material containing one or more contaminating metals so as to produce a substantially continuous stream of the resulting gaseous product, preferably of relatively constant volume I and composition and practically free of oxidizing gases, and conducting this substantially continuous stream of the gaseous prod uct through an appropriate eliminating medium maintained under reducing conditions at an elevated temperature but sufficiently low to effect substantial removal of the contaminating metal or metals from the gaseous product. The gaseous product, thus substantially freed of lead, and/or other contaminating metals, passes on to the subsequent treatment operation for the recovery of its zinc .content. The eliminating medium is appropriately confined and arranged intermediate the zinc smelting chamber and the zinc recovery apparatus so that the gaseous product of the smelting operation passes in a. substantially continuous stream from the reducmixture of zinciferous material and carbonaceous reducing-agent, preferablybriquetted or otherwise agglomerated, is admirably e-eliminating medium should provide a v; ad a ted as the eliminating medium. I .4 Th

' -multiplicity of tortuous paths for the flow l .therethrough of the gaseous product and ass f'lhes'e conditions are 'satis when the'eliminating medium is composed of Iabody of aggregates. .The'aggregates may shouldyet be sufliciently porous to permit the-free passage ofthe gaseous product. actorily attained beinaturally formed such as crushed or fbrokon coahore and the-like, or may be artifieial'ly formed such as briquettes, sinter,

crushed-or broken refractories and the like.

I The aggregates should be approximately uniformin' size in order that the porosity of the eliminating medium as a whole'may be substantially uniform. Furthermore, in order toprovide the desired multiplicity of tortu- 'ous. gas passages, the aggregates should not be too large. We have secured very satisfactory results with .an eliminating medium composed of briquettes approximately three 'as oxides, sulfides, or the like.

inches in diameter or thickness confined in a vertically disposed cylinder about 15 inches internal diameter and about 6 feet long or high, where approximately one ton of zinc metal was recovered each 24 hours from the gaseous product passing through the elimiv phere ree of any oxidizing influence, in

order to inhibit the oxidation of metallic lead and zinc, and, if necessary, to reduce any oxidized lead or zinc that might be present in the gaseous product. Should air or other oxidizing gas leak into or otherwise enter the enclosure for the eliminating medium, the effectiveness of the lead removal is seriously impaired, if not completely de-' stroyed. Preferably, the smelting operation is conducted so that the gaseous product thereof consists mainly of carbon monoxide and metallic zinc vapor with only a fraction of a percent of carbon dioxide. Where the carbon dioxide content of the gaseous product of the smelting operation exceeds about 1 to 2% the eliminating medium should be composed of or contain a material capable at the prevailing elevated temperature of reducing carbon dioxide, such, for example, as coal, coke, charcoal or other carbonaceous material, in order to insure the necessary reducing conditions for effective lead removal.

While we are not now prepared to offer any positive theory of what actually takes place in the eliminating-medium in the course of the practice of the invention, we will state What we now consider the most acceptable explanation of the phenomena underlying the invention, since this explanation furnishes plausible reasons for the necessity of observing the precautions and conditions herein described. The contaminating metals are present in the zinciferous material as compounds of the metals, such, for example, Certain of these metal compounds, forexample, lead oxide and lead sulfide, volatilize readily at the temperatures prevailing in the zinc smelting charge, although the boiling temperatures of the metals themselves are considerably higher. These volatilized metal compounds are in contact with carbon monoxide in the smelting chamber and are thereby reduced and form minute metal particles which accompany the gaseous product of the smelting operation. Or it may be that the metal compounds are directly reduced without first volatilizing. Unless thus reduced to the metallic state, these readily volatile metal compounds will remain with the gaseous product-and not be removed therefrom in the passage through the eliminating medium; hence the necessity of maintaining the eliminating medium under reducing conditions.

The reduced contaminating metals, are probably present in the gaseous product as very minute molten metal particles or droplets'resembling a mist. In passing through the multiplicity of tortuous gas passages provided by the eliminating medium these minute metal particles are thrown against the surfaces of the medium and caused to coalesce to someextentthere y forming larger particles less readily carried along by the gas stream. Such coalescence of the molten metal droplets is promoted where the surface of the eliminating medium is of such a character as to be wetted by the molten metal particles. It is further possible that the molten metal droplets, with little or no coalescence, are mechanically entrapped in the eliminating medium due to the tortuous passages therein, and thereby removed from the gaseous product. Whatever the true explanation may be, the facts remain that under the conditions of operation herein described the gaseous product is very substantially freed of contaminating metals and that 'thecontaminating metals removed from the gaseous product remain with the eliminating medium in a form less readily returned to the gaseous product than the form in which these metals exist in t he zinciferous material of the smelting charge.

Coalescence of the minute molten particles or droplets of the contaminating metals can bepromoted by maintaining the eliminating medium at a substantially lower temperature than the zinc smelting temperature, but preferably not so lowas I to condense any substantial amount of zinc vapor. Inpassing through the eliminating medium maintained at such lower temperatures, the concentration of the minute metal particles in a unit volume of gas isincreased, thereby increasing the possibilities of collision with one whether and the formation of larger particles or droplets. Moreover, this higher concentration of the metal droplets in a unit volume of gas results in more frequent and ready impingement of the droplets against the surfaces of the eliminating medium and thereby promotes the possibilities of coalescence and the more complete removal of the contaminating metals from the gaseous product. It is, accordingly, our preferred practice to maintain the eliminating medium at a temperature. intermediate the temperature at which zinc is reduced rom its compounds and the temperature at which metallic zinc vapor is condensed, and of course below the temperature at which lead (or other con- Laminating metal) will remain with the gaseous product, under the prevailing operating conditions.

robably The desired temperature regulation and control of the elimlnating medium may be eflected in any appropriate and convenient manner. This may be conveniently done b surrounding the eliminatin medium wit means for varying or adjustmg'the heat rad1at1on therefrom. We have secured excellent results in practice by confining-the elimmating medium in a vertical tube several feet 1n length and surrounded by heat insulating material of variable thickness or effectiveness. By appropriately adjusting the effectiveness of the heat insulating material, the radiation of heat from the tube can be so controlled as to maintain the desired temperature of the eliminating medium.

We have found that the character and comosition of the gaseous product resulting rom the zinc smeltin operation has an important bearing on tfie effectiveness of the removal of the lead and other contaminat- 1ng metals in accordance with the principles of our invention. The best results are obtained when the gaseous product is a substantially continuous stream of zinc vapor and carbon monoxide relatively constant in volume and composition and practically free of oxidizing gases. Such a gaseous product may be advantageously obtained in the process of smelting an agglomerated or briquetted charge of zinciferous and reducing materials in accordance with the principles disclosed in the copendin application of Messrs. Breyer and Bunce, S erial No. 163,902, filed January 27 1927 Where the process of the aforementioned Breyer and Bunce application is carried out in an upright or vertical retort, the improvements of the present invention ma advantageously be embodied in the process y providmg an upper prolongation of the retort, above the reducing zone therein, adapted to confine th e eliminating medium which in this case will be composed of a body or column of the agglomerated zinc smeltin charge itself about to be advanced or intro uced into the smeltlng zone of the retort. The agglomerated charge as a whole then progressively passes through the vertical retort and its prolon ation and is heated in the reducing zone 0 the retort to a sufficiently high temperature to reduce compounds of zinc and volatilize the resulting metallic zinc and in the prolongation of the retort is maintained at an appropriate temperature to prevent volatilization of lead compounds and to eifect substantial removal of lead (and/or other contaminating metals) from the gaseous product of the reduction, preferably without condensing an substantial amount of zinc vapor. The eliminating medium is thus superposed on the zinc smelting charge undergoing reduction and, with appropriate renewal or introduction of fresh charge at the top, progressively descends from the eliminating zone to the smelting zone, and the worked-off or exhausted agglomerates are appropriately withdrawn from .the bottom of the retort. The de-leaded gaseous product is withdrawn from the rolongation at or near the top of the de-lea 'ng body of agglomerates and is conducted to the zinc recovery apparatus, such as a condenser for zinc metal. To prevent air or oxidizing ses being carried into the eliminatin me ium during the introduction of fresh c arge,-it is our preferred pra tice to introduce the charge at a temperature at which there is sufiicient gas evolution from the fresh charge toprevent the entraining of air. Under these condition of operation, it is of course necessary to maintain the eliminating medium at acarefully regulated temperature below that of zinc reduction, in order "to avoid reduction of the zinciferous material of the eliminating medium with the consequent decrease in the effectiveness of the medium for removing lead. v

Practicing our present invention in the manner described in the preceding paragraph, with the eliminating medium maintained at a carefully regulated temperature of about 800 to 900 0., we have obtained zinc metal containing from 0.019 to 0.050% of lead from a zinc concentrate containing from -70% of zinc and 1.5 to 3.5% of lead.

' Following the same procedure, but omitting the deleading operations of the present invention, the resulting zinc metal contains from 0.5 to 1.25% lead. Likewise, working thissame ore in an ordinary zinc distillation furnace in accordance with the customary spelter retort practice, the resulting zinc metal contains 1% lead and over.

Applying the principles of the invention to a zinc ore containing 'a relatively small amount of lead, smelted in accordance with the Breyer and Bunce method hereinbefore particularly described, we have succeeded in producing zinc metal containing from 0.0024 to 0.0032% lead. Treating this same ore by the same procedure, but omitting the features of the present invention, the resulting zinc metal contains from 0.08 to 0.12% lead. Likewise, in treating this same ore in accordance with the present spelter retort practice the resulting zinc metal contains from 0.08 to 0.12% lead.

The practice of the invention correspondingly lowers the percentages of other contaminating metals presentin the resulting zinc metal, as compared with the percentages of these metals that are found in zinc metal produced by the heretofore customary or known methods of zinc smelting; Thus, we have succeeded by the'practice of the invention in reducing the percentages of such metals from readily determinable amounts to substantially negliglible and practically 'indeterminable amounts.

Various forms ofapparatus, other than those heretofore referred to, may be employed in practicing the invention. In any case the eliminatin medium, appropriately confined or enclose is disposed intermediate the zincsmelting chamber and the zinc recovery apparatus. The length of the eliminating medium, in the direction of gas flow, should be sufliciently long to effect substantially complete removal of lead from the gaseous product passing therethrough. Moreover, the eliminating medium should preferably be susceptible of convenient temperature control. While the eliminating medium may be periodically renewed, as its lead-removing capacity becomes lessened, it is our preferred practice to progressively move the eliminating medium through its enclosure, preferably in 'a direction opposite to that of the direction of flow of the gaseousproductmnd to renew the medium from time to time by fresh material added thereto at a temperature approximating the temperature at which the medium is maintained. Thus, vertically disposed cylindrical receptacles are especially suited for confining or enclosing the eliminating medium, since the heat radiation from such receptacles can be conveniently and accurately controlled, the eliminating medium can be conveniently renewed therein or progressive-' 1y passed therethrough, and the gaseous prodnot can be conveniently conducted thereto and withdrawn therefrom.

While it is our preferred practice to conduct the elimination of the contaminating metals without substantial condensation of metallic zinc vapor in the eliminating medium, this is not essential, since whatever zinc is condensed in the eliminating medium can be subsequently revolatilized and. recovered.

S uch subsequent revolatilization and recovery of any condensed zinc is particularly simple where the eliminating medium is composed of one or more ingredients of the zinc smelting charge, since in such a case the material of theeliminating medium, after ithas completed its role in the eliminating operation, may be introduced into the zinc smelting chamber where any condensed zinc is-revolatiliz ed and returned to the gaseous product. In such a case it is, of course, desirable that the transfer of the material from-the eliminating operation to thesmelting operation be effected with aslittle loss of 'heat as possible.

While we, have hereinbefore particularly mentioned the recovery of the metallic zinc vapor from the deleaded gaseous product in the form of zinc metal or spelter, it is to be understood that the zinc vapor may berecovered in other forms of zinc products. Thus,

or may be oxidized and collected as zinc oxide. In any case, the practice of the invention enables the production of zinc products more nearly free from lead and .simila'rcontamithe zinc vapor may be condensed as zinc dust, J

not of the zinc smelting operation and in par- -ticular lead, t1n, ant1mony, bismuth, germanating metals than could otherwise be obtained by pyrometallurgical methods from the same zinciferous materials.

In the appended claims we intend the term contaminating metal to. cover any metal whose boiling temperature is above that of zinc but which accompanies the gaseous prodnium and probably thallium, aluminum and magnesium.

We claim:

1. The improvement in the reduction of zinciferous material eontaining'at least one contaminating metal which comprises conducting the gaseous product of the reducing operation through a hot eliminating medium maintained under reducing conditions at a temperature sufficiently low to effect substantial removal of said contaminating met-a1 from said gaseous product, renewing said eliminating medium from time to time by fresh eliminating material added thereto at a temperature approximating that, at which the medium is maintained, and subjecting the thus-treated gaseous product to appropriate treatment for the recovery of the zinc content thereof.

2. The improvement in the reduction of. zinciferous material containing at least one contaminating metal which 1 comprises conducing the gaseous product of the reducing operation through a hot eliminating medium maintained under reducing conditions at a temperature sufficiently low to effect substantial removal of said contaminating metal from said gaseous product, progressively movingsaid eliminating medium in a directionopposite to the direction of flow of the gaseous product therethrough, renewing said eliminating medium from time to time by fresh eliminatingmaterial added thereto at a temperature approximately that at which the medium is maintained, and subjecting the thus-treated gaseous product to appropriate treatment for the recovery of the zinc content thereoffl" v; v

3. The improvement in the reduction of zinciferous material containing atleast one contaminating metal which comprises conducting the gaseous product of the reducing operation through. an eliminating medium which will withstand'the prevailing temperature and not react with or contaminate metallic zinc vapor so as to effect the subsequent recovery of zinc, progressively moving said eliminating medium through the path *of flow of the gaseous product, and subjectate treatment for the recovery of the zinc ing the gaseous product thus substantially freed of said eliminating metal to appropricontent thereof.

' firTheimprovement in the reduction of an agglomerated charge of mixed zinciferous material and carbonaceous reducing agent containing at least one contaminating metal which comprises progressively passing the agglomorated charge through a, reduction chamber, conducting the gaseous product of the reducing operation through an eliminating medium which will withstand the prevailingtemperature and not react with or contaminate metallic zinc vapor so as to effect the subsequent recovery of zinc, progressively passing said eliminating medium through the path of flow of the gaseous product, and sub ecting the gaseous product thus substantially freed of said contaminating metal to appropriate treatment for the recovery of the zinc content thereof.

5. The method of reducing zinciferous ma- .terial containing tin in objectionable amount uct thus substantially freed of said tin to a propriate treatment for the recovery of t e zinc content thereof.

6. The improvement in the reduction of zinciferous material containing. at least one contaminating metal which comprises conducting the gaseous product of the reducing operation through a hot eliminating medium removed from and kept out of contact with p the reducing operation, said eliminating medium being maintained under reducing conditions and which will withstand the prevailing temperature and not react with or contaminate metallic zinc vapor so as to effect the subsquent recovery of zinc, maintaining said eliminating medium at a temperature adapted to effectsubstantialremoval of said contaminating metal from said gaseous product without condensing any substantial amount of zinc vapor, progressively moving said eliminating medlum through the path of flow of the gaseous product, and subjecting the gaseous product thus substantially freed of said contaminating metal to appropriate treatment for the recovery of the zinc content thereof.

7. The improvement in the reduction of zinciferous material containing at least one contaminating metal which comprises conducting the gaseous product of the reducing operation through a hot eliminatin medium maintained under reducing conditions at a temperature sufliciently low to effect substantial removal of said contaminating metal from said gaseous roduct, renewing said eliminating medium y rogressively moving the medium and adding resh eliminating material thereto at a tern erature approximating that at which the me ium is maintained, an

subjecting the gaseous product thus substan-' tially freed of said contaminating metal to' app opriate treatment for the recovery of the zinc'content thereof. Y

8. The improvement in the reduction of zinciferous material containing at least one contaminating metal which comprises conducting a substantially continuous stream of the gaseous product of the reducing operation through a substantially uniformly porous v eliminating medium composed of a material which will withstand the prevailing temperature and not react with zinc, maintaining said eliminating medium at an elevated temperature sufliciently low to eflect substantial removal of said contaminating metalfrom said gaseous product without condensing any substantial amount of zinc vapor, renewing said eliminating medium from time to time by fresh eliminating material added thereto at a temperature approximating that at which the medium is maintained, and appropriately recovering the zinc content of the thus-treated gaseous product.

9. The improvement in the reduction of zinciferous material containing at least one contaminating metal which comprises conducting a substantially continuous stream oi the gaseous product of the reducing operatior eliminating medium by progressively moving the medium and adding fresh eliminating material thereto at a temperature approximating that at which the medium is maintained, and appropriately recovering the zinc content of the thus-treated gaseous product.

10. The improvement in the reduction of zinciferous' material containing at least one contaminating metal which comprises conducting a substantially continuous stream of the gaseous product of the reducing operation through a substantially uniformly porous eliminating medium composed of a material which will withstand the prevailing temperature and not react with zinc, progressively moving said eliminating medium in a direction opposite to the direction of flow of the gaseous product therethrough, renewing said eliminatin medium from time to time by fresh eliminating material added thereto at a temperatureapproximating that at which whereof we aflix our signatures,

EARL H. BUNGE; GEORGE 'r. MAHLER.