US1718378A - Method of producing zinc - Google Patents

Description

June 25, 1929. QUENEAU 1,718,378

METHOD OF PRODUCING ZINC Original Filed Feb. 3,. 1927 L 12v VENTOR l BY flqgusf/h Leo/7 Jean Que/760a Patented June 25, 1929.

UNITED STATES 1,718,378 PATENT OFFICE.

AUGUSTIN LEON JEAN QUENEAU, OF NEW YORK, N. Y.

nnrnon or rnonuome zmc.

Application filed February 3, 1927, Serial No. 165,720. Renewed November 20, 1928.

The invention is in part a continuation of the invention described and claimed in my allowed co-pending application Serial No. 81,748 filed January 16, 1926 for the method of producing zinc.

The invention relates to the recovery of zinc from various zinc oxides such as calcined natural carbonates, roasted zinc blende, artificial oxides or any other form of commercial zinciferous material in the form of oxide. The reduction of zinc presents problems which require that it be smelted somewhat differently than other metals such as iron, copper, lead, et cetera. A handicap in the fire metallurgy of zinc is that the reduction,

temperature of zinc oxides is above the boiling point of the metal (920 centigrade). For this reason, it is apparent that instead of liberating a liquid metal as in the case of iron, copper and lead, when zinc is brought to a reducing temperature the metal freed from its combination with oxygen appears as a gas. In this physical form, owing to its extreme state of subdivision, it is very readily oxidized and when cooled below the melting point, the gasified metal coalesces with reluctance to a liquid. Various attempts have been made to raise the boiling point of zinc above its reducing point so as to permit the utilization .of the conventional form of blast furnace for the reduction of zinc ores. These attempts, however, have not met with success. The present practice in zinc fire metallurgy is the same in principle today as it has been for the past 100 years. My invention contemplates the reduction of zinc by subjecting it to the action of hydrogen according to a special method which will be apparent from the following specification and claims when read in connection with the accompanying drawing.

It is well known that zinc oxide can be read- I ily reduced ata relatively low temperature (from 454 C. upwards) by subjecting it to the action of hydrogen according to the reversible equation ZnO +H =H O +Zn. This reaction however, is of no substantial commercial or practical value for the reason that the reduced zinc is reoxidized by the liberated water vapor as quickly as such reduced zinc is formed. My improved method overcomes this difficulty and solves the problem in a novel manner.

It willbe understood that my improved method is also adapted to be practiced in connection with existing retorting plants. In

such case, the retort furnace will be utilized to a maximum capacity for the production of slab zinc. The blue powder or oxides which collect in thecondensers of the usual retorting plants will be treated for further reduction while such zinc oxide or so-called blue powder is held in the molten bath.

In order that the invention as defined with particularity in the appended claims. may be understood by those skilled in the art, I will described in detail the various steps involved in reducing suitable zinc oxide in any of its commercial forms such as calcined natural carbonates oxides, roasted zinc blende, artificial oxides or the like.

The material is first crushed or pulverized to such degree that it will pass through say a 60 mesh screen and is then completely dehydrated. 7

As a medium for effecting the reaction a molten bath of anhydrous chlorides, I preferably use ternary chlorides of sodium, potas sium and calcium of the general molecular formula; 50 N aCl, KC], CaCl and in vwhich ternary salt part of the sodium chloride is with advantage replaced in varying proportion by sodium, aluminum and 'calcium fluorides. The molecular formula given is merely an illustration and may vary.. The selected ternary salt melts at 490 6., and above that temperature it is a mobile liquid. It can be heated within a wide range of temperature, up to 700 C., and over, without loss through volatilization. It is inert toward zinc oxide or metal.

The dry zinc oxide is added to the molten anhydrous mixed salts in a mixing kettle together with crushed anhydrous calcium oxide (quick lime) in the proportion of 2 parts of calcium oxideby weight to 1 part of zinc oxide, ZnO. For 100 parts of the mixed solids, approximately 75 parts of the molten chlorides are used.

Calcium oxide, has a powerful aflinity for water and reacts as follows:

CaO+H O=Ca (OH) +229,000 calories.

The hydrate formed does not fully dissociate under the influence of heat until 580 C. has been reached. Up to that temperature it holds firmly 31% of the total water of the normal hydrate. The tension of the water vapour does not reach a pressure of 760 mm. of mercury until the temperature mentioned: 580 C. The release of the last water takes place only at that temperature.

45 the-reaction. This material is further very The presence of the calcium oxide has a further beneficial effect in lowering the temperature pf fusion of the mixed salts.

In the proportion of 100 parts of solids for 75 parts of molten chlorides a fluid pulp is .readily maintained by any suitable mechanipension of the solids in the liquid medium.-

The temperature 'of the pulp is maintained throughout at the optimum temperature: 550 while a stream of anhydrous hydrogen, preferably preheated, is forced through the mass at its lowest point. The reduction of the suspended zinc oxide proceeds. The liberated metal, liquid phase, drops to the lowest level owing'to its higher specific gravity, 6.5, while the liberated water vapour, steam, immediately combines with the circulating large mass of anhydrous calcium oxide to form the solid calcium hydrate, thus efliciently removing the steam from contact with the reduced metal. Fig. 1 of the drawing illustrates the kettle in which the reduction is carried out. Fig. 2 is a detail view showing a modified form of gas outlet fitting.

' The reduction of zinc oxide is carried out in a covered kettle A of cast iron, steel, or of special alloy, of the general form of a 1 caustic pot or of a parkes process kettle. In

order to prevent any contamination of the reduced zinc by the metal of the kettle, the

' latter is lined with substantial blocks of from floating by a metallic ring 0 securelybolted to the top of the, kettle, which presses on the upper edge of the graphite lining.

-I usegraphite as it is inert toward hydrogenat the'temperatures maintained through desirable for contact with metals such as iron,-zinc,- etc, and its heat conductivity is superior to that of cast iron.

The agitation'of the pulp is maintamed for example by an impeller ofpaddle d. fastened to avertigal-shaft e support from a frame work outside of the kettle and rotated by any suitable source of power :0. A gland g is rovicled in the kettle cover to prevent any ee passage of gas (air or hydrogen, etc.) through the shaft opening.

To protect the metal of the shaft from the I reduced zinc it is lined with graphite sleeves s. The impeller d may be made of graphite or of chemical stoneware. The introduction of the hydrogen is'preferably made through thevertical shaftwhich is made hollow. It is provided. at its upper extremity wlth. a stufiing box 5; through which the stationary hydrogen gas main 5 enters the rotating hollow vertical shaft; the hydrogen gas escapes from the hollow shaft at its lowest point through one hole 7' as in Fig. 1' or a series of holes 9' as in Fig. 2 for the proper distribution of the reacting gas through the pulp.

The process is preferably carried on substantially at atmospheric pressure and in a continuous; manner. For instance, the anhydrous molten salt is added from the aforementioned mixing kettle together with the suspended zinc and calcium oxides at a predetermined rate; the pulp entering through a metallic tube 70 dipping below the level of the pulp in the reaction kettle so as to maintain an hydraulic seal; and in the same manner, an equivalent volume of the chlorides with the suspended impoverished'zinc oxides, calcium oxides and calcium hydrate outflows from the kettle over the baflie weir Z.

The metallic zinc'z may be tapped at intervals through a tap hole 9 by removing a plug p located at the lowest point of the kettle, or it may be continuously removed as formed through a lower siphon m owing to the large difference of specific gravity between the pul and the molten zinc (3.

' for the pulp against 6.5 for the molten metal) The metal is then cast in the usual slabs.

The hydrogen gas passed in excess to that absorbed by the reaction leaves the kettle through the pipe n. The hydrogen is then freed from all moisture. It is slightly compressedand it may be then passed through the following'kettle or kettles or stored for further use.

The overflowing pulp passes into a second or a series of similar reaction kettles, placed in Gascade. Finally, from the last kettle of the series, the issuing pulp passes to a suitable leaching apparatus. The gangue is freed by counter current washing of any chlorine compounds. It can be then discarded together with the hydrated lime, as waste. The aqueous solution of the recuperated chlorides is concentrated in an suitable manner, well known in the arts, an finally it is dehydrated lOD in a vacuum pan or caustic pot, or in both;

the dry salt is then sent to a melting kettle in which it is fused and rendered anhydrous by boiling. It then passes to the mixing ket -tle"for another cycle of operations.

The hydrogen used in the process may be obtained from any of the well known sources of this gas, as from the electrolysis of water kerosene, gasolene or from tars, benzoid, etc. 1

The reduction reaction being endothermic the reaction and the other kettles are ex-.

The heating could also be done internally by means of electrical resistance through the pulp by passing an alternating current through suitable electrodes.

While I have above referred to maintaining the pulp at a temperature of 550 C., the range of temperature may be extended to 850875 C. without departing from the specific conditions of the disclosed process, viz: to reduce zinc at a temperature below the boiling point of the metal, 920 (3., so as to obtain it directly as a liquid.

, If the temperature of operation is selected above 580 C. the selected reducing agent is preferably a fluid hydrocarbon, and the addition of calcium oxide is dispensed with.

Owing to the cracking of the injected hydrocarbon there is a liberation and deposition of elemental carbon in an extreme state of division and in a very active form. This carbon exerts a favorable influence in maintaining the strong reducing conditions primarily caused by the presence of hydrogen or light hydrocarbons. This additive reducing influence of carbon and carbon compounds, such as carbon monoxide, etc., has a beneficial effect on any water vapor formed by the reduction of the zinc oxide with the subsequent production of hydrogen and carbon dioxide The pot or kettle method above described is adapted for treating zinc oxide quite regardlessof the manner or source from which the oxide is secured. The pot process is peculiarly well adapted for the treatment of purified zinc oxide such as the so-called blue powder which results from the fire metallurgy of zinc using the usual zinc retort furnace. The process is also applicable for treatment of oxides obtained from the burning of zinc furnace residues, zinc condensers and old retorts;

The most natural field for the method described would be in conjunction with existing retorting plants.

Under such circumstances the retort furnace would be utilized to its maximum capacity for the production of slab zinc. That is to say, the furnace would be charged only with roasted ore and would not include any of the so-called between products. It is known to those skilled in the art that in the usual method of operating a retort furnace a large percentage of the retorts are used to treat the between products which include the blue powder oxides recovered from the condensers. By my method the retort furnace would be used at full capacity for reduction of roasted ore. This will greatly increase the efii'ciency or output of the retort furnace as compared with prior or standard practice. The blue powder oxides taken from the condensers of the retort furnace can be very advantageously subjected to the action of the fluid reducing agent as above described while the so-called blue powder or oxide is held in the molten bath. The condensers and retorts which become disabled in use will preferably be crushed-and treated in the Waelz process and the impure zinc oxide rc-' covered from such treatment would be subjected to the pot reduction treatment as above described. By combining the pot reduction process with the treatment of ores in the retort furnace, the capacity of the retort furna'ce can be increased from 25% to 30% with a corresponding reduction in the operating costsof the plant.

The Waelz process above referred to consists essentially in treating in a rotary kiln, the "finely comminuted zinc retort residues old condensers, retorts, etc. The combustion of the carbon contents, usually from 25% to 35%, gives the necessary heat to maintain the kiln at the required temperature, and to reduce the zinc and lead contents of the residues. The reduced metals are immediately reoxidized and are carried away in a'fine state of division with the combustion gases, the oxides are separated from the waste gases either by filtration through textile bags or by electric precipitation.-

The foregoing detailed description is to be construed in an illustrative rather than a limiting sense inasmuch as various modifications may be made by those skilled in the art without departing from the invention as defined in the appended claims. i

What I claim is 1. In the production of zinc, the method which includes subjecting zinc oxide-t0 the action of a fluid reducing agent while the oxide is held in a molten bath.

2. In a production of Zinc, the method which includes subjecting zinc oxide to the action of hydrogen while theoxide is held in material containing zinc oxide to treatment in a molten bath ofanhydrous chlorides and passing a stream of hydrogengas through the mass.

6. In the production of zinc, the method which consists in dehydrating and crushing zinc oxide, feeding the same to a molten bath of anhydrous chlorides and passing hydrogen gas through the bath.

7. In the production of zinc, the method which consists in subjecting dried crushed zinc oxide to treatment in a molten bath of anhydrous ternary chlorides of sodium, potassium and calcium and discharging hydrogen in the bath.

8. In the production of zinc, the method which consists in dehydrating and pulverizing zinc oxide and subjecting it to the reducing action of hydrogen while immersed in a bath of anhydrous chlorides.

9. In the production of zinc, the method which consists in providing a molten bath of anhydrous chlorides of the alkali and alkali-earth groups, adding dried crushed zinciferous material. to the bath and passing hydrogen gas through the bath.

10. In the production of zinc, the method which consists in providing a molten pulplike bath of anhydrous chlorides, adding comminuted zincifero'us material to the molten bath, passing hydrogen gas through the bath, withdrawing the reduced metallic zinc from the lower part of the bath and discharging the spent pulp at a level higher than that of the reduced metal. r

11. In the production of zinc, the method which consists in providing a molten pulplike bath of anhydrous chlorides and calcium oxide, adding comminuted zinciferous material to the molten bath, passing hydrogen gas through the bath, withdrawing the reduced metallic zinc from the lower part of the bath and discharging the spent pulp at a level higher than that of the reduced metal.

12. In theproduction of zinc, the method which consists in subjecting comminuted zinc oxide to the action of hydrogen while such zinc oxide is held in suspension in a molten pulp-like mass of anhydrous chloride and calcium oxide.

13. In the production of zinc, the method which includes subjecting comminuted zinc oxide to the action of hydrogen while such zinc oxide is held in suspension in a molten pulp-like mass containing anhydrous chlorides and oxides having a great affinity for water vapor at the temperature at which the reaction is carried on.

14. In the production of zinc, the method which consists-in dehydrating and crushing zinc oxide and subjecting the latter to the action of hydrogen gas while such crushed zinc is held in suspension in a molten bath containing anhydrous chlorides and calcium oxide.

15. In'the production of zinc, the method which consists in dehydrating and pulverizing zinc oxide and subjecting it to the reducing action of hydrogen while such pulverized zinc oxide is held in suspension in a molten bath containing calcium oxide.

' 16. In the production of zinc, the method which consists in dehydrating and pulverizing zinc oxide and subjecting it to the reducing action of hydrogen while such pulverized zinc oxide is held in suspension in a molten bath containing anhydrous chlorides and calcium oxide so that the liberated water vapor combines with the calcium oxide.

17. In the production of zinc, the method which consists in subjecting zinc oxide to the reducing action of hydrogen while the oxide is held in a molten bath containing an alkaline earth oxide.

18. In the production of zinc, the method which includes subjecting the ore to heat treatment and condensing the lnetallic zinc and subjecting the powdered zinc oxide thus produced to the action of a fluid reducing agent while said oxide is held in a molten bath.

19. In the production of zinc, the method which includes treating the zinc ore in a retort to recover metallic zinc and the powdery zinc oxide and subjecting the latter to the action of a fluid reducing agent while said oxide is held in a molten bath.

20. In the production of zinc, the method which includes treating the zinc ore in a retort to recover metallic zinc and the powdery zinc oxide and subjectin said oxide to the action of hydrogen while the oxide is held in a molten bath.

21. In the production of zinc the method which includes treating the zinc ore in a retort, removing the powdery zinc product from the condensers and subjecting it to the action of hydrogen while said product is held in a molten bath.

22. In the production of zinc, the method which includes treating the 'zinc ore in a retort, removing the powdery zinc product from the condensers and subjecting it to the action of hydrogen while said product is held in a molten bath containing an alkaline earth oxide.

23. In the production of zinc, the method which includes treating the zinc ore in a retort, removing the powdery zinc product from the condensers and subjecting it to the action of hydrogen while said product is held in a molten bath containing calcium.

action of hydrogen while said product is held insuspension in a molten pulp-like mass of anhydrous chloride and calcium oxide.

In witness whereof, I have hereunto signed my name. 7

AUGUSTIN LEON JEAN QUENEAU.

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