US3271134A

US3271134A - Extraction of zinc

Info

Publication number: US3271134A
Application number: US299888A
Authority: US
Inventors: Derham Leslie Jack
Original assignee: National Smelting Co Ltd
Current assignee: National Smelting Co Ltd
Priority date: 1962-08-20
Filing date: 1963-08-05
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06
Also published as: GB971729A; ES290936A1

Description

Sept. 6, 1966 L. J. DERHAM 3,271,134

EXTRACTION OF ZINC Filed Aug. 5, 1963 2 Sheets-Sheet l p 6, 1966 1.. J. DERHAM EXTRACTION OF ZINC 2 SheetS -Sheet Filed Aug.

United States Patent 3,271,134 EXTRACTION 0F ZINC Leslie Jack Derham, Avonrnouth, England, assignor to The National Smelting Company Limited, London, England, a British company Filed Aug. 5, 1963, Ser. No. 299,888 Claims priority, application Great Britain, Aug. 20, 1962, 31,919/ 62 14 Claims. (Cl. 7587) The invention relates to a process for producing zinc metal by the reduction of finely divided oxidic zinciferous material.

In the pyrometallurgical production of zinc metal, zinc oxide is reduced, directly or indirectly,'by carbon. In both electrothermal and retort processes, the carbon appears mainly as carbon monoxide, so that the overall reaction is:

This reaction absorbs a large amount of heat, which in the electrothermic process is provided by electrical energy and in the retort process is provided by heat generated in an external combustion chamber. Electrical energy is usually expensive, and the transmission of large amounts of heat through retort walls is also expensive and restricts the amount of zinc that can be produced in a single smelting unit.

In the blast furnace smelting of zinc, the heat required for the reduction of zinc oxide is generated in the furnace Where the zinc oxide is being reduced. This enables a large production of zinc to be attained in a single unit and with a good full economy. However, one drawback of the zinc blast furnace is that it requires an expensive sintering process to be carried out upon the charge to be fed to the furnace.

The present invention, like the blast furnace, has the advantage that the carbonaceous material introduced into the furnace acts as both a fuel and a reducing agent, but the present invention has the further advantage that it enables zinc to be reduced from zinc concentrate that has been either flash-roasted or oxidized in a fluidized bed, and that a further sintering of the charge is unnecessary. It can also treat pulverulent by-products such as flue dusts or granulated lead blast furnace slag-s.

The invention consists in a method for extracting zinc from a finely divided oxidic zinciferous material substantially free from volatizable arsenic and sulphur comprising the steps of: introducing the finely divided oxidic zinciferous material and finely divided carbonaceous material into, a generally circular and vertical reduction zone, and entraining the material by, a swirling spiral stream of an oxygen-containing gas at such temperature that reduction to zinc vapour takes place and all other non-volatile components assume a molten free-flowing form; separating these other components; and condensing the zinc vapour to give metallic zinc.

The invention further consists in a method of extracting zinc comprising the steps of: introducing a mixture of (A) pulverulent oxidic zinciferous material substantially free from volatizable arsenic and sulphur and (B) a pulverulent carbonaceous reducing agent, into a chamber; simultaneously introducing an oxygen-containing gas in such a fashion as to impart a whirling, swirling, downwardly spiraling, motion to the gas within the chamber and to entrain the finely divided mixture; maintaining a temperature such that the zinc oxide is reduced to zinc vapour while the carbon is oxidized to CO/CO mixture and any gangue material melts to a slag, separating the slag from the gas stream; and feeding the zinc vapour to a condenser.

The invention still further consists in a method for extract-ing zinc from a zinc-sulphide concentrate which con- 3,271,134 Patented Sept. 6, 1966 "ice tains arsenic as an impurity, in which the zinc-sulphide concentrate is roasted to remove nearly all the sulphur and produce a calcine consisting mainly of zinc oxide, this calcine being then reduced to zinc vapour and the zinc vapour then being condensed to zinc metal, characterized in that the zinc-sulphide concentrate is first heated in a neutral atmosphere wherebf the arsenic is almost completely removed; the remaining sulphur is then almost completely removed by roasting; the oxide zinciferous material obtained together with finely divided carbonaceous material, is introduced into, and entrained by, a moving stream of an oxygen-containing gas at such temperature that reduction to zinc vapour takes place and all other non-volatile components assume a molten free-flowing form; these other components are separated; and the zinc vapour condensed to give metallic zinc.

This sulphide concentrate advantageously contains copper and the oxidic zinciferous material is preferably free from lead and tin. The reasons for this are described below.

Preferably all the other components melt to a slag but the method according to the invention may still be used if some components are not melted, provided they are trapped in the molten slag and do not cause this to lose its free-flowing character.

The term oxidic zinciferous compounds include zinc oxide in the free form (ZnO) or combined with acidic oxides (e.g. ZnCO or Zn SiO The finely divided oxidic zinciferous material and the carbonaceous material preferably separately (but possibly together) and one or both preferably being preheated may be introduced into the gas stream by various methods.

In one possible mode of operation, the reaction is carried out in a furnace chamber and the zinciferous and/ or the carbonaceous material are dropped in at the top of the furnace. Alternatively, where a suitable inlet duct is provided for the oxygen-containing gas the zinciferous and/or carbonaceous material may be injected into the entering stream of gas in the inlet duct. If more than one such duct, e.g. a subsidiary duct, is provided a small proportion of the gas may be led through this to entrain the zinciferous and/ or carbonaceous material. Also, at least the carbonaceous material may be introduced into the moving stream of oxygen-containing gas in a separate entraining stream of nitrogen. This is valuable when a carbonaceous fuel is used preheated to such an extent that there is danger of it igniting.

A pulverulent fiux, such as lime and silica, may be introduced into the stream of oxygen-containing gas when necessary in order to ensure that the slag formed is of suitable composition to become molten and free-running.

In a preferred embodiment, the reduction is carried out in a whirling current of gas in a cyclone separator containing air or oxygen-enriched air. The use of oxygenenriched air further improves the fuel economy by reducing the amount of nitrogen that has to be heated during the process.

The main bulk of the oxygen-containing gas required for the process is introduced horizontally, e.g. through tuyeres in a direction oblique to and preferably tangentially to the radius of the cyclone cross-section so that it imparts a whirling, swirling, downwardly spiraling, motion and preferably a rotating motion to the charge. Uniform whirling or rotating motion of the air within the cyclone is generally to be preferred, but turbulence may have a useful effect in certain instances.

The-carbonaceous material in the charge is conveniently pulverized coke breeze or anthracite dust, which materials are cheaper than high-grade metallurgical coke; although other carbonaceous materials may be used, they should preferably be of low hydrogen content, and bituminous coal with a high content of volatiles is therefore less suitable. Any hydrogen present in the fuel finally appears in the gases partly as hydrogen and partly as water vapour, and it has been found that, although by means of the lead-splash condenser, zinc vapour can be condensed without any important amount of oxidation even in the presence of considerable amounts of carbon dioxide, the presence of Water vapour in large amounts causes some oxidation of zinc vapour. In view of this, water should preferably be excluded as much as possible.

Preferably, according to the present invention the oxygen-containing gas is preheated, in order to improve the fuel economy of the process.

The relative amounts of carbon in the charge and of oxygen in the air (or other oxygen-containing gas, e.g. oxygen-nitrogen mixture) are governed by the consideration that the reaction of the carbon with the oxygen in the air and with the oxygen combined as zinc oxide must be such as to form a mixture of carbon monoxide and carbon dioxide; preferably the CO /CO ratio by volume should lie between 0.6 and 1.6. The relative amounts of zinc oxide and carbon in the charge are determined by the consideration that the heat of combustion of the carbon to a mixture of carbon monoxide and carbon dioxide must be sufficient to provide heat for decomposing zinc oxide into Zinc vapour and oxygen, melting the slag, providing sensible heat for the gaseous reaction products and for heat losses, etc.

The invention further consists in zinc extracted by the method described above.

The invention still further consists in apparatus for extracting zinc by the method as described above, comprising a refractory-lined (e.g. brick lined) cyclone; a slag chamber beneath the cyclone to collect the molten material running down the cyclone walls; and a condenser for zinc vapour connected to an otftake in the slag chamber.

The slag chamber may have an upper tapping hole to run off the molten material from time to time and a lower tapping hole to empty the chamber, and may furthermore be fitted with one or more tuyeres to reduce further any zinc oxide contained in the slag. The cyclone may have external cooling coils or alternatively be Water-jacketed or have water-cooled sections in the walls to minimise corrosion difficulties. The cyclone is preferably a vertical shaft of circular horizontal cross-section, so designed that the molten slag formed of molten droplets which are thrown onto the cyclone walls by means of the centrifugal action of the whirling gas. They then coalesce into a molten slag which runs down the walls and can be collected at a horizontal otftake near the bottom, whence the gas, now free from slag, is conveyed to, e.g. a leadsplash condenser, which may be of the type described in British patent specification No. 572,961. Thus, -a gas/ liquid separation takes place within the cyclone itself and this allows a cleaner separation of the product gas from the liquid or solid products. The spiral movement of the gas within the chamber allows a longer retention time for the reduction of the zinc oxide to take place in the furnace.

The invention will be more fully understood with reference to the following discussion of the chemical reactions taking place.

If the zinciferous material being treated is an oxidized zinc concentrate of fairly high-grade (containing about 60% zinc) and if the air blast used is preheated to about 600 C., the amount of carbon needed is about 0.8 times the weight of zinc. Sufiicient air is introduced to burn approximately three quarters of the carbon to carbon monoxide and one quarter to carbon dioxide, so that this combustion may formally be written:

Typically for each gram-atom of zinc reduced, about 4.5 moles of carbon are consumed, and the initial combustion 4 of this carbon can be regarded as proceeding somewhat as follows:

4.5C+2.7O =3.6CO+0.9CO

The zinc oxide is then reduced by carbon monoxide:

ZnO+CO=Zn(g) +CO Adding these two equations together gives:

4.5C+2.7O +ZnO=2.6CO+1.9CO +Zn(g) Some carbon monoxide is used also in reducing ferric oxide to the ferrous state and in other minor reactions, so that the final gas may contain, with 1.0 mole zinc vapour, 2.4 moles CO and 2.1 moles CO with (if the oxygen was introduced as air) 10.3 moles of nitrogen. After the zinc has been removed, the gas contains about 14% CO and 16% CO. The combustion of this gas can be used to provide the heat required for preheating the air introduced into the furnace.

In order to ensure efficient condensation of zinc vapour to zinc metal in the lead-splash condenser, it is important that, apart from permanent gases, the gases conveyed to the condenser should contain no large concentrations of species other than zinc vapour, and in particular should contain no vapours that can react with zinc vapour.

Amongst the elements that are volatilized under the conditions of operation are arsenic, sulphur, lead and tin. Arsenic is mainly volatilized as the element since under the condition of operation of the furnace almost all arsenic compounds are decomposed with production of arsenic vapour which interferes with condensation effi ciency by reacting with zinc to form zinc arsenide:

In the absence of lead or tin, sulphur is volatilized to only a limited extent, probably as carbonyl sulphide (COS). In the presence of lead or tin, sulphur is volatilized to a much greater extent, and the sulphides of these metals then react with zinc in the condenser to form zinc sulphide:

In order to ensure good condensation efiiciency, it is necessary that the zinciferous material charged to the furnace should be substantially free from arsenic, and either substantially free from sulphur or substantially free from lead and tin.

The commonest raw material for zinc production is a zinc sulphide concentrate, which usually contains arsenic and lead as impurities. We have discovered that when such a zinc concentrate is heated in an inert atmosphere to a temperature within the range 950 C. to 1150 C. the arsenic is almost completely removed, and that this same treatment removes most of any lead, tin and cadmium contained in the concentrate. As an illustration of the possibility of volatilizing impurity metals (Pb, Cd and As) the following are the results of some experimental work in which samples of zinc blende were heated in a mufile furnace in which a neutral or slightly reducing atmosphere was maintained:

Arsenic content of impure blend=0.l%

After /2 hour it had dropped to 0.0075

After 1 hour it had dropped to 0.0045

The zinc sulphide concentrate, with these impurities removed, can then be roasted to yield an oxidized product suitable for charging to the furnace. This oxidised product contains only a small amount of sulphur, which, in the absence of lead and tin, is not volatilized to a great extent when treated in the furnace according to the invention. The presence of copper in the charge is advantageous, since it combines strongly with the sulphur and hinders volatilization of sulphur compounds.

The invention will be further described with reference to the accompanying drawings, in which,

FIGURE 1 represents a vertical section along II of FIGURE 2 a cyclone furnace for carrying out the method of the invention,

FIGURE 2 is a section along II-II of FIGURE 1,

FIGURE 3 is a section along III-III of FIGURE 1.

A cyclone 1 has an upper air inlet 2 with inlet orifice 2a and a lower outlet throat 3, and is surrounded by cooling coils 4. The throat 3 leads to a slag-collecting and zinc vapour receiving chamber 5 provided with tapping holes 6 and 7 and tuyeres 8 and 9 to reduce any zinc oxide present in the slag. This slag-collecting chamber 5 has an offtake 10 leading via duct 11 to a condenser system, for instance, a lead-splash condenser (not shown).

It has been found convenient to make the cyclone furnace from the following materials in the parts specified.

Lining of slag-collecting chamber 5: tapering portion of cyclone-refractory concrete.

Cyclone and offtake covers: chrome-magnesite.

Exterior of slag-collecting chamber: insulating concrete.

Exterior of oiftake and of upper part of slag-collecting chamber: heat-insulating brick.

Lining of air-inlet 2 and upper part of cyclone: carborundum.

The cyclone furnace operates as follows:

Air (or oxygen-enriched air), roasted zinc concentrate and pulverised fuel are blown in through inlet 2 and orifice 2a. The zinc oxide is reduced to zinc vapour and the solid constituents melt to a slag which runs down the cooled cyclone walls into the slag chamber 5. The zinc vapour is drawn off through the throat 3 up through olitake 10 and into a condensing system, e.g. a lead-splash condenser.

The slag may be drawn off periodically through tapping hole 6, or when it is desired to empty the chamber completely through tapping hole 7. The tuyeres 8 and 9 are provided for use if it is necessary to further reduce any zinc oxide retained in the slag, e.g. by use of more carbonaceous fuel.

I claim:

1. In the method of smelting a mixed charge of finely divided oxidic zinciferous material and carbonaceous fuelreducing agent suspended in a stream of oxygen containing gas moving downwardly in a vertically disposed reduction zone, the improvement in combination therewith which comprises:

(a) the finely divided oxidic zinciferous material and the finely divided carbonaceous fuel-reducing agent suspended in the stream of oxygen containing gas are injected under pressure horizontally and tangentially into the upper portion of a vertically disposed reduction zone generally in the shape of a cyclone, with its larger end at the top and its smaller but open end at the bottom;

(b) a swirling downwardly spiraling motion of suflicient strength is imparted to the charge to cause it to pass into and around the peripheral upper portion of the cyclone-shaped reduction zone and into and around the inwardly inclined peripheral lower portion of the cyclone-shaped reduction zone;

(c) the temperature of the upper and lower portions of the reduction zone is kept sufficiently high to oxidize the carbon in the charge to a mixture of carbon dioxide gas and carbon monoxide reducing gas to reduce the zinc oxide in the charge with the carbon monoxide and to vaporize the resulting zinc, and to melt non-volatilizable metal compounds normally present in the charge and carbon ash impurities to :a slag;

(d) the swirling downwardly spiraling motion of the charge is maintained throughout the reduction zone sufiiciently long to provide the detention time required to effect the reduction of the oxidic zinciferous material and to melt the non-volatilizable metal compounds and ash impurities to a slag;

(e) the resultant droplets of molten slag are forced centrifugally to the periphery of the inwardly inclined and gradually constricted lower portion of the cyclone-shaped reduction zone;

(f) the droplets of molten slag are there coalesced and dropped through the open bottom of the cycloneshaped reduction zone, and gathered in a molten slag collecting zone, immediately below the reduction zone, as a pool of molten slag;

(g) molten slag is tapped from the pool of molten slag;

and

(h) the resultant zinc vapour is passed downwardly from the reduction zone into the molten slag collecting zone and from above the top of the pool into a condensing system for the separate recovery of the 2. Method according to claim 1, in which the reduction zone is externally cooled to increase the rate of heat loss from within the reduction zone.

3. Method according to claim 1, in which the oxidic zinciferous material introduced into the reduction zone is substantially free of lead, tin, cadmium, arsenic and sulphur.

4. Method according to claim 1, in which the zinciferous material is essentially in the form of zinc-sulphide concentrate; the concentrate is roasted to produce oxidic zinciferous material; and the resultant oxidic zinciferous material is introduced into the reduction zone.

5. Method according to claim 1, in which the zinciferous material is essentially in the form of zinc-sulphide concentrate containing compounds of arsenic, lead, cadmium and sulphur as impurities; the zinc sulphide concentrate is heated in an atmosphere inert to the metal compounds normally present as impurities in the concentrate to decompose the metal compounds and to volatilize and remove substantially all of the arsenic, lead and cadmium; the resulting arsenic-lead-cadmium free concentrate is roasted in the presence of air to remove nearly all of the remaining sulphur to produce a caleine consisting mainly of oxidic zinc; and the resultant oxidic zinciferous material is introduced into the reduction zone.

6. Method according to claim 5, in which the zinciferous material in the form of zinc-sulphide concentrate containing copper is roasted in the presence of the air to remove most of the sulphur and to form the oxidic zinciferous material of the charge; and the copper present in the charge is combined with the remaining sulphur to hinder volatilization of sulphur compounds in the reduction zone.

7. Method according to claim 1, in which a pulverulent flux is added to and is suspended in the suspended charge to help make the droplets of slag molten and free-running and thus aid in their coalescence.

8. Method according to claim 1, in which a pulverulent flux in the form of an oxide is added to and is suspended in the suspended charge to help make the droplets of slag molten and free-flowing and thus aid in their coalescence.

9. Method according to claim 1, in which a pulverulent flux selected from the group consisting of lime and silica is added to and suspended in the suspended charge to help make the droplets of slag molten and free-flowing and thus aid in their-coalescence.

10. Method according to claim 1, in which a reducing agent is introduced into the pool of molten slag to reduce zinc oxide present in the slag.

11. In apparatus for smelting a mixed charge of finely divided oxidic zinciferous material and carbonaceous fuelreducing agent suspended in a stream of oxygen-containing gas moving downwardly in a vertically disposed reduction shaft, the improvement in combination therewith which comprises:

(a) the vertically disposed reduction shaft of the smelting furnace is refractory-lined and is in the shape generally of a cyclone with its larger end at the top and its smaller end at the bottom, the lower portion of the shaft being frusto-conical in shape, tapering 10 downwardly and inwardly towards its lower end so that its cross-sectional area is gradually constricted to a bottom outlet throat;

(b) an insulated charge-feeding device connects the upper exterior portion of the smelting furnace with the upper interior portion of the reduction shaft, the charge-feeding device having a conduit extending therethrough that connects the upper exterior portion of the smelting furnace with the upper interior portion of the reduction shaft horizontally and tangentially to permit the charge to assume a swirling, downwardly spiraling, motion,

(c) a combined slag collecting and Zinc vapour receiving chamber is located immediately below the bottom of the vertical shaft to collect a pool of molten slag and to permit separation of zinc vapour therefrom;

(d) at least one slag-tapping conduit extends through the Wall of the slag collecting chamber for removing molten slag therefrom; and

(e) a zinc vapour outlet offtake, separate and distinct from the reduction shaft, connects the upper portion of the slag collecting and zinc vapour receiving chamber for the passage of zinc vapour therefrom.

12. Apparatus according to claim 11, in which the smelting furnace is provided with means for cooling the vertical reduction shaft to increase the rate of heat loss from its reduction zone.

13. Apparatus according to claim 11,.in which the zinc vapour oiftake connects the upper portion of the slag collecting chamber with a condensing system for recovering zinc.

14. Apparatus according to claim 11,in which the slag References Cited by the Examiner UNITED STATES PATENTS 1,150,841 8/1915 Doherty 75-86 1,236,395 8/1917 Berglund 7586 1,923,511 8/1933 Scheil 756 1,977,117 10/1934 Debuch 757 2,342,368 2/1944 Queneau 7586 XR 2,475,607 7/ 1949 Garbo 7586 XR 2,530,078 11/ 1950 Ramsing 266-- XR 2,650,159 8/1953 Tarr 6 2,951,756 9/1960 Cavanagh 7540 2,973,260 2/ 1961 Nogiwa 266-24 3,017,261 1/ 1962 Lumsden 75-86 FOREIGN PATENTS 921,861 5/ 1947 France.

30 HYLAND BIZOT, Primary Examiner.

BENJAMIN HENKIN, DAVID L. RECK, Examiners.

H. W. CUMMINGS, H. W. TARRING,

Assistant Examiners.

Claims

1. IN THE METHOD OF SMELTING A MIXED CHARGE OF FINELY DLIVIDED OXIDIC ZINCIFEROUS MATERIAL AND CARBONACEOUS FUELREDUCING AGENT SUSPENDED IN A STREAM OF OXYGEN CONTAINING GAS MOVING DOWNWARDLY IN A VERTICALLY DISPOSED REDUCING ZONE, THE IMPROVEMENT IN COMBINATION THERWITH WHICH COMPRISES: (A) THE FINELY DIVIDED OXIDIC ZINCIFEROUS MATERIAL AND THE FINELY DIVIDED CARRBONACEOUS FUEL-REDUCING AGENT SUSPENDED IN THE STREAM OF OXYGEN CONTAINING GAS ARE INJECCCTED UNDER PRESSURE HORIZONTALLY AND TANGENTIALLY INTO THE UPPER PORTION OF A VERTICALLY DISPOSED REDUCTION ZONE GENERALLY IN THE SHAPE OF A CYCLONE, WITH ITS LARGER END AT THE TOP AND ITS SMALLER BUT OPEN END AT THE BOTTOM; (B)Z A SWIRLING DOWNWARDLY SPIRALING MOTION OF SUFFICIENT STRENGTH IS IMPARTED TO THE CHARGE TO CAUSE IT TO PASS INTO AND AROUND THE PERIPHERAL UPPER PORTION OF THE CYCLONE-SHAPED REDUCTION ZONE AND INTO AND AROUND THE INWARDLY INCLINED PERIPHERAL LOWER PORTION OF THE YCLONE-SHAPED REDUCTION ZONE; (C) THE TEMPERATURE OF THE UPPER AND LOWER PORTIONS OF THE REDUCTION ZONE IS KEPT SUFFICIENTLY HIGH TO OXIDIZE THE CARBON IN THE CHARGE TO A MIXTURE OF CARBON DIOXIDE GAS AND CARBON MONOXIDE REDUCING GAS TO REDUCE THE ZINC OXIDE IN THE CHARGE WITH THE CARBON MONOXIDE AND TO VAPORIZED THE RESULTING ZINC, AND TO MELT NON-VOLATILIZABLE METAL COMPOUNDS NORMALLY PRESENT IN THE CHARGE AND CARBON ASH IMPURITIES TO A SLAG; (D) THE SWIRLING DOWNWARDLY SPIRALING MOTION OF THE CHARGE IS MAINTAINED THROUGHOUT THE REDUCTION ZONE SUFFICIENTLY LONG TO PROVIDE TO DETENTION TIME REQIRED TO EFFECT THE REDUCTION OF THE OXIDIC ZINCIFEROUS MATERIAL AND TO MELT THE NON-VOLATILIZABLE METAL COMPOUNDS AND ASH IMPURITIES TO A SLAG; (E) THE RESULTANT DROPLETS OF MOLTEN SLAG ARE FORCED CENTRIFUGALLY TO THE PERIPHERY OF THE INWARDLY INCLINED AND GRADUALLY CONSTRICTED LOWER PORTION OF THE CYCLONE-SHAPED REDUCTION ZONE; 8F) THE DROPLETS OF MOLTEN SLAG ARE THERE COALESCD AND DROPPED THROUGH THE OPEN BOTTOM OF THE CYCLONESHAPED REDUCTION ZONE, AND GATHERED IN A MOLTEN SLAG COLLECTING ZONE, IMMEDIATELY BELOW THE REDUCTION ZONE, AS A POOL OF MOLTEN SLAG; (G) MOLTEN SLAG IS TAPPED FROM THE POOL OF MOLTEN SLAG; AND (H) THE RESULTANT ZINC VAPOUR IS PASSED DOWNWARDLY FROM THE REDUCTION ZONE INTO THE MOLTEN SLAG COLLECTING ZONE AND FROM ABOVE THE TOP OF THE POOL INTO A CONDENSING SYSTEM FOR THE SEPARATE RECOVERY OF THE ZINC.

11. IN APPARATUS FOR SMELTING A MIXED CHARGE OF FINELY DIVIDED OXIDIC ZINCIFEROUS MATERIAL AND CARBONACEOUS FUELREDUCING AGENT SUSPENDED IN A STREAM OF OXYGEN-CONTAIN ING GAS MOVING DOWNWARDLY IN A VERTICALLY DISPOSED REDUCTION SHAFT, THE IMPROVEMENT IN COMBINATION THEREWITH WHICH COMPRISES: (A) THE VERTICALLY DISPOSED REDUCTION SHAFT OF THE SMELTING FURNACE IS REFRACTORY-LINED AND IS IN THE SHAPE GENERALLY OF A CYCLONE WITH ITS LARGER END AT THE TOP AND ITS SMALLER END AT THE BOTTOM, THELOWER PORTION OF THE SHAFT BEING FRUSTO-CONICAL IN SHAPE, TAPEROING DOWNWARDLY AND INWARDLY TOWARDS ITS LOWER END SO THAT ITS CROSS-SECTIONAL AREA IS GRADUALLY CONSTRICTED TO A BOTTOM OUTLET THROAT; (B) AN INSULATED CHARGE-FEEDING DEVICE CONNECTS THE UPPER EXTERIOR PORTION OF THE SMELTING FURNACE WITH THE UPPER INTERIOR PORTION OF THE REDUCTION SHAFT, THE CHARGE-FEEDING DEVICE HAVING A CONDUIT EXTENDING THERETHROUGH THAT CONNCTS THE UPPER EXTERIOR POROF THE SMELTING FURNACE WITH THE UPPER INTERIOR PORTION OF THE REDUCTION SHAFT HORIZONTALLY AND TANGENTIALLY TO PERMIT THE CHARGE TO ASSUME A SWIRLING, DOWNWARDLY SPIRALING, MOTION, (C) A COMBINED SLAG COLLECTING AND ZINC VAPOUR RECEIVING CHAMBER IS LOCATED IMMEDIATELY BELOW THE BOTTOM OF THE VERTICAL SHAFT TO COLLECT A POOL OF MOLTEN SLAG AND TO PERMIT SEPARATION OF ZINC VAOUR THEREFROM; (D) AT LEAST ONE SLAG-TAPPING CONDUIT EXTENDS THROUGH THE WALL OF THE SLAG COLLECTING CHAMBER FOR REMOVING MOLTEN SLAG THEREFROM; AND (E) A ZINC VAPOUR OUTLET OFFTAKE, SEPARATE AND DISTINCT FROM THE REDUCTION SHAFT, CONNECTS THE UPPER PORTION OF THE SLAG COLLECTING AND ZINC VAPOUR RECEIVING CHAMBER FOR THE PASSAGE OF ZINC VAPOUR THEREFROM.