US1743886A - Electric smelting of zinc ore - Google Patents

Description

Jan. 14, 1930. E. c. GASKILL ELECTRIC SMELTING OF ZINC ORE Filed Nov. 17. 192

INVENTQR. By 224 M Mx% ATTORNEY. My

Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE EARL C(GASKILIL, RED B ANK, NEW JERSEY, ASSIGNOB T0 ST. JOSEPH LEAD COMPANY, OE YORK, N. Y., A CORPORATION OF NEW YORK ELEQTRIC SMELTING or'zmc o'er:

Application m r November-17, 1920. SeriaLNo. 148,801.

v This invention relates generally to the electric smelting of zinc ore and more particularly to a method for producing zinc or zinc oxide by the reduction of loose ore in a furnace of the electric resistor type.-

So far as I am aware, no practical method of electric smelting of zinc ores has been heretofore developed.

It is a general object of the present invention to provide a process or method for electrically smelting zinc ore in a furnace of the electric resistor type, and by continuous, as

distinguished from batch, operations.

.The apparatus required for carrying out the process, includes, as its most important element, a furnace structure of the vertical shaft, electric resistor type. The furnace is formed of suitablerefractory materials and provided with annular electrodes formed of graphite, or other suitable material, mounted at the upper'and lower ends of the reducing.

[zone of the furnace. The electrodes are massive in construction and the openlngs therethrough register with the furnace bore or chamber so that the charge in the chamber ripheri'es thereof. The upper extremity of the furnace is sealed, 1n operation, against the-ingress of air or the escape of gases.

Avfeature of the invention resides in the preheating of material to be treatedin two stages. In the first stage the material is heated to a temperature of approximately 600 C. to drive off moisture. Thematerial is then charged into a second preheater forming part of the furnace structure in which the temperature of the material is raised to 900, or 1000 C., or the reducing temperature, in order to economize current in the reducing operation.

I'have found that the smelting of zinc ore in a furnace ofthe electric resistor type can be considerably facilitated by sintering the ore before subjecting it to the reducing operation, although the reduction of the ore can be obtained without the preliminary sintering, if necessary. The sintering of the ore may be achieved as a part or extension of the roasting operation to which zinc ores, and particularly ores of the sulphide type, are subjected. The'sintering efiect can be obtained by a local intensification of the application of heat to the ore as it passes through the roaster. The sintering action is greatly facilitated by the presence of iron contained in many zinc ores, and which may be added, if desired, as an aid to the sintering action, although the sintering effect can be obtained in other ways.

A sintered condition of the ore charged into the furnace contributes to the success of the smelting operationin that the charge is in a good mechanical condition to flow down the shaft without clogging or jamming and, in addition, possesses a porous structure which aids in heating the charge through the impermeation of the material by the hot gases evolved in the reducing operation. The porous nature of the sintered chargegreatly facilitates the free passage therethrough of gases and vapors resulting from the reduction reactions and thereby assists in their removal from the furnace chamber. Another advantageous feature of the use of sintered material resides in the fact that sintered ore, unlike ore that has not been sintered, when heated, becomes a relatively good conductor of electricity and, thereby facilitates the passing ofcurrent through the charge to effect the reducing operation.

It has been statedthat the presence of iron in the ore facilitates the sintering operation. I have foundthe iron to be useful in other respects which aid substantially in the reducing of theore. In the application of heat to the sintered-material in the upper part of the furnace metallic iron is liberated and still further increases the conductive properties of the material. The liberated iron also aids in the reduction of the zinc ore and apparently possesses a chemical activity or instability which results. in the taking up by the iron of the oxygen combined with the zinc so that zinc is set free.

, In the operation of a furnace in which the process can be-carried out the mass of heated and sintered ore which is passed into the furnace chamber between the electrodes is sufficiently conductive to provide a path of the flow of current between the electrodes while, at the same time, offering suflicient resistance to the flow of current to roduce the in-. crease in temperature required to liberate zinc from the ore. The reducing operation has been found to take place with much greater rapidit under the conditions named than in the o d retort practice. sults, in part, because the electrical resistance of the charge is very much less than the thermal resistance. The efficiency of the operation is much higher than that of the retort practice, in part because the internal application of heat through the action of the electric current is much more eflective than is the external application of heat which must penetrate through the thermally non-0onductive material.

I have found also that the efficiency of operation of the furnace is considerably increased by a reducing effect produced by the action of the electric current itself. In other words a reducing action is achieved which is greater than could be expected from the moderate temperatures existing in the smelting zone between the electrodes. The action of the current is believed to produce an ionization effect which facilitates the setting free of the zinc and directly converting electrical into chemical ener y.

This electrical e ect is so pronounced that if, when the-furnace has been operating at approximately 200 volts, with a pyrometric indication thatthe temperature conditions are suflieiently high for satisfactory reduction and with a liberal flow 'of zinc va or issuing from the furnace, the voltage 'e increased" to 400 without changing other conditions, the increased voltage causes the power input to be more than doubled with a proportionate increase inthe amount of vapor liberated. These changes in the power input and the amount of vapor roduced are accompanied by an astonishing lowering of the furnace temperature, thereby indicating that at or over certain critical potentials reduction takes place at lowered temperatures with an increase in simplicity and efiiciency of the reducing operation.

In operations conducted in a furnace of the type described it has been found that in no partof the reducing chamber of the furnace does there exist a higher temperature than the optimum temperature known to be needed for the purpose of reduction of the ore. There exists no hot spots in the reducing chamber and the control and selection of uniform temperatures suitable for the pur ose is readily efi'ected. The uniformity an efficiency of temperature produced results in part through the upward passage throu h the descending massof material in the re ucing zone of hot gases which imper'mea te and heat all portions of the porouslmass of material constituting the charge.

amaaaa This re-.

In the drawing a single, diagrammatic v1ew has been provided to illustrate an em-.

bodiment of means for carrying out the process.

Referrin to the drawing for a more detailed description of the invention, a vertical shaft furnace is shown at 10 in which the temperature required for the smelting or the reduction of the ore is provided by way of two annular electrodes 11 and 12 which are mounted in the wall of the furnace at the upper and lower ends of the reducin zone thereof. The walls of the furnace are formed of any suitable heat refractory material and are provided at vertically separated intervals with annular overhanging portions 13 which serve to provide spaces free from solid material and from which vapors evolved in the reducing action. can be freely drawn by means of tuyere openings 14 terminating in the grooves or recesses 15 beneath the overhanging shoulders 13. With this construction, the clog ing of the tuyere openings or passages by t e solid matenal of the charge can nottake place and the passage of vapors through the openings is insured.

In order to prevent the access of air to the interior of the furnace chamber 16, a hinged closure member 17 is provided at the upper end of the furnace shaft-which is normally kept closed in operation while providing means for gaining access to the interior of the furnace for any purpose.

A preheatingdevice 18 is provided into which the material to be treated is delivered by means of a conveyor 19. By means of oil or gas burners, the charge present in the preheater 18 is brought up to a temperature such as will drive off all the moisture content of the material in the chamber of the preheater.

A temperature of approximately 690 C. is

approporiate for this purpose and this temperature is not so high as to injure the material of which the preheater and adjacent parts are formed.

From the preheater 18 a valve or gate 20 operates to feed material through the inclined passageway 21 into the upper end 22 of the furnace. The hot material in a thorough 1y dry condition and free of Water vapor then finds its way into the chamber of a preheating unit 23 in which the temperature is brought u to a higher point ap roximating that at W ich the reduction of the charge takes place through the action of current supplied through the electrodes 11 and 12. A

good temperature, suitable for the purpose, approximates 1000 C. and the production of this temperature by means of the consumption of oil or gas as fuel in the preheater 23 serves to initiate the reduction of any iron oxide present in the ore as well as to economize in the consumption of electric current in the reducing operation.

The feeding device 20 is preferably automatically operated through a control exer cised by the level of the material in the furnace so that a column of material is continuously maintained in bridging relation to the electrodes 11 and 12, thereby producing continuous as distinguished from batch operations.

From the smelting zone ofthe furnace, which extends between the electrodes 11 and 12, the tuyere passages lead into condensers 24 in which the zinc vapor is condensed to liquid, or to a vertical pipe 25 through which the vapors and air are drawn and burned at the port 50 as a result of the action of a blower 26 and thence pass through a separator 27 into a bag room 28 in which bags 29 are suspended for the collection of the oxide dust'in a known manner. It will thus be seen that in the same operation both the metallic or spelterform of the zinc may be ob. tained and the oxide form so that either or both the ultimate products may be obtained in the-operation of the apparatus described.

It will be seen that the condensers-24 are mounted at different elevations or levels along the side wall of the furnace 10. By this method of condensing I am enabled to obtain different varieties of different types of spelter or metallic zinc. denser there will be obtained zinc having cadmium intermixed therewith. In the lower condenser 24 zinc having lead intermixed therewith will be obtained. In condensing vapors in the tuyere openings be tween the uppermost and the lowermost condensers illustrated, a substantially pure formconductivity in the mass of material to en-.

able current to flow through the column of material between the electrodes, carbon in the .form of coke, coal or the like, is intermixed with the charge before it is fed into thefurnace. I may make use also of the iron content of the ore for this purpose andthereby reduce to a considerable extent the proportion of carbonaceous material used for this purpose. I contemplate the elimination of carbon for adding conductivity and making use only of so much carbon as is needed in the reducing operation.

I have-found that the use of iron, in addition to adding to the electrical conductivity of the charge, is a useful agent in bringing about the reduction of'the charge. In exer- In the uppermost con-' 'c'ising this function, iron oxide is apparently reduced in the second reheater 23 as well as in the upper part of t e smelting zone adjacent the upper electrode 11. The liberated iron, which is in solid form, as it travels downwardly through the reducing zone, apparently produces an ionization or chemical instability which results in the taking up by the iron of oxygen from the zinc oxide compounds contained in the ore with the result that zinc is set free through the presence'of the iron as well as through the reducing action of the carbon monoxide produced through the action of the heating current on a carbonaceous material admixed with the charge. The use of iron therefore has a twofold action within the furnace in that it adds to the conductivity of the charge and in addition it facilitates the reducing action.

I have found that the action of electric current on a charge contained in a furna ce of the type described produces a reducing action on thecharge which is substantially greater than could be expected from the temperatures attained in the smeltin zone" between the electrodes. I have found that through a considerable range the voltage of current sup plied to the electrodes can be increasedwith-' out bringing about a corresponding increase in temperature within the furnace. On the contrary, I have found that an actual drop in temperature follows the increase of voltage of the current up to a pointcfound most effective or efiicient by actual trial; When this condition is attained, it'has been found that a greater increase in the amount of material reduced is obtained than can be measured by the increase of voltage of the current supplied to the furnace. This increase in the quantity of material produced by the operation of the furnace with an actual drop in the temperatures attained within thefurnace chamber indicates that the action of the current does something more than merely zinc compounds with an ionization effect which results in or facilitates the reduction of the ore and the liberating of the zinc. In other words, under the conditions named, there appears to be a direct conversion of the electrical into chemical energy withoutan intermediate conversion of electrical energy into heat followed by a conversion ofheat into chemical energy.

By reason of the assistance providedby the iron in bringing about the reduction of the zinc compounds and also through the part which the electric current itself. plays in the reducing operation, the reducing action takes place in a furnace of the type described at a considerably lower temperature than has heretofore been found necessary for furnace which takes the form of a cooling cylinder 31 through which the spent charge or residue passes from the furnace chamber. The lower extremity ofthe cooling tube 31 terminates in a water seal provided in a bowl-v shaped member 32 which is rotated on a shaft 33 in such manner that a stationary plow or scraper 34 directs material from the bowl 32 onto a conveyor 35 leading to a suitable discharge point. Water is provided for the water seal through a pi e 36 and an overflow 37 in the bowl 32 directs water into an annular trough-shaped member 38 from which it is conveyed to a Waste connection.

A feature of the invention resides in. the

preliminary treatment of the ore before it is charged into the reducing furnace 10.v I

' have found that reducing operations in a furnace of the type described are greatly facilitated if the ore charged into the furnace is in content of the ore facilitate the wind box member.

a sintered form. The sintering of the ore can be produced simultaneously or in supplement to a roasting operation on a machine of the type shown at 39 in the drawing. This machine includes a ho per 40 in which the material is placed an from which it is delivered to a series of pans 41 havin perforated bottoms and arranged to travel horizontally over a wind box structure 42 connected by means of a ipe 43 with any suitable source of exhaust. 11 oil burner 44 is placed at the point of delivery of the material from the hopper 40 to the receptacles 41 and serves to ignite the sulphur ordinarily present in the ore.- When once ignited, the material is subjected to the desired roasting and sintering action by reason of the burnin of the sulphur d by the vigorous down draft provided by the wind box struc- :ure throu h the relatively thin layers of material passmg along the open upper face of The desirable sintered condition of the ore which is obtained from the apparatus shown at 39 may be produced with various ores through the use of a sufiicient intensity of heat. However, I find ductor of'electricity while roasted 'sinter is a -is excluded an Y\ Y; relatively good conductor. The sinteredore not onl assists in the conductivity of the charge at the mechanical condition of the sinter facilitates the free flowing of the charge downwardly through the bore of the furnace. The reduction of the iron oxide near the upper part of the furnace leaves the metallic iron in a anular condition resembling sand and it willbe seen that this physical structure faciltates the flowing action referred to. The material thus roasted and brought to the desired condition of sinter is delivered from the end of the machine 39 ceous material is delivered from the mixture 48 into hopper or boo tr49of the conveyor 19 for delivery into the p'reheater 18 of the furnace structure.

It will thus be seen that I have provided a method for the reduction of zinc ores in a furnace of a shaft type to which the access of air a reducing atmosphere is maintained. The charge in the furnace chamber is continuously renewed as fast as it is lowered in the reducing operation so that the uniform temperature which is necessary for the carrying out of a reducing operation without the formation of blue powder is achieved. In addition, the preparation of the furnace facilitates the reduction of ore in nace chamber before the material passes into the reducing zone adds still further to the effectiveness of the process. The use of iron as a part of the natural content of the ore or as an ingredient added thereto before reduction aids in the carrying out of the reducing operation. The control of current in such manner that the maximum production of liberated metal is obtained while at the same time an actual lowering of the temperature reduction takes place is a distinct achievement in the new process of ore reduction described. The production of spelter or metallic zinc and also of zinc oxide in the same furnace as well as the production of spelter of different grades is another advantage of the process set forth. In addition, the production of zinc oxide in connection with a sealed type of electric resistor furnace results in the formation of zinc oxide of a superior quality as com pared with zinc oxide hertofore produced by known processes.

What I claim is:

1. The process for smelting zinc ore which comprises sintering the ore to make the body of the ore more porous and more conductive v in the reducing operation then in mlxlng carbonaceou material with the sintered ore, and then in passing electric current through the mixture to reduce the ore and liberate the 2. The process of reducing zinc ore 'which comprises feeding aloose mixture of sintered zinc ore and carbonaceous material in a vertical column between spaced electrodes, whereby the charge forms a resistance between the electrodes, passing an electric current therethrough to heat and reduce the ore and vaporize the zinc, withdrawing the spent material from the lower end of the column and removing the zinc vapor.

3. The process as claimed in claim 2 in which the charge is preheated before-passing it between the electrodes.

4. The process of reducing zinc ore which comprises feeding a loose mixture of zinc ore and carbonaceous material in a vertical col umn between spaced electrodes, whereby the charge forms a resistance between the-electrodes, passing an electric current therethrough to heat and reduce the ore and vapor- 'ize the zinc without substantial slagging .or

fusion of the charge, withdrawing the spent materialfrom the lower end of the column and removing the zinc vapor.

) EARL c. GASKILL.

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