US2183535A - Recovering zinc - Google Patents

Description

Dec. y19, 1939.

J.v o; BETTERTON Er AL Fild Feb. llas, 1958' 2 sheets-sheet 1 Patented Dec. 19, 1939 l nEcovEmNG zrNc Jesse 0. Bettcrton,A Metuchen, and Melville` F.

Perkins, Elizabeth, N. J., assignors to American Smelting and Refining Company, New York, N. Y., a corporation of New Jersey Application February 18, j1938, Serial No. 191,144

g Claims. (Cl. 'i5-26)I This invention relates to the production of zinc. s

Various proposals-have been advanced in the past for producing zinc by subjecting zinc oxide O to a ash reduction and condensing the resulting zinc vapor. In general, these proposals contemplated `injecting a finely-divided charge of zinc oxide and carbonaceous reducing agent, with or without ux, into a retort wherein the oxide is reduced in suspension by a suitable reducing l gas, e. g., carbon monoxide or methane and immediately thereafter recovering zinc from the gaseous products of reduction by various conventional condensation methods. However, those u skilled in the art have been unable to translate such proposals inte terms ofV successful commercial practlse;

SubsequentlyAt was found that the'fiiash reduction of zinc oxide and condensation of thel .zinc vapor could be successfully practised by conducting the gaseous products of reduction',

on their way from the ash chamber to the condenser, through a suitable reducing andflltering medium, e. g., a bed of incandescent coke. vFor 86 details of such a process the reader is referred to United States Letters Patent No. 2,096,779 granted October 26,'1937 to George P. Bartholomew and Edward P. Fleming to United States lLetters Patent No. 2,181,148 granted Nov. 28, 1939 80 to Melville F. Perkins and Roland G. Crane.

` `The present invention constitutes a meritorious advance in the art by providing, for the iirst time. a process in which zinc oxide is ash reduced and the zinc vapor content of thev gaseous $5 products of reduction directly condensed and recovered without any intermediate or conditioning treatment. In short, the new process renders it unnecessary to conduct the vapors through a reducing or filtering medium priorto condensa- In accordance with the invention, zinc oxide is reduced by passing same in a, finely-divided,

non-compacted state through a suitable reduccordingly, for purposes of illustration, it will be y described, for the most part, with reference to flash reducing the zinc oxide by passing same through a vertical retort with coke dust and the use of carbon monoxide gasastthe quenching fluid. I

Although the4 novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims append- 5 y ed thereto, the invention itself, as vto its objects and advantages, and the manner in which it may be carried out, may be better understood by reference to the following description taken in connection with the accompanying drawings 10 forming 'a part thereof in which Fig. 1 Ais a diagrammatic, sectional elevation of one form of apparatus for carrying into practise the process of the invention.

Fig. 2'is an equilibrium diagram between car- 15 l bon monoxide and carbon dioxide showing the percentage of each at given temperatures, and

Fig. 3 is a graphic representation of the vapor pressures of zinc with dew points of various mixtures of zinc with other vapors indicated thereon. 20

Referringto Fig. l, there is shown a charge hopper ,I0 with` screw conveyor I2 for delivering ,charge to flash shaft I4 vertically disposed in furnace I6 which is equipped with burners I8. Off-take 20 leads from the top of shaft I4 to 25 quenching throat 22, the latter discharging into collecting or recovery means 24 which is provided with tap 25, service door .29 and thermocouple 26. A fan 21 driven by motor 28 is connected onits suction side with collector 24 by pipe 30, lter 30 32 and pipe 34. On the compression side of blower 21 is pipe 36 provided with vent 38, said pipe passing through temperature'control means 40 and into throat 22.

Employing the apparatus just described,l the 35 process of the invention may be practised as follows: the furnace is brought to zinc reduction temperature and a pre-heated, yiinely=divided charge of zinc oxide and coke fed from hopper I0 to the flash shaft I4 wherein the zinc oxide 40 is reduced as the charge falls to the bottom of the shaft. The reduction may be expressed by the equations and is preferably so controlled that the oxide is reduced practically in toto and the gases accompanying :the zinc vapor, as it is withdrawn through the off-take 20, are predominantly carbon monoxide.

'As the hot zincky vapors from the off-take 20 enter the throat 22 they are met by and intermixed with a stream of carbon monoxide in which zinc vapor as contemplated herein minimizes blue temperature, quantity and velocity are so correlated as to instantly quench the zinc which is recovered in the collector 24. The zinc is withdrawn as desired through tap 25'and the carbon monoxide is withdrawn through pipe 30, passed through filter 32 and recirculated to the throat 22 after passing through temperature control means 40, any excess gas being vented from the system at 38. Solid particles of iiy ash, carbon and the like which may be entrained in the gas stream from the ash reducer can be removed from the collector 24 through door 29.

The instant and sudden quenching of thehot powder formation thereby enhancing zinc recovery. This may be better understood by refere'nce to Figs. 2 and 3 and by a consideration of the principles underlying zinc reoxidation and blue powder formation.

It is well known that at certain temperatures carbon monoxide dissociates according to the reversible-reaction Y and Fig. 2 shows that at temperatures in the vicinity of 1000 C. the equilibrium condition calls for substantially all carbon monoxide. At such temperature the rate of the producer gas reaction and its reversal is rapid `thereby permitting attainment of the equilibrium condition within a short time. At temperatures of, say, 800 C.- 900 C., the equilibrium conditions call for appreciable quantities of carbon dioxide but the rate of reaction in the vicinity of these temperatures is very slow thereby requiring long periods of time for attainment of the equilibrium condition. Accordingly, by cooling the gas in a sufficiently short interval'of time it is possible to freeze the high from Zinc Smelting from a Chemical and Thervmodynamic Viewpoint by C. G. Maier, U. S.

Department of Commerce, Bureau of Mines Bulletin 324 is pertinent.

Zinc is a moderately strong basic metal. By

analogy with the alkaline earth and alkali metals,

which areknown to reduce carbon monoxide at elevated temperatures, zinc also might be expected to reduce carbon monoxide.\ The reaction has been written:

This equation is obimnuslyhe reversal of the steady-state condition of continuous reduction and involves the reversal of the producer-gas reaction Equation (1) is then not a complete reaction, since carbon dioxide is omitted At 1 atmosphere pressure equilibrium is possible only at 857 C.

.The mechanism of reaction (1) then consists of the consecutive' or simultaneous reactions Of these the first is known to be slow below about 1,100 C., but the second is perceptible above l30o" c. and is very rapid about about 550 c.

Then the rate at which zinc is oxidized by carbon is determined by the slow step, the reversal 'of the producer-gas reaction, or the dissociation of carbon monoxide.

Reference to the (producer-gas reaction) shows that large amounts of carbon dioxide would be present in the equilibrium mixture at temperatures below 850 C., but it is also known that below 850 C. the rate of dissociation becomes increasingly slow, and in the absence of a very active catalyst months or even years might be necessary to reach the equilibrium concentration."

Referring to Fig. 3, in which typical zinc vapors resulting from the flash reduction of zinc oxide by carbon monoxide and by methane, respectively, are indicated, it will be seen that it is necessary to pass through the zone of rapid reoxidation of zinc (i. e., the zone of rapid reversal of the producer gas reaction) before the dew point of zinc is reached. vBy the present process, the quenching fluid cools the zinc vapor from theA flash shaft so rapidly products formed by the aforesaid reversible reac- -tions is innocuous but, in'addition, it has been found that deleterious components may even be present in appreciable amounts without destroying the commercial value of theV process. Once the lower temperature levels have been attained,

the danger of appreciable reoxidation is slight and it is simply a matter of completing the cooling and collecting the zinc in a suitable manner.

The term zinc oxide in the present specification and claims is used in the generic-sense as embracing all ores, calcines, etc., in which zinc is present in the oxidized* state.

For purposes of illustration the new process has been described with reference to the use of carbon monoxide in eiecting both the fiash reduction and the quenching steps but the ,process is not so limited and may be practised with other mediums within the scope of the appended claims.

What is claimed is: Y

1. In the art of producing zinc by reducing zinc oxide in gaseous suspension and condensing the zinc vapor, thatimprovement which consists in directly subjecting the zinc vapor from the reduction operation without intermediate conditioning treatment to instantaneouscooling by intermixing same with a quenchingfiuid.

2. The process for producing zinc which Aconsists in subjecting a charge comprising zinc oxide and carbonaceous reducing agent to a flash reduction, directly intermixing the gaseous products-of reduction containing the zinc vapor with a cold stream of carbon monoxide gas without prior conditioning of the former thereby to immediately quench they zinc vapor to a temperature at which reactions conducive to zinc reoxidation proceed only at harmless rates, and recovering zinc from the quenched vapor.

JESSE ou.' BETTERTON. MELVILLE F. PERKINS.

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