US1691714A - Process of reducing the cadmium content of zinc ore - Google Patents

Description

Nov. 13, 1928. 1,691,714

0. GERLACH ET AL PROCESS OF -I {EIDUCII J(.T THE CADMIUM CONTENT OF ZINC ORE Filed Dec. 5, 1926 Patented Nov. 13, 1928 UNITED. STATES A 1,691,714 TENT OFFICE.

OSCAR GERLACH, 0F PERU, AND .NILS OSTMAN, O F LA SALLE, ILLINOIS, ASSIGNORS TO MATTHIESSEN. & HEGELER ZINC 00., OF LA SALLE, ILLINOIS, A CORPORATIONOF ILLINOIS.

PROCESS OF REDUCING THE OADMIUM CONTENT OFZI'NC OIRCE.

Application filed December 3, 1926. 2 Serial Ito. 152,376.

It is the object of the present invention to reduce the content of cadmium in zinc ore prior to the processing of the ore for zinc in order that the spelter when obtained 6 may not contain objectionable quantities of cadmium. With this object in view the ore at a suitably high temperature is subjected to the action of steam in the presence of a carbonaceous material or carbon. We be- 10 lieve the action to be that the steam reacting with the carbon present forms carbon monoxide gas and hydrogen which, at the temperatures employed, reduced the cadmium to the metallic state in which it is vaporized and so removed from the ore. The invention is aplicable to sulphide, oxide, carbonate and silicate ores of zinc. In the case of sulphides, the process may be used after the ore has been roasted. Preferably, and as a matter of heat economy, the ore is treated while still hot from the roast. It may be transferred directly from the roasting furnaee to a chamber in which it is subjected to the cadmium reducing process. Before it is fed into said chamber it may be mixed with coal or other carbonaceous matters. Preferably, however, it is charged into the reducing chamber without such admixture and then sprayed with oil, which may be petroleum or a product thereof. The hydrocarbons of the oil are, of course, broken up at the temperatures employed and carbon deposited. Steam is introduced either at the same time with or imediately after the oil and is reduced by the carbon from the oil forming hydrogen and carbon monoxide which, together with the gases from the oil, form the reducing agents which act upon the cadmium present in the ore.

The temperature maintained in the reducing chamber is preferably between about l500 and 1800 F. or even somewhat higher. It is desirable, however, not to employ too high temperatures as to do so would result in the removal of unnecessarily large quantities of the zinc from the ore. Even at the temperatures given there is a loss of a little zinc but the loss is'not serious in view of the superior metal obtained by reason of the removal of cadmium. The latter reduces and volatilizes at somewhat lower temperatures than zinc and even below the temperatures which we employ and at which zinc is also reduced. But by the introduction of being, say,

steam, as described, and limitation of the amount of reducing agent introduced, there is a selective. removal of cadmium rather In the drawingaccompanying and form- I ing a part of this specification we have shown an apparatus in'which our process may be carried out, though it is to be understood that the invention is independent of the particular apparatus employed. In said drawing, Figure 1 is a longitudinal vertical section showing a part of a furnace of the well known Hegeler ,typ'e modified for the practice of our process, and Figfl, a transverse section through a part thereof on the plane of the line 2-2 of Fig. 1.

The upper chambers a, I), a, of the furnace are used for roasting the ores in the usual manner. The lowermost roasting chamber a communicates with the; reducing chamber d by means of the chute or. passage e, through which the ore falls after the roasting is finished. The ore is rabbled or raked through the chamber a? in which a bed or body of ore is maintained on the hearth with an ample gas space thereover. Steam is introduced through a pipe f and oil through a pipe 9. The usual fines are provided for leading away the gases and fumes from the roasting'and reducing chambers but preferably a separate fine is provided for the reducing chamber. In order to maintain a reducing atmosphere in chamber (2 it is necessary that it be substantially closed off from chamher 0 but this may be accomplished by maintaining a suflicient depth of ore in passage e as shown in Fig. 1.

Preferably a somewhat higher temperature is maintained in the reducing chamber than in the roasting chambers, the excess from one hundred to one hundred and fifty degrees. This may be accomplished by means of externally applied heat in the usual manner. Ordinarily, however, and in our actual practice of the invention, the partial combustion of the oil and carbon by oxygen furnished by the ore and air leakage is sufiicient to maintain the desired temperature. v

- As an example of the actual practice of ourinvention on a roasted ore containing 0.4% to 0.5% of cadmium and about 70% zinc, we have treated thirty seven to forty tons of ore per twenty four hours at a temperature of about 1800 F. using five to ei ht gallons of oil per hour, with the result t at the cadmium was substantially driven off with an unimportant loss of zinc.

We claim:

1. A process of removing cadmium from oxygen-containing zinc ore which comprises subjecting the ore to steam and an amount of reducing agent suflicient to reduce the cadmium but not a material part of the zinc contained in the ore at a temperature at which both cadmium and zinc reduce.

2, A process of removing cadmium from oxygen-containing zinc ore which comprises maintaining the ore at a temperature at which cadmium will reduce from its ox gen and treating itwhile so maintained wit 1 oil and steam. I

3. A process of'removing cadmium from oxygen-containing zinc ore which comprises maintaining the ore at a temperature of about 1800 F. and treating it with steam and a reducing agent. a

4. A process of removing cadmium from oxygen-containing zinc ore which comprises maintaining the ore at a temperature of about 1800 F. and treating it with steam and oil.

5. A process ofremoving cadmium from oxygen-containing z'inc ore which consists in maintaining the ore at a temperature at which cadmium oxide in the presence of a reducing agent will reduce, spraying it with oil and supplying steam. Y

6. A process of removing cadmium from oxygen-containing zinc ore which comprises maintaining the ore at a temperature of about 1800 degrees F., supplying steam to the ore and spraying the ore with oil.

OSCAR GERLACH. NILS OSTMAN.

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