US2000171A - Reduction of oxygeneous nickel or nickel copper compounds - Google Patents

Description

May 7, 1935. A. M. GRONNINGSAETER 2,000,171

REDUCTION OF OXYGENEOUS NICKEL OR NIICKEL COPPER COMPOUNDS Filed Aug. 15, 1933 2 Sheets-Sheet 1 YNJ Patented May. 1, 1935 y UNITED STATES REDUCTION oF oxYGENEoUs NICKEL on NICKEL CorreaY COMPOUNDS yAnton Muin Gronningsaeter, New York, N. Y.. assigner to Falconbrldge Nickel Mines limited, Toronto, Ontario, Canada.

Application Augustl, 1933, Serial No. v685,225 In Norway` August 27, 1932 zolaims. (C1. 'z5-s6) This invention relates `to the reduction of oxygeneous nickel or nickel-copper compounds by means of gaseous reducing agents and more particularly to the reduction of materials obkl tained by roasting sometimes followed by leaching of nickel copper matte.

It is known that nickel oxide is reduced by watergas at a'temperatureof 350-400 C. and higher. This reaction is made use of for examl0 ple in the manufacture of nickel for use as a catalyst and in theMond process for the refining of nickel.

In the Mond process the reduction is carried out in multiple hearth furnaces of iron with a revolving shaft'carrying arms with rabbles, by means of which the material is stirred and moved from hearth to hearth. To maintain the reaction temperature, outside heat must be supplied. For thisipurpose some of the floors ofA the furnace are provided with interior chambers (muilles) through whichjhot gas is passed.` It is' self-evidentl that the temperature of the mufe floors must be higher than that desired in the treated material. This fact, however, represents a factor of risk because the reduced nickel has a tendency to sinter `by being'brought into immediate Contact with the hot muflle oor,

so that it cakes and becomes hard.

The diniculties become particularly. great when for some reason it is desired to effect the reduction at a. comparatively high temperature near the sintering temperature of the reduced nicke1maten'a1. This is for example the `ease in the manufacture of nickel material to be employed for cementing out copper, for neutralizacidic nickel salt solutions and for the like urposes. Y .Other inventors have proposed for the purpose'of extraction 01"'v nickel, to reduce nickeliferous pres by heating with reducing gases having a temperature higher than that which is needed for reduction lof the nickel. Inthese cases however, no particular attention is paid to the physical and chemical properties of the product obtained, which in these cases are of no greatimportance. The reactivity of the reduced nickel obtained is greatly dependent on the temperature during the reduction. If the temperature rises too high, sintering will occur,

and this will unfavourably affect the reactivity.

of the product obtained, and may at the same time cause considerable mechanical troubles with the operation of the furnace; sintering in i the present case will therefore cause great prac- -to the desired temperature.

tical drawbacks in the preparation and the use of the product. g-

The present invention has for its object a process by means of which it is made possible to leffect the reduction at such elevated tem- '5 peratures as mentioned above-for example between 400 and 550 C. without theabove mentioned drawbacks of sintering and caking of the reduced material making itself felt.

It is characteristic for this process that the 10 heating does not or only in part take place .indirectly through the mule walls; the heating, at least partly; takes place directly by effecting the reduction by means of a reducing gas having, when 'it enters the furnace, .a tem- 15 perature which is considerably higher than that at which the reduction takes place. 1f the reduction is to be effected at a temperature of 40G-550 C. it will for example be suitable to use a reducing gas having atemperature of be- 20 tween 500 and 700 C. at the point of entrance into the furnace. The heat content of the gas will then, as experience has'proved, usually be sucient to heat the furnaceand the material The temperature 25 ofthe entering reducing gas is so controlled as to maintain the material leaving the reduction space at .a temperature of between 400-550 degrees centigrade.

When the furnace is operated in this way, the 30 floor ori-which the material rests and against which it is pressed by means of the rabbles., will have a Ylower temperature than the material.

itself so that local overheating will not take 35 place.

The supply of heat to the furnace may in its entirety vbe effected by means of hot reducing gas but this method may also be combinedlwith the above mentioned indirect heating, for ex- 40 ample by passing gases having approximately the same temperature as that at which the reduction shall take place, through the muille floors of the furnace. It is usually preferred, however, to limit the vuse of indirect heating 45 to the upper oors, where the material is dried and preheated. f

When the furnace is operated in accordance with the invention, it has been found to be possible to maintain the material in the critical 50 zone'of the furnace at a temperature just below the sintering temperature of the reduced material-for example of about 450500 C. or even higher-without meeting any drawbacks in the form of sintering or caking By these means increased capacity of the furnace and a better utilization of the reducing gases are obtained at the same time as it is made possible to operate the furnace uninterruptedly for very long vperiods of time without mechanical vdifficulties advantageous way of heating consists in producing the required gas in an electrically heated' Watergas generator, from which the'gas "escapes at a temperature suitable for introduction into the reduction furnace. If it is found that the gas coming fromV the gas generator in some instance has too low av temperature for the purpose, the gas on its way to the reduction furnace may be passed through a heating apparatus of a suitable construction, for example an electric furnace. The invention may be considered in conjunctionwith the following description and the accompanying drawings, in which:

Fig. 1 is an elevation partly in section. of a reduction furnace of the character above mentioned; n

Fig. 2 is a section on lthe line 2-2Yof Fig. 1; Fig. 3 is a section on the line 3-3 of Fig. 1; and Fig. 4 is a section on the line 4-4 of Fig. 1.

vThe reduction furnace shown is of the multiple hearth type, comprising a plurality of spaced and superposed shelves I laterally supported in close proximity to a shaft II centrally and vertically disposed 'within a heat-insulated outer furnace shell I2. The shaft is appropriately supported on its bottom, and is provided with suitable driving gears. Av plurality of spaced and superposed muflies I3 alternate with the shelves, the tops of the muflles being adapted to function as shelves. An annular space I4 is provided between the central shaft and the mules. `Each muifle (see Fig. 3) has a dampered gas inlet I5, and agas outlet IIS.

A feed hopper I'I is mounted on the top of the furnace structure, the lower end of the hopper being provided with a damper to regulate the amount of finely divided material deposited onto `the top shelf of the furnace. The central shaft is provided with a` series of spaced and super- `posed rabble' l,arms I8 provided with teeth I9 adapted to scrape against the tops of the muilles and shelves. The bottom `0f the furnace is provided witli an outlet 20, which 'communicates with a hopper 2| for receiving nely divided nickel powder.

, Referring to Fig. 1, a'water gas generator 22 communicates by means of a conduit. 23 with a,l

l Vance matte' material undergoing rabbling.

furnace and extends to the bottom of a combustion chamber 28 communicating with a gas distributing chamber 29. y

Referring to Figs. 2 and 3 more particularly, it will, be seen that the distributing chamber 29 is separated by a wall from a spent gas receiving chamber 30 that communicates with a stack 3|.

In operation, finely divided leached matte, consisting, for example, of a mixture of nickel oxide (S0-65% nickel) and copper oxide (11- 14% copper) is introduced into feed hopper I1, from which regulated amounts are intermittently dropped onto the top muille I3 by suitable operation of the hopper damper. The central shaft II is set in motion, which operates to rotate rabble arms I8 and their scraping teeth I9.

At the same time, reducing gas produced in generator 22 is introduced into the bottom of the reduction furnace by way of inlet 25. This gas may or may not be preheated in the'preheater 24, as desired or necessary to accomplish the desired type of reaction within the reduction furnace. The gas is preferably made to enter the bottom of the reduction furnace at a temperature of 50G-'700 C. The gas rises upwardly through passageways I4 and 26, while rabbled matte material falls downwardly through the same 'passageways It will thus be seen that the matte n finely divided form is progressively acl-'- through the reduction zone of the furnace in a direction generally counter-current to and in direct contact with the hot reducing gases, which are at a temperature suiciently high to effect reduction of oxygeneous nickel compounds present in the matte. At the same time, the temperature of the gases is carefully selected so that the' matte material does not fuse, this manner, a highly reactive nickel powder is obtained.

In a present preferred practice of the invention, the finely divided matte material is also indirectly heated. To this end, the gases leaving the top of the furnace by way of outlet 21 are passed into the combustion chamber 28V where they are ignited. The hot gaseous products of combustion then pass into the distributing chamber 29 where they may be by-passed through one or more of the mules I3. Gas thus entered into a mufle by way of inlet I5 passes completely through the muflle and out at the exit I6 into the spent gas receiving conduit 30, from which it escapesthrough the stack 3I. The amount of gas introduced into the mule is properly regulated by operating the dampers I6.

Since the gases produced in-generator 22 are introduced into the bottom of the reduction furnace at substantially their maximum temperature, it may usually not be advisable to effect maximum simultaneous indirect heating of the Under this circumstance, it is advisible, for example, to close the dampers of the lowermost muies, and then only passgaseous products of combustion through one or more of the uppermost mules.

As stated above, in the present preferred practice of the invention, hot reducing gases are introduced into the bottom of the reduction furnace at a temperature of 50G-700 C. The material Withdrawn from the bottom of the reduction furnace has a temperature of 450-500 C. or even higher.

By following the procedure herein outlined, the reactivity of `the nickel powder produced is greatly increased. Highly reactive nickel powder is intimately dropped through the outlet 2l into the hopper 2l filled withfr'water, so that the hotnickelpowderiscooledintheabsenceot air, thus objectionable oxidation o! the nickel powder. Highly reactive nickel produced in this manner is most effectively employed in the cementation of copper and the neutralization of acidic nickel electrolyte. A

l. The improvement in method of preparing reactive metallic nickel powder by the reduction of nickel oxide, nickel-copper oxide and the like, which comprises progressively advancs ing the nickel oxide bearing material in nely divided form through a reduction zone in a direction generally countercurrent to and in direct contact with hot reducing gases, and at thesame time indirectly heating the nickel oxide bearing material during its rst stages of movement through the reduction zone, said hot reducing gases being introduced into the iinal stage of the reduction zone at a temperature lletween 500700 C.to heat the material directly duringits iinal stages oi reduction. and to maintain the treated material leaving the-reduction zone at a temperature between 40o-550? C. whereby sintering of the material is avoided and 'a highly. reactive nickel powder is obtained.

2. The improvement in the method of prepar. ing reactive metallic nickel powder bythe reduction of nickel oxide, nickel-copper oxide and the like, which comprises progressively advancingthe nickel oxide bearing material in finely divided form through a reducton zone n a direction generally countercurrent to and in direct contact with hot reducing gases, and at the same time indirectly heating the nickel oxide bearing material during its iirst Astages of movement through the reduction zone, said hot reducing gasesgbeing introduced into the ilnal stage of the reduction zone at a temperature suillcientlyhigh to heat the materiall directly during its ilnal stages ofv reduction and to maintain the treated material leaving the reduction zone at a temperature between 400450 C. whereby sinterling of the material is avoided and a highly reactive nickel powder is obtained.

ANTON MARTIN GRONNINGSAEIER.

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