Method and arrangement for producing metal powder

Abstract

In a method for producing metal powder, the first part of an acid-containing starting solution is fed on the anode side of an electrolytic cell as anolyte, to contact the anode and supply material containing yield metal, and a second part of the acid-containing starting solution, which also contains intermediary metal, is fed on the cathode side of the electrolytic cell, to contact the cathode as catholyte. Yield metal is oxidized and dissolved in the anolyte by leading electric current in the anode. The yield metal contained in the second part of the starting solution is reduced on the cathode side. Anolyte solution and catholyte solution are fed to a precipitating chamber for mixing the dissolved, oxidized yield metal and the second part of the starting solution containing reduced intermediary metal.

Description

FIELD OF THE INVENTION[0001]The invention relates to the production of finely divided metal powder. In particular, the invention relates to a dissolution-precipitation method and arrangement for producing metal powder.BACKGROUND OF INVENTION[0002]Generally the end product in many metal manufacturing processes is a plate-like object in cathode form. This kind of end product is obtained for example by means of pyrometallurgical production routes utilizing electrolysis. In these methods, a metal anode that is pyrometallurgically made of a concentrate is electrolytically refined to cathode copper, which can for example be cast into products with various different forms. These types of methods can be used for producing copper, nickel or cobalt products, among others.[0003]However, in the production of metals, in many cases it would be advantageous for instance with respect to further processing, if the metal received as the end product of the manufacturing process would be obtained in so...

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Benefits of technology

[0012]Among the advantages of the invention, let us point out for example good controllability of the particle size of the precipitating yield metal powder, which is made possible particularly by the feeding of the anolyte solution and cathode solution, to be mixed together, in a separate precipitation chamber, in which case the mixing ratio of said solutions can be controlled easily and accurately, as well as optimized according to the process conditions. Moreover, when the precipitation step takes place in a separate precipitation chamber, away from the vicinity of the electrodes, the effect of the electrodes in the precipitation process and in collecting the precipitate can be minimized, so that the reliability of the process is improved. Also the recovery of the yield metal precipitate becomes easier and more reliable. With a correct mixing ratio and an effective precipitate recovery, the creation of yield metal agglomerates can be prevented in the precipitation step, and consequently the homogeneity of the yield metal particles contained in the powder is enabled with respect to their size. A correct mixing ratio also facilitates a process with a better efficiency, which can be utilized for reducing the amount of energy needed in the process for producing a certain quantity of yield metal mass.

[0016]In an embodiment of the invention, the first part of the starting solution contains intermediary metal for boosting the dissolution of yield metal on the anode side. In an embodiment of the invention, the first part of the circulating solution created as a result of mixing the anolyte solution and the catholyte solution is returned to anolyte. In an embodiment of the invention, the first part of the starting solution is composed of the first part of the circulating solution. Further, in an embodiment of the invention, the second part of the circulating solution created as a result of mixing the anolyte solution and the catholyte solution is returned to catholyte. Further, in an embodiment of the invention, the second part of the starting solution is composed of the second part of the circulating solution. Moreover, in an embodiment of the invention, the circulating solution is returned essentially completely back to electrolyte, in which case the circulating solution is essentially composed of the first part of the circulating solution and of the second part of the circulating solution. When an anolyte solution that is formed of the first part of the starting solution and a catholyte solution that is formed of the second part of the starting solution are mixed together, there is created yield metal powder as the yield metal that was oxidized and dissolved in the anolyte is reduced, and the intermediary metal that was reduced in the catholyte is oxidized. The obtained circulating solution is recirculated in an arrangement to be used in the process in one of the embodiments of the invention, so that the circulating solution is partly or completely, after the mixing step and after the yield metal precipitate is separated from the solution, returned back to anolyte and / or catholyte. Now the intermediary metal is again reduced in the catholyte. Thus it is possible to realize an electrolytic regeneration of the intermediary metal in the catholyte, which means that in some embodiments of the invention, it is essentially not necessary to feed in the process new solution containing intermediary metal. In addition, when also the anolyte in some embodiments of the invention contains intermediary metal, said intermediary metal intensifies the dissolution of the yield metal in such process conditions, for example with relatively low acid contents, where dissolution with the combined effect of electric current and acid solution would not be efficient.

[0019]In order to efficiently separate the precipitation step from the electrolytic cell and to realize this step in a controlled fashion and essentially completely in a separate precipitation chamber, the anolyte and the catholyte can in an embodiment of the invention be separated by means of an electroconductive diaphragm. In this document, the term “electroconductive diaphragm” refers to a diaphragm that is electroconductive to such extent that the diaphragm facilitates an effective operation of the electrolytic cell. However, in some embodiments of the invention, the electroconductivity of the diaphragm may be lower than the electroconductivity of those solutions that are mechanically separated by the diaphragm. Consequently, the purpose of the diaphragm is to mechanically separate the solutions located on different sides of the diaphragm, i.e. to serve as a mechanical obstacle, while at the same time being electroconductive to that extent that the electrolytic cell is capable of functioning effectively. This diaphragm divides the electrolytic cell to an anode part (or anode side), where the anolyte is located, and to a cathode part (or cathode side), where the catholyte is located. Thus the anolyte and the catholyte cannot be mixed together without disturbing the anode and cathode reactions, and metal powder cannot be formed in the vicinity of those electrodes in the electrolytic cell. For further intensifying the separation of the anode and the cathode, it is possible to use in between the anode side and the cathode side two partition diaphragms, and a separator solution can be fed in between said diaphragms.

[0022]In an embodiment of the invention, the supply material containing yield metal is placed in the anode. Further, in an embodiment of the invention, the yield metal located on the anode side of the electrolytic cell is placed in the anode of the electrolytic cell. When the supply material containing yield metal is placed in the anode, the rate per unit of time of the electric current passing through the yield metal, and consequently also the mass of the dissolving yield metal per unit of time, can be efficiently controlled. The advantage of this embodiment is a particularly precise control of the dissolving reaction by means of electricity; yield metal is dissolved accurately according to the used quantity of electricity in the course of the given time period according to Faraday's laws. Moreover, the kinetics in the dissolution step are rapid, as the quantity of yield metal dissolved in the anolyte is directly proportional to the charge that has flown through the anode. Thus also the quantity of yield metal that is dissolved in the anolyte can be efficiently and accurately controlled, which facilitates a more precise control of the process dynamics, and an improvement in reliability.

[0024]In an embodiment of the invention, the electrolytes are placed in an oxygen-free environment, in order to prevent the oxidation of the yield metal and / or intermediary metal that is contained in the electrolytes. This makes it easier to control the acid content of the electrolytes, which means that the balance of chemical reactions taking place in the different solutions of the process and containing for example yield metal and / or intermediary metal can be adjusted more accurately, which in turn improves the reliability and efficiency of the process, among others.

Problems solved by technology

The problem with this method is that the catholyte solution is conducted directly to the anode chamber, wherefore it is not possible to effectively control the mixture ratios of the catholyte solution and the anolyte solution.

Moreover, in the method copper is precipitated directly into the anode chamber, which makes it more troublesome to remove the precipitated copper from the electrolytic arrangement.

These problems constitute a risk for the creation of copper agglomerates, which makes it more difficult to control the particle size of copper powder.

A drawback with the method and arrangement illustrated in the publication US2005 / 0023151 is, among others, an unreliable recovery of copper from the cathodes, owing for example to the precipitation of copper in various different locations in the chamber containing electrodes, and to the attachment of copper on the cathode.

Owing to the above mentioned drawbacks, among others, it is difficult to control the grain size of copper powder and of the morphology of copper particles, as well to achieve a homogeneous quality with separate electrodes.

In addition, the precipitation of copper directly onto the cathode also depends on the cathode material and on the surface morphology, which in part increases the unreliability of the method.

In said method, also the dissolution of precious metal takes place in a reaction with said other metal, which weakens the control of the process kinetics as well as the efficiency thereof, and makes the method and the arrangement used therein fairly complicated.

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