Claims:
What we claim is
1. The method of removing iron and cobalt from a partially refined nickel matte, and recovering the cobalt contained in the matte, without substantial loss of nickel, which consists essentially of energetically washing the matte in a fused state with anhydrous nickel chloride to form a mixture of fused chlorides, decanting the matte, separating the purified matte from the fused chlorides, adding water to the fused chlorides to form an aqueous solution of the chlorides, and treating the aqueous solution of the chlorides to recover the cobalt and the nickel chloride contained therein.
2. The method as set forth in claim 1, wherein the recovered nickel chloride is used for washing fresh quantities of the partially refined nickel matte.
3. A method of removing iron and cobalt from a partially refined nickel matte, which consists essentially of energetically washing the matte in a fused state with a mixture of anhydrous nickel chloride and potassium chloride.
4. A method of removing iron and cobalt from a partially refined nickel matte, which consists essentially of energetically washing the matte in a fused state with nickel chloride and removing the resultant chloride salts.
5. The method as set forth in claim 4, wherein the energetic washing by means of the nickel chloride is performed by mixing and stirring the nickel chloride with the matte, said stirring being carried out by a mechanical agitator constituting a permanent fixture of the ladle in which the mixing step is performed.
6. The method as set forth in claim 4 wherein the energetic washing by means of the nickel chloride is performed by mixing and stirring the nickel chloride with the matte, said stirring being performed by using a mechanical agitator detachably mounted to the ladle in which the mixing step is performed.
7. The method as set forth in claim 4, wherein the energetic washing by means of the nickel chloride is performed by mixing and stirring the nickel chloride with the matte, said stirring being performed by blowing a neutral gas through the mixture.
8. The method as set forth in claim 7, wherein said neutral gas consists of nitrogen.
9. The method as set forth in claim 7, wherein said neutral gas consists of argon.
Description:
This invention relates to the removal of the iron and cobalt from a partially refined nickel matte.
The removal of the iron and cobalt contents of a nickel matte prepared by a metallurgical process is carried out at present by using pyro-smelting processes or chemical or electrochemical processes. A pyro-smelting or pyrometallurgical process consists essentially in effecting a thorough removal of the iron content of a nickel matte in a Bessemer converter by blowing air and injecting silica, and subsequently carrying out a thorough cobalt removal also by blowing air, the entrained highnickel slag gangues being recycled.
The inconveniences characterizing this known method are on the one hand an indisputable lack of selectivity between the cobalt and nickel in regard to oxygen, which is attended by considerable amounts of nickel being entrained in the slag, and on the other hand the loss of the cobalt content in the slags which is not recoverable.
Moreover, this process burdens the nickel matte manufacturing line and increases considerably the cost of this matte.
The refined matte obtained by this process is subsequently roasted for producing nickel oxide and the latter is subsequently reduced to prepare pure nickel.
The scope of the hitherto known chemical and electrochemical processes, beginning from an initially partially refined matte containing for instance 76 percent Ni, 2 percent Co and 2 to 3 percent Fe, consists of elaborating high-purity nickel metal (minimum Ni content = 99.9 percent) and extracting the cobalt content in a commercially easily exploitable form, such as the hydrate of cobalt or its salts.
From the point of view of iron and cobalt removal, these processes have in common an iron, nickel and cobalt separation in an aqueous nickel solution (nickel sulfate or nickel chloride, or in most instances nickel chloride sulfate) through conventional oxidation and hydrolysis methods applied to the iron in the form of ferric iron and to the cobalt in the form of trivalent cobalt.
These methods, for the elaboration of nickel metal and the cobalt extraction, imply the construction of complete chemical or electrochemical equipment which, under present economic conditions, are financially advantageous only if very large amounts of pure nickel must be produced.
It is an essential object of the present invention to provide a method of removing iron and cobalt from a partially refined nickel matte by combining the above-mentioned pyrometallurgical and chemical processes while avoiding the inconveniences of each.
The method of this invention is characterized in that a partially refined nickel matte is energetically and thoroughly washed in a fused state with nickel chloride as a chloridizing substance. The use of such chloridizing substance, which is preferred to an oxidizing agent as in the case of oxidation in a Bessemer converter, leads to a considerably improved selectivity in the refining of nickel mattes.
Furthermore, nickel chloride is easy to prepare according to conventional methods in the nickel industry and is free of noxious and dangerous elements, other than chlorine of course.
The energetic washing of the matte with nickel chloride is carried out, according to this invention, by mixing and stirring the nickel chloride with the nickel matte either by using a mechanical stirring device secured permanently or detachably to the ladle in which the mixing takes place, or by any other suitable and known stirring means, such as by blowing neutral gas, notably argon or nitrogen.
When the fused nickel matte is washed with nickel chloride, according to the method of this invention, the cobalt sulfide and iron sulfide are selectively decomposed by the nickel chloride to release cobalt chloride and iron chloride. In order to permit the recovery of these cobalt and iron chlorides, it is contemplated according to this invention to add a suitable solvent for these chlorides to the nickel chloride used as a chloridizing agent in the washing operation, the solvent being for example potassium chloride, to avoid the release of gases while permitting the recovery of the chlorine as well as the metals.
Then the refined nickel matte is separated from the chlorides by a differential density method, which is advantageous in that it facilitates the separation of the chlorides from the matte in a suitable apparatus, before casting or granulating the matte.
The recovery of cobalt and the elimination of iron are effected, according to this invention, from an aqueous solution readily obtained when pouring the chlorides in water, this procedure being advantageous in comparison with hitherto known chemical or electrochemical processes in that this solubilization is carried out by using a lesser number of steps. In fact in the known chemical processes many operations such as casting the matte, then crushing, grinding and sieving, and eventually lixiviating, are necessarily inserted between the production of the molten matte and forming of the aqueous nickel solution. In the electrochemical processes the operations inserted between production of the molten matte and the aqueous nickel solution are casting the matte in the form of anodes, fitting the anodes in the electrolytic cells, and carrying out electrolysis proper of these anodes.
The regeneration of nickel chloride by extracting the iron and cobalt contents thereof and recycling the purified nickel chloride is subsequently carried out through conventional chemical methods.
The method of this invention permits an advantageous and simple vaporization of the cobalt from the hydrate of cobalt extracted during the purification of nickel chloride. It is known that in pyrometallurgical refining processes the cobalt content is entrained in the slag and that it is extremely difficult and costly to recover the cobalt from this slag. It is also known that in chemical processes the cobalt is extracted only after a great number of other operations.
It is another feature of the present invention to permit the commercial construction of relatively simple units for carrying out this high-efficiency matte refining method, which comprises a smelting block, in which a nickel-bearing substance (such as a nickel matte) is mixed with a chloridizing substance (such as nickel chloride), and another unit for purifying impure nickel chloride. This high-efficiency refining of the matte is advantageous, in comparison with other processes, in that it affords a greater flexibility in the initial preparation of matte, whether highly-refined or unrefined, while permitting the insertion, in an existing commercial plant and without resort to heavy investments, of complementary equipment capable of improving either the quality of the end products or the operation of the complete production line.
In order to afford a clearer understanding of this invention there is illustrated in the accompanying drawing a block diagram showing the complete sequence of operations for removing iron and cobalt from a matte in conjunction with the purification of impure nickel chloride. This diagram comprises the following reference numerals and operations:
1 -- Smelting the matte,
2 -- Mixing the liquid matte with the nickel chloride and preferably potassium chloride, preferably in a ladle equipped with an agitator,
3 -- Decanting and casting the matte into suitable equipment permitting the separation of the matte and the chlorides,
4 -- Granulating the matte, or casting the matte into ingots,
5 -- Adding make-up nickel chloride to compensate for the nickel entrained with the hydrate of cobalt and increasing the nickel content in the matte,
6 -- Re-introducing purified nickel chloride for carrying out further cobalt-removing operations,
7 -- Extracting as per 3 hereinabove the molten chlorides which consist of a mixture of nickel chloride, potassium chloride (preferably), iron chloride and cobalt chloride,
8 -- Forming an aqueous solution of said chlorides, preferably in a vessel (ladle) equipped with an agitator,
9 -- Removing the iron content of the impure nickel chloride preferably in the presence of potassium hypochloride and carbonate of nickel. However, any other suitable and conventional iron-removing process may be adequate in this case,
10 -- Removing the cobalt from the impure nickel chloride, preferably by using trivalent nickel, such as Ni(OH)3 ,
11, 12 and 13 -- Collecting the purified nickel chloride and subsequently concentrating it, preferably in a double-walled steam-heated evaporator, followed by crystallization performed preferably in a continuous centrifuge and stoving according to conventional methods, and recycling the purified and concentrated nickel chloride as per 6, and
14 -- Manufacturing nickel sulfate or chloride to be used as the basic material in the elaboration of make-up nickel chloride 5, carbonate of nickel 15 and trivalent hydrate of nickel 16.
The preparation of these various salts is carried out according to conventional methods not within the scope of the present invention. A description of such methods will be found for instance in "GMELIN, Handbuch der Anorganischen Chemie," 8.Auflage, Nickel, Teil B, Verlag Chemie 1966, on pages 482-484 for the preparation of nickel hydrate and on page 840 for the preparation of nickel carbonate, both from nickel chloride or nickel sulfate. The transformation of nickel sulfate to nickel chloride, for instance by reaction with chlorhydric acid, is dealt with on pages 560 and 566 of the same volume.
The following is an example illustrating a typical manner of carrying out this invention. In this example all the figures are to be understood by weight, or as percentages.
A matte having the composition:
Ni = 72.25% Fe = 1.76% Co = 1.90% S = 24.09%
i.e., for Ni = 100 , Fe = 2.43 and Co = 2.62,
is introduced into a smelting furnace heated to a temperature of 900° to 1,000° C., and subsequently cast into a mixing ladle with molten nickel chloride. In this example the composition of the nickel chloride assays as follows:
for Ni = 100, Co = 0.46
The matte and NiCl2 proportions are for example as follows: for : matte = 100,
26.28 of anhydrous nickel chloride (with
a 25% Ni content).
The mixture of matte and molten chloride is stirred about 15 minutes, whereafter the cobalt sulfide and iron sulfide decomposition reactions take place. These reactions are : CoS + NiCl2 ➝ CoCl2 + NiS FeS + NiCl2 ➝ FeCl2 + NiS
An exchange takes place between the cobalt, iron and nickel contents of the matte, on the one hand, and the chloride, on the other hand.
Thus, the nickel content in the matte increases and the refined matte (in the example considered herein) assays as follows:
Ni = 75.99% Fe = 0.02% Co = 0.12% S = 23.87%
i.e., for Ni = 100, Fe = 0.026 and Co = 0.157.
The unpurified nickel chloride assays as follows at the end of the matte purifying operation :
for Ni = 100, Fe = 13 and Co = 17.
This impure nickel chloride is dissolved in water contained in a vessel equipped with an agitator.
The water proportion is 5.21 liters per kilogram of nickel contained in the molten chloride.
This solution is subsequently purified in two steps, i.e., an iron-removing step followed by a cobalt-removing step.
In this example the iron-removing step comprises an oxidation of the earthy iron into ferric iron by using potassium hypochlorite :
2 Fe + KClO + 2H+➝2Fe++++ KCl + H2 O
and a hydrolysis of the ferric iron by using carbonate of nickel :
The amount of carbonate of nickel (containing 13 percent of Ni) introduced is :
75 kilograms per 100 kg of Ni treated in the impure chloride.
After the iron-removing operation the nickel chloride content is as follows :
for Ni = 100, Fe = nil , Co = 14.4.
The iron precipitate is filtered through a filter-press; in this example, 860 grams of Fe are collected per kg of treated Ni.
The cobalt is removed by using trivalent nickel hydrate according to the following reaction :
The amount of hydrate of Ni introduced is 1.05 kg (assaying 16% Ni) of hydrate of Ni per kg of treated Ni.
The cobalt hydrate precipitate is filtered by using a filter press. The hydrate of cobalt thus collected contains 14.4 kg of Co per 100 kg of treated Ni, and entrains one part of Ni per 5 parts of cobalt.
The pure nickel chloride solution is subsequently concentrated, crystallized in a continuous centrifuge and eventually stoved according to conventional methods.
Of course, the present invention should not be construed as being limited by the specific example described hereinabove, which is only for purposes of illustrating the manner in which the invention may be carried out in practice;. Various modifications may be made without departing from the basic principles of the invention as set forth in the appended claims.