U.S. patent application number 10/781549 was filed with the patent office on 2004-08-19 for method for the reduction of nickel from an aqueous solution.
Invention is credited to Fugleberg, Sigmund, Hamalainen, Matti, Knuutila, Kari.
Application Number | 20040159187 10/781549 |
Document ID | / |
Family ID | 8555576 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040159187 |
Kind Code |
A1 |
Hamalainen, Matti ; et
al. |
August 19, 2004 |
Method for the reduction of nickel from an aqueous solution
Abstract
The invention relates to a method for the precipitation of
nickel from an aqueous solution containing its sulphate as a
metallic powder suitable as an alloying element for refined steel.
In this method, nickel reduction takes place continuously in one or
several autoclaves at a temperature of 80-180 .degree. C. and
hydrogen pressure of 1-20 bar, whereby the production capacity can
be raised significantly, compared to batch processes made in
correspondingly dimensioned devices or equipment.
Inventors: |
Hamalainen, Matti;
(Aittaluodonkatu, FI) ; Fugleberg, Sigmund;
(Eerikinkatu, FI) ; Knuutila, Kari;
(Gallen-Kallelankatu, FI) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
345 Park Avenue
New York
NY
10154-0053
US
|
Family ID: |
8555576 |
Appl. No.: |
10/781549 |
Filed: |
February 17, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10781549 |
Feb 17, 2004 |
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10129867 |
May 9, 2002 |
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6712874 |
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10129867 |
May 9, 2002 |
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PCT/FI00/00933 |
Oct 27, 2000 |
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Current U.S.
Class: |
75/374 ;
75/255 |
Current CPC
Class: |
C22B 23/0461 20130101;
B22F 9/26 20130101; C22B 23/043 20130101 |
Class at
Publication: |
075/374 ;
075/255 |
International
Class: |
B22F 009/24 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 1999 |
FI |
19992408 |
Claims
1. A method for the reduction of nickel powder suitable as a
component of refined steel, from an aqueous solution containing
nickel sulphate in a pressurised space using hydrogen reduction,
characterised in that reduction occurs continuously at a
temperature between 80-180.degree. C. and at hydrogen pressure
between 1-20 bar in at least one autoclave equipped with a
mixer.
2. A method according to patent claim 1, characterised in that
reduction occurs at a temperature between 110-160.degree. C. and at
hydrogen pressure between 2-10 bar.
3. A method according to patent claim 1, characterised in that
reduction occurs in at least one autoclave, which is divided into
sections by partitions, and where each section is equipped with a
mixer.
4. A method according to patent claim 3, characterised in that the
solution surface of the slurry decreases by section in the
direction of the solution flow.
5. A method according to patent claim 1, characterised in that
reduction occurs in several autoclaves, which are arranged in
series and equipped with mixers.
6. A method according to patent claim 5, characterised in that the
autoclaves are single-sectioned.
7. A method according to any of the above patent claims,
characterised in that the autoclaves arranged in series are both
single and multi-sectioned.
8. A method according to some of the above patent claims,
characterised in that the autoclaves are essentially cylindrical in
shape.
9. A method according to patent claim 1, characterised in that the
nickel content of the aqueous solution containing nickel sulphate
to be fed into the pressurised space is at least 30 g/l.
10. A method according to patent claim 9, characterised in that the
nickel content of the aqueous solution of nickel to be fed into the
pressurised space is at least 50 g/l, preferably at least 80
g/l.
11. A method according to patent claim 1, characterised in that the
composition of the aqueous solution containing nickel sulphate to
be fed into the pressurised space, that is the feed solution, is
adjusted at the feed solution preparation stage.
12. A method according to patent claim 1, characterised in that a
reduction catalyst is used to aid reduction.
13. A method according to patent claim 12, characterised in that
iron (II) sulphate, FeSO.sub.4, is used as reduction catalyst.
14. A method according to patent claim 12, characterised in that
chrome (II) sulphate, CrSO.sub.4, is used as reduction
catalyst.
15. A method according to patent claims 11 or 12, characterised in
that the reduction catalyst is added to the feed solution at the
preparation stage.
16. A method according to patent claim 12, characterised in that
the reduction catalyst is added to the feed solution just before
the solution is fed into the pressurised space.
17. A method according to patent claim 12, characterised in that
the reduction catalyst is fed directly into the pressurised
space.
18. A method according to patent claim 1, characterised in that the
solution to be fed into the pressurised space is neutralised at the
preparation stage with ammonia so that the mole ratio becomes
1.6-2.4.
19. A method according to patent claim 1, characterised in that the
nickel solution is neutralised with ammonia in the pressurised
space so that the mole ratio becomes 1.6-2.4.
20. A method according to patent claim 1, characterised in that the
nickel solution contains practically no ammonium sulphate.
21. A method according to patent claim 1, characterised in that the
suspension of nickel powder and solution is removed from the
pressurised space and from which suspension the nickel powder is
separated.
22. A method according to patent claim 21, characterised in that
the nickel remaining in the end solution after separation is
removed by sulphide precipitation or ion exchange.
23. A method according to patent claim 21, characterised in that at
least part of the nickel remaining in the end solution after
separation is removed as a binary salt
NiSO.sub.4.(NH.sub.4).sub.2SO.sub.4.6H.sub.2O.
24. A method according to patent claim 23, characterised in that
when the majority of the nickel from the end solution has been
recovered as a binary salt, the residual nickel is removed from the
end solution either by sulphide precipitation or ion exchange.
25. A method according to patent claim 23, characterised in that
binary salt NiSO.sub.4.(NH.sub.4).sub.2SO.sub.4.6H.sub.2O is
dissolved in the preparation stage of the feed solution and
returned as feed for the continuous hydrogen reduction of nickel in
a pressurised space.
26. A method according to patent claim 23, characterised in that
binary salt NiSO.sub.4.(NH.sub.4).sub.2SO.sub.4.6H.sub.2O is
dissolved in the preparation stage of the feed solution and fed to
the hydrogen reduction of nickel as a batch process.
27. A method according to some of the above patent claims,
characterised in that binary salt
NiSO.sub.4.(NH.sub.4).sub.2SO.sub.4.6H.sub.2O is dissolved using
ammonia.
28. Nickel powder, characterised in that the powder is made by
hydrogen reduction of an aqueous solution containing nickel
sulphate, performed continuously in a pressurised space at a
temperature between 80-180.degree. C. and a hydrogen pressure of
1-20 bar.
29. Nickel powder according to patent claim 28, characterised in
that a catalyst is used in reduction.
29. Nickel powder according to patent claim 28, characterised in
that the iron content of the nickel powder is 0.1-2.0%.
30. Nickel powder according to patent claim 28, characterised in
that the iron content of the nickel powder is 0.6-1.4%.
Description
[0001] The present invention relates to a method for the
precipitation of nickel as a metallic powder suitable for the
production of refined steel from an aqueous solution containing its
sulphate. In this method, nickel reduction takes place continuously
in one or several autoclaves at a temperature of 80-180.degree. C.
and hydrogen pressure of 1-20 bar, whereby the production capacity
can be raised significantly, compared to batch processes made in
correspondingly dimensioned devices or equipment.
[0002] The production of nickel from an aqueous solution by
hydrogen reduction in autoclaves as batches has been in use on
industrial scale since the 1950s. The method is described in
articles such as: Benson, B., Colvin, N.: "Plant Practice in the
Production of Nickel by Hydrogen Reduction", pp. 735-752 in the
conference publication: Wadsworth, M. E., Davies, F. T. (ed.):
"Unit processes in Hydrometallurgy", International Symposium in
Hydrometallurgy, Dallas, Feb. 24-28, 1963, Gordon and Breach, New
York, 1964. The production method described in the article is still
in use through-out the industry and according to the article the
method based on the batch principle comprises the following stages:
nucleus reduction, reduction and leaching.
[0003] In the batch process, nickel nuclei are made in an autoclave
by hydrogen reduction using an FeSO.sub.4 catalyst. When the nuclei
are ready, the mixers are stopped, the nuclei are allowed to settle
and the solution on top of the nuclei powder is blown off. In the
reduction stage the actual process solution is fed into the
autoclave and metallic nickel is reduced from this with hydrogen on
top of the nuclei. Reduction typically occurs at temperatures of
199-204.degree. C., and at overpressures of 24-31 bar. When
reduction has ended, the mixers are stopped, the powder is allowed
to settle to the bottom of the autoclave and the solution is
removed from on top of the settled powder. The method is repeated
50-60 times and some nickel powder is also removed when the
solution is removed. The reduction series or cycle is finished when
the particle size of the nickel powder grows so large that its
suspension in the autoclave becomes difficult or when the reduction
time of one batch becomes too great. At the end of the reduction
cycle the whole autoclave is emptied. Any metallic nickel stuck to
the inner structure of the autoclave is dissolved off between
cycles.
[0004] It is clear to a person skilled in the art that the actual
reduction stage of the batch process comprises at least the pumping
of the pre-heated solution to the autoclave, the hydrogen reduction
of the batch of the nickel solution, the settling of the nickel
powder and blowing off the residual solution from the top of the
nickel powder. All these sub-stages are performed as consecutive
actions, not simultaneously. However, only the hydrogen reduction
of the nickel solution is effective time from a production point of
view and it can be calculated from the above-mentioned article by
Benson and Colvin, that this operation uses only 45% of the total
time. The capacity of the method can be calculated from this
article as:
251 batches.times.46 g Ni/I/(14d*24 h/d)=approx. 34 (g Ni/I)/h.
[0005] The article by Evans, D. J. I.: "Production of Metals by
Gaseous Reduction from Solution", Processes and Chemistry, Paper
35/Advances in Extractive Metallurgy, A symposium in London, 17-20
Apr., 1967, The Institution of Mining and Metallurgy, mentions that
the particle size generated by the nuclei reduction described above
is of the order of 0.001 mm.
[0006] Metallic nickel production by hydrogen reduction as a
continuous process is presented in U.S. Pat. No. 2,753,257. The
patent mainly describes reduction in batch processes, but the
examples also mention continuous processes. In relation to
continuous processes it is stated that a maximum yield of 80% can
be achieved and that the batch method should be used for better
results. It is characteristic of the said method firstly that the
composition of the solution is adjusted twice, and secondly that
the iron present in the solution has an adverse effect on the
functioning of the method.
[0007] In U.S. Pat. No. 2,753,257 the composition of the solution
is first adjusted to the optimum demanded for self-nucleation. In
the second stage the composition of the solution is adjusted so
that it is optimal for the reduction of the metal powder on top of
the metal nuclei. It is also supposed in the method that iron is
eliminated from the solution by some known method to content levels
that do not interfere with the reduction of the metallic powder.
The method is performed at a temperature range of 218-232.degree.
C. and at 52-55 bar of over pressure.
[0008] Another continuous process is presented in U.S. Pat. No.
3,833,351. This describes a method for the production of copper,
nickel, cobalt, silver or gold powders from a solution prepared by
acid or ammoniacal leaching. Powder production is carried out by
reduction with hydrogen gas in a continuous vertical tubular
reactor, where the height to diameter ratio of the reactor is at
least 10:1. In the patent description it states that powders can be
produced in the reactor even in atmospheric conditions. However,
the section describing the production of nickel for example reveals
that if reduction is carried out in conditions where the average
temperature of the reactor is 93.degree. C. and the pressure about
32 bar (Table III, Run 2), the resultant solid matter contains only
55% nickel. If economically viable results are required, reduction
must be carried out in conditions where the total pressure is for
instance in the range of 33 bar and the average temperature
140.degree. C. with a maximum temperature of 225.degree. C. (Run
1), whereby the amount of nickel powder formed is 90% of the solid
matter. The resulting nickel is not only impure but also extremely
fine and thus awkward to handle. The size of the powder produced
was 0.001-0.002 mm for copper and so small for nickel and cobalt
that ordinary settling and filtering may no longer work, requiring
perhaps even magnetic separation in order to separate the particles
from the solution. The fineness of the powder also greatly hinders
washing. This method has never been implemented on industrial
scale.
[0009] Autoclaves equipped with partitions are used for continuous
precipitation and leaching autoclaves, as described e.g. in the
article by F. Habashi, Pressure Hydrometallurgy: Key to Better and
Nonpolluting Processes, Engineering and Mining Journal, Feburary
1971, pp. 96-100 and May 1971, pp. 88-94. Partition walls have not
been used in reduction autoclaves.
[0010] From the above, we can conclude that the nickel hydrogen
reduction method has worked relatively well in the batch process,
and attempts to convert to a continuous process have been rather
poor. The reasons for this have probably been the high temperatures
and pressure used in reduction processes, which have made it
difficult to change the process over to a continuous one.
[0011] A continuous process is cheaper than a batch process,
because the production capacity of equipment of the same size is
greater than that of a batch process. Now, with the method of the
present invention, nickel powder especially suitable as an alloying
element for refined steel can be produced by performing continuous
hydrogen reduction of a nickel sulphate-containing aqueous solution
in a pressurised space in easier conditions than earlier, wherein
the hydrogen pressure is in the range of 1-20 bar and the
temperature in the range of 80-180.degree. C., (preferably with
hydrogen pressure from 2-10 bar and the temperature from
110-160.degree. C.). According to the invention, at least one
autoclave is used as the pressurised space, being equipped with
partition walls, which divide it into several sections with mixers,
or several consecutive autoclaves with mixers, which autoclaves may
be single or multi-sectioned. The invention is particularly
advantageous when using nickel sulphate solutions obtained in acid
leaching and which therefore do not practically contain ammonium
sulphate. The essential features of the invention will be made
apparent in the patent claims.
[0012] Nickel sulphate-containing aqueous solutions are generally
prepared by leaching either nickel concentrate such as laterites or
pyrometallurgically produced nickel mattes. The leaching may be
either acid or ammoniacal. The nickel content of the sulphate
solution usually remains lower in concentrate leaching than in
matte leaching, but if liquid-liquid leaching is used as one
solution purification step, the nickel content can easily rise to
over 100 g/l. In the framework of this invention, reduction is
performed from a solution with a nickel content of minimum 30 g/l,
preferably at least 50 g/l and most advantageously minimum 80
g/l.
[0013] For reduction in a pressurised space, the composition of the
nickel sulphate solution feed is adjusted before reduction in a
preparation stage, which comprises a number of mixing reactors. The
adjustment of the solution composition is carried out only once. If
there is any iron in the solution, ferrous sulphate is made use of
to form nuclei, on which nickel powder is reduced. If the amount of
iron in the solution is not sufficient as it is, iron is added to
the solution. In place of iron or in addition to it, chrome can be
used for nucleus formation as chrome (II) sulphate CrSO.sub.4.
Ammonia can also be used for composition adjustment as can the feed
of other additives and admixtures normally used in reduction.
[0014] If autoclaves divided into sections are used in embodiments
of the invention, the upper edges of the partitions are essentially
horizontal and their heights from the lowest point of the bottom of
the autoclave is graded so that the height of the partition walls
seen in the direction of the solution flow decreases, so that the
surface of the solution in the sections decreases correspondingly.
Gradation can of course be implemented in some other suitable way,
for example, so that the partitions are the same height, but have
discharge slots or apertures at different heights. The purpose of
the partitions is to improve the efficiency of the autoclave.
[0015] The method of the invention is described further by the
accompanying drawings, where
[0016] FIG. 1 is a vertical section of the principles of an
autoclave of the prior art and
[0017] FIG. 2 a vertical section of the principles of an autoclave
divided into sections with partitions according to the
invention.
[0018] FIG. 1 is an example of a reduction autoclave 1 of the prior
art, functioning on a batch basis, which autoclave is
single-sectioned and equipped with a feed and discharge pipe 2 for
the slurry to be reduced, mixers 3, gas feed pipe 4 and gas exhaust
pipe 5. The number of mixers in the autoclave can be changed as can
the positions of the slurry and gas feed points. Reduction
autoclaves of the prior art do not have partitions dividing the
space into sections--the whole pressurised space is integrated.
[0019] When the method according to the present invention is
implemented in a single autoclave, it is preferable to use an
autoclave as in FIG. 2, which is in principle the same type as
presented above, but equipped with partitions 6 and a discharge
pipe 7 for the solution and the solid material at the back section
of the autoclave. The autoclave shown in the figure is a typical
horizontal cylindrical shape. When the suspension of solution and
solid matter have been discharged from the autoclave, the nickel
powder is separated from the end solution by well-known methods
such as filtration. As stated above, the heights of partitions 6
are graded from the bottom 8 of the autoclave so that the height of
the partition walls decreases in the direction of the solution
flow. The number of mixers and sections 9 is not restricted to the
four shown in the diagram, but can be changed. Preferably there
will be 3-6 sections divided by partitions, but that can also vary
if the need arises. The mixers may be single or multi-bladed. It is
clear to a skilled person that the partitions may include apertures
and other standard components to improve the efficiency and ease
operation of the autoclave at various points, in the normal
way.
[0020] An autoclave according to this invention may also be an
integral type as in FIG. 1, wherein several of them are positioned
one after the other in a series in continuous methods. In this case
the single autoclave is equipped with a separate discharge pipe 7
for removing the solution as in FIG. 2, through which the solution
is conveyed to the next autoclave. A combination of said autoclaves
may also be used i.e. there may be single-section and multi-section
autoclaves connected consecutively in a series. A single-section
autoclave may also be for example a vertical cylindrical form, but
single-section autoclaves are also always equipped with mixers.
[0021] When hydrogen reduction of an aqueous nickel solution
(nickel sulphate solution) is performed with the method now
developed, significantly lower temperatures and pressures can be
used in the autoclave than shown in the prior art. Thanks to this,
the hydrogen reduction of a nickel solution can be converted or be
made continuous from the start, whereby the capacity of the
autoclave or the group of autoclaves rises considerably compared to
the batch process. Thus the nickel solution hydrogen reduction
process can be operated continuously, when the hydrogen pressure is
in the range of 1-20 bar and the temperature from 80-180.degree.
C., preferably at a temperature of 110-160.degree. C. with the
hydrogen pressure in the range of 2-10 bar.
[0022] For example Fe.sup.2+ and Cr.sup.2+ are used as reduction
catalysts, which are added to the reduction feed solution at the
feed solution preparation stage, just before the solution is
charged into the autoclave or directly into the reduction
autoclave. The catalyst is charged at least partially in solution
form. Fe.sup.2+ and Cr.sup.2+ as catalysts are not harmful to the
quality of the product. Two thirds of the nickel produced in the
world is currently used in the production of refined steel.
Consequently, any iron contained in the nickel is of no concern.
Should chrome be used as reduction catalyst instead of iron, traces
of the former will not cause any problems in refined steel
production either. Iron and chrome compounds are preferably iron
(II) and chrome (II) sulphates, but it is also possible to use
other such chemical compounds as catalysts that do not harm refined
steel production or that are removed from the nickel powder during
the sintering of briquettes.
[0023] Where necessary well-known additives are used with the
purpose of preventing the plating of metal on the autoclave walls
and other inner elements, and/or of influencing the form of the
powder flakes or their agglomeration or dispersion tendencies.
[0024] The acid generated in reduction is neutralised preferably
with ammonia. Advantageously ammonia is mixed into the solution at
the preparation stage before the solution is fed into the
autoclave, but an ammonia addition may also be made directly into
the autoclave. In both cases, it is beneficial to select the amount
of ammonia so that the mole ratio NH.sub.3/Ni (=added ammonia/total
amount of nickel in feed) is 1.6-2.4.
[0025] If the metallic nickel generated in the autoclave includes
hydroxide-containing compounds, they can be leached off in the
method described in U.S. Pat. No. 3,833,351 with an ammonium
hydroxide and/or sulphuric acid solution and the solution obtained
returned to a part of the process prior to reduction i.e. the
solution preparation stage, preferably to its final reactor.
[0026] When the capacity of the present method is calculated in the
same way as for embodiments of the prior art, a result of 100-130
(g Ni/I)/h is obtained. The capacity achieved with the method of
the present invention is thus at least twice that of the method
described in the prior art. With the present developed method
nickel powder suitable as raw material for the refined steel
industry as such, in briquette form or in briquettes and sintered,
can now be produced at an amazingly large capacity, at an amazingly
low temperature and pressure.
[0027] After reduction occurring in a pressurised space there is
always a little nickel left in the solution i.e. in the end
solution to be removed after separation of the nickel powder. The
method now developed allows for variation in nickel content in the
end solution. If this so-called residual nickel amount is very
small, e.g. under 1 g/l, it may be recovered by for instance
sulphide precipitation or ion exchange, and returned to a stage in
the process preceding reduction. If the amount of residual nickel
is greater, it can also be crystallised from the end solution in a
known way such as by cooling, evaporation and if necessary using
ammonium sulphate additive as nickel ammonium sulphate. The small
amount of nickel left in the solution after crystallisation can be
removed, for example, by sulphide precipitation or ion
exchange.
[0028] If the nickel content of the remaining solution is fairly
small, the resulting nickel ammonium sulphate
NiSO.sub.4.(NH.sub.4).sub.2SO.sub.- 4.6H.sub.2O can be dissolved
with an addition of ammonia into the feed solution at the autoclave
feed solution preparation stage, whereby the nickel cycle in the
process is made as short as possible.
[0029] If the nickel content of the residual solution is so great
that returning NiSO.sub.4.(NH.sub.4).sub.2SO.sub.4.6H.sub.2O to the
nickel autoclave reduction would raise the ammonium sulphate
content of the reduction feed solution so much that the reduction
of nickel would be slowed down significantly, the
NiSO.sub.4.(NH.sub.4).sub.2SO.sub.46H.sub.- 2O can be dissolved
with ammonia into a solution containing ammonium sulphate and the
solution thus obtained fed further as in the method described in
the Benson and Colvin article into a separate autoclave operating
on the batch principle.
[0030] The invention is illustrated in more detail by the following
examples:
EXAMPLE 1
[0031] A test was made in a horizontal cylindrical autoclave, which
was divided into six sections by partitions. In addition to the
sections the partitions further divided the autoclave into two
spaces: the gas space above the upper edges of the partitions and
the solution or slurry space around the partitions. The total
volume of the autoclave was 75 l, of which the gas volume was about
a third and the slurry volume about 50 l.
[0032] The upper edges of the section partitions were essentially
horizontal and their heights from the bottom graded so that the
height of the partitions dropped in the direction of the slurry
flow. Thus the highest partition was in the feed section of the
autoclave and the lowest between the last two sections. Along with
the partitions the slurry surface level also decreased towards the
back section of the autoclave. Owing to this the slurry fed into
the first section flowed from one section to the next by the effect
of gravity ending finally in the last section, from where the
slurry was removed from the autoclave by means of the prevailing
gas pressure in the autoclave.
[0033] Each section was equipped with an effective rotating mixer
with a basically vertical shaft with two mixing elements on the
same shaft as shown in FIG. 2. The mixers sucked the hydrogen gas
from the gas space and dispersed it into the slurry, thus speeding
up the dissolving of the hydrogen and the forming of nickel. The
mixers also kept the nickel generated in the autoclave well
suspended, which helped it to proceed from one section to
another.
[0034] The ammonium sulphate free solution used in the tests had
been through solution purification and contained on average 108 g
Ni/I as sulphate. Gaseous ammonia was added to this as neutralising
agent so that the mole ratio was 2.2 mole NH.sub.3/mole Ni and
ferrous sulphate in aqueous solution in order to form the nuclei so
that the weight ratio became 0.007 g Fe.sup.2+/1 g Ni. The addition
of ammonia took place as a continuous process in several mixing
reactors operating in series and at normal pressure. The slurry
generated was pumped continuously into the autoclave so that the
average retention time in the autoclave was 0.9 h. The addition of
ferrous sulphate was made just before the solution was fed into the
autoclave i.e. into the feed pipe between the last mixing reactor
and the autoclave.
[0035] The temperature of the mixing reactors was 80.degree. C. and
the temperature of the autoclave was about 120.degree. C. and the
hydrogen pressure 5 bar. The test lasted 56 hours, during which
time an average of 5.3 kg Ni/h was fed into the autoclave as
solution and as precipitate. The end solution to be removed from
the autoclave after nickel separation contained on average 4.6 g
Ni/I, in other words 0.25 kg Ni/h and the iron content of the
solution was 0.11 g/l. The yield of nickel to metal was thus about
95% and the calculated production capacity of the autoclave
regarding slurry volume about 100 (g Ni/I)/h.
EXAMPLE 2
[0036] The autoclave described above was used in the test and the
ammonium sulphate free nickel sulphate solution used as feed had
been through solution purification and contained on average 113 g
Ni/I. Gaseous ammonia was added to this so that the mole ratio was
2.0 mole NH/mole Ni and ferrous sulphate was added so that the
weight ratio became 0.007 g Fe.sup.2+/1 g Ni. The addition of
ammonia and ferrous sulphate took place as in example 1. The
average retention time of the slurry in the autoclave was 0.8
h.
[0037] The temperature of the mixing reactors was 80.degree. C. and
the temperature of the autoclave was about 120.degree. C. and the
hydrogen pressure 5 bar. The test lasted 78 hours, during which
time an average of 6.7 kg Ni/h was fed into the autoclave as
solution and as precipitate. The end solution to be removed from
the autoclave after nickel separation contained on average 2.2 g
Ni/I, in other words 0.14 kg Ni/h and the iron content of the
solution was 0.17 g/l. The yield of nickel to metal was thus about
98% and the calculated production capacity of the autoclave
regarding slurry volume about 130 (g Ni/I)/h.
[0038] As stated above, the production capacities achieved in the
examples are considerably higher than the capacities apparent from
the articles mentioned in the prior art. The examples presented
above include a larger campaign, where nickel powder was produced
with an iron content of 0.1-2.0% and analysis otherwise
corresponding to LME classification. According to sieve analyses of
the powders, their 50% passing through grain size was about 0.050
mm, i.e. extremely large in comparison with that in the
above-mentioned method of the prior art--powder produced by
so-called nuclear reduction, where the grain size is of the order
of 0.001 mm. The grain size is also larger than the powder produced
by the method in U.S. Pat. No. 3,833,351, where at most it (copper
powder) was of the order of 0.002 mm.
[0039] The powders produced in the examples were pressed and
sintered into briquettes, which after sintering in a hydrogen
atmosphere contained 0.64-0.91% Fe, about 0.01% S and about 0.02% C
and which had a compression strength of over 3000 kg/cm.sup.2. The
product is suitable for use in the refined steel industry.
EXAMPLE 3
[0040] The following pair of tests illustrate the effect of the
ammonium sulphate content of the reduction autoclave feed solution
on the nickel reduction rate. The tests were made in a
three-sectioned continuous, FIG. 2 type autoclave, with the
following operating conditions: temperature 120.degree. C. and
hydrogen pressure 5 bar. The feed slurries were prepared as in
example 2 and were pumped continuously to the autoclave so that the
retention time was 70 min i.e. about 23 min/section. In test 3.1
the slurry did not contain any ammonium sulphate, but in test 3.2
the amount was 34 g/l. The results obtained were as follows:
1 TABLE 1 (NH.sub.4).sub.2SO.sub.4 Ni content content in of
solution g/l Test feed g/l Section 1 Section 2 Section 3 3.1 0 27.5
12.6 2.7 3.2 34 34.1 21.3 16.0
[0041] The table shows the slowing effect of ammonium sulphate on
the reduction rate of nickel sulphate. It also shows that the
nickel content of the end solution of test 3.2, that is the
solution coming from the third section, was 16.0 g/l and the
ammonium sulphate content of the feed solution 34 g/l, which as
moles are approximately of equal size. In fact in the case of test
3.2 the crystallised NiSO.sub.4.(NH.sub.4).sub.2SO.su-
b.4.6H.sub.2O from the reduction end solution can be returned to
the reduction autoclave without essentially altering its
operation.
EXAMPLE 4
[0042] The following series of tests illustrate the effect of
temperature and pressure on the reduction rate. The series of tests
was made in the same continuous, 6-sectioned autoclave as the tests
in examples 1 and 2. The test conditions and results were as
follows:
2 TABLE 2 Feed Conditions Ni NH.sub.3/Ni Fe T .rho..sub.H2 Product
Test g/l mole/mole g/l .degree. C. bar Ni g/l 4.1 100 2.3 0.5 120
5.0 15 4.2 100 2.3 0.5 130 5.0 7 4.3 100 2.3 0.5 130 2.5 22
[0043] The feed did not contain ammonium sulphate and product
refers to the nickel powder from the autoclave end solution after
separation. The amount of feed was 50 l/h or a total retention time
of 1 h.
[0044] These results show that a relatively small change in
temperature and hydrogen pressure can have a considerable effect on
nickel reduction rate and on the nickel content of the autoclave
end solution.
EXAMPLE 5
[0045] The crystallisation of
NiSO.sub.4.(NH).sub.4SO.sub.4.6H.sub.2O from the reduction end
solution was also tested. The test was made in a small laboratory
mixing reactor. The feed solution, which contained about 5 g/l
nickel and about 100 g/l ammonium sulphate, was taken from the
campaign of examples 1 and 2.
[0046] In the crystallisation test, solid ammonium sulphate was
added to the feed solution so that the solution content was 380 g/l
(NH.sub.4).sub.2SO.sub.4. After this the pH of the solution was
adjusted to a value of 3 and its temperature to 40.degree. C., when
it was mixed in the reactor for 60 min. During mixing, the analyses
of the samples taken from the reactor were as follows:
3 TABLE 3 Ni content of Mixing time solution min g/l 0 4.2 10 0.89
30 0.63 60 0.78
[0047] This shows that the residual nickel in the reduction end
solution can easily be crystallised to a level where the final
nickel can be removed, for instance by sulphide precipitation or
ion exchange.
* * * * *