Note: Descriptions are shown in the official language in which they were submitted.
Pc-~125 104~8~
The present invention relates to processes for
purifying chlorides of alkali or alkaline earth metals,
and is particularly applicable to the cleaning of chloride
salts used in processes for purifying nickel mattes by
chlorination.
The selective chlorination of impurities present
in a nickel matte has been the subject of much recent
study. In Canadian Patent No. 955,756, assigned
in common with the present invention, there is described
the process wherein nickel chloride dissolved in a fused
chloride solvent is used to chlorinate impurities such
as iron, copper and cobalt for removal thereof from a
nickel matte. In this process the molten matte to be
chlorinated is contacted with a molten salt mixture con-
sisting of a solvent salt, such as common salt or a mixture
of sodium and potassium chlorides, and nickel chloride.
Thus at the end of the purification process, the
supernatant salt mixture consists of the solvent salt
loaded with the chlorides of the impurities removed from
the nickel matte as well as unreacted nickel chloride.
This loaded salt must be treated to remove, and if desired
recover, the impurity chlorides so that the salt can be re-
cycled. In such a salt-cleaning treatment it is highly
desirable not to remove any nickel chloride present in
the loaded salt since this is required upon subsequent
recycling of the salt.
In the process described in the aforementioned
Canadian Patent, the salt is cleaned by electrolyzing it
in the molten state. Fused salt electrolysis is, of course,
a complex technology and is predicated on the local availa-
bility of electrical power. Moreover such a cleaning process
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also removes nickel chloride from the salt. Alternative
salt cleanin~ methods suggested hy other workers in the field
have been far less attractive in that they involve the energy
intensive cycle of dissolving the salt in water, purifying
the solution and then evaporating to dryness to regenerate
to solvent chlorides.
It is an object of the present invention to provide
an improved, convenient process for the regeneration of
solvent salts used in matte purification processes.
` 10 It is a further and important object of the in-
vention to provide a process of low energy consumption which
does not involve the solution of the salt and subsequent
evaporation.
~ccording to the invention a process for refining
a salt comprisinq at least one of the chlorides of alkali and
alkaline earth metals, to remove therefrom at least one im-
purity selected from the group consisting of the chlorides
of iron, nickel, cobalt, copper, lead, arsenic, zinc, manga-
nese, cadmium, silver, bismuth, gold, tin, tungsten and
titanium, comprises producing fragments of the salt, leaching
the fragments with an organic liquid comprising a reagent which
is effective to form with said at least one impurity an addi-
tion complex soluble in the organic liquid, and separating
the impurity loaded organic liquid from the refined salt.
The invention is particularly applicable to the
refining of a loaded salt which has been used as impurity sol-
vent in a nickel matte refining process, and which contains,in
the form of chloride impurities, at least about 0.5% by weight
of nickel and at least about 0.1~ by weight of one or more of:
iron, cobalt and copper.
The present invention further provides a process
of refining a nickel matte to remove therefrom at least
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one impurity metal, selected from the group consisting of
iron, cobalt, copper, lead, arsenic, zinc, manganese,
cadmium, bismuth, tin, tungsten and titanium, by selec-
tively chlorinating the impurity metal(s), dissolving the im-
purity metal chloride(s) in a molten salt comprising at least
one chloride of an alkali or alkaline earth metal, and separat-
ing the impurity-loaded salt from the refined matte, wherein
the improvement comprises producing fragments of the loaded
salt, leaching the fragments with an organic liquid comprising
a reagent effective to form with at least one impurity metal
chloride in the loaded salt an addition complex soluble in
the organic liquid, and separating the impurity loaded
organic liquid from the purified salt.
Where, as is common, the salt contains significant
amounts of nickel chloride, which may have been added as
an anhydrous reaqent or formed in situ as a result of bub-
bling chlorine through the matte to be refined, it is a
particular advantage of the process of the present invention
that the complexing reagent chosen for the salt cleaning
reaction may be one which reacts selectively or preferentially
with the impurity metal chlorides rather than with the nickel
chloride present in the salt.
It is of course essential that the complexing
reagent used be inert with respect to the solvent salt which
is to be cleaned, and that it be effective for forming an
addition complex with the impurity metal chloride in the
absence of an aqueous phase. Thus the many chelating agents -
which are effective only in liquid-liquid ion exchange re-
actions, would not be effective for leaching the impurities
from the solid salt in the present process. Reagents which
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are known to be capable of forming addition complexes
with, for example, chlorides of iron, cobalt or copper
and which can therefore be used in the present process
include primary, secondary and tertiary amine hydrochlo-
rides as well as quaternarv ammonium chlorides.
In practice the complexing reagent is used in
the form of a solution, the solvent being an aliphatic or
aromatic hydrocarbon or an alcohol or a mixture thereof.
Numerous commercially available solvents may be used, the
only essential requirement being the insolubility of the
salt to be refined in the solvent used to dissolve the
complexing reagent. Preferred solvents include kerosene,
xylene, isodecanol or mixtures thereof.
It is important that the loaded salt to be puri-
fied be in the form of particles sufficiently small to
enable the extraction of impurities to proceed rapidly
to a high degree of completion. Such particles could be
obtained by granulation of the molten salt, or by cooling
to solidify the salt and subsequently grinding it. It is
preferred that the loaded salt be ground to particles
smaller than about 200 microns, and preferably smaller than
about 50 microns. Such a particle size enables satisfactory
extraction results to be obtained when the residence time
of the salt in the extractant is of the order of one hour
for each stage of extraction. In general more than one
stage of extraction will be needed according to the
initial composition of the salt. The purified salt is
finally recovered by filtration, and after rinsing thereof
with organic solvent and drying,it can be reused in the
metal purification process. The organic extractant used
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for purification of the salt can be recycled after appro-
priate purification, for example by contact with an aqueous
phase which dissolves the impurities.
The invention will be more readily understood
from the following specific description of examples of
salt purification in accordance with the invention.
EXAMPLE
An organic extraction solution was prepared in
the following manner. A mixture was made up which comprised,
by volume, 68 parts of kerosene, 12 parts of isodecanol and
20 parts of a reagent made by General Mills, Inc. and known
by the trade name Alamine 336, which is a tri-alkyl amine
with the alkyl chains containing 8-10 carbon atoms. The
mixture was reacted with 4.5 N hydrochloric acid, after
which the aqueous phase was separated from the organic
phase which was then used for leaching impurities from a
loaded salt in the following manner.
An impure sodium chloride was synthesized in
order to simulate a loaded salt which might be obtained
when one type of nickel sulfide is refined in the presence
of molten sodium chloride. The synthetic mixture was
prepared by melting sodium chloride together with chlorides
of nickel, copper, cobalt and iron and cooling to obtain
a solid containing the following metal values:
Copper: 4.15 weight percent
Nickel: 4.55 weight percent
Cobalt: 0.50 weight percent
Iron: 0.22 weight percent
This synthetic loaded salt was ground to
-100 mesh, Tyler Screen Size (TSS) and was leached by the
104t~866
organic liquid described above using a two stage leaching
procedure. The first stage leach consisted of contacting
lon grams of the salt with 250 mls of the organic liquid
at 25C for one hour. At the end of this time the partially
purified salt was separated by filtration, washed with
130 mls of kerosene and then filtered and dried. This dried
salt was then suhjected to a second stage of leaching by
contactin~ it with 200 mls of the organic liquid at 25C
for one hour, at the end of which it was again separated,
washed, iltered and dried. The metal values present in
the salt before and after each of the leaching stages are
given in Table 1 below:
TABLE
SALT
Weight Composition ~ ~t. ~) .
Stage 1 (g) Cu Ni Co Fe_
Initial 100 4.15 4.55 0.50 0.22
Final 94 1.15 4.85 0.10 0.07
Stage 2
Initial 88 1.15 4.85 0.10 0.07
Final 88 0 80 4 55 0 06 0.05
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Whereas the extraction of copper from the salt was
less efficient in this test than the extraction of either
cobalt or iron, it will be seen that the organic reagent
used achieved the desired effect of extracting a large part
of the copper, cobalt and iron but very little of the nickel.
This is most readily apparent from the comparison of the
percentage extraction of each of the metal values in each
stage of the process, which are shown in Table 2 below:
TABLE 2
_ METAL EXT~A~TION (%)
Cu N r Co Fe
Stage 1 74 0 81 7 d
Stage 2 30 6 40 29
Overall 82 6 89 79
EXAMPLE II
The organic solution for this test was prepared
by reacting 4.5 N hydrochloric acid with a mixture compris-
ing, by volume, 20 parts of the tertiary amine: Alamine
336, with 80 parts of xylene, and separating the aqueous
phase from the mixture.
A sample of the synthetic calt described in
Example I was ground to -325 mesh (TSS) and leached con-
secutively with 250 mls and 225 mls of the organic solution, ~-
following the same two stage leach procedure as described
in Example I. Tables 3 and 4 below show the satisfactory
results obtained in this refining test.
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TABLE 3
SALT
Weight Composition (wt. ~)
(~) Cu Ni Co Fe
Stage 1
Initial100 4.154.55 0.50 0.22
Final 95 1.444.55 0.07 0.03
Initial89 1.444.55 0.07 0.03
Final 88 0.984.30 0.03 0.03
_ - .
TABLE 4
. ,
. METAL EXTRACTION (~
Cu Ni Co Fe :
Stage 1 67 5 87 87
Stage 2 33 7 57 1
. Overall 78 12 94 87 ;~
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EXAMPLE III
For this test, the organic solution used was
identical to that described in Example II above. In this
case however the impure salt was synthesized so as to
simulate the type of composition obtained when nickel
sulfide is refined by chloridization in the presence of a
sodium chloride-potassium chloride mixture. Thus the impure
salt was prepared by melting 7 parts by weight of sodium
chloride with 3 parts by weight of potassium chloride and
small amounts of the chlorides of copper, nickel, cobalt
and iron so as to give a metal content of:
Copper: 1.50 weight percent
Nickel: 1.52 weight percent
Cobalt: 1.80 weight percent
Iron: ~.80 weight percent.
A 100 gram sample of this synthetic salt was
leached in turn with 300 mls and 250 mls of the organic
solution following the same procedure described in connection
with Example I. Table 5 below shows the composition of the
salt during the extraction, while Table 6 shows that
after the second stage of leaching only lq% of th~ nickel
chloride had been extracted from the salt while between
93 and 98% of the chlorides of iron, copper and cobalt had
been eliminated.
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TABLE 5
. . . . _
__ SALT
Wei~ht Co~ ?Sitio~ I (wt- %?
Stage 1 ~g?_ Cu ~i Co Fe_
Initial 100.0 1.50 1.52 1.80 2.80
¦Final ¦93 6 10.36 ¦ 1.52 ¦ 0. 7 ¦ 0.94
Initial 86.2 0.36 1.52 0.37 0.94
Final 81 1 0.06 1 42 0.03 0.-l
TABLE 6
.
P~ETAL EXTRACTION ( % ) _
Cu N~l Co Fe ¦
Stage 1 78 6 81 69
Stage 2 84 12 92 79
Overall 96 17 98 93
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It will be readily understood by those skilled
in the art that the benefits of the present invention,
i.e. the convenient removal of chloride impurities from
a salt mixture without the need to dissolve the salt and
thereafter reevaporate the solution, can be realized with
the aid of many organic reagents other than those specified
in the preceding examples. Thus use can be made of any
of the various primary, secondary and tertiary amines known
to be effective for complexing cobalt, copper and iron.
Although in general such extractants have been advocated
for use in liquid-liquid extraction processes, they are in
fact effective in the non-aqueous extraction involved in
the process of the present invention because, unlike chelat-
ing agents, they do not rely on an ion-exchange mechanism.
It will be further understood that while the salt
refining process of the invention is particularly applicable
to the regeneration of the solvent salt mixtures described,
it is also useful in other metallurgical processes. For
example, in the process of electrorefining with the aid of a
fused chloride electrolyte, it is necessary from time to
time to remove impurities which have accumulated in the
electrolyte. The process of the present invention can be
used effectively for refining such electrolytes.
Thus although the present invention has been
described in conjunction with preferred embodiments, various
modifications of the reagents and conditions described may
be resorted to without departing from the scope of the in-
vention which is defined by the appended claims.
. .,
