Note: Descriptions are shown in the official language in which they were submitted.
PC- ~-CAN 1l~ 5
The present invention relates to processes for
purifyinq nickel mattes by chlorination, and in particul~r
to the cleaning of chloride salts used in such processes.
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 consisting 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 nickel puri-
fication 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 recycled.
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 avail-
ability of electrical power. Alternative salt cleaning
methods suggested by other workers in the field have been
far less attractive in that they involve the energy in-
tensive 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
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an improved, convenient process for the regeneration of sol-
vent salts used in matte purification processes.
It is a further and important ohject of the in-
vention to provide a process of low energy consumption
which does not involve the dissolution of the salt and
subsequent evaporation.
The present invention provides a process of refin-
ing a nickel matte to remove therefrom at least one impurity
metal selected from the group consisting of iron, copper,
cobalt, lead, chromium, zinc, manganese, cadmium and tin,
by selectively chlorinating the impurity metal(s), dissolving
the impurity metal chloride(s) in a molten salt comprising at
least one alkali metal chloride, and separating the impurity-
loaded salt from the refined matte, wherein the improvement
comprises producing fragments of the loaded salt, leaching
the fragments with an aqueous solution having a pH lower than
5, and being saturated with said at least one alkali metal
chloride, thereby causing the impurity metal chloride(s) in
the loaded salt to dissolve in said aqueous solution, and
separating the impurity loaded aqueous solution from the
purified salt.
The invention is particularly applicable to the re-
fining of a nickel matte containing at least about 0.1% by
weight of one or more of the impurity metals: iron, cobalt
and copper.
The solubility of alkali metal chlorides in water
is of course high, e.g~, in the case of sodium chloride a
saturated solution at 25C contains over 250 grams per liter
of the salt. Nevertheless, such concentrated solutions have ~-
been found effective to leach impurity chlorides from a loaded
salt. During the leach some alkali metal chloride may crystal-
lize out of the solution as the impurity chlorides are
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dissolved, and as a result the total weiqht of alkali metal
chlorides may be somewhat greater in the purified salt than
in the loaded salt.
Refining of the solvent salt mixture of a matte
purification process is not resorted to until the salt
mixture contains a significant amount of chloride impurities,
i.e., an amount which corresponds to at least 0.5% by weight,
of at least one of the impurity metals in ~uestion. It is
important that the loaded salt to be refined be in the form of
particles sufficiently small to enable the extraction of im-
purities to proceed rapidly to a high degree of completion.
Such a form could be obtained bv qranulatinq the molten salt,
however, it is preferred to cool the salt and subsequently
grind it to particles smaller than about 300 microns, e.g.,
-48 mesh (Tyler Screen Size). Such a particle size enables
satisfactory extraction results to be obtained when the salt
is contacted with the aqueous solution for periods of the order
of about one hour. In general more than one stage of extrac-
tion will be needed according to the initial composition of
the loaded salt and the degree of refining desired. A pre-
ferred procedure for leaching the impurities from the salt
comprises a multi-stage countercvrrent extraction. After the
extraction the purified salt is recovered by filtration from
the aqueous solution.
The saturated solution used to leach the loaded salt
must ke acidified to a pH lower than 5. For the removal of - ;-
some specific impurities, e.g., iron, a much lower pH is
desirable to achieve good extraction levels. For this reason
it is preferred that the saturated solution have a pH of the
order of 1-2, e.g., 1.5. The use of high temperatures during
the leach is unnecessary for most of the impurities in question
and indeed undesirable in view of the energy requirements, as
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well as the increase in concentration and ~ensity of the satu-
rated solution resulting from the increased solubility of the
alkali metal chlorides in water. ~atisfactory results are
ohtained when the leach is performed at a temperature of ab~ut 25C.
The invention will he more readily understood from
the following specific description of examples of solvent salt
purification in the process of the invention.
EXAMPLE I
~ nickel matte containing, by weight, 0.48% copper,
1.71~ cobalt and l.nS% iron was chlorinated in the presence
of molten sodium chloride at 850C. A three stage counter-
current operation was used with a residence time of 1, 2
and 0.5 hours, respectively, in the three stages. The loaded
solvent salt obtained from the first stage, i.e., having the
highest contents of iron, nickel and copper was used for ~-
the following test.
450 grams of the loaded salt which contained, by
weight, 0.40% copper, 1.65~ nickel, 1.40% cobalt and 1.27%
iron were refined as follows. The salt was ground so as to
pass through a 48 mesh (Tyler) screen and leached at 25C.
using a procedure intended to simulate a three stage counter-
current extraction. The impure salt was contacted succes- `
sivelv with leach solutions in each of three extraction --
vessels, the ratio of solution weight to salt weight being
1.5 in each stage and the residence time in each vessel
being 30 minutes. ~ach of the leach solutions consisted
of a saturated solution of sodium chloride acidified to
pH 1.5. The third stage solution contained no iron, nickel, -
cobalt or copper, while the second and first stage solutions
3~ contained deliberately added increasing amounts of each of
these metals. The metal valueSpresent in both the salt
and the solution entering and leaving each stage of the ~ ~
':
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, . , ~ :.
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extraction were determined and are given in Table 1 helo~:
TABLE
:Analysis of salt(wt.~) ' Analysis of Solution(~/l)
:Cu :Ni :Co :Pe :Cu .Ni :Co :~e
1st :Input : 0.40: 1.6S: 1.40S 1.27: 0.10~ 4.2 : 0.47: 0.20 :
Stage:Output: 0.13: 0.47: 0.14: 0.27: 2.60:14.0 :11.9 : 7.4
2nd :Input : 0.13: 0.47: 0.14: 0.27: 0.05: 1.0 : 0.09: 0.08 :
Stage:Output: 0.11: 0.22: 0.06: 0.17: 0.26: 2.9 : 0.85: 0.50 :
3rd :Input : 0.11: 0.22: 0.06: 0.17: 0 : 0 : 0 : 0
Stage:Output: 0.11: 0.22: 0.05: 0.14: 0.03: 0.19: 0.06: 0.08 :
.. . .... . . _ _ .
Table II below shows the extent of extraction in
each ~taqe expressed as the percentage of the amount of a
given element enterina the stage, as well as the overall
extraction expressed as the percentage of the amount of a
given metal in the initial loaded salt.
TABLE II
~ : Extraction (%)
Impurity: - _ .
Metal .Staae 1: Staae 2: Staae 3: Overall:
~._ __ _. _ "_
Cu : 68 : 15 : 0 : 73
20 Ni :72 : 53 : 0 : 87 : ~ -
Co : 90 : 57 : 17 : 93
Fe : 79 : 37 : 18 : 89
. _ _ . _ . _ . .
EXAMPLE II
A salt mixture was prepared which contained 65.9%
by weight of sodium chloride and 15.6% by weight of potassium
chloride, the balance being made up of chloride impurities
corresponding to:
Cu : 2.14% by weight
Ni : 5.00% by weight
Co : 0.73% by weight
Fe : 1.60~ by weight
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Two samples of 400 g. each, ground to pass through a 28 mesh
(Tyler) screen, were leached with aqueous solutions saturated
with sodium and potassium chlorides. In each case 600 g. of
solution were used and the pH o the ~olution was 1.5,
however, the temperature of the solution was 55C. for one
test (sample A) and 24C for the other (sample B). Table III
below shows the extraction achieved by contacting the
samples with the respective solutions for one hour.
TABLE III
:Solutlon : Extraction (%)
Sample:Temp.(C): Cu :~ Ni Co : Fe
. _
.
A : 55 : 79.7 : 82.5 : 80.8 : 79.1
B : 24 : 80.0 : 84.5 : 83.0 : 76.9
_ _ . . . . . _ . _ ... _
It will be seen from the above results that the
extraction was as efficient at 24C as at the higher
temperature.
EXAMPLE III
A salt mixture containing 66.8% by weight of -
sodium chloride and 15.2~ by weight of potassium chloride
was prepared, the balance comprising chloride impurities
in amounts corresponding to:
Cu : 2.45~ by weight
Ni : 3.20% by weight
Co : 0.80~ by weight --
Fe : 0.60% by weight ~ -
This salt mixture was leached with a saturated ~;
solution of sodium chloride and potassium chloride in water, -
having a pH of 2.2. All other leaching conditions were
identical to those described for Sample A in example II above. -
At the end of one hour, the percentage of each impurity metal
extracted was determined by analysis of the salt and found
to be:
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Cu : 82.7~
Ni : 82.5%
Co : 86.2%
Fe : 37.8%
A comparison of the above results with those
obtained in the two tests of example II shows that the use
of the higher pH led to a marked drop in the iron extraction,
although efficient extraction of the other metals was
obtained. It will therefore be appreciated that where iron
is one of the impurities to be extracted from the salt, a
p~ below 2 and preferably no higher than 1.5 should be used.
While the present invention has been described
in conjunction with preferred embodiments thereof, various
modifications can be made to the conditions specified
without departing from the scope of the invention which is
defined by the appended claims.
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