Note: Descriptions are shown in the official language in which they were submitted.
1319826
TREATMENT OF SULPHURIC ACID SOLUTIONS CONTAINING TELLURIUM,
COPPER SULPHATE AND MINOR IMPURITY ELEMENTS
This invention relates to tne treatment of
sulphuric acid solutions containing tellurium, copper
sulphate and minor impurity elements, and more
particularly to the treatment of leach liquor originating
from the treatment of slimes produced during electrolytic
refining of copper.
Canadian Patent No. 1091035 discloses a process
for treating slimes from the electrolytic refining of
copper wherein the slimes are leached with sulphuric acid
under an oxygen partial pressure of up to 50 p8i and at
elevated temperature until copper and tellurium in the
slimes are substantially dissolved. A liguid-solid
separation is then performed to separate the solid leached
slimes from the leach liquor and the leach liquor is
further treated in a cementation reactor with metallic
copper to cement tellurium as copper telluride. The
remaining solution is sent to a copper sulphate plant for
the production of copper sulphate. In the copper sulphate
plant, the leach liquor remaining after removal of
tellurium is passed through a bed of copper particles to
form a copper sulphate solution which is later
crystallized to form CuS04 5H20.
The above process requires two separate beds of
copper particles, one for the cementation of tellurium and
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one for the production of a copper sulphate solution prior
to crystalization of copper sulphate.
Applicant has surprisingly found that cementation
of the tellurium as copper telluride and production of the
copper sulphate solution can be carried out in the same
reaction vessel thereby eliminating a lot of eguipment and
simplifying the process.
The process, in accordance with the present
invention, comprises the steps of recirculating the
sulphuric acid solution containing tellurium, copper
sulphate and minor impurity elements between a first tank
containing the solution and a second reactor tank
containing a bed of copper particles for a time interval
6ufficient to cement eubstantially all (i.e. over 95% of)
the tellurium present in the sulphuric acid solution as
copper telluride, adding oxygen to the first and/or the
second tank to form a copper sulphate solution during
recirculation of the sulphuric acid solution between the
first and second tanks, and separating the cemented copper
telluride from the copper sulphate solution.
The process is normally carried out at a
temperature higher than 70C, preferably near the boiling
point of the sulphuric acid solution and the sulphuric
acid content of the solution is preferably between about
100 and 150 g/l at the beginning of the operation. These
are known requirements for tellurium cementation.
When the tellurium concentration in the sulphuric
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acid solution is hlgh, it i8 preferable to recirculate the
solution until the tellurium content falls below about 2.0
g/l before adding oxygen to form the copper sulphate
solution.
The invention will now be disclosed, by way of
example, with reference to the accompanying drawings and
examples. In the drawings,
Figure 1 is a flow diagram of the treatment
process in accordance with the present invention; and
Figure 2 is a diagram illustrating the
concentration of tellurium in solution versus reaction
time.
Referring to Figure 1, there is shown a flow
diagram of the process in accordance with the present
lS invention. The sulphuric acid solution containing
tellurium, copper sulphate and minor impurity elements,
hereinafter called leach liguor, which is stored in a
container 10 is introduced into a first tank 12. The
liquor in the tank is agitated by a stirrer 14 and
recirculated several times by a pump 16 between the first
tank 12 and a second reactor tank 18 filled with copper
particles for a period of time sufficient to cement
substantially all the tellurium present in solution as
copper telluride. The preferred reactor tank is made as
described in Canadian application no. 439,206 filed
October 18, 1985. Applicant has surprisingly found that
the copper telluride cement did not firmly adhere to the
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copper particles but was immediately released upon
formation and remained in suspension in the solution. The
size of the tanks and the flow rate of the leach liguor is
preferably such that the retention time of the liquor in
the first tank is about two minutes and in the 6econd
reactor tank about 0.5 minute. Air is introduced in the
first tank or the second tank or both to oxidize the
remaining leach liquor to form a copper sulphate solution.
The so-produced copper sulphate solution containing the
copper telluride cement is then passed through a filter
press 20 to separate the cemented copper telluride from
the copper sulphate solution.
Various tests were made to determine:
1) The compatibility of the simultaneous treatment of the
leach liquor for the removal of tellurium and for the
production of a copper sulphate solution in the same bed
of copper particles.
2) The degree of precipitation of copper telluride.
3) The efficiency of production of copper sulphate
solution.
It was surprisingly found that the precipitation
of copper telluride did not affect the circulation of the
leach liquor or the formation of the copper sulphate
solution. Generally, the flow of solution remained
constant during recirculation and gradually decreased at
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the end as the specific gravity of the copper sulphate
solution approached 1.4, as it normally happens when
treating a leach liquor from which tellurium has been
previously removed. The pressure at the base of the tank
18 remained normal. No pumping problems were encountered
during transfer of the solution between the first and the
second tanks. There was no blocking of the reaction vessel
during the continued production of copper telluride and of
copper sulphate solutlon which i8 believed to be due to
the fact that the copper telluride cement did not adhere
to the copper particles but was immediate~y released upon
cementation and remained in suspension in the copper
sulphate solution while said solution was circulated in
the two tanks.
The results of the tests carried out to determine the
degree of precipitation of copper telluride are shown in
the following Table I and Figure 2.
1319826
U ~ . _ N
æ o % ~ ~
O O ~ O O O
. z ~ O O O O O
~u _ c,
-- O _ ~N N
I,U ~ N N ~ N N
~-- y ~;;; ~ O ~ I~ ~ o
U ~ ' ~ t~ O.
~ ~ -- N O O~ In O O~
$~ æ æ æ æ æ
Z "~
~n~ ______
~ <I ~ ~ ~ N 58 ,~
~oU~ _____--
U ~y ~ o o U~ o o o
~ O t-- ~ N O~ N
l_ .
V O _ N ~ ~ U~
~3~9826
Table I and Figure 2 lllustrate that more than
96.5% of the tellurium was precipitated in the first two
tests. The tellurium concentration at the beginning of the
first two tests was 0.44 and 1.44 g/l respectively and
after 4 hours, was reduced to 0.01 and 0.05 g/l,
respectively, as shown in Figure 2. However, in the third
test, wherein the tellurium concentration was higher at
the beginning of the test ~2.4 g/l), the tellurium
concentration was only reduced to 1.5 g/l within the total
reaction time.
The results of the third test indicated that for a
relatively high initial tellurium concentration (e.g. ~ than
2 g/l), precipitation of copper telluride was incomplete
within the time period normally required for the formation
of the copper sulphate solution.
In tests 4 and 6, oxygen addition was delayed by 2
and 4 hours, respectively. The initial tellurium
concentration was 2.56 and 1.70 g/l, respectively, and
after 2 and 3 hours, respectively, was reduced to 0.05 g/l.
For comparison purposes, it may be seen that in test 5
wherein oxygen was added from the beginning, it took
five hours to reduce a tellurium concentration of 1.79 g/l
whereas the same reduction in test 6 was achieved after
only three hours. From the above results, it appears
that, for high tellurium concentrations, it is preferable
to delay the addition of oxygen required for the formation
of the copper sulphate solution until the tellurium
1319~2g
concentration in solution i8 lower than 2 g/l in order to
be able to reduce the tellurium concentration in the
solution to less than 0.05 g/l within the time period
normally required for the formation of the copper sulphate
solution.
As shown in Table I, the temperature of the leaeh
liquor during the reaction should be highsr than 70-C,
preferably close to the boiling point of the solution.
Steam addition into tank 12 i~ thus required to heat the
solution. The free acid eoneentration should also be
higher than about 100 g/l but lower than 150 g/l at the
beginning of the reaction. Sulphuric acid addition into
the tank 12 may be required to ad~ust the H2S04
concentration.
When comparing ths effieiency of production of the
eopper sulphate solution, using the process in aceordance
with the invention wherein tellurium is eoneurrently
removed with the produetion of the eopper sulphate
solution, with that obtained when using a leaeh liquor
from which tellurium had been previously removed, it was
found that the percentages of copper dissolution and
oxygen utilization were about the same. Efficieneies
higher than 90% for Cu and about 60% for 2 respeetively,
were obtained. The two concurrent reactions taking plaee
in accordance with this invention are:
Te(OH)6 + 5Cu- + 3H2S04 ~ Cu2Te + 3CuS04 + 6H20 (1)
131982~
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Cu + ~2 + H2S4 ~ CuS04 + H20 (2)
Although reaction (1) produces some copper
sulphate, the ma;or portion of the copper sulphate
solution is produced by reaction (2). The reaction times
during simultaneous precipitation of copper telluride and
production of copper sulphate solution were between 7 and
12 hours which is about the same as during th- production
of copper sulphate solution from a leach llquor from which
tellurium had been previously removed.
