Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
" 1070504
1 BACKGROUND OF THE INVENTION
___________________________
Field of the Invention
This invention relates to a hydrometallurgical method
which comprises removing arsenic from an arsenic-containing
solution, such solutions typically resulting from industrial
processes for the production of copper are most commonly en-
countered in a copper electrolyzing process or from a process
for purifying a copper electrolytic solution (hereinafter
referred to as "a copper electrolytic solution and the like"),
such as a copper electrolytic solution, a solution resulting
from the concentration of the liquid effluent resulting from
the electrolysis of a copper electrolytic solution until arsenic
is a~out to precipitate (to be referred to as a "decopperized
electrolytic solution"), or a solution resulting from the de-
copperizing electrolysis of the above-mentioned solution until
arsenic is about to electrodeposit. More specifically, it
relates to a method for extracting arsenic using an organic
solv~nt which comprises bringing the above copper electrolytic
solution and the like into contact with an organic phase to
transfer arsenic into the organic phase.
Description of the Prior Art
Some arsenic is présent in ore materials processed in
non-ferrous metallurgy, especially in copper ores. Most of the
arsenic encountered in copper refining is recovered as dust
from smelting, for example, in a flash smelting furnace, or
from a copper-making process, for example, in a converter or
a refining furnace, and recycled. However, a part of the arsenic
is accumulated in a waste sulfuric acid solution resulting from
a gas washing step at the time of collecting sulfur dioxide.
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,~o70S04
1 Still another part of the arsenic is accumulated in a copper
electrolytic solution and the like in a copper electrolyzing
step. Accordingly, arsenic accumulates within the copper-refining
system unless the arsenic is removed from the system.
In order to remove arsenic from a copper electrolytic
solution and the like, a decopperizing electrolysis has typically
been used as a purifying step to remove arsenic in the form of
an electrolytic slime together with the copper. In decopperizing
electrolysis performed to remove arsenic from a copper electro-
lytic solution and the like or a solution resulting from theconcentration of an electrolytic solution containing arsenic
until arsenic is about to precipitate (to be referred to as a
decopperized electrolytic solution), it is difficult to separate
arsenic from copper, especially when it is considered that the
arsenic is generally recycled to an earlier step (e.g., to a
converter or refining furnace) in the form of a mixed slime of
copper and arsenic for further utilization of the copper. Such
a method cannot be viewed as a basic procedure to remove arsenic.
In addition, in later stages of decopperizing electrolysis, toxic
gases such as arsine (AsH3) are generated, and high costs are
needed to render the arsine harmless. -At the same time, the
current efficiency is reduced since the copper concentration
decreases. The process, hence, becomes inefficient.
Another known method involves removing arsenic as a
sulfide. When arsenic is removed by adding hydrogen sulfide
gas to a copper electrolytic solution or to a decopperizing
electrolytic solution for the purpose of purification, the
efficiency of the reaction of the hydrogen sulfide is low, and,
at the same time, co-precipitation of copper cannot be avoided.
Accordingly, an extra step is ncessary to separate copper and
~070504
1 arsenic from a mixed precipitate of arsenic sulfide and copper
sulfide.
The above processes can be summarized as follows.
Assuming the first operational step is a copper electrolysis,
the starting material is, of course, a copper electrolytic
solution. Following copper electrolysis, a major portion of
the copper has usually been removed from the copper electrolytic
solution by the electrolysis. The "spent" copper electrolytic
solution is usually divided into two portions, a major portion
thereof is recycled for the formation of additional copper
electrolytic solution and a minor portion is concentrated, whereby
arsenic can be eliminated by concentration and CuSO4 nH20 removed
to provide a decopperized electrolytic solution. The decopperized
electrolytic solution is commonly subjected to decopperizing
electrolysis, providing substantial proportions of Cu and a
decopperized solution. The decopperized solution can be subjected
to dearsenizing electrolysis, if desired, and the product thereof
recycled along with the major portion of the "spent" copper
electrolytic solution to form additional copper electrolytic
solution-
On the other hand, for a smelting process, typicallycrude copper is intially fed to a flash smelting furnace in
mat form. The product of the flash smelting furnace is copper
sulfide which is typically forwarded to a converter (copper-
ma~ing processing) which results in obtaining of crude copper.
The output of the converter is forwarded to a refining furnace
wherein some Cu and other materials such as Zn are removed and
recycled to the flash smelting furnace and waste products such
as SO2 are removed by washing. The product of the refining
furnace is formed into a semi-crude copper anode, and subjected
to copper electrolysis, arsenic being present therein.
'1070504
1 SU~RY OF THE INVENTION
________________________
We have now found that by bringing a copper electrolytic
solution and the like into contact with an organic solvent phase
containing tributyl phosphate, arsenic in the electrolytic solu-
tion or the like can be selectively extracted into the organic
phase.
According to this invention, there is thus provided a
method for removing arsenic from a copper electrolytic solution
and the like which comprises bringing the copper electrolytic
solution and the like into contact with an organic solvent phase
containing tributyl phosphate to thereby extract arsenic present
in said solution into the organic solvent phase.
DETAILED DESCRIPTION OF THE INVENTION
_____________________________________
The present invention is thus directed to the removal
of arRenic from a copper electrolytic solution and the like by
a liquid-liquid extraction method instead of resorting to con-
ventional methods involving the addition of hydrogen sulfide
gas or decopperizing electrolysis.
The copper electrolytic solution and the like treated
in accordance with the present invention typically comprises at
least copper ions, arsenic ions and sulfuric acid. On a typical
commercial scale, copper ions are present in an amount above
about 30 g/Q, arsenic ions in an amount a~ove about 1 g/Q and
sulfuric acid (as ~2S04; hereafter the same) in an amount above
about lSO g/Q. Other conventional components may be present,
of course, for ~xample, nickel ions in an amount a~ove about
1 g/Q are typically encountered in copper electrolytic solutions
and the like on an industrial scale.
1070504
1 It will be apparent to one skilled in the art that
copper electrolytic solutio~ and the like, e.g., decopperized
electrolytic solutions and decopperized solutions, are not
limited in any special fashion, and that such solutions can
have various compositions depending upon the exact industrial
scheme which is involved. However, as with any process inven-
tion, it is possible to describe certain solutions which are
commonly, but notinvariably, encountered in the art, and these
are set forth below to assist one skilled in the art in under-
standing the general environment of the present invention; the
description which follows regarding various solutions is not to
be construed as limitative, however.
One co~monly encountered copper electrolytic solution
comprises from about 30 to about 60 g/Q of Cu, from about 150
to about 250 g/Q H2SO4, from about 1 to about 7 g/Q As, and
typically, minor portions of Sb (on the order of about 0.1 to
about 0.7 g/Q) and Ni in an amount of about 1 to about 20 g/Q.
Typica~y decopperized electrolytic solutions resulting
therefrom contains Cu in an amount of from about 15 to about
30 g/Q, H2SO4 in an amount of from about 200 to 350 g/Q and As
in an amount of from about 3 to about 10 g/~, with conventionally
Sb being present in an amount of about 0.2 to about 1.0 g/Q and
Ni being present in an amount of about 1 to about 30 g/Q.
A decopperized solution, on the other hand, with results
from the decopperizing electrolysis of such a decopperized
electrolytic solution will typically contain about 0.01 to about
5 g/Q copper, about 270 to about 600 g/R H2SO4 and about 3 to
about 10 g/Q As, with Sb and Ni conventionally being present
in amounts on the order of about 0.2 to about 1.0 g/Q and about
1 to about 30 g/Q, respectively.
1070504
1 The tributyl phosphate (TBP for short) used as an
extracting reagent in the present invention has the structure
[CH3 (CH2) 30] 3P=O. TBP is generally used in a suitable organic
solvent since it has a specific gravity close to that of water
and a high viscosity.
The organic solvent which essentially serves as a
diluent may, for example, be a hydrocarbon, especially kerosene
(a (C12-C15)paraffin).
The extent of dilution is arbitrary, but generally,
10 TBP is diluted so that it is contained in a proportion of about
50 to about 75% by volume in the resulting organic phase. When
TBP is diluted so that the resulting organic phase contains a
larger amount of TBP, the specific gravity and the viscosity of
the organic phase increase, and after contact with the aqueous
phase the organic phase and the aqueous phase tend to form an
emulsion. When the dilution is performed so that the resulting
organic phase contains too small of an amount of TBP, i.e.j
substantially less than about 50% by volume, phase separability
is good, but the amount of arsenic extracted during each contact
decreases and the efficiency becomes low.
Sometimes good phase separation is obtained by adding
a higher alcohol, such as 2-ethylhexanol, dodecyl alcohol, etc.,
to the organic phase, in an amount of about 5% by volume or less.
The higher alcohol has the effect of preventing the separation
of the organic phase into two phases which often occurs when
the concentration of arsenic in the organic phase increases, and
ensures extraction with good efficiency.
The contacting of the organic phase with the aqueous
solution phase is effected in any conventional manner, most
preferably merely by mixing the two phases with stirring. When
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1070504
1 ideal mixing is carried out, the contact time is sufficiently
5 to 10 seconds, but in actual operations the contact time is
preferably about 30 seconds.
There is no particular limit on the temperature of the
extraction system, but there is a tendency that arsenic is
easier to extract into the organic phase as the temperature is
lower, e.g., the temperature is preferably about 10 to about 20 C.
The volume ratio of the organic phase to the aqueous
phase (to be referred to as the "0/A ratio") at the time of con-
tact is not restricted in any particular manner. However, thereis a tendency that the arsenic content of the aqueous phase after
extraction decreases with increasing 0/A ratios. Based on the
preceeding discussion, it is believed that one skilled in the
art will easily be able to determine optimum ~/A ratios for any
particular processing sequence. As a general guideline, an 0/A
ratio on the order of about 1:1 will typically be most preferred
from an industrial scale operational viewpoint.
When an organic phase containing TBP is used, arsenic
can be extracted from a copper electrolytic solution or the like
without being affected by other metal elements such as Sb, Cu,
Ni, etc. present therein. However, the sulfuric acid concentra-
tion of the aqueous phase affects arsenic extraction and there
is a tendency that the results of the extraction become better
as the sulfuric acid concentration is increased, e.g., to about
300 to 400 g/Q. The organic phase containing TBP, however, tends
to extract sulfuric acid to some extent, and as the sulfuric
acid concentration of the a~ueous phase treated is increased,
the amount of sulfuric acid extracted becomes higher.
~he industrial operation of the extracting method of
this invention can be performed by a batch extraction or a con-
tinuous extraction, i.e., a counter-current extraction in multi-
1070504
1 stages, the optimum number of stages being established in accord-
ance with conventional chemical engineering techniques. In order
to extract arsenic with good efficiency, counter-current extrac-
tion in multi-stages is most preferred. The extracting apparatus
can be freely selected from those in general industrial use, for
example, a mixer settler, a rotary disc contacter, a pulse column,
or a centrifugal extractor.
If desired, a stripping can be performed to remove -
arsenic from the organic phase. The aqueous phase that can be
used for such a stripping may, for example, be an alkaline
solution such as an aqueous solution of sodium hydroxide, an
aqueous solution of sodium carbonate or an aqueous ammonia solu-
tion, but water is most suitable as it is readily available. By
contacting such an aqueous phase with the organic phase containing
arsenic, it is possible to strip the arsenic into the aqueous ~ !
phase. As a result of stripping, the organic phase is regenerated,
and it can be recycled to the extracting operation. While not
to be construed as limitative, industrial scale operation is
typically carried out using an alkali solution in an amount of
about 1.2 to about 1.5 times the equivalent of the arsenic and
sulfuric acid present (molar equivalents; moles of alkali per
mole of arsenic and sulfuric acid).
The optimum contact ratio of the organic phase to the
aqueous phase in the above stripping procedure is determined
utilizing conventional chemical engineering principles; on an
industrial scale, the contact ratio will generally be about
3:1 to ahout 10:1, with more preferred operation occurring when
the contact ratio is about 5:1. The time of stripping is
primarily decided upon by the total ~olumes of the aqueous phase
and the organic phase, and the concentrations thereof, but on an
~070504
1 industrial scale using systems as are commonly encountered
stripping is successfully carried out for about 30 seconds at
a temperature of from about 20 to about 30C.
The arsenic can be recovered from the aqueous solution
after stripping in a simple manner by reducing, i.e., by blowing
sulfur dioxide into the aqueous solution, prior to or after
concentrating the aqueous solution, to crystallize out the
arsenic as arsenic trioxide. In order to increase the rate of
recovery of the arsenic trioxide, it is preferred to blow sulfur
dioxide into the aqueous solution to thereby reduce the arsenic
in the aqueous solution into the trivalent state. The optimum
ratio of sulfur dioxide to the aqueous solution can be det~rmined
utilizing conventional chemical engineering principles, but,
generally speaking, sulfur dioxide is blown into the aqueous
solution in an amount of from about 2 to about 10 times the
equivalent of the arsenic in the solution (molar equivalents)
at slightly above atmospheric pressure for about 10 to about 30
mlnutes. The temperature is optionally selected, and typically
the temperature is just the inherent temperature of the aqueous
solution as it is received from the preceeding process step.
By the method of this invention as described above,
arsenic can be removed from a copper electrolytic solution and
the like, and the removed arsenic can be recovered in the form
of arsenic trioxide, for example.
Another method for recovery of the arsenic from the
a~ueous solution after stripping is to precipitate arsenic
trisulfide by adding a sulfiding agent such as hydrogen sulfide,
sodium sulfide or sodium hydrogen sulfide to the system.
The main purpose of the present invention is to extract
arsenic from a copper electrolytic solution or the like with TBP
g _
1070504
1 at good efficiency. The invention can also be applied to other
sulfuric acid aqueous solutions containing arsenic. However,
when the arsenic acid is contained in the trivalent state, for
example, in the case of a waste sulfuric acid solution in a
gas washing process of a sulfuric acid plant, the efficiency
of the extraction in accordance with this invention has been
found to be reduced. A copper electrolytic solution or the
like is characterized in that arsenic is present in a proportion
of about 50 wt% or more in a higher valency state other than the
trivalent state, i.e., in the pentavalent state.
Since hydrogen sulfide gas is not used in the method
of this invention, pollution and offensive odors can be pre-
vented. Since the result of extracting arsenic is better as
the sulfuric acid concentration is higher, arsenic can be removed
at good efficiency even from a copper electrolytic solution, a
solution before decopperizing electrolysis, or a solution
subjected to decopperizing electrolysis, all of which have a
high sulfuric acid concentration, e.g., about 320 to about
390 g/Q.
When the method of this invention is applied to a copper
electrolytic solution and the like, the organic phase containing
TBP selectively extracts arsenic and some sulfuric acid, and does
not extract copper, nickel, antimony, and chlorine, etc., con-
tained in the copper electrolytic solution and the like extent.
Accordingly, it is possible to separate arsenic from other
elements, especially copper. So, no arsenic-copper separation
step is required.
While toxic gases are generated in a conventional de-
copperizing electrolysis, the working environment can be markedly
improved ~y the present invention. This is a substantial ad-
vantage in actual operations.
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1070504
1 The following Examples illustrate the present invention
in qreater detail without limiting the same. All examples were
conducted at atmospheric pressure and at normal room temperature,
unless otherwise indicated. It is to be specifically noted
that the pressure of operation is not of importance to the present
invention and typically atmospheric pressure will be used.
Nothing would prohibit the use of sub- or super-atmospheric
pressures, but little is to be gained in the sense of process
efficiency by going to such more complicated systems.
Example l
In this example, arsenic was extracted from a copper
electrolytic solution obtained from a copper electrolysis plant
and a decopperizing electrolytic solution by batch-wise operation.
lO0 cc of each of these solutions and lO0 cc of a
kerosene-TBP phase containing 50~ by volume TBP were placed in
a separating funnel, shaken at room temperature using a shaker
for 5 minutes, and then allowed to stand to permit the mi~;ture
to separate into two phases. The concentrations of the components
in the aqueous phase were analyzed, and the results are shown in
Table l.
Table l
Components Analysis of aqueous phase (g/liter)
As Sb Cu -2
Starting
Copper electrolytic
solution (before 5.18 0.52 46.8 215
extraction)
Finishing
Copper electrolytic
solution (after 4.53 0.52 26.3 348
30 extraction)
~070504
1 Table 1 Continued
ComponentsAnalysis of aqueous phase (g/liter)
AsSb Cu
Starting
Solution before de-
copperizing electrolysis 8.10 0.72 26.3 348
(before extraction)
Finishing
Solution before de-
copperizing electrolysis 5.24 0.72 26.3 329
(after extraction)
Example 2
4.09 liters of a solution obtained by cooling a copper
electrolytic solution obtained from a copper electrolysis plant
to room temperature and then filtering the same (aqueous phase),
to remove the deposited Sb2O5, Sb2O3 As2O5 and 9.64 liters of
kerosene containing 50% by volume TBP and 5% by weight of 2-
ethylhexanol (organic phase) were prepared, and subjected to
a con~inuous extraction.
The apparatus used for the extraction was a rotary disc
contacter having an inner diameter of 50 mm, a column length of
600 mm and containing 22 partition walls and rotary discs. The
flow rate of the organic phase was 121 cc/min., and the flow
rate of the filtered copper electrolytic solution was 51 cc/min.
The extraction was carried out at room temperature for 80 minutes
while the discs were rotated at a speed of about 500 rpm.
Further, a continuous stripping was performed using
9.66 liters of the organic phase into which arsenic had been
extracted, and 8.28 liters of water. The same rotary disc
contacter as above was used for the stripping. The flow rate
of the organic phase was 60 cc/min., and the flow rate of the
aqueous phase was 52 cc/min. The stripping was carried out fcr
- 12 -
~070504
1 160 minutes at room temperature while rotating the discs at a
speed of 400 rpm.
The results of these tests are shown in Table 2.
Table 2
Copper Electrolytic Solution Organic Solvent Before
Before Extraction Extraction
4.09 Q 9.64 Q
Cu 46.8 g/Q
H2SO4 236 g/Q (965 g)
As 4.72 g/Q (19.3 g)
Sb 0.52 g/Q
Extraction
Solution After Extraction Organic Solvent After
Extraction
4.07 Q 9.66 Q
Cu 46.9 g/Q Cu Trace
H2SO4 223 g/Q (908 g) H2SO4 5.9 g/Q (57 g)
As 2.18 g/Q (8.9 g) As 1.08 g/Q (10.4 g)
Sb 0.52 g/Q Sb Trace
Stripping
Water 8.28 Q
Water (aqueous phase) Organic Solvent
After Stripping After Stripping
8.30 Q 9.64 Q
Cu Trace Cu Trace
H2SO4 6-9 g/Q(57 g) H2SO4 <0.01 g/Q
As 1.25 g/Q (10.4 g) As <0.01 g/Q
Sb Trace Sb Trace
Example 3
A continuous extraction was performed using 5.0 liters
of a copper electrolytic solution obtained from a copper electro-
lysis plant before decopperizing electrolysis (aqueous phase)
and 11.2 liters of kerosene containing 50~ by volume of TBP and
1070S04
1 5% by volume of 2-ethylhexanol (organic phase). The same
apparatus as was used in Example 2 was used for the extraction.
The flow rate of the organic phase was 112 cc/min., and the
flow rate of the aqueous phase was 50 cc/min. The extracting
was performed at room temperature for 100 minutes while rotating
the discs at a speed of about 500 rpm.
A continuous stripping was carried out using 11.5 liters
of the organic phase into which arsenic had been extracted and
10.9 liters of water. The same apparatus as was used in the
t stripping of Example 2 was used. The flow rate of the organic
phase was 58 cc/min., and the flow rate of the aqueous phase
was 55 cc/min. The extraction was carried out at room temperature
for 200 minutes while rotating the discs at a speed of about
400 rpm.
The results are shown in Table 3.
Table 3
Copper Electrolytic Solution Organic Solvent Before
Before Extraction Extraction
, . __ . .
5.0 Q 11.2 Q
Cu 26.8 g/Q
H2SO4 348 g/Q
As 7.8 g/Q (39.0 g)
Sb 0.72 gJQ
Extraction
Organic Solvent
Solution After Extraction
- After Extractlon
4 7 Q 11.5 Q
Cu 28.1 g/Q Cu Trace
H2SO4 325 g/Q ~2SO4 16 g~
As 0.55 g/Q (2.59 g) As 3.17 g/Q (36.41 g)
Sb 0.75 g/Q Sb Trace
- 14 -
1070504
1 Table 3 continued
Stripping
Water 10.9 Q
Water (aqueous phase) Organic Solvent
After Stripping After Stripping
11.2 Q 11.2 Q
Cu Trace Cu Trace
H2S04 16.4 g/Q H2S04 <0.01 g/Q
As 3.25 g/Q (36.41 g) As <0.01 g/Q
Sb Trace Sb Trace
One liter of the extract resulting from the stripping
was heated to boiling and concentrated to 107 cc. Thereafter,
the concentrated extract was cooled to room temperature while
blowing about 8Q of sulfur dioxide thereinto for 15 minutes to
crystallize out 2.5 g of arsenic trioxide crystals. The crystals
after being washed with water contained 75.6% of As.
While the invention has been described in detail and
with reference to specific embodiments thereof, it will be
apparent to one s~illed in the art that various changes and
modifications can be made therein without departing from the
spirit and scope thereof.
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