Note: Descriptions are shown in the official language in which they were submitted.
~ ~741~`~54
RECOVERY OF INDIUM IN CONJUNCTION WITH THE REMOVAL
OF CADMIUM, ZINC AND COPPER FROM LEAD, COPPER AND
ZINC SMELTER OR REFINERY DUSTS
This invention relates to the recovery of indium
in conjunction with the re~al of cadmiu~, zinc, and
copper from lead blast furnace dusts, copper furnace
dust, and other lead, copper and zinc smelter or refinery
dusts.
Significant amounts of indium are often present in
the above dusts. In addition, cadmium is present in minor
amounts in lead, copper and zinc ores and the refinery
dusts may contain large circulatory loads of cadmium.
These materials represent enviromental and occupational
hazards; thus it is of interest to be able to remove the
cadmium. If the indium could be recovered in conjunction
with the removal of cadmium, the economics of the cadmium
removal would be greatly improved.
Presently, there are several commercial processes for
recovery of indium from smelter dusts. Most of these are
used to recover indium from zinc calcine or zinc oxide
fume produced from the treatment of lead blast furnace slag.
Indium is produced by acid leaching zinc oxide fume, and
by processing the slag obtained in the treatment of lead
,
~ 7'~Ds4
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blast furnace bullion dross. Ind~um bearing residues
may also be processed by mixing with chloridizing agents
and fuming~ The resultant fume is treated to recover
indium,lead, and cadmium. Although these processes
could probably be used to treat copper and lead
furnace dust, most involve a large number of steps,
since they are intended to produce indium metal. If the
indium in lead and copper furnace dusts could be
recovered in the form of a saleable concentrate, rather
than as indium metal, a simpler process might be fea-
sible.
Conventional processes for cadmium recovery in lead
smelters usually involve a sulfuric acid leach and zinc
cementation or ion exchange. In this regard, the initial
steps for indium recovery would be similar. In addition
to indium and cadmium, copper and zinc are leached by
sulfuric acid. These are recoverable, along with cadmium,
by conventional methods used by electrolytic zinc re-
fineries. This would involve pH adjustment to remove such
impurities such as iron, arsenic, antimony and bismuth,
copper and cadmium removed by zinc cementation and recovery
of zinc by electrolysis, or as a basic zinc carbonate as
described by Hull P.G. et al, Australian Institute of
Mining and Metallurgy Conference, Tasmania, May 1977,
page 299-307. These processes involve a large number of
steps which renders the operation very expensive.
It is therefore the object of the present invention
to provide a method for separating indium from cadmium,
zinc and copper present in lead, copper and zinc dusts
7'~DS4
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and for recovering such metals.
The process, in accordance with the invention, com-
p~lses the steps of leach;`ng the dusts with strong
sulfuric acid to form a leach solution containing
indium, cadmium, copper, zinc and other metals present
in the dusts~ adding ammomium hydroxide to the leach
solution to precipitate indium, and filtering to re-
cover the indium in the filter cake while cadmium, zinc,
and copper remain in the filtrate.
The concentration of sulfuric acid is preferably about
180-220 gpl and the temperature of the leach solution
about 90-100C. To the leach solution, ammomium hydroxide
is added to the pH of 4.6-5.0 if small amounts of copper
are present, and to the pH of 9 if substantial amounts
of copper are present.
The lead, copper and zinc dusts normally contain,
in addition to indium, other constituents such as iron,
aluminum, bismuth, tin, antimony and arsenic. The ammomium
hydroxide precipitate will retain the iron, aluminum,
bismuth, tin, antimony and arsenic and some of these metals
may be economically recovered. The ammomium hydroxide pre-
cipitate will generally contain about 2-5% by weight of
indium (depending on indium concentration in original dust)
and the cake produced by filtering such precipitate is
normally dried at about 100C and sent to an indium
refinery to recover indium. The indium cake is readily
soluble in H2SO4and may be processed by conventional
indium recovery techniques $uch as precipitatiQn as
1~74~54
-- 4 --
indium phosphate~ as described in U.S. P~tent 2,241,438.
If indium is to be recovered by fumLn~, the ~ndium cake
would first have to be calcined.
Most of the cadmium, zinc and copper will pass to the
filtrate after addition of ammomium hydroxide and fil-
tration but the indium precipitate also retains a
signiflcant amount of cadmium, zinc and copper and further
refining may be required. This may be done by redissolv-
ing with sulfuric acid, reprecipitation with ammomium
lQ hydroxide and filtering to recover additional cadmium,
zinc and copper to produce a filter cake which contains
a greater concentration of indium than found in the first
precipitate. This second step could be omitted if there is
only relatively small amounts of the total cadmium, zinc
and copper found in the first precipitate.
To cover the cadmium, zinc and copper in the fil-
trate from the ammomium treatment, calcium hydroxide is
added, and the ammomium hydroxide removed by distillation.
The ammomium hydroxide can then be recycled. The residue,
after filtration and drying, could be used by an elec-
trolytic zinc refinery as a neutralizing agent. The
copper, zinc and cadmium would be recoverable. In addition,
many of the impurities detrimental to the electrolytic
zinc process would be removed with the indium precipitate.
The proposed method for indium recovery avoids the
large number of steps required by the known processes.
Iron, bismuth, arsenic and antimony are removed along
with the indium in the ammomium prec~pItate. ConceiYably,
~ ~74~DS4~ 5 -
the copper and cadm~um could be recovered by zinc
cementation after adjustment to s~itable pH. However,
sepa~ation of the copper and cadmium from the zinc is
not essential, Distillation with lime to recover
ammomi~m hydroxide will also precipitate copper and
cadmi~m along with the zinc. The residue should be
suitable as a neutralizing agent for an elect~olytic
zinc plant. Since the zinc plant would have treatment
facilities for removing cadmium and copper, this would
avoid having to process the cadmium (and copper) at
the lead smelter.
In general, the proposed procedure would allow a
smelter to recover indium in the form of a potentially
saleable concentrate, as well as recovering cadmium,
copper and zinc in a form that could be processed by an
electrolytic zinc refinery. The lead, as well as any
insoluble copper, would be recoverable as a residue
that can bè processed by a lead blast furnace.
The invent;on will now be disclosed, by way of
example, with reference to the accompanying drawing
which shows a diagramatic flow diagram illustrating
the main steps of the process.
Indium bearing dusts are leached with 180 gpl
sulfuric acid. The leach solution is heated at 90-100C,
m~xed and filteEed to produce a lead cake which is
returned to the lead smelter, The filtrate is treated with
ammam~um hydroxide to pH 4~6 if no or little copper present.
- If s-ubstantial amounts of copper are present, an excess
iL~74~5~
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of ammomium hydroxide is added to a pH of ~Ø The
ammomium hydroxide precipitate is filtered to form a
cake containing the indium. If lead smelter dusts are
treated, the leach solution normally contains, in
addition to indium, cadmium, zinc and copper, other
constituents such as iron, aluminum, bismuth, tin,
antimony and arsenic. The ~mmomium hydroxide precipitate
will retain the iron, aluminum, bismuth, tin, antimony
and arsenic.
The ammomium hydroxide precipitate, which may
contain about 2-5% by weight of indium, is filtered
and dried at a temperature of about 100C prior to
being sent to an indium refinery to recover indium. The
indium cake is readily soluble in sulfuric acid and may
be processed by conventional indium refinery techniques.
After treatment with ammomium hydroxide and filtration,
most of the cadmium, zinc and copper pass to the filtrate
but the ammomium hydroxide precipitate may retain a
substantial amount of cadmium, zinc and copper. Therefore,
the indium precipitate is preferably redissolved with
180 gpl sulfuric acid and the leach solution mixed and
treated with additional ammomium hydroxide and refiltered
to recover additional cadmium, zinc and copper.
Lime (Ca(OH)2) is added to the ammomium hydroxide
filtrate originating from the first and second stages of
ammomium hydroxide precipitation and filtrate distilled
to recover the ammomium hydroxide. The distilled ammomia
may be recycled. The residue is filtered, dried at 100C
74~54
-- 7 --
and sent to a zinc refinery. Eletrolytic refining would
be adequate since most of the impurities that effect
electrolytic recovery of zinc have been remo~ed by the
ammomium hydroxide precipitation. Cadmium and copper can
also be recovered by conventional methods. The filtrate
may be discarded or recycled. The applicant has found
that treatment using other alkaline materials (lime,
sodium hydroxide, sodium carbonate) either alone or in
combination with ammomium hydroxide; will also precipitate
indium. However, the precipitates produced are more bulky
and will not separate indium from copper, cadmium or zinc
as effectively as ammomium hydroxide alone.
The invention will now be disclosed by way of
example, with reference to the following specific examples:
EXAMPLE I: Extraction of Indium from Lead Furnace Dusts
A slagging baghouse dust, from a lead blast furnace
was chosen, because of the relatively high indium
content (0.20%)
The dust was leached at 100C for a period of 15-20
minutes, with 180 gm/l sulfuric acid, in the proportion
of 5gm of dust for each lOOml of acid solution. The slurry
was filtered, and the filtrate analysed.
TABLE I: Analysis of Slagging Baghouse Dust and Filtrate
from Sulfuric Acid Leach
Pb Cu Cd Zn In
% in Dust 62,35 0.068 4.7 9.5 0.20
% of the total Q.02 0.7 79 68 80
in the Sulfuric
Acid Leach
.,
~74q~54
- 8 ~
Thus, the sulfur~c acid leach dissolved 80% of
the ~ndium present in the dust.
To a portion of the filtrate, ammomium hydroxide
was added, to br;~ng the pH of the solution to 4.6. The
precipitate was removed by filtration, dried at 60C,
and analyzed for indium. Analysis of the filtrate re-
maining after ammomium hydroxide precipitation indicated
that the precipitate contained better than 98% of the
indium present in the sulfuric acid leach solution.
The precipitate contained 3.58% indium.
EXAMPLE II: Extraction of Indium from Copper Furnace
Cottrell Dusts
Two samples of copper furnace cottrell dust were
examined. The samples analysed as follows:
TABLE II: Analysis of Copper Furnace Dust
Sample # %Pb %As ~Cu %Sb ~Bi %In %Cd ~Zn
1 33.60 0.67 2~52 0.098 0.70 0.148 1.01 15.6
2 40.15 0.64 2.00 0.089 0.53 0.119 1.00 12.9
To the above samples (-35 mesh) 220gm/1 sulfuric
acid was added, in the proportion of 50gm of sample for
each lOOml of acid. The resultant slurry was heated for
15 minutes with stirring at 100C. This was filtered,
to produce 200ml of filtrate for 50 gm of dust.
The residue was dried, and the weight determined.
The leach filtrate was analysed.
The leach solution was neutralized with ammomium
hydroxide, with a excess added, to bring the pH to 9Ø
The precipitate was removed by filtration, dried at 60C,
-~ ~74~:~5~
g
weighed and analysed. The filtrate remaining after
the ammomium hydroxide precipitation was retained.
To a portion of the ammomium hydroxide filtrate,
calcium hydroxide was added, and the slurry heated to
boiling for a period of 30 minutes. The slurry was
filtered, and the residue dried and weighed. The
filtrate was also retained for analysis.
The weights of the residues and precipitates are
listed in Table III. These are expressed as a percent
of the original weight of the dust samples.
TABLE III: Percent Weights of Residues and Precipitates
for Leach Tests on Contrell Dusts
Sample # Sample Sulfuric Acid Ammomium Hydroxide Calcium
Weight Leach Residue Precipitate Hydroxide
Residue
1 100.0 63.0 5.88 154.1
2 100.0 70.6 4.38 129.9
The results for the analysis of the dusts,
and residues are listed in Table IV.
1~.i74'~:~54
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T~BLE IV: Analysis of Products form Cottrell Dust
Leach Tests
Sample # Original Dust Ammomium Hydroxide Calcium Hydroxide
Sample (%) Precipitate (%) Residue (%)
Indium
1 0.148 2.42 0.004
2 a.. ll9. 2.65 0-004
Cadmium
1 1.01 0.786 0.518
2 1.00 1.015 0.590
Copper
1 2.52 0.94 0.853
2 2.00 0.68 0.670
Zinc
1 15.6 23.3 8.60
2 12.9 . 20.4 8.58
The results for the analysis of the sulfuric acid
leach solution are shown in Table V. In addition, the
percentages of the metals present in the ammomium
hydroxide precipitate and the calcium hydroxide residue
(after ammomium distillation) are shown. These are
expressed as % of the metal originally in the leach
solution.
~ :~7~P54
TABLE Y: Analysis of Leach Solution and Percentage of
Metals 1~ the Ammomium Hydroxide and Calcium
Hydroxide Residue expressed as percent contained
in the Leach Solution.
Sample # gm/l in Sulfuric % of Total in ~O of Total in
Leach Solution Ammomium Calcium Hydroxide
Precipitate Residue
Indium
1 0.369 97.3~2
2 0.293 99.2~2
Cadmium
1 2.10 5.49 95.0
2 2.10 5.30 91.2
Copper
1 3.36 4~11 97.7
. 2 2.24 3.33 97.1
Zinc
1 36.8 9.30 90.4
2 30.9 7.23 90.2
The results shown in Table V are based on the results
and weights of residues shown in Tables III and IV.
Because of limitation of the assay procedures, some
of these results will not total exactly to 100~.
The results $or the filtrate from the calcium hydroxide
residue are not shown here, as this filtrate did not
contain significant portions of the total copper, cadmium
and zinc.
1~74~5~
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In Table YI, the results are expressed as a. percentage
of the metal continued in the original dust samples.
~ABLE VI: Analysis of Leach Test Products Expressed as
Percent Contained in the Original Dust Sample
Sample # % of Total% of Total % of Total
in Sulfuric in Ammomium Calcium Hydroxide
Acid Leach Hydroxide Residue
Solution Precipitate
Indium
1 99.3 96.6 <2
2 98.3 97.5 <2
Cadmium
1 83.2 4.57 79.0
2 84.0 4.45 76.6
Copper
1 53.3 2.19 52.1
2 44.8 1.49 43.5
Zinc
1 94.4 8.78 85.3
2 95.8 6.93 86.4
XAMPLE III: Reprecipitation of the Ammomium Hydroxide
Precipitate.
The precipitate produced with ammomium hydroxide
contained significant amounts of zinc, cadmium and
copper, as noted previously (Tables V & VI). A sample
of the precipitate, when redissolved with 180g/1
sulfuric acid, and reprecipitated with ammomium hydroxide
at pH 9 produced a precipitate that weighed 52% less than
the original precipitate. The results of this test
are shown in Table VII.
4~5~
- 13 -
TABLE VII: Second Precipitation - Assay Results.
First Second % of Total in
PrecipitationPrecipitation Second
. % % Precipitate
Indium2.30 4.91 99%
Cadmium 0.76 0.25 15.8
Copper0.78 0.15 9.0
Zinc 18.9 8.09 20.1
Thus most of the copper, lead and zinc contained in
the first precipitate can be recovered by dissolving
with sulfuric acid and reprecipitating with ammomium
hydroxide.
A composite of ammomium hydroxide precipitate was
prepared to determine the major elements. Results of
the analysis of this sample are.presented in the
following Table VIII.
TABLE VIII: Composite Ammonia Precipitate Analysis
% In 2.32 % Zn18.9 % L01* 23.7
% Sb 0.17 % Cu0.78 % Fe 7.75
% Bi 1.64 % As0.52 % SnO2 2.34
% Te 0.03 % S6.12 % Al O 9.70
% Pb 0.31 % Ag0.0006 % Cu 0.05
% Cd 0.76 ~ Se0.03 %Mg 0.34
% Tl 0.01
* Sample ignited for 1/2 hour at 500C.
If the figures shown in Table VIII are converted to
the most likely oxides and added up, the total will be
95.7%. The loss of weight cn ignition was assumed to
be due to water and ammomium hydroxide. The major
~.~!l74~?S4
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elements appear to be iron, aluminum and zinc.
Iron and aluminum will be detrimental to the refining
of indium, but can be separated from indium by con-
ventional means. In the precipitation with ammomium
hydroxide, the iron and aluminum probably aid in the
precipitation of the indium.
From the above examples, it may be observed that:
1) In general, leaching with 180-220gm/1 sulfuric acid
dissolved 80% of indium from slagging baghouse dust
and 98% or better from the cottrell dust. Also, 79%
of the cadmium and 68% of the zinc were leached from
the slagging baghouse dust. During leaching of the
cottrell dust, 83-84% of the cadmium, 45-53% of the
copper, and 94-96% of the zinc were dissolved
(Table VI). It was also found that the residue left
after the sulfuric acid leach essentially contained
all of the lead. Although not mentioned in the
examples, additional leaching with sulfuric acid
dissolved only about 3.5% of the cadmium, and between
5.8 and 8.5% of the copper remaining.
2) For the slagging baghouse leach solution, ammomium
hydroxide addition to pH 4.6 produced an acceptable
precipitate at 3.58% indium, and contained essentially
all the indium present in the leach solution. For the
cottrell dusts containing larger amounts of
copper, a p~ of ~.0 was required to produce an
acceptable precipitate.
~L~'74~5~
- 15 -
Although not mentioned in the examples, it was found
that sodium carbonate, and calcium hydroxide by them-
selves or in combination with ammomium hydroxide would
remove all of the indium at pH 4.5- 5.5. However, the
precip;tates were more bulky, and contained much larger
amounts of the cadmium, copper and zinc than that produced
by ammomium hydroxide alone. Adjustment of a cottrell
dust leach solution to a pH of 2 - 2.5 with calcium
hydroxide alone allowed 82-90% of the copper, 91-93% of
the cadmium, and 93-94% of the zinc to pass into the
filtrate. However, only 38-55% of the indium was pre-
cipitated.
3) The addition of ammomium hydroxide precipitated
practically all of the indium, and allowed 90-95% of
the cadmium, and 97-98% of the copper, and 90-92% of the
zinc to pass into the filtrate. Also, because of the
small amount of precipitate produced by ammomium
hydroxide, as compared to calcium hydroxide or sodium
carbonate, the indium can be concentrated about 10-20
times that in the original dust, and can contain up
to 2-4% indium.
4) The precipitation with ammomium hydroxide gives good
separation of indium from copper, cadmium and zinc.
A further improvement can be effected by redissolving
the precipitate with sulfuric acid and reprecipitating
with ammomium hydroxide.
51 The presence of ammomium hydroxide in the filtrate
may interfere with the later recovery of copper, cadmium
1~4~5~
~ 16 -
and possibly zinc. However, applicant has found that
ammomi~m hydroxide can be removed by addit~on of lime
and distillatIon to recover the ammonia. The residue
~emaining after distillation can be leached with
sulfuric acid to recover the copper, cadmium and zinc.
This- leaching procedure was tried with the above
mentioned cottrell dusts and gave an overall recovery
of 87~95% of the copper, 76-84~ of the cadmium and
8Q-85% of the zinc contained in the sulfuric acid leach.
61 Applicant has also found that, in addition to
copper, cadmium and zinc, other constituents found in
dust are also leached with strong sulfuric acid. It
has been noted that 1.5-2.0% of the total arsenic,
6,9-9.9~ of the antimony and 6.9-12.7~ of the bismuth
are also leached with the sulfuric acid. The subsequent
ammomium precipitation removed better than 95% of the
leached arsenic, antimony and bismuth along with the
indium,
Although the invention has been disclosed with
reference to the removal of indium, cadmium, copper and
zinc from lead dusts, 1t is to be understood that the
invention is not limited to lead dusts but also apply
to copper and zinc dusts.
