CA1174054A - Recovery of indium in conjunction with the removal of cadmium, zinc and copper from lead, copper and zinc smelter or refinery dusts - Google Patents

Abstract

ABSTRACT OF DISCLOSURE:

A process for separating indium from cadmium, zinc and copper in zinc dusts comprises leaching the dusts with a strong sulfuric acid to form a leach solution containing indium, cadmium, zinc and other metals, adding ammomium hydroxide to the leach solution to a pH at least 4.6, and filtering the solution to form a filter cake containing indium and a filtrate containing cadmium, zinc and copper. If the dust contains significant amounts of copper, precipitation of indium with ammomium hydroxide is done at a pH 9Ø The filtrate from the ammomium hydroxide precipitation procedure is treated with lime and the ammonia removed by distillation. The ammonia distillate may be recycled. The residue after filtration and drying may be processed at a zinc refinery to recover zinc, copper and cadmium.

Description

~ ~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 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 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 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~

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 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 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~

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~

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 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~

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.

Claims (7)

1. A method for separating indium from cadmium, zinc, copper and other metals present in lead, copper, and zinc dusts comprising:
a) leaching the dusts with strong sulfuric acid to form a leach solution containing indium, cadmium, zinc, copper and other metals;
b) adding ammomium hydroxide to the leach solution to a pH of at least 4.6; and c) filtering the solution to form a filter cake containing indium and a filtrate containing cadmium, zinc and copper.

2. A process as defined in Claim 1, wherein the con-centration of sulfuric acid is about 180-220 gpl and the temperature of the leach solution about 90-100°C.

3. A process as defined in Claim 1, wherein the dust contains significant amounts of copper and wherein precipitation of indium with ammomium hydroxide is done at a pH of 9.0 to more adequately separate copper, zinc and cadmium from indium.

4. A process as defined in Claim 1, 2 or 3, wherein the ammomium hydroxide precipitate is further refined by redissolving with strong sulfuric acid and re-precipitating with ammonium hydroxide to remove most of the remaining cadmium, zinc and copper from indium.

5. A process as defined in Claim 1, further comprising the steps of adding lime to the ammonium hydroxide filtrate, distilling the ammonium hydroxide filtrate to recover ammonia and filtering to produce a filter cake containing cadmium, copper and zinc and a filtrate which is discarded, or recycled.

6. A process as defined in Claim 5, wherein the ammonia distillate is recycled.

7. A process as defined in Claim 5, wherein the cake produced by the last mentioned filtering operation is sent to an electrolytic zinc refinery to be used as a neutralizing agent, with subsequent recovery of zinc, copper and cadmium by conventional means.