CA1040867A - Separation of iron from zinc solutions or slurries - Google Patents
Separation of iron from zinc solutions or slurriesInfo
- Publication number
- CA1040867A CA1040867A CA207,567A CA207567A CA1040867A CA 1040867 A CA1040867 A CA 1040867A CA 207567 A CA207567 A CA 207567A CA 1040867 A CA1040867 A CA 1040867A
- Authority
- CA
- Canada
- Prior art keywords
- solution
- iron
- oxidation
- sulfur dioxide
- oxygen
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B19/00—Obtaining zinc or zinc oxide
- C22B19/20—Obtaining zinc otherwise than by distilling
- C22B19/26—Refining solutions containing zinc values, e.g. obtained by leaching zinc ores
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
ABSTRACT OF THE DISCLOSURE
To enable its removal down to very low levels from zinc sulfate solutions or slurries, iron is oxidized to the ferric state by using sulfur dioxide/oxygen mixtures under specified conditions.
To enable its removal down to very low levels from zinc sulfate solutions or slurries, iron is oxidized to the ferric state by using sulfur dioxide/oxygen mixtures under specified conditions.
Description
~04Q8~7 The present invention relates to improvements in a process for the separation of iron from zinc solutions or slurries.
In the hydrometallurgical production of zinc a zinc sulfate liquor is produced by leaching the "calcine"
(essentially zinc oxide) resulting from the roasting of sulfide ores. This liquor usually contains some iron and prior to the electrowinning of zinc from the liquor it is necessary to remove any iron present. In general, the removal of iron involves firstly the oxidation of any ferrous iron to the ferric state and subsequently preci-pitation of the ferric iron.
A known method of oxidizing ferrous iron to ferric iron in ~olutions such as nickel and cobalt sulfates involves the use of sulfur dioxide/oxygen mixtures. This method is described in U.S. Patent No. 2,816,819. However while this method is well-known in the context of the extraction of nickel or cobalt, it has never been considered in the context of zinc production. This may be due to the 2Q fear of build up of sulfate ions in the electrolyte which is continuously recirculated during the leaching/electro-winning process.
Whatever the reasons may be, it is a fact thatthe oxidation process described in U.S. Patent No. 2,816,819, has never been advocated for use in zinc solutions or slurries and thus its effectiveness in enabling the removal of iron down to the desired very low levels in such media has never heretofore been determined. Instead in present zinc refining practice the oxidation of ferrous iron is commonly performed with the aid of manganese dioxide. While the cost ,, ' , 104~)8f~
of this oxidant is low, a practical disadvantage of the procesQ is the tendency for the liquor to pick up manga-nese which subsequently precipitates anodically during the electrowinning.
Alternative oxidants for achieving the ~errous to ferric oxidation include potassium permanganate but this has not gained widespread use for economic reasons.
The use of air as an oxidant ha~ been considered but it has been reported that practicable rates of oxidàtion are achieved only at pH values of 5 or more. Working at such pH's is undesirable due to the possibility of hydro-lizing any copper values present.
It has been no~ found that suitably chosen gaseous mixtures of sulfur dioxide and oxygen are capable of oxidizing the iron in a zinc sulfate liquor or slurry at a practicable rate, provide an improved method of oxidizing the iron to enable its removal down to very low levels without introducing undesirable ions, such as manganese, into the system. Moreover it has been found that the use of such gaseous mixtures does not cause significant suIfate ion build up, and that any build up which does occur aan be controlled bleeding such as precipitation of calcium sulfate, or preferably precipitation of some or all of the oxidized iron as a basic ferric sulfate.
According to the invention, in a process for separating iron from a zinc sulfate solution or slurry wherein any ferrous iron present is converted to ferric iron and thereafter separated by precipitation, the im- -provement comprises adjusting the solution pH, if necessary, to a value between 0.5 and 4.0 and the solution temperature 104~)8~7 to at least 50C while contacting the solution with a gaseous mixture containing oxygen and sulfur dioxide, the volume ratio of oxygen to sulfur dioxide being between 400:1 and 1:1, to effect oxidation of the iron.
The sulfur dioxide~oxygen mixture is effective for oxidizing iron whether the lattex be entirely in solution or wholly or partly in ~olid form as a precipitate in the slurry. While a wide range of gas mixture composi-tions can be used for the oxidation, i.e. an oxygen to sulfur dioxide ratio from as low as 400:1 to as high as the theoretical maximum of 1:1, the reaction kinetics may be unsatisfactory at very low sulfur dioxide contents. A
preferred gas composition is one where the oxygen to sulfur dioxide ratio ~ls betweeh 39:1 and 9:1, e.g. a gas mixture containing 5~ by volume of sulfur dioxide, the balance being oxygen.
The solution should be maintained at a temperature of at least 50C, commensurate with a satisfactory reaction rate. In general temperatures within the range 85C-95a~.
Advantageously the pH of the solution is adjusted to a value of from 1.8 to 3Ø
Where the pH of the solution is maintained at a value of 3.5 or higher during the oxidation, the ferric iron will precipitate in the course of the oxidation as a hydroxide. Where the pH is maintained during the oxidation at a value of say 1.8-~.0, it is necessary to adjust the pH subsequent to oxidation in order to precipitate the oxidized iron. This adjustment may consist of adding calcine or otheswise raising the pH to 3.5 to precipitate ~erric h~xxldo, Alternatively, the solution can be .
~, . ,, , , ~
acidified to a pH of 1.5 or less in the presence of potassium, sodium or ammonium ions thereby precipitating a basic ferric sulfate.
According to one aspect of the present invention substantially all the oxidized iron is precipitated as a hydroxide. If this process is used on a continuous basis whereby the spent solution is recycled to the leaching operation, there is a need for preventing sulfate build up in the solution. This tends to occur because of the presence of some zinc sulfate in the calcine, and, possibly to a slight extent, because of the use of sulfur dioxide/oxygen mixtures for the oxidation. In order to control the sulfate ion level in the recycled solution, recourse is had to selective bleeding operations where sulfate is precipitated, for example as gypsum by adding lime to the solution, or as a basic ferric sulfate as described above.
According to another aspect of the invention substantially all the iron present is precipitated as a basic ferrisulfate. The conditions for effecting such a precipitation are well ~nown and are described, for example, in U.S. Patent No. 3,434,947. Such a precipitation causes the liquid to become depleted with respect to sulfate ions.
Therefore, if the liquid is to be recirculated continuously in the leaching/electrowinning cycle, it will be necessary from time to time to replenish the electrolyte by addition of sulfuric acid thereto. ~-According to yet another aspect of the invention, the iron present is precipitated a~ basic ferrisulfate only to an extent sufficient to maintain the sulfate ion : . , , 1046)867 concentration in the electrolyte constant at the desired level. According to this aspect of the invention a sufficient amount of basic ferri~ulfate is precipitated to counteract the tendency for sulfate build up. The remainder of the iron is precipitated as a hydroxide by raising the pH of the liquid to about 3.5 at the completion of the oxidizing step.
The invention will now be particularly described with reference to specific examples.
A clear solution was used, containing approximately 100 g/l of zinc, 2 g/l of manganese and 2 g/l of ammonium ions in a sulfate medium. U~ing 1 litre of this solution a gaseous mixture having the composition of 5-10% by volume of sulfur dioxide, balance oxygen, was bubbled through the solution at a flow rate corresponding to 200 ml/minute of oxygen. The temperature was maintained at 85C during the oxidation process which lasted two hours. The solution pH dropped in the course of the process from an initial value of 2.7 to a final value of 1.8.
The ferrous ions concentration was reduced in the course of the proce~s from 5.9 g/l to trace level. At the end of the oxidation proces~ the pH was increased to 3.5 by addition of calcine. Following precipitation of the ferric ions, the solution was analyzed for iron and found to contain only a trace level thereof.
In these examples a slurry was used which comprised a liquor having a ~imilar composition to the solution of Example 1 and containing the solid residue from a calcine leach.
" , : :
,,' ~ ' ' ' ' ., . , ' ' :' . . . :, ~)4l~867 The details of the oxidation conditions are ~hown in the following Table 1, unspecified conditions being identical to those of Example 1.
% S2 in Duration ~Temp gas mix- of oxida- pH ~e - (g/l) ,E~le C ture ,tion (hrs) Initial ~inal Initial nal
In the hydrometallurgical production of zinc a zinc sulfate liquor is produced by leaching the "calcine"
(essentially zinc oxide) resulting from the roasting of sulfide ores. This liquor usually contains some iron and prior to the electrowinning of zinc from the liquor it is necessary to remove any iron present. In general, the removal of iron involves firstly the oxidation of any ferrous iron to the ferric state and subsequently preci-pitation of the ferric iron.
A known method of oxidizing ferrous iron to ferric iron in ~olutions such as nickel and cobalt sulfates involves the use of sulfur dioxide/oxygen mixtures. This method is described in U.S. Patent No. 2,816,819. However while this method is well-known in the context of the extraction of nickel or cobalt, it has never been considered in the context of zinc production. This may be due to the 2Q fear of build up of sulfate ions in the electrolyte which is continuously recirculated during the leaching/electro-winning process.
Whatever the reasons may be, it is a fact thatthe oxidation process described in U.S. Patent No. 2,816,819, has never been advocated for use in zinc solutions or slurries and thus its effectiveness in enabling the removal of iron down to the desired very low levels in such media has never heretofore been determined. Instead in present zinc refining practice the oxidation of ferrous iron is commonly performed with the aid of manganese dioxide. While the cost ,, ' , 104~)8f~
of this oxidant is low, a practical disadvantage of the procesQ is the tendency for the liquor to pick up manga-nese which subsequently precipitates anodically during the electrowinning.
Alternative oxidants for achieving the ~errous to ferric oxidation include potassium permanganate but this has not gained widespread use for economic reasons.
The use of air as an oxidant ha~ been considered but it has been reported that practicable rates of oxidàtion are achieved only at pH values of 5 or more. Working at such pH's is undesirable due to the possibility of hydro-lizing any copper values present.
It has been no~ found that suitably chosen gaseous mixtures of sulfur dioxide and oxygen are capable of oxidizing the iron in a zinc sulfate liquor or slurry at a practicable rate, provide an improved method of oxidizing the iron to enable its removal down to very low levels without introducing undesirable ions, such as manganese, into the system. Moreover it has been found that the use of such gaseous mixtures does not cause significant suIfate ion build up, and that any build up which does occur aan be controlled bleeding such as precipitation of calcium sulfate, or preferably precipitation of some or all of the oxidized iron as a basic ferric sulfate.
According to the invention, in a process for separating iron from a zinc sulfate solution or slurry wherein any ferrous iron present is converted to ferric iron and thereafter separated by precipitation, the im- -provement comprises adjusting the solution pH, if necessary, to a value between 0.5 and 4.0 and the solution temperature 104~)8~7 to at least 50C while contacting the solution with a gaseous mixture containing oxygen and sulfur dioxide, the volume ratio of oxygen to sulfur dioxide being between 400:1 and 1:1, to effect oxidation of the iron.
The sulfur dioxide~oxygen mixture is effective for oxidizing iron whether the lattex be entirely in solution or wholly or partly in ~olid form as a precipitate in the slurry. While a wide range of gas mixture composi-tions can be used for the oxidation, i.e. an oxygen to sulfur dioxide ratio from as low as 400:1 to as high as the theoretical maximum of 1:1, the reaction kinetics may be unsatisfactory at very low sulfur dioxide contents. A
preferred gas composition is one where the oxygen to sulfur dioxide ratio ~ls betweeh 39:1 and 9:1, e.g. a gas mixture containing 5~ by volume of sulfur dioxide, the balance being oxygen.
The solution should be maintained at a temperature of at least 50C, commensurate with a satisfactory reaction rate. In general temperatures within the range 85C-95a~.
Advantageously the pH of the solution is adjusted to a value of from 1.8 to 3Ø
Where the pH of the solution is maintained at a value of 3.5 or higher during the oxidation, the ferric iron will precipitate in the course of the oxidation as a hydroxide. Where the pH is maintained during the oxidation at a value of say 1.8-~.0, it is necessary to adjust the pH subsequent to oxidation in order to precipitate the oxidized iron. This adjustment may consist of adding calcine or otheswise raising the pH to 3.5 to precipitate ~erric h~xxldo, Alternatively, the solution can be .
~, . ,, , , ~
acidified to a pH of 1.5 or less in the presence of potassium, sodium or ammonium ions thereby precipitating a basic ferric sulfate.
According to one aspect of the present invention substantially all the oxidized iron is precipitated as a hydroxide. If this process is used on a continuous basis whereby the spent solution is recycled to the leaching operation, there is a need for preventing sulfate build up in the solution. This tends to occur because of the presence of some zinc sulfate in the calcine, and, possibly to a slight extent, because of the use of sulfur dioxide/oxygen mixtures for the oxidation. In order to control the sulfate ion level in the recycled solution, recourse is had to selective bleeding operations where sulfate is precipitated, for example as gypsum by adding lime to the solution, or as a basic ferric sulfate as described above.
According to another aspect of the invention substantially all the iron present is precipitated as a basic ferrisulfate. The conditions for effecting such a precipitation are well ~nown and are described, for example, in U.S. Patent No. 3,434,947. Such a precipitation causes the liquid to become depleted with respect to sulfate ions.
Therefore, if the liquid is to be recirculated continuously in the leaching/electrowinning cycle, it will be necessary from time to time to replenish the electrolyte by addition of sulfuric acid thereto. ~-According to yet another aspect of the invention, the iron present is precipitated a~ basic ferrisulfate only to an extent sufficient to maintain the sulfate ion : . , , 1046)867 concentration in the electrolyte constant at the desired level. According to this aspect of the invention a sufficient amount of basic ferri~ulfate is precipitated to counteract the tendency for sulfate build up. The remainder of the iron is precipitated as a hydroxide by raising the pH of the liquid to about 3.5 at the completion of the oxidizing step.
The invention will now be particularly described with reference to specific examples.
A clear solution was used, containing approximately 100 g/l of zinc, 2 g/l of manganese and 2 g/l of ammonium ions in a sulfate medium. U~ing 1 litre of this solution a gaseous mixture having the composition of 5-10% by volume of sulfur dioxide, balance oxygen, was bubbled through the solution at a flow rate corresponding to 200 ml/minute of oxygen. The temperature was maintained at 85C during the oxidation process which lasted two hours. The solution pH dropped in the course of the process from an initial value of 2.7 to a final value of 1.8.
The ferrous ions concentration was reduced in the course of the proce~s from 5.9 g/l to trace level. At the end of the oxidation proces~ the pH was increased to 3.5 by addition of calcine. Following precipitation of the ferric ions, the solution was analyzed for iron and found to contain only a trace level thereof.
In these examples a slurry was used which comprised a liquor having a ~imilar composition to the solution of Example 1 and containing the solid residue from a calcine leach.
" , : :
,,' ~ ' ' ' ' ., . , ' ' :' . . . :, ~)4l~867 The details of the oxidation conditions are ~hown in the following Table 1, unspecified conditions being identical to those of Example 1.
% S2 in Duration ~Temp gas mix- of oxida- pH ~e - (g/l) ,E~le C ture ,tion (hrs) Initial ~inal Initial nal
2 85 5-10 1.0 2.4 2.4 1.18 0.083
3 85 2.5 2.5 2.3 2.7 2.95 0.012
4 952.5-5.0 1.1 2.5 2.5 4.17 2.57 952.5-10 0.75 3.0 3.0 2.57 1.22 6 95 5.0 0.5 3.0 3.0 0.232 Trace -It will be seen that in all cases the ferrous ion concentration was substantially reduced.
In the caqe of Ex~mple 6, it was possible to dis- '~
continue the gas flow after half an hour since continuous monitoring of the Redox potential (using a platinum electrode and a standard calomel electrode) showed a change from + 200 to + 630 mV, indicating a very high ferric to ferrous ratio. This was confirmed by analysi~ which revealed only a trace level of ferrous ions.
A measure of the effectiveness of the gas mixture can be derived by calculating the oxidation rate (grams of ferrous ions per litre per hour). This figure can then be ,~
compared with the theoretical oxidation rate derived from ' '"
. .
1~40867 the flow rate of gas mixture and its composition. The results of such comparisons for each of the Examples 1-6 are expressed as "efficiency of gaseous mixture (~)"
in Table 2 below.
Efficiency Oxidation of Gaseous Example Rate ~g/l hr)Mixture (~) l 2.95 78 2 1.10 29 3 0.74 100 approx.
4 1.40 63 1.80 62 6 0.46 16.
It will be seen from the above that sulfur dioxide/oxygen mixtures can be very effective for the oxidation of ferrous ions in zinc sulfate solutions or slurries.
It will be understood that where the precipita-tion of basic sulfate is ùsed to remove all the iron from the solution, the resulting depletion of the solution with respect to sulfate ions may necessitate addition of the latter.
Alternately the iron can be removed after its oxidation by precipi~ation of both hydroxide and basic :
sulfate, in balanced amounts, so as to maintain the desired sulfate level in the electrolyte.
' ' ~ .
.. ... .
, . . . . . . .
In the caqe of Ex~mple 6, it was possible to dis- '~
continue the gas flow after half an hour since continuous monitoring of the Redox potential (using a platinum electrode and a standard calomel electrode) showed a change from + 200 to + 630 mV, indicating a very high ferric to ferrous ratio. This was confirmed by analysi~ which revealed only a trace level of ferrous ions.
A measure of the effectiveness of the gas mixture can be derived by calculating the oxidation rate (grams of ferrous ions per litre per hour). This figure can then be ,~
compared with the theoretical oxidation rate derived from ' '"
. .
1~40867 the flow rate of gas mixture and its composition. The results of such comparisons for each of the Examples 1-6 are expressed as "efficiency of gaseous mixture (~)"
in Table 2 below.
Efficiency Oxidation of Gaseous Example Rate ~g/l hr)Mixture (~) l 2.95 78 2 1.10 29 3 0.74 100 approx.
4 1.40 63 1.80 62 6 0.46 16.
It will be seen from the above that sulfur dioxide/oxygen mixtures can be very effective for the oxidation of ferrous ions in zinc sulfate solutions or slurries.
It will be understood that where the precipita-tion of basic sulfate is ùsed to remove all the iron from the solution, the resulting depletion of the solution with respect to sulfate ions may necessitate addition of the latter.
Alternately the iron can be removed after its oxidation by precipi~ation of both hydroxide and basic :
sulfate, in balanced amounts, so as to maintain the desired sulfate level in the electrolyte.
' ' ~ .
.. ... .
, . . . . . . .
Claims (6)
1. In a process for separating iron from a zinc sulfate solution or slurry wherein any ferrous iron present is converted to ferric iron and thereafter separated by precipitation, the improvement comprising adjusting the solution pH, if necessary, to a value between 0.5 and 4.0 and the solution temperature to at least 50°C while contact-ing the solution with a gaseous mixture containing oxygen and sulfur dioxide, the volume ratio of oxygen. to sulfur dioxide being between 400:1 and 1:1, to effect oxidation of the iron.
2. A process according to claim 1 wherein the solution pH is maintained at 1.8 to 3.0 during the oxidation of the iron.
3. A process according to claim 1 wherein said contacting the solution with a gaseous mixture comprises bubbling an oxygen/sulfur dioxide mixture through the solution, the volume ratio of oxygen to sulfur dioxide being between 39:1 and 9:1.
4. A process according to claim 1 wherein after the oxidation at least part of the ferric iron is precipitated as a basic sulfate by adjusting the solution pH to a value below 1.5 in the presence of added ions from the group potassium, sodium and ammonium.
5. A process according to claim 4 wherein the remainder of the ferric iron is precipitated as a hydroxide by raising the pH of the solution to a value of at least 3.5, the relative amounts of hydroxide and basic sulfate precipitated being balanced so as to maintain the sulfate ion concentration in the solution substantially constant.
6. A process according to claim 1 wherein the tempera-ture of the solution is maintained at a value between 85 and 95°C during the oxidation of the iron.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA207,567A CA1040867A (en) | 1974-08-22 | 1974-08-22 | Separation of iron from zinc solutions or slurries |
| GB7820/75A GB1494564A (en) | 1974-08-22 | 1975-02-25 | Separation of iron from zinc-containing solutions |
| RO7581769A RO67416A (en) | 1974-08-22 | 1975-03-24 | PROCEDURE FOR DISSOLUTION OF SOLUBLE FIRE OR ZINC POLL |
| BE155632A BE828218A (en) | 1974-08-22 | 1975-04-22 | IMPROVEMENTS FOR THE SEPARATION OF IRON IN ZINC SOLUTIONS OR WHEELS |
| FR7525736A FR2282477A1 (en) | 1974-08-22 | 1975-08-20 | IMPROVEMENTS FOR THE SEPARATION OF IRON IN ZINC SOLUTIONS OR SLUDGE |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA207,567A CA1040867A (en) | 1974-08-22 | 1974-08-22 | Separation of iron from zinc solutions or slurries |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1040867A true CA1040867A (en) | 1978-10-24 |
Family
ID=4100945
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA207,567A Expired CA1040867A (en) | 1974-08-22 | 1974-08-22 | Separation of iron from zinc solutions or slurries |
Country Status (5)
| Country | Link |
|---|---|
| BE (1) | BE828218A (en) |
| CA (1) | CA1040867A (en) |
| FR (1) | FR2282477A1 (en) |
| GB (1) | GB1494564A (en) |
| RO (1) | RO67416A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1594851A (en) * | 1977-05-16 | 1981-08-05 | Interox Chemicals Ltd | Extraction of zinc |
| US6391270B1 (en) * | 1999-12-23 | 2002-05-21 | Noranda Inc. | Method for removing manganese from acidic sulfate solutions |
| FR2805281B1 (en) * | 2000-02-23 | 2002-09-27 | Recupac | PROCESS FOR RECOVERING STEEL DUST |
| WO2010057274A1 (en) * | 2008-11-24 | 2010-05-27 | Bhp Billiton Olympic Dam Corporation Pty Ltd | Process for controlled oxidation of a ferrous solution |
-
1974
- 1974-08-22 CA CA207,567A patent/CA1040867A/en not_active Expired
-
1975
- 1975-02-25 GB GB7820/75A patent/GB1494564A/en not_active Expired
- 1975-03-24 RO RO7581769A patent/RO67416A/en unknown
- 1975-04-22 BE BE155632A patent/BE828218A/en unknown
- 1975-08-20 FR FR7525736A patent/FR2282477A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| RO67416A (en) | 1982-02-26 |
| BE828218A (en) | 1975-10-22 |
| FR2282477A1 (en) | 1976-03-19 |
| GB1494564A (en) | 1977-12-07 |
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