CA1331098C - Recovery of thallium - Google Patents
Recovery of thalliumInfo
- Publication number
- CA1331098C CA1331098C CA 566166 CA566166A CA1331098C CA 1331098 C CA1331098 C CA 1331098C CA 566166 CA566166 CA 566166 CA 566166 A CA566166 A CA 566166A CA 1331098 C CA1331098 C CA 1331098C
- Authority
- CA
- Canada
- Prior art keywords
- lead
- chloride
- thallium
- salt
- contained
- 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 - Lifetime
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
- C22B61/00—Obtaining metals not elsewhere provided for in this subclass
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
RECOVERY OF THALLIUM
Abstract Molten anhydrous chloride salt comprising a mixture of zinc chloride, thallous chloride, lead chloride, lead oxychloride and lead monoxide is poured into water to partially dissolve the salt and to disintegrate the undissolved portion of the salt. Sulphuric acid is added to the mixture to convert the contained lead to insoluble lead sulphate and to complete the dissolution of the contained zinc. The mixture is treated with chlorine, to oxidize the contained thallium to soluble thallic ion. Lead sulphate is removed from the mixture by filtration.
The filtrate is treated with a reducing agent, preferably sulphur dioxide or a soluble sulphite, to convert dissolved thallium ion to relatively insoluble thallous chloride. The thallous chloride product is filtered off, washed, dried and packaged. The filtrate, containing the zinc originally present in the chloride salt, and a minor proportion of the thallium, is treated to recover the contained thallium.
Abstract Molten anhydrous chloride salt comprising a mixture of zinc chloride, thallous chloride, lead chloride, lead oxychloride and lead monoxide is poured into water to partially dissolve the salt and to disintegrate the undissolved portion of the salt. Sulphuric acid is added to the mixture to convert the contained lead to insoluble lead sulphate and to complete the dissolution of the contained zinc. The mixture is treated with chlorine, to oxidize the contained thallium to soluble thallic ion. Lead sulphate is removed from the mixture by filtration.
The filtrate is treated with a reducing agent, preferably sulphur dioxide or a soluble sulphite, to convert dissolved thallium ion to relatively insoluble thallous chloride. The thallous chloride product is filtered off, washed, dried and packaged. The filtrate, containing the zinc originally present in the chloride salt, and a minor proportion of the thallium, is treated to recover the contained thallium.
Description
DESCRIPTION OF INVENTION
~331098 This invention relates to a method for removing and recovering thallium from spent molten chloride salt such as obtained from a lead purification process in which molten thallium-containing lead is contacted with molten anhydrous zinc chloride. The spent salt comprises a mixture of zinc chloride, thallo~s chloride, lead chloride, lead oxychloride and lead ~no~ide.
Thallium occurs in many lead ores as a minor constituent. In the recovery of lead from these ores, the thallium may tend to accompany the lead due to the chemical similarity of the two elements. If the thallium content is excessive, the lead may not meet purity standards. It then becomes necessary to find a method of removing thallium from lead.
Known methods for removing thallium from lead include the common step of contacting molten thallium-containing lead with a suitable molten chloride salt, such as zinc chloride, lead ~ ..
chloride, ammonium chloride or mixtures thereof. Thallium is extracted from the lead and accumulates in the molten salt.
Such known methods are disclosed in Polish Patent No. 46,715 ~Styrski, et al, 1963; CAS citation 59:14939b); in Japanese Patent Appl'n. No. 52/143,918 (Miyata, 1977; CAS citation 89:63103u); and in Japanese Patent Appl`n. No. 53/71,623 published June 26, 1978 (Sumita~ 1978; CAS citation 89:201055h).
1331~
3.
However, these references leave unsolved the problem of how to dispose of the spent thallium-enriched salt. Thallium is ~ highly toxic and should not be allowed to disperse into the environment.
Co-pending patent application Ser. No. 566,167 filed May 6, 1988 discloses an improved method and apparatus for removal of thallium from lead. The removal of thallium from lead with.the use of zinc chloride is carried out by contacting molten thallium-containing lead with an excess of molten zinc chloride at a temperature of about 400DC. Thallium is displaced from the lead and enters the molten salt where it accumulates as dissolved thallous chloride. In addition to thallous chloride and unreacted zinc chloride, the spent molten salt resulting fr~m this process contains lead chloride, lead oxychloride and lead monoxide. It is believed that zinc oxychloride may also be present in the mixture.
.'" '''' "
Typically, to lower the thallium content of lO00 kg of lead from an initial value of about lO0 ppm to a final value of about lO ppm, approximately l kg of fresh zinc chloride is used. The zinc chloride may contain up to 5 mole ~ lead chloride. The contact time required ranges from about l/2 hour to several hours, depending on the efficiency of the method used for contacting the lead and salt phases. The final spent ' ~, .~'":
. ~.
31~8 4.
salt weighs about 1.25 kg and contains, on a weight basis, about 6 to 7% thallium, 30 to 35% zinc, 20 to 25~ lec~d, 30 to 35% chlorine and 1 to 2% oxygen.
In separating the spent thallium-rich salt from the purified lead it is advantageous to maintain both phases in the molten state. Keeping the purified lead molten facilitates further processing, such as casting into anodes for electrorefining.
Keeping the spent salt molten and moving it to thallium recovery processing, immediately after separation from the lead, eliminates the storage and handling problems that would ., occur if the salt were allowed to solidify. Solidified spent salt is hygroscopic due to its zinc chloride content and rapidly begins to liquefy on exposure to the air.
An efficient method has been discovered for removing and recovering thallium from zinc chloride-based spent salt and for obtaining a concentrated thallium product which can be stored safely.
In the present invention, thallium recovery is initiated by pouring the molten spent salt into a volume of stirred water.
20 Quenching in this manner partially dissolves the salt and disintegrates the undissolved portion into fine particles. The mixture i6 then acidified to a p~ of about one by addition of , . ' ~,';
3 1 ~
5.
sulphuric acid. This neutralizes the oxidic lead and zinc species present, and precipitates substantially all of the lead contained in the mixture as insoluble lead sulphate and completes the dissolution of the contained zinc. The mixture is then treated with chlorine to oxidize the contained thallium to soluble thallic species. The mixture is filtered to remove the precipitated lead sulphate. The lead sulphate retains a small amount of thallium and is sent to lead smelting. The filtrate is treated with a reducing agent, such as sulphur dioxide or a soluble sulphite, to convert soluble thallic species to relatively insoluble thallous chloride. The thallous chloride product is filtered off, washed, dried and packaged for storage. The remaining filtrate contains the zinc originally present in the quenched salt and a minor proportion of the thallium. This filtrate is sent to effluent treatment where heavy metals are precipitated. The heavy-metal precipitate is sent to lead smelting.
In the reduction step, sulphur dioxide or a soluble sulphite may be usêd as the reducing agent. Sodium sulphite proved effective in laboratory tests. Sulphur dioxide would be preferred for plant-scale operation. Other moderately strong reducing agents, such as ammonium bisulphite or hydrazine, would be suitable.
" `' ~33~098 6.
In its broad aspect, the method of the invention for recovering thallium contained in a molten chloride salt containing zinc chloride, thallous chloride, lead chloride, lead oxychloride and lead monoxide comprises the steps of feeding the molten ~ -chloride salt to a bath of water for partial dissolution of the salt and disintergration of the undissolved portion of the said salt, adding an effective amount of sulphuric acid to the said bath to convert contained lead to insoluble lead sulphate and to complete dissolution of contained zinc, adding an effective amount of chlorine to oxidize contained thallium to soluble thallic ion, removing insoluble lead sulphate by filtration to produce a filtrate, subjecting the filtrate to reduction to convert said dissolved thallic ion to insoluble thallous chloride and removing thallous chloride by filtration for - :
subsequent recovery of thallium and to produce a filtrate containing zinc and residual thallium.
Sulphuric acid is added in an amount to acidify the bath to a ;
pH of about 1 and chlorine is added as chloride gas until the bath mixture is saturated with chloride. -~
The filtrate is subjected to reduction by the addition of an efféctive amount of a reducing agent selected from the group consisting of sulphur dioxide, sodium sulphite, ammonium bisulphite and hydrazine, preferably sulphur dioxide or soluble suphite. -~
~31~8 .. ~ .. -,. .
7.
The following example illustrates the application of the ;~ - -invention. - ~-'''.''''''' ''' Thallium-containing molten lead was contacted with molten zinc chloride containing about 5 mole ~ lead chloride. After 2 1/2 hours of contact at about 400C, the thallium-enriched spent salt was separated from the iead and allowed to solidify. The spent salt, weighing 1370 g and containing 4.9~ thallium, was re-melted by heating to 425C in a fireclay crucible and poured carefully into 2 litres of vigorously stirred cold water. A
temperature rise of 50 Celcuis degrees was observed. Part of the salt, comprising most of the zinc chloride content, dissolved. The undissolved part disintegrated to fine powder, held in suspension by stirring. To reduce the density of the slurry, 0.74 litre of water was addQd.
Concentrated 96~ sulphuric acid was added slowly to the mixture at 60C until a final pH value of 1.0 was reached, to provide complete dissolution of the remaining undissolved zinc and complete conversion of the contained lead to solid lead sulphate. The amount of acid required was 203 9.
'' Chlorine gas was then injected into the mixture at 60C, while monitoring the solution potential using a platinum electrode versus a standard calomel electrode. Chlorine addition was .. 13310g8 8.
continued until the mixture was saturated with chlorine, at a potential of + 1080 mv, ensuring complete oxidation of the contained thallium to soluble thallic ion. About 93 g of chlorine was used.
The mixture was filtered to remove lead sulphate. The lead sulphate, after washing and drying, weighed 743 g and retained 5~ of the thallium present in the initial chloride salt.
Solid sodium sulphite was added incrementally to the filtrate at 54C, while monitoring the solution potential and the thallium concentration. Thallous chloride precipitated until the potential had dropped to + 500 mv. Below this potential, no further precipitation occurred. A total of 41 g of sodium sulphite was used.
The thallous chloride product was filtered off, washed and dried. It weighed 739 and contained 83% thallium, representing 90~ of the thallium present in the initial chloride salt. The final filtrate contained 4% of the thallium present in the initial salt.
It will be understood that modifications can be made in the embodiment of the invention illustrated and described herein without departing from the scope and purview of the invention as defined by the appended claims.
..-:` "'" ', .': :''
~331098 This invention relates to a method for removing and recovering thallium from spent molten chloride salt such as obtained from a lead purification process in which molten thallium-containing lead is contacted with molten anhydrous zinc chloride. The spent salt comprises a mixture of zinc chloride, thallo~s chloride, lead chloride, lead oxychloride and lead ~no~ide.
Thallium occurs in many lead ores as a minor constituent. In the recovery of lead from these ores, the thallium may tend to accompany the lead due to the chemical similarity of the two elements. If the thallium content is excessive, the lead may not meet purity standards. It then becomes necessary to find a method of removing thallium from lead.
Known methods for removing thallium from lead include the common step of contacting molten thallium-containing lead with a suitable molten chloride salt, such as zinc chloride, lead ~ ..
chloride, ammonium chloride or mixtures thereof. Thallium is extracted from the lead and accumulates in the molten salt.
Such known methods are disclosed in Polish Patent No. 46,715 ~Styrski, et al, 1963; CAS citation 59:14939b); in Japanese Patent Appl'n. No. 52/143,918 (Miyata, 1977; CAS citation 89:63103u); and in Japanese Patent Appl`n. No. 53/71,623 published June 26, 1978 (Sumita~ 1978; CAS citation 89:201055h).
1331~
3.
However, these references leave unsolved the problem of how to dispose of the spent thallium-enriched salt. Thallium is ~ highly toxic and should not be allowed to disperse into the environment.
Co-pending patent application Ser. No. 566,167 filed May 6, 1988 discloses an improved method and apparatus for removal of thallium from lead. The removal of thallium from lead with.the use of zinc chloride is carried out by contacting molten thallium-containing lead with an excess of molten zinc chloride at a temperature of about 400DC. Thallium is displaced from the lead and enters the molten salt where it accumulates as dissolved thallous chloride. In addition to thallous chloride and unreacted zinc chloride, the spent molten salt resulting fr~m this process contains lead chloride, lead oxychloride and lead monoxide. It is believed that zinc oxychloride may also be present in the mixture.
.'" '''' "
Typically, to lower the thallium content of lO00 kg of lead from an initial value of about lO0 ppm to a final value of about lO ppm, approximately l kg of fresh zinc chloride is used. The zinc chloride may contain up to 5 mole ~ lead chloride. The contact time required ranges from about l/2 hour to several hours, depending on the efficiency of the method used for contacting the lead and salt phases. The final spent ' ~, .~'":
. ~.
31~8 4.
salt weighs about 1.25 kg and contains, on a weight basis, about 6 to 7% thallium, 30 to 35% zinc, 20 to 25~ lec~d, 30 to 35% chlorine and 1 to 2% oxygen.
In separating the spent thallium-rich salt from the purified lead it is advantageous to maintain both phases in the molten state. Keeping the purified lead molten facilitates further processing, such as casting into anodes for electrorefining.
Keeping the spent salt molten and moving it to thallium recovery processing, immediately after separation from the lead, eliminates the storage and handling problems that would ., occur if the salt were allowed to solidify. Solidified spent salt is hygroscopic due to its zinc chloride content and rapidly begins to liquefy on exposure to the air.
An efficient method has been discovered for removing and recovering thallium from zinc chloride-based spent salt and for obtaining a concentrated thallium product which can be stored safely.
In the present invention, thallium recovery is initiated by pouring the molten spent salt into a volume of stirred water.
20 Quenching in this manner partially dissolves the salt and disintegrates the undissolved portion into fine particles. The mixture i6 then acidified to a p~ of about one by addition of , . ' ~,';
3 1 ~
5.
sulphuric acid. This neutralizes the oxidic lead and zinc species present, and precipitates substantially all of the lead contained in the mixture as insoluble lead sulphate and completes the dissolution of the contained zinc. The mixture is then treated with chlorine to oxidize the contained thallium to soluble thallic species. The mixture is filtered to remove the precipitated lead sulphate. The lead sulphate retains a small amount of thallium and is sent to lead smelting. The filtrate is treated with a reducing agent, such as sulphur dioxide or a soluble sulphite, to convert soluble thallic species to relatively insoluble thallous chloride. The thallous chloride product is filtered off, washed, dried and packaged for storage. The remaining filtrate contains the zinc originally present in the quenched salt and a minor proportion of the thallium. This filtrate is sent to effluent treatment where heavy metals are precipitated. The heavy-metal precipitate is sent to lead smelting.
In the reduction step, sulphur dioxide or a soluble sulphite may be usêd as the reducing agent. Sodium sulphite proved effective in laboratory tests. Sulphur dioxide would be preferred for plant-scale operation. Other moderately strong reducing agents, such as ammonium bisulphite or hydrazine, would be suitable.
" `' ~33~098 6.
In its broad aspect, the method of the invention for recovering thallium contained in a molten chloride salt containing zinc chloride, thallous chloride, lead chloride, lead oxychloride and lead monoxide comprises the steps of feeding the molten ~ -chloride salt to a bath of water for partial dissolution of the salt and disintergration of the undissolved portion of the said salt, adding an effective amount of sulphuric acid to the said bath to convert contained lead to insoluble lead sulphate and to complete dissolution of contained zinc, adding an effective amount of chlorine to oxidize contained thallium to soluble thallic ion, removing insoluble lead sulphate by filtration to produce a filtrate, subjecting the filtrate to reduction to convert said dissolved thallic ion to insoluble thallous chloride and removing thallous chloride by filtration for - :
subsequent recovery of thallium and to produce a filtrate containing zinc and residual thallium.
Sulphuric acid is added in an amount to acidify the bath to a ;
pH of about 1 and chlorine is added as chloride gas until the bath mixture is saturated with chloride. -~
The filtrate is subjected to reduction by the addition of an efféctive amount of a reducing agent selected from the group consisting of sulphur dioxide, sodium sulphite, ammonium bisulphite and hydrazine, preferably sulphur dioxide or soluble suphite. -~
~31~8 .. ~ .. -,. .
7.
The following example illustrates the application of the ;~ - -invention. - ~-'''.''''''' ''' Thallium-containing molten lead was contacted with molten zinc chloride containing about 5 mole ~ lead chloride. After 2 1/2 hours of contact at about 400C, the thallium-enriched spent salt was separated from the iead and allowed to solidify. The spent salt, weighing 1370 g and containing 4.9~ thallium, was re-melted by heating to 425C in a fireclay crucible and poured carefully into 2 litres of vigorously stirred cold water. A
temperature rise of 50 Celcuis degrees was observed. Part of the salt, comprising most of the zinc chloride content, dissolved. The undissolved part disintegrated to fine powder, held in suspension by stirring. To reduce the density of the slurry, 0.74 litre of water was addQd.
Concentrated 96~ sulphuric acid was added slowly to the mixture at 60C until a final pH value of 1.0 was reached, to provide complete dissolution of the remaining undissolved zinc and complete conversion of the contained lead to solid lead sulphate. The amount of acid required was 203 9.
'' Chlorine gas was then injected into the mixture at 60C, while monitoring the solution potential using a platinum electrode versus a standard calomel electrode. Chlorine addition was .. 13310g8 8.
continued until the mixture was saturated with chlorine, at a potential of + 1080 mv, ensuring complete oxidation of the contained thallium to soluble thallic ion. About 93 g of chlorine was used.
The mixture was filtered to remove lead sulphate. The lead sulphate, after washing and drying, weighed 743 g and retained 5~ of the thallium present in the initial chloride salt.
Solid sodium sulphite was added incrementally to the filtrate at 54C, while monitoring the solution potential and the thallium concentration. Thallous chloride precipitated until the potential had dropped to + 500 mv. Below this potential, no further precipitation occurred. A total of 41 g of sodium sulphite was used.
The thallous chloride product was filtered off, washed and dried. It weighed 739 and contained 83% thallium, representing 90~ of the thallium present in the initial chloride salt. The final filtrate contained 4% of the thallium present in the initial salt.
It will be understood that modifications can be made in the embodiment of the invention illustrated and described herein without departing from the scope and purview of the invention as defined by the appended claims.
..-:` "'" ', .': :''
Claims (5)
1. A method for recovering thallium contained in a molten chloride salt containing zinc chloride, thallous chloride, lead chloride, lead oxychloride and lead monoxide comprising the steps of feeding the molten chloride salt to a bath of water for partial dissolution of the salt and disintegration of the undissolved portion of the said salt, adding an effective amount of sulphuric acid to the said bath to convert contained lead to insoluble lead sulphate and to complete dissolution of contained zinc, adding an effective amount of chlorine to oxidize contained thallium to soluble thallic ion, removing insoluable lead sulphate by filtration to produce a filtrate, subjecting the filtrate to reduction to convert said dissolved thallic ion to insoluble thallous chloride and removing thallous chloride by filtration for subsequent recovery of thallium and to produce a filtrate containing zinc.
2. A method as claimed in claim 1 in which sulphuric acid is added in an amount to acidify the bath to a pH of about 1.
3. A method as claimed in claim 2 in which chlorine is added as chlorine gas until the bath mixture is saturated with chlorine.
4. A method as claimed in claim 3 in which the filtrate is subjected to reduction by the addition of an effective amount of a reducing agent selected from the group consisting of sulphur dioxide, sodium sulphite, ammonium bisulphite and hydrazine.
5. A method as claimed in claim 3 in which the filtrate is subjected to reduction by the addition of an effective amount of sulphur dioxide.
10,
10,
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 566166 CA1331098C (en) | 1988-05-06 | 1988-05-06 | Recovery of thallium |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 566166 CA1331098C (en) | 1988-05-06 | 1988-05-06 | Recovery of thallium |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1331098C true CA1331098C (en) | 1994-08-02 |
Family
ID=4137981
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 566166 Expired - Lifetime CA1331098C (en) | 1988-05-06 | 1988-05-06 | Recovery of thallium |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1331098C (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108565439A (en) * | 2018-05-28 | 2018-09-21 | 河南工程学院 | A kind of preparation method of hydration lead oxychloride micro-nano structure crystal |
| CN117778772A (en) * | 2023-12-28 | 2024-03-29 | 常熟理工学院 | Method for recycling thallium in thallium-containing sludge by utilizing waste incineration fly ash and product thereof |
-
1988
- 1988-05-06 CA CA 566166 patent/CA1331098C/en not_active Expired - Lifetime
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108565439A (en) * | 2018-05-28 | 2018-09-21 | 河南工程学院 | A kind of preparation method of hydration lead oxychloride micro-nano structure crystal |
| CN108565439B (en) * | 2018-05-28 | 2020-10-02 | 河南工程学院 | Preparation method of hydrated lead oxychloride micro-nano structure crystal |
| CN117778772A (en) * | 2023-12-28 | 2024-03-29 | 常熟理工学院 | Method for recycling thallium in thallium-containing sludge by utilizing waste incineration fly ash and product thereof |
| CN117778772B (en) * | 2023-12-28 | 2024-08-30 | 常熟理工学院 | Method for recycling thallium in thallium-containing sludge by utilizing waste incineration fly ash and product thereof |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed | ||
| MKEC | Expiry (correction) |
Effective date: 20121205 |