CA1257019A - Method of cyanide destruction - Google Patents
Method of cyanide destructionInfo
- Publication number
- CA1257019A CA1257019A CA000490821A CA490821A CA1257019A CA 1257019 A CA1257019 A CA 1257019A CA 000490821 A CA000490821 A CA 000490821A CA 490821 A CA490821 A CA 490821A CA 1257019 A CA1257019 A CA 1257019A
- Authority
- CA
- Canada
- Prior art keywords
- sludge
- copper sulphate
- treatment vessel
- treatment
- clarifier
- 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
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- Treatment Of Water By Oxidation Or Reduction (AREA)
- Treatment Of Sludge (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An improved method for the destruction of cyanide in waste waters is provided, wherein cyanide is oxidized by hydrogen peroxide in the presence of copper as catalyst.
The treatment is carried out in a suitable vessel under agitation to which hydrogen peroxide and copper sulphate are fed with the waste waters, and the waters from the vessel are discharged into a clarifier where sludge is formed at the bottom. This sludge is then recycled to the treatment vessel in lieu of at least part of the copper sulphate. The operation is carried out at the natural temperature of the waste waters, i.e. between about 0°C
and 20°C.
An improved method for the destruction of cyanide in waste waters is provided, wherein cyanide is oxidized by hydrogen peroxide in the presence of copper as catalyst.
The treatment is carried out in a suitable vessel under agitation to which hydrogen peroxide and copper sulphate are fed with the waste waters, and the waters from the vessel are discharged into a clarifier where sludge is formed at the bottom. This sludge is then recycled to the treatment vessel in lieu of at least part of the copper sulphate. The operation is carried out at the natural temperature of the waste waters, i.e. between about 0°C
and 20°C.
Description
125~0~9 METHOD OF CYANIDE DESTRUCTION
This invention relates to an improved method for the destruction of cyanide in waste waters which contain unacceptably high levels thereof, such as effluents or tails from gold and silver mill operations. The invention particularly relates to those effluent treatments wherein cyanide is oxidized using hydrogen peroxide in the presence of copper as catalyst.
It is already known to oxidize cyanide by H2O2 in aqueous solutions where copper is added as a catalyst.
For example, U. S. Patent No. 3,617,567 discloses a process for the destruction of cyanide in aqueous solutions using hydrogen peroxide and a soluble metal compound catalyst such as Cu, which is used in a concentration of from about 5 to 1,000 ppm. The solution in this case must be maintained at a pH between about 8.3 and 11 and at a temperature of about 20C to 75C to achieve the desired destruction of cyanide anions.
In such a process the cost of the copper catalyst (which is usually copper sulphate because this is the cheapest and most readily available copper compound soluble in water) represents a very significant portion of the total reagent costs. For example, the annual reagent costs to treat 200 m3/h of reclaim water containing 10 ppm of cyanide would be about Can. $ 300,000 for H2O2 plus copper sulphate treatment. If copper sulphate ,.
1~5~J0~9
This invention relates to an improved method for the destruction of cyanide in waste waters which contain unacceptably high levels thereof, such as effluents or tails from gold and silver mill operations. The invention particularly relates to those effluent treatments wherein cyanide is oxidized using hydrogen peroxide in the presence of copper as catalyst.
It is already known to oxidize cyanide by H2O2 in aqueous solutions where copper is added as a catalyst.
For example, U. S. Patent No. 3,617,567 discloses a process for the destruction of cyanide in aqueous solutions using hydrogen peroxide and a soluble metal compound catalyst such as Cu, which is used in a concentration of from about 5 to 1,000 ppm. The solution in this case must be maintained at a pH between about 8.3 and 11 and at a temperature of about 20C to 75C to achieve the desired destruction of cyanide anions.
In such a process the cost of the copper catalyst (which is usually copper sulphate because this is the cheapest and most readily available copper compound soluble in water) represents a very significant portion of the total reagent costs. For example, the annual reagent costs to treat 200 m3/h of reclaim water containing 10 ppm of cyanide would be about Can. $ 300,000 for H2O2 plus copper sulphate treatment. If copper sulphate ,.
1~5~J0~9
-2-additions were decreased by 50% the annual costs would be reduced to Can. $ 220,000, a saving of Can. $ 80,000.
The principal obj ect of the present invention is, therefore, to achieve a substantial reduction of copper sulphate additions within the H202 cyanide oxidizing systems, while performing the same or improved cyanide destruction operation.
A further object of the present invention is to provide a continuous cyanide destruction process which can operate at the natural temperatures of the waste waters twithout preheating~, i.e. between about 0C and 20C, at a satisfactory rate.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, at least a portion of the copper sulphate reagent required for the treatment of the waste waters to remove excess cyanide with the use of hydrogen peroxide is withdrawn by recycling to the treatment vessel the sludge from the clarifier into which the waste waters are discharged after treatment. This treatment of waste waters can be carried out at the natural temperatures of such waste waters, namely between ooc and 20C and a pH of about 6 to 10.5. The weight ratio of H202 to CN normally required during treatment is between about 2:1 and 4:1 and that of Cu to CN - between about 0.1:1 and 2:1 or a Cu content of between about 5 ~ 25~019
The principal obj ect of the present invention is, therefore, to achieve a substantial reduction of copper sulphate additions within the H202 cyanide oxidizing systems, while performing the same or improved cyanide destruction operation.
A further object of the present invention is to provide a continuous cyanide destruction process which can operate at the natural temperatures of the waste waters twithout preheating~, i.e. between about 0C and 20C, at a satisfactory rate.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, at least a portion of the copper sulphate reagent required for the treatment of the waste waters to remove excess cyanide with the use of hydrogen peroxide is withdrawn by recycling to the treatment vessel the sludge from the clarifier into which the waste waters are discharged after treatment. This treatment of waste waters can be carried out at the natural temperatures of such waste waters, namely between ooc and 20C and a pH of about 6 to 10.5. The weight ratio of H202 to CN normally required during treatment is between about 2:1 and 4:1 and that of Cu to CN - between about 0.1:1 and 2:1 or a Cu content of between about 5 ~ 25~019
-3-and 100 ppm. Thus, in accordance with the present invention, rather than using fresh CuS04 as catalyst for the treatment, at least a portion of this reagent can be replaced by the sludge from the clarifier which, it has been found, contains a copper compound, believed to be copper hydroxide (Cu(OH)2), produced during the treatment operation. This sludge can, therefore, be effectively recycled and reused to replace all or a portion of the required copper reagent, thereby resulting in considerable savings as already mentioned above. It is also surprising that such operation can be carried out at temperatures between about 0C and 20~C rather than at higher temperatures as indicated in U. S. Patent No. 3,617,567.
This makes it possible to operate at a natural temperature of the waste waters, without pre-heating, resulting in additional operating savings.
Thus, the present invention provides a novel method for the destruction of cyanide in waste waters containing unacceptably high levels thereof, which comprises: feeding said waste waters into a suitable treatment vessel under agitation; controllably introducing hydrogen peroxide into said treatment vessel in such amount as to oxidize sufficient cyanide and thereby reduce its content to an acceptable level; and adding sufficient copper sulphate into said treatment vessel to catalyse the reaction; the waters from the treatment vessel being discharged to a ~ 2~01~3 clarifier where sludge is formed at the bottom, which sludge is recycled to the treatment vessel in lieu of at least part of the required copper sulphate. The operation is preferably carried out at a pH between 6 and 10.5 and at a natural temperature of the waste waters. If the pH
drops below the desired level, it can be raised to such level by addition of lime or a similar alkaline material as is well known in the art. The hydrogen peroxide can be added as a 30-70% H202 solution of commercial grade.
The agitation of the treatment vessel may also be carried out or assisted by air sparging.
The residence time of the waste waters in the treatment vessel depends on many factors, such as the temperature at which the treatment is carried out, the size of the vessels compared to the feed rate of the solution, the levels of cyanide in the feed and, of course, the final acceptable level of cyanide which must be achieved by the treatment and which, in most cases, is below 1 ppm. The usual retention time is of the order of ~ to 1 hr.
Moreover, instead of one treatment vessel, there may be used a plurality of such vessels in series.
The present invention will now be described with reference to the appended drawing which illustrates schematically the novel method.
As shown in the drawing, tank 10 is provided as the treatment vessel and it is agitated by stirring means 11.
12~i~019 Into this tank the waste water is fed together with appropriate quantities H202 and CUSO4, and the tank is agitated for a sufficient period of time to reduce the amount of cyanide in the waste water to an acceptable level. Once this is achieved, the waters from the tank are discharged to a clarifier 12 to which a flocculant is also added as is well known in the art. In the clarifier, the sludge accumulates at the bottom which contains a source of Cu which is believed to be Cu(OH)2 produced by reaction of originally employed CuS04. The sludge is then recycled to tank 10 to replace all or part of the CUSO4.
It should be noted that CuS04 can always be used to supplement the Cu requirement if the amount of Cu in the sludge is insufficient. Such CuS04 can be added directly into the tank or into the sludge or waste water conduits, as desired.
As already mentioned, instead of one tank 10, several such tanks in series can be used and also instead of clarifier 12 any other suitable equipment which will ; 20 produce the desired sludge can be employed. Any excess sludge from the clarifier can be returned back to the clarifier and/or sent to disposal as shown in the drawing.
Also, the clarifier overflow is sent to disposal or to further treatment which may be required to remove other impurities present in the waste waters.
The novel system may be operated batchwise or 12~
continuously, but the preferred mode is a continuous operation.
EXAMPLE
Hemlo reclaim water, (CN: 2 ppm) which is the water from the tailings pond at the Hemlo Golden Giant gold mill, was charged into a 150 m3 tank at the rate of 350 m3/hr. The temperature of the water depends on the time of the year when treatment takes place, but at the time of this test it was about 10C. The pH of the reclaim water was about 9.
A 35% solution of H202 was added at a rate of 6 liters/hr and Cu~04~5H20 was added at a rate of 3 kg/hr (in the form of an aqueous solution). The tank was continuously agitated with an average retention time of 25 minutes and its contents were continuously passed to a second identical tank where agitation continued with a further retention of 25 minutes and then to a third identical tank where agitation continued for another retention time of 25 minutes. From the third tank the water was fed to a clarifier and the operation was continued until sufficient sludge accumulated at the bottom of the clarifier. The overflow from the clarifier contained about 0.2 ppm CN which more than met the environmental requirement and was discharged from the property. When enough sludge was accumulated, the addition 25 of copper sulphate to the first tank was entirely stopped 1~5~
and in its stead the sludge was recycled to the first tank at a rate of 80 liters/min.
This produced the same reduction of CN to about 0.2 ppm, while entirely eliminating the use of the copper sulphate reagent and thereby resulting in considerable savings.
Also, if there is insufficient sludge available, it can be recycled at a lower rate so that only part of CUSO4 originally employed is added. This also would result in substantial savings for the operation.
Obviously, various waste waters and effluents may be treated in accordance with this invention to reduce their CN content to an environmentally acceptable level.
This makes it possible to operate at a natural temperature of the waste waters, without pre-heating, resulting in additional operating savings.
Thus, the present invention provides a novel method for the destruction of cyanide in waste waters containing unacceptably high levels thereof, which comprises: feeding said waste waters into a suitable treatment vessel under agitation; controllably introducing hydrogen peroxide into said treatment vessel in such amount as to oxidize sufficient cyanide and thereby reduce its content to an acceptable level; and adding sufficient copper sulphate into said treatment vessel to catalyse the reaction; the waters from the treatment vessel being discharged to a ~ 2~01~3 clarifier where sludge is formed at the bottom, which sludge is recycled to the treatment vessel in lieu of at least part of the required copper sulphate. The operation is preferably carried out at a pH between 6 and 10.5 and at a natural temperature of the waste waters. If the pH
drops below the desired level, it can be raised to such level by addition of lime or a similar alkaline material as is well known in the art. The hydrogen peroxide can be added as a 30-70% H202 solution of commercial grade.
The agitation of the treatment vessel may also be carried out or assisted by air sparging.
The residence time of the waste waters in the treatment vessel depends on many factors, such as the temperature at which the treatment is carried out, the size of the vessels compared to the feed rate of the solution, the levels of cyanide in the feed and, of course, the final acceptable level of cyanide which must be achieved by the treatment and which, in most cases, is below 1 ppm. The usual retention time is of the order of ~ to 1 hr.
Moreover, instead of one treatment vessel, there may be used a plurality of such vessels in series.
The present invention will now be described with reference to the appended drawing which illustrates schematically the novel method.
As shown in the drawing, tank 10 is provided as the treatment vessel and it is agitated by stirring means 11.
12~i~019 Into this tank the waste water is fed together with appropriate quantities H202 and CUSO4, and the tank is agitated for a sufficient period of time to reduce the amount of cyanide in the waste water to an acceptable level. Once this is achieved, the waters from the tank are discharged to a clarifier 12 to which a flocculant is also added as is well known in the art. In the clarifier, the sludge accumulates at the bottom which contains a source of Cu which is believed to be Cu(OH)2 produced by reaction of originally employed CuS04. The sludge is then recycled to tank 10 to replace all or part of the CUSO4.
It should be noted that CuS04 can always be used to supplement the Cu requirement if the amount of Cu in the sludge is insufficient. Such CuS04 can be added directly into the tank or into the sludge or waste water conduits, as desired.
As already mentioned, instead of one tank 10, several such tanks in series can be used and also instead of clarifier 12 any other suitable equipment which will ; 20 produce the desired sludge can be employed. Any excess sludge from the clarifier can be returned back to the clarifier and/or sent to disposal as shown in the drawing.
Also, the clarifier overflow is sent to disposal or to further treatment which may be required to remove other impurities present in the waste waters.
The novel system may be operated batchwise or 12~
continuously, but the preferred mode is a continuous operation.
EXAMPLE
Hemlo reclaim water, (CN: 2 ppm) which is the water from the tailings pond at the Hemlo Golden Giant gold mill, was charged into a 150 m3 tank at the rate of 350 m3/hr. The temperature of the water depends on the time of the year when treatment takes place, but at the time of this test it was about 10C. The pH of the reclaim water was about 9.
A 35% solution of H202 was added at a rate of 6 liters/hr and Cu~04~5H20 was added at a rate of 3 kg/hr (in the form of an aqueous solution). The tank was continuously agitated with an average retention time of 25 minutes and its contents were continuously passed to a second identical tank where agitation continued with a further retention of 25 minutes and then to a third identical tank where agitation continued for another retention time of 25 minutes. From the third tank the water was fed to a clarifier and the operation was continued until sufficient sludge accumulated at the bottom of the clarifier. The overflow from the clarifier contained about 0.2 ppm CN which more than met the environmental requirement and was discharged from the property. When enough sludge was accumulated, the addition 25 of copper sulphate to the first tank was entirely stopped 1~5~
and in its stead the sludge was recycled to the first tank at a rate of 80 liters/min.
This produced the same reduction of CN to about 0.2 ppm, while entirely eliminating the use of the copper sulphate reagent and thereby resulting in considerable savings.
Also, if there is insufficient sludge available, it can be recycled at a lower rate so that only part of CUSO4 originally employed is added. This also would result in substantial savings for the operation.
Obviously, various waste waters and effluents may be treated in accordance with this invention to reduce their CN content to an environmentally acceptable level.
Claims (15)
1. A method for the destruction of cyanide in waste waters containing unacceptably high levels thereof, which comprises: feeding said waste waters into a suitable treatment vessel under agitation; controllably introducing hydrogen peroxide into said treatment vessel to oxidize sufficient cyanide, thereby reducing its content to an acceptable level; and adding sufficient copper sulphate into said treatment vessel to catalyse the oxidation; the waters from the treatment vessel being discharged to a clarifier where sludge is formed at the bottom, which sludge is recycled to the treatment vessel in lieu of at least part of the required copper sulphate.
2. Method according to claim 1, wherein the treatment is carried out at a pH between about 6 and 10.5
3. Method according to claim 2, wherein the pH is controlled by addition of lime.
4. Method according to claim 1, wherein the treatment is carried out at the natural temperature of the waste waters.
5. Method according to claim 4, wherein said temperature is between about 0°C and 20°C.
6. Method according to claim 1, wherein the amount of H2O2 added is such that the ratio of H2O2 to CN is between about 2:1 and 4:1.
7. Method according to claim 1, wherein the amount of copper sulphate and/or sludge added is such that the ratio of Cu to CN is between 0.1:1 and 2:1.
8. Method according to claim 1, the amount of copper sulphate and/or sludge added is such that the Cu content is between about 5 and 100 ppm.
9. Method according to claims 1 or 6, wherein the H202 is used in the form of a 30-70% solution of commercial grade.
10. Method according to claims 1 or 7, wherein the copper sulphate is used in the form of a suitable aqueous solution.
11. Method according to claims 1 or 7, wherein said sludge is used to replace at least 50% of the copper sulphate.
12. Method according to claims 1 or 7, wherein, once sufficient sludge is accumulated in the clarifier, said sludge is used to replace the totality of the copper sulphate.
13. Method according to claim 1, 6 or 7, wherein the oxydation is allowed to proceed in the treatment vessel until the CN level in the overflow from the clarifier is below 1 ppm.
14. Method according to claim 1, wherein the treatment vessel comprises a plurality of tanks connected in series and the waste waters are transferred from one tank to the next and then to the clarifier.
15. Method according to claims 1 or 14, which is operated on a continuous basis.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000490821A CA1257019A (en) | 1985-09-16 | 1985-09-16 | Method of cyanide destruction |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000490821A CA1257019A (en) | 1985-09-16 | 1985-09-16 | Method of cyanide destruction |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1257019A true CA1257019A (en) | 1989-07-04 |
Family
ID=4131391
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000490821A Expired CA1257019A (en) | 1985-09-16 | 1985-09-16 | Method of cyanide destruction |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1257019A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102642986A (en) * | 2012-04-20 | 2012-08-22 | 上海化学工业区中法水务发展有限公司 | Method and device for treating organic cyanide wastewater |
| CN105481080A (en) * | 2016-01-12 | 2016-04-13 | 成都迅德科技有限公司 | Water treatment oxidization device |
| CN108137358A (en) * | 2015-10-29 | 2018-06-08 | 株式会社片山化学工业研究所 | The processing method of the waste water containing cyanide complex and the inorganic agent for this method |
-
1985
- 1985-09-16 CA CA000490821A patent/CA1257019A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102642986A (en) * | 2012-04-20 | 2012-08-22 | 上海化学工业区中法水务发展有限公司 | Method and device for treating organic cyanide wastewater |
| CN108137358A (en) * | 2015-10-29 | 2018-06-08 | 株式会社片山化学工业研究所 | The processing method of the waste water containing cyanide complex and the inorganic agent for this method |
| CN105481080A (en) * | 2016-01-12 | 2016-04-13 | 成都迅德科技有限公司 | Water treatment oxidization device |
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| MKEX | Expiry |