CA1065272A - Treatment of dilute cyanide solutions - Google Patents
Treatment of dilute cyanide solutionsInfo
- Publication number
- CA1065272A CA1065272A CA242,861A CA242861A CA1065272A CA 1065272 A CA1065272 A CA 1065272A CA 242861 A CA242861 A CA 242861A CA 1065272 A CA1065272 A CA 1065272A
- Authority
- CA
- Canada
- Prior art keywords
- anode
- cathode
- cell
- bed
- cyanide
- 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
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/46104—Devices therefor; Their operating or servicing
- C02F1/46109—Electrodes
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/46104—Devices therefor; Their operating or servicing
- C02F1/46109—Electrodes
- C02F1/46114—Electrodes in particulate form or with conductive and/or non conductive particles between them
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D21/00—Processes for servicing or operating cells for electrolytic coating
- C25D21/16—Regeneration of process solutions
- C25D21/20—Regeneration of process solutions of rinse-solutions
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
- C02F1/4672—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electrooxydation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/467—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction
- C02F1/4676—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electroreduction
- C02F1/4678—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrochemical disinfection; by electrooxydation or by electroreduction by electroreduction of metals
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/46104—Devices therefor; Their operating or servicing
- C02F1/46109—Electrodes
- C02F2001/46133—Electrodes characterised by the material
- C02F2001/46138—Electrodes comprising a substrate and a coating
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/46104—Devices therefor; Their operating or servicing
- C02F1/46109—Electrodes
- C02F2001/46152—Electrodes characterised by the shape or form
- C02F2001/46157—Perforated or foraminous electrodes
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/16—Nitrogen compounds, e.g. ammonia
- C02F2101/18—Cyanides
Abstract
ABSTRACT OF THE DISCLOSURE
Apparatus and method for treating dilute metal cyanide solution employs an electrolytic cell with an anode and cathode having an irregular surface for example a mesh structure. The solution for treatment is circulated up through the cell to fluidise a bed of non-conducting particles adjacent the electrodes.
The ratio between the effective areas of the cathode and the anode is between 1.3:1 and 2:1.
Apparatus and method for treating dilute metal cyanide solution employs an electrolytic cell with an anode and cathode having an irregular surface for example a mesh structure. The solution for treatment is circulated up through the cell to fluidise a bed of non-conducting particles adjacent the electrodes.
The ratio between the effective areas of the cathode and the anode is between 1.3:1 and 2:1.
Description
065%7Z
The present invention relates to the treatment of dilute cyanide solutions.
In many industrial operations such as, for example, electro-plating, articles are dipped into concentrated cyanide solutions.
After removing from the cyanide solutions, the articles require rinsing to free them of cyanide contamination. This rinsing is - commonly performed in flowing water and produces an aqueous efflu-ent containing cyanide in solution. Although the concentration of cyanide in such effluents is relatively low (typically less than 1~ 1000 milligrammes per litre), these effluents still present a ; very considerable disposal problem due to the high toxicity of even dilute cyanide solutions.
Further, the cyanide present may be that of a heavy metal, such as copper, zinc, cadmium etc., as in many plating solutions.
Since heavy metals are toxic, they also must be removed from the effluent before it can be discharged to a sawer.
Hitherto, it has been the normal practice to treat effluents, such as wash solutions from electroplating plant, in a separate effluent treatment plant. The cyanide is u~ually destroyed by alkaline chlorination. In thi~ proces~, alkali i8 added to adjust the pH and then either gaseous chlorine or sodium hypochlorite is added. The treated effluent is then allowed to stand for about half an hour and checked for excess chlorine, the presence of which indicates completeness of cyanide removal. The pH is then adjusted to precipitate the heavy metals which are allowed to settle as a - sludge of metal hydroxides. This sludge i8 subsequently removed and disposed of by tipping, possibly after being dewatered.
This effluent treatment process has a number of disadvantages.
A separate effluent treatment plant has to be built independently -- 1 -- .
'~
1065;~72 of the electroplating or other industrial process plant. The effluent treatment process involves delaying discharge of the effluent for a sufficient time to ensure completeness of the various treatment reactions. The necessary chemicals for the treatment process have to be purchased. Further, the treatment process produces a sludge, disposal of which is becoming increasing-ly difficult due to environmental considerations. Also, the value of the heavy metals in the wash solution is lost since they are removed as worthless hydroxide sludge.
Another method of destroying cyanides in solution employs an electrochemical treatment process. If a cyanide solution is used as the electrolyte in an electrolytic cell, the cyanides can be oxidized to cyanates at the anode of the cell. Cyanates are considerably le~s toxic than cyanides. However, the cyanide solu-tions in the wash waters from, for example, an electroplating plant are of an extremely low concentration and tend to be inef-ficiently destroyed in normal electrolytic cells.
In Canadian Patent No. 1,050~478 issued on March 13, 1979 to The Electricity CouncilJ there is disclosed an electrolytic cell having a flat or curved rigid plane electrode in a liquid electro-lyte, the electrode having a non-smooth surface, for example being formed of apertured material or material having surface irregu-larities and there being provided a fluidized bed of non-conducting particles adjacent the surface of the electrode. The effect of the fluidized bed in conjunction with the particular form of electrode is to break up the surface layer of electrolyte ad-jacent the electrode and to cause mixing of the electrolyte. This mixing of the electrolyte prevents the formation of a surface layer depleted of ions until a much higher current density is reached ` ~06S272 compared with what occurs in the cell without any such mechanical mixing. This enables the cell to be used successfully for electrolysing substances in dilute solutions.
According to the present invention there is provided apparatus for treating dilute metal cyanide solutions comprising an electro-lytic cell having a cathode and an anode, the cathode and anode having irregularly shaped effective surfaces, and being disposed relative to one another so that the ratio between the effective surface areas of the cathode and the anode is between 1.3:1 and
The present invention relates to the treatment of dilute cyanide solutions.
In many industrial operations such as, for example, electro-plating, articles are dipped into concentrated cyanide solutions.
After removing from the cyanide solutions, the articles require rinsing to free them of cyanide contamination. This rinsing is - commonly performed in flowing water and produces an aqueous efflu-ent containing cyanide in solution. Although the concentration of cyanide in such effluents is relatively low (typically less than 1~ 1000 milligrammes per litre), these effluents still present a ; very considerable disposal problem due to the high toxicity of even dilute cyanide solutions.
Further, the cyanide present may be that of a heavy metal, such as copper, zinc, cadmium etc., as in many plating solutions.
Since heavy metals are toxic, they also must be removed from the effluent before it can be discharged to a sawer.
Hitherto, it has been the normal practice to treat effluents, such as wash solutions from electroplating plant, in a separate effluent treatment plant. The cyanide is u~ually destroyed by alkaline chlorination. In thi~ proces~, alkali i8 added to adjust the pH and then either gaseous chlorine or sodium hypochlorite is added. The treated effluent is then allowed to stand for about half an hour and checked for excess chlorine, the presence of which indicates completeness of cyanide removal. The pH is then adjusted to precipitate the heavy metals which are allowed to settle as a - sludge of metal hydroxides. This sludge i8 subsequently removed and disposed of by tipping, possibly after being dewatered.
This effluent treatment process has a number of disadvantages.
A separate effluent treatment plant has to be built independently -- 1 -- .
'~
1065;~72 of the electroplating or other industrial process plant. The effluent treatment process involves delaying discharge of the effluent for a sufficient time to ensure completeness of the various treatment reactions. The necessary chemicals for the treatment process have to be purchased. Further, the treatment process produces a sludge, disposal of which is becoming increasing-ly difficult due to environmental considerations. Also, the value of the heavy metals in the wash solution is lost since they are removed as worthless hydroxide sludge.
Another method of destroying cyanides in solution employs an electrochemical treatment process. If a cyanide solution is used as the electrolyte in an electrolytic cell, the cyanides can be oxidized to cyanates at the anode of the cell. Cyanates are considerably le~s toxic than cyanides. However, the cyanide solu-tions in the wash waters from, for example, an electroplating plant are of an extremely low concentration and tend to be inef-ficiently destroyed in normal electrolytic cells.
In Canadian Patent No. 1,050~478 issued on March 13, 1979 to The Electricity CouncilJ there is disclosed an electrolytic cell having a flat or curved rigid plane electrode in a liquid electro-lyte, the electrode having a non-smooth surface, for example being formed of apertured material or material having surface irregu-larities and there being provided a fluidized bed of non-conducting particles adjacent the surface of the electrode. The effect of the fluidized bed in conjunction with the particular form of electrode is to break up the surface layer of electrolyte ad-jacent the electrode and to cause mixing of the electrolyte. This mixing of the electrolyte prevents the formation of a surface layer depleted of ions until a much higher current density is reached ` ~06S272 compared with what occurs in the cell without any such mechanical mixing. This enables the cell to be used successfully for electrolysing substances in dilute solutions.
According to the present invention there is provided apparatus for treating dilute metal cyanide solutions comprising an electro-lytic cell having a cathode and an anode, the cathode and anode having irregularly shaped effective surfaces, and being disposed relative to one another so that the ratio between the effective surface areas of the cathode and the anode is between 1.3:1 and
2:1, a bed of non-conducting particles in the cell adjacent the effective surfaces of the cathode and anode, means for circulating a dilute metal cyanide solution through the cell as the electrolyte to flow upwardly through the bed to fluidise the bed and means for passing a current between the cathode and anode in the cell to deposit metal at the cathode and oxidise cyanide at the anode.
With this apparatus, the metal in the solution will be de-pO8 ited at the cathode of the cell at the same time as the cyanide is oxidised at the anode. Thus, the apparatus of the invention has the significant advantage of recovering the heavy metals from the wash solution as well as de~troying the cyanides. Because, the effective area of the cathode is greater than that of the anode, there i8 a higher current density at the anode than at the cathode. These conditions tend to optimize the oxidisation of cyanide at the anode and deposition of metal at the cathode. The anode and the cathode may be constructed of mesh materials. Then the difference in effective area may be achieved by the anode having a greater open area than the cathode. The anode should be made of an inert material such as platinised titanium or lead dioxide coated titanium. However~ the cathode may be constructed
With this apparatus, the metal in the solution will be de-pO8 ited at the cathode of the cell at the same time as the cyanide is oxidised at the anode. Thus, the apparatus of the invention has the significant advantage of recovering the heavy metals from the wash solution as well as de~troying the cyanides. Because, the effective area of the cathode is greater than that of the anode, there i8 a higher current density at the anode than at the cathode. These conditions tend to optimize the oxidisation of cyanide at the anode and deposition of metal at the cathode. The anode and the cathode may be constructed of mesh materials. Then the difference in effective area may be achieved by the anode having a greater open area than the cathode. The anode should be made of an inert material such as platinised titanium or lead dioxide coated titanium. However~ the cathode may be constructed
3 --" ' - ' ' .:
`-- 1065Z72 of other materials as well. For example, if copper cyanide is being electrolysed, the cathode may be of copper if a homogeneous material is required after metal deposition thereon.
According to another aspect of the invention, there is pro-vided a method of treating a dilute metal cyanide solution com-prising the steps of providing an electrolytic cell having a cathode and an anode, the cathode and anode having irregularly shaped effective surfaces and being disposed relative to one another so that the ratio between the effective surface areas of the cathode and the anode is between 1.3:1 and 2:1, providing a bed of non-conductinq particles in the cell adjacent the effective surface~ of the anode and the cathode, circulating the dilute metal cyanide solution to be treated through the cell as the electrolyte to flow upwardly through the bed to fluidise the bed, and pa~sing a current between the cathode and the anode to deposit metal on the cathode and oxidise cyanide at the anode.
The invention may be used, for example, in an electroplating shop where a cyanide solution is used as the plating electrolyte.
Then, the invention may be used to ~eat the effluent from rinsing baths to destroy cyanide~ in solution therein before discharge to a sewer. Preferably, however, the invention is used to maintain a low level of cyanide concentration in a wash solution in a primary treatment or rinsing bath for articles being plated, by recirculat-ing the wash solution through the cell.
Thus, the apparatus of the invention may include a treat-ment bath for rinaing articles contaminated with metal cyanides, said means for circulating being adapted to recirculate dilute metal cyanide solution from the rinse bath through the cell.
This apparatus may readily be incorporated into the --- 1065Z~7Z
processing line of the industrial procesæ in which the articles become contaminated. In the electroplating example, the plated articles are removed from the plating solution and given a primary rinse in the rinse bath. The level of cyanide and metal ioas in the rinse bath is maintained low by recirculating the wash solution through the electrolytic cell and thereby oxidising the cyanide to cyanate and plating off the metal. Further rinsing of the articles after removal from the primary rinse bath can be carried out in the normal way in flowing water and due to the low level of contaminants on the articles after primary rinsing, the secondary rinse water may have sufficiently low toxicity to be discharged directly to the sewer.
Examples of the present invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic representation of a treatment apparatus according to the invention, and Figures 2 and 3 illustrate the anode and cathode respective-ly of the cell in the apparatus of Figure 1.
In the drawings, an electrolytic cell 10 is operative to destroy cyanide9 in a washing ~olution contained in a treatment tank 11. The solutlon in the tank 11 is recirculatod through the cell 10 by means of a pump 12. The cell 10 has an anode 13 and two cathodes 14 which become immersed in the recirculated solution in the cell. The solution pumped from the tank 11 by the pump 12 enters the bottom of the cell 10 and passes through a distributor plate 15. The distributor plate 15 supports a bed 16 of non-conducting particles and thi-C bed is fluidized by the upward passage therethrough of the colution from the tank 11 under the influence of the pump 12. The pumped solution passes from the top , ' ' ' . ' `-` 10652~7Z
of the cell 10 through a duct 17 feeding it back to the treatment tank 11. The bed of particles when fluidized fills the spaces between the anode and the cathodes up to a level just below the out-let point of the cell leading into the duct 17.
The effective cathode area provided by cathodes 14 is larger than the effective area provided by anode 13 so that the current density at the anode is larger than that at the cathode. This is conueniently done by forming the anode 13 and the cathodes 14 as meshes 25 and 26 respectively (shown enlarged in Figures 2 and 3) and making the open area of mesh 25 greater than that of mesh 26. Then, as the wash solution contains metal cyanides, both the oxidisation of cyanide at the anode and the deposition of metal at the cathode can be optimised. To energise the cell, a power supply 18 is connected to pass an electrolysing current be-tween the anode 13 and cathodes 14.
Anode 13 and cathodes 14 are conveniently formed of platinis-ed titanium or lead dioxide coated titanium. The particles of the fluidized bed 16 may be spherical particles formed of glass, ~-sand or plastics material or any other material which i8 inert with respect to the electrolyte. The apertures in the meshes 25 and 26 of the electrodes are made larger than the diameter of the particles in bed 16 so that the particles can pass through. The distributor plate 15 may be formed with apertures or slots of sufficiently small sizes to prevent passage therethrough of the bed particles. Alternatively plate 15 may be a porous plate.
-In operation, articles contaminated with a concentrated cyanide solution, for example from a plating bath, are dipped in the tank 11 to rinse off the contaminating substance. Excess build up of cyanide in the treatment tank 11 would reduce the 1065;~7Z
efficiency of the rinsing operation. However, this excess build up is prevented by recirculating the washing solution in tank 11 through the cell 10 in which the cyanides are oxidised around anode 13 to become relatively non-toxic cyanates. Further, metal such as copper in a copper plating plant is deposited on cathodes 14.
After rinsing in tank 11 articles can be further rinsed in flowing water without the flowing water being sufficiently contaminated with cyanides or metals to require treatment before disposal to the sewers.
In a first test example, the effect of repeated rinsing of contaminated articles in the wash solution was imitated by con-tinuously pumping into the tank 11 a made-up concentrated plating solution contained in a vessel 20. This solution had the approxi-mate composition: copper cyanide 26 g/l, sodium cyanide 35 g/l, ~odium carbonate 30 g/l and Rochelle Salt 45 g/l. In the test example, the treatment tank 11 had the dimensions 16 inches by 18 inches by 30 inches. The total volume of wash solution was 100 litres. The anode was formed of a titanium mesh coated with lead dioxide and had an overall size of 90 s~uare inches and a~ open area of approximately 53%. Thus as both ~aces o~ the anode 13 were effective the effective anode area was 84.6 square inches.
Two copper mesh electrodes were used as the cathodes 14, one on each side of the anode. The size of each cathode was 105 square inches and the open area was approximately 43%. Only one face of each cathode was effective so the effective cathode area was 120 square inches. Thus, the ratio of cathode to anode area was approximately 1.4 to 1 producing a correspondingly higher anode current density to cathode current density.
Before starting a test run, plating solution from vessel 20 - .
~65Z72 was added to the wash water in the treatment tank to give a copper concentration of approximately 200 mg/1 and a cyanide concentration of approxLmately 370 mg/l. In addition 10 g/l of sodium sulphate was added to the solution in the treatment tank, thereby to raise the conductivity of the wash solution and lower the power costs of the process.
The power supply 18 was arranged and connected to set up a potential difference of 3 volts between the anode and the cathodes.
; This voltage produced a current of 7 amps, giving an anode current density of about 12 amps per square foot and a cathode current density of approximately 8.4 amps per square foot. Plating solu-tion wa~ pumped from vessel 20 into the treatment tank 11 so as to add copper thereto at approximately 2~ mg per minute and cyanide at approximately 46 mg per minute. The test was continued for seven hours. The level of copper in the treatment tank at the start of the test was 207 mg/l and after seven hours was reduced ~;
to 163 mg/l. The cyanide ConCentratiQn was reduced from 370 mg/l to 298 mg/l. Thus it can be seen that, in this example, the electrolysis had not only kept pace with the addition of copper cyanide and sodium cyanide but had in fact reduced their concen-trations in the treatment tank. During the seven hour test period, 12.8 g of copper were removed and 26.7 of cyanide destroyed by 49 ampere hours of electricity. The copper recovered was of high purity.
In a second test example, a silver cyanide solution was provided in the vessel 20 instead of copper cyanide. The solution contained 90.9 grams per litre of -cilver cyanide salts, 85.86 grams per litre of potassium cyanide plus small quantities of two commercial brighteners. The two cathodes were formed of copper :~06527Z
mesh as for the first example, but the anode was formed of a platinised titanium mesh.
The apparatus was run for seven hours with solution being added ~o the treatment tank 11 at an average rate of 82 mls/hr.
The power supply 18 was set and the open area of the mesh electrodes was such that the anode current density was 10 amps per square foot and the cathode current density was 6 amps per square foot.
- During the run, the cyanide concentration in the treatment tank was an average value of 469 ppm and the silver concentration 146 ppm. The pH was 9.6. In total 575 mls of solution from vessel 20 were added, 4.~54 grams of high purity silver recovered and 7.973 grams of cyanide destroyed.
A third test example employed a zinc cyanide plating solution from an electroplating shop. The solution contained 52.98 grams/litre of zinc and 42 grams/litre of cyanide. A total of 320 mls of this solution was added to the treatment bath over a 5 hour run. The zinc concentration was 268 ppm at the start of the run and 136 ppm at the end; the respective figures for cyanide being 343 ppm and 306 ppm. The current efficiency for ~0 zinc recovery was 49.8~ and the rate of cyanide destruction was 0.34 grams/ampere hour.
In practice the rate of addition of cyanides to the solution in the treatment tank i8 unlikely to remain constant and in order to simulate this a further experiment was carried out in which the rate of addition of the strong cyan~ e solution was varied.
In addition two large volumes of strong cyanide solution were added to simulate a 'shock' loading.
The results are presented in the table.
-RATE OF STRONG TOTAL VOLUME
TDME (hrs) SOLUTION ADDEDOF STRO~G Zn CONCn CN CONCn Lml/h~ SOLUTION ADDED (ppm)- (pp~) 7 91 680 99 Not measured At this point 500 mls of the strong solution was added and then the rate of addition via the peristaltic pump was also increased 49 - 4290 3 81 -~
At this point 200 mls of the strong solution was added 49 87 4490 109 165 :
77 ~ 6930 166 320 ~
The overall current efficiency for zinc deposition over : ~ -the 77 hours was 39% and the rate of cyanide destruction O. 376 g ~ :
CN /A~. -
`-- 1065Z72 of other materials as well. For example, if copper cyanide is being electrolysed, the cathode may be of copper if a homogeneous material is required after metal deposition thereon.
According to another aspect of the invention, there is pro-vided a method of treating a dilute metal cyanide solution com-prising the steps of providing an electrolytic cell having a cathode and an anode, the cathode and anode having irregularly shaped effective surfaces and being disposed relative to one another so that the ratio between the effective surface areas of the cathode and the anode is between 1.3:1 and 2:1, providing a bed of non-conductinq particles in the cell adjacent the effective surface~ of the anode and the cathode, circulating the dilute metal cyanide solution to be treated through the cell as the electrolyte to flow upwardly through the bed to fluidise the bed, and pa~sing a current between the cathode and the anode to deposit metal on the cathode and oxidise cyanide at the anode.
The invention may be used, for example, in an electroplating shop where a cyanide solution is used as the plating electrolyte.
Then, the invention may be used to ~eat the effluent from rinsing baths to destroy cyanide~ in solution therein before discharge to a sewer. Preferably, however, the invention is used to maintain a low level of cyanide concentration in a wash solution in a primary treatment or rinsing bath for articles being plated, by recirculat-ing the wash solution through the cell.
Thus, the apparatus of the invention may include a treat-ment bath for rinaing articles contaminated with metal cyanides, said means for circulating being adapted to recirculate dilute metal cyanide solution from the rinse bath through the cell.
This apparatus may readily be incorporated into the --- 1065Z~7Z
processing line of the industrial procesæ in which the articles become contaminated. In the electroplating example, the plated articles are removed from the plating solution and given a primary rinse in the rinse bath. The level of cyanide and metal ioas in the rinse bath is maintained low by recirculating the wash solution through the electrolytic cell and thereby oxidising the cyanide to cyanate and plating off the metal. Further rinsing of the articles after removal from the primary rinse bath can be carried out in the normal way in flowing water and due to the low level of contaminants on the articles after primary rinsing, the secondary rinse water may have sufficiently low toxicity to be discharged directly to the sewer.
Examples of the present invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a schematic representation of a treatment apparatus according to the invention, and Figures 2 and 3 illustrate the anode and cathode respective-ly of the cell in the apparatus of Figure 1.
In the drawings, an electrolytic cell 10 is operative to destroy cyanide9 in a washing ~olution contained in a treatment tank 11. The solutlon in the tank 11 is recirculatod through the cell 10 by means of a pump 12. The cell 10 has an anode 13 and two cathodes 14 which become immersed in the recirculated solution in the cell. The solution pumped from the tank 11 by the pump 12 enters the bottom of the cell 10 and passes through a distributor plate 15. The distributor plate 15 supports a bed 16 of non-conducting particles and thi-C bed is fluidized by the upward passage therethrough of the colution from the tank 11 under the influence of the pump 12. The pumped solution passes from the top , ' ' ' . ' `-` 10652~7Z
of the cell 10 through a duct 17 feeding it back to the treatment tank 11. The bed of particles when fluidized fills the spaces between the anode and the cathodes up to a level just below the out-let point of the cell leading into the duct 17.
The effective cathode area provided by cathodes 14 is larger than the effective area provided by anode 13 so that the current density at the anode is larger than that at the cathode. This is conueniently done by forming the anode 13 and the cathodes 14 as meshes 25 and 26 respectively (shown enlarged in Figures 2 and 3) and making the open area of mesh 25 greater than that of mesh 26. Then, as the wash solution contains metal cyanides, both the oxidisation of cyanide at the anode and the deposition of metal at the cathode can be optimised. To energise the cell, a power supply 18 is connected to pass an electrolysing current be-tween the anode 13 and cathodes 14.
Anode 13 and cathodes 14 are conveniently formed of platinis-ed titanium or lead dioxide coated titanium. The particles of the fluidized bed 16 may be spherical particles formed of glass, ~-sand or plastics material or any other material which i8 inert with respect to the electrolyte. The apertures in the meshes 25 and 26 of the electrodes are made larger than the diameter of the particles in bed 16 so that the particles can pass through. The distributor plate 15 may be formed with apertures or slots of sufficiently small sizes to prevent passage therethrough of the bed particles. Alternatively plate 15 may be a porous plate.
-In operation, articles contaminated with a concentrated cyanide solution, for example from a plating bath, are dipped in the tank 11 to rinse off the contaminating substance. Excess build up of cyanide in the treatment tank 11 would reduce the 1065;~7Z
efficiency of the rinsing operation. However, this excess build up is prevented by recirculating the washing solution in tank 11 through the cell 10 in which the cyanides are oxidised around anode 13 to become relatively non-toxic cyanates. Further, metal such as copper in a copper plating plant is deposited on cathodes 14.
After rinsing in tank 11 articles can be further rinsed in flowing water without the flowing water being sufficiently contaminated with cyanides or metals to require treatment before disposal to the sewers.
In a first test example, the effect of repeated rinsing of contaminated articles in the wash solution was imitated by con-tinuously pumping into the tank 11 a made-up concentrated plating solution contained in a vessel 20. This solution had the approxi-mate composition: copper cyanide 26 g/l, sodium cyanide 35 g/l, ~odium carbonate 30 g/l and Rochelle Salt 45 g/l. In the test example, the treatment tank 11 had the dimensions 16 inches by 18 inches by 30 inches. The total volume of wash solution was 100 litres. The anode was formed of a titanium mesh coated with lead dioxide and had an overall size of 90 s~uare inches and a~ open area of approximately 53%. Thus as both ~aces o~ the anode 13 were effective the effective anode area was 84.6 square inches.
Two copper mesh electrodes were used as the cathodes 14, one on each side of the anode. The size of each cathode was 105 square inches and the open area was approximately 43%. Only one face of each cathode was effective so the effective cathode area was 120 square inches. Thus, the ratio of cathode to anode area was approximately 1.4 to 1 producing a correspondingly higher anode current density to cathode current density.
Before starting a test run, plating solution from vessel 20 - .
~65Z72 was added to the wash water in the treatment tank to give a copper concentration of approximately 200 mg/1 and a cyanide concentration of approxLmately 370 mg/l. In addition 10 g/l of sodium sulphate was added to the solution in the treatment tank, thereby to raise the conductivity of the wash solution and lower the power costs of the process.
The power supply 18 was arranged and connected to set up a potential difference of 3 volts between the anode and the cathodes.
; This voltage produced a current of 7 amps, giving an anode current density of about 12 amps per square foot and a cathode current density of approximately 8.4 amps per square foot. Plating solu-tion wa~ pumped from vessel 20 into the treatment tank 11 so as to add copper thereto at approximately 2~ mg per minute and cyanide at approximately 46 mg per minute. The test was continued for seven hours. The level of copper in the treatment tank at the start of the test was 207 mg/l and after seven hours was reduced ~;
to 163 mg/l. The cyanide ConCentratiQn was reduced from 370 mg/l to 298 mg/l. Thus it can be seen that, in this example, the electrolysis had not only kept pace with the addition of copper cyanide and sodium cyanide but had in fact reduced their concen-trations in the treatment tank. During the seven hour test period, 12.8 g of copper were removed and 26.7 of cyanide destroyed by 49 ampere hours of electricity. The copper recovered was of high purity.
In a second test example, a silver cyanide solution was provided in the vessel 20 instead of copper cyanide. The solution contained 90.9 grams per litre of -cilver cyanide salts, 85.86 grams per litre of potassium cyanide plus small quantities of two commercial brighteners. The two cathodes were formed of copper :~06527Z
mesh as for the first example, but the anode was formed of a platinised titanium mesh.
The apparatus was run for seven hours with solution being added ~o the treatment tank 11 at an average rate of 82 mls/hr.
The power supply 18 was set and the open area of the mesh electrodes was such that the anode current density was 10 amps per square foot and the cathode current density was 6 amps per square foot.
- During the run, the cyanide concentration in the treatment tank was an average value of 469 ppm and the silver concentration 146 ppm. The pH was 9.6. In total 575 mls of solution from vessel 20 were added, 4.~54 grams of high purity silver recovered and 7.973 grams of cyanide destroyed.
A third test example employed a zinc cyanide plating solution from an electroplating shop. The solution contained 52.98 grams/litre of zinc and 42 grams/litre of cyanide. A total of 320 mls of this solution was added to the treatment bath over a 5 hour run. The zinc concentration was 268 ppm at the start of the run and 136 ppm at the end; the respective figures for cyanide being 343 ppm and 306 ppm. The current efficiency for ~0 zinc recovery was 49.8~ and the rate of cyanide destruction was 0.34 grams/ampere hour.
In practice the rate of addition of cyanides to the solution in the treatment tank i8 unlikely to remain constant and in order to simulate this a further experiment was carried out in which the rate of addition of the strong cyan~ e solution was varied.
In addition two large volumes of strong cyanide solution were added to simulate a 'shock' loading.
The results are presented in the table.
-RATE OF STRONG TOTAL VOLUME
TDME (hrs) SOLUTION ADDEDOF STRO~G Zn CONCn CN CONCn Lml/h~ SOLUTION ADDED (ppm)- (pp~) 7 91 680 99 Not measured At this point 500 mls of the strong solution was added and then the rate of addition via the peristaltic pump was also increased 49 - 4290 3 81 -~
At this point 200 mls of the strong solution was added 49 87 4490 109 165 :
77 ~ 6930 166 320 ~
The overall current efficiency for zinc deposition over : ~ -the 77 hours was 39% and the rate of cyanide destruction O. 376 g ~ :
CN /A~. -
Claims (11)
1. Apparatus for treating dilute metal cyanide solutions comprising an electrolytic cell having a cathode and an anode, the cathode and anode having irregularly shaped effective surfaces, and being disposed relative to one another so that the ratio between the effective surface areas of the cathode and the anode is between 1.3:1 and 2:1, a bed of non-conducting particles in the cell adjacent the effective surfaces of the cathode and anode, means for circulating a dilute metal cyanide solution through the cell as the electrolyte to flow upwardly through the bed to fluidise the bed and means for passing a current between the cathode and anode in the cell to deposit metal at the cathode and oxidise cyanide at the anode.
2. Apparatus as claimed in claim 1 wherein the cathode and anode are formed as meshes.
3. Apparatus as claimed in claim 2 wherein the cathode and anode have mesh apertures which are larger than the particles in the bed, so that the particles can pass through.
4. Apparatus as claimed in claim 3 wherein the cathode mesh has an open area ratio which is smaller than that of the anode mesh.
5. Apparatus as claimed in claim 4 wherein the cell contains a mesh cathode on each side of the anode.
6. Apparatus as claimed in claim 1 including a treatment bath for rinsing articles contaminated with metal cyanides, said means for circulating being adapted to recirculate dilute metal cyanide solution from the rinse bath through the cell.
7. Apparatus as claimed in claim 2 wherein at least one of the cathode and the anode is made of platinised titanium.
8. Apparatus as claimed in claim 2 wherein at least one of the cathode and the anode is made of lead dioxide coated titanium.
9. Apparatus as claimed in claim 2 wherein the cathode is made of copper.
10. A method of treating a dilute metal cyanide solution comprising the steps of providing an electrolytic cell having a cathode and an anode, the cathode and anode having irregularly shaped effective surfaces and being disposed relative to one another so that the ratio between the effective surface areas of the cathode and the anode is between 1.3:1 and 2:1, providing a bed of non-conducting particles in the cell adjacent the effective surfaces of the anode and the cathode, circulating the dilute metal cyanide solution to be treated through the cell as the electrolyte so that it flows upwardly through the bed to fluidise the bed, and passing a current between the cathode and the anode to de-posit metal . . . . . . . . . . . . . . . . . .
on the cathode and oxidise cyanide at the anode.
on the cathode and oxidise cyanide at the anode.
11. A method as claimed in claim 10 wherein the dilute metal cyanide solution being treated is recirculated through a treatment bath for rinsing articles contaminated with metal cyanides.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB267/75A GB1483126A (en) | 1975-01-03 | 1975-01-03 | Electrolytic treatment of dilute cyanide solution and cell therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065272A true CA1065272A (en) | 1979-10-30 |
Family
ID=9701349
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA242,861A Expired CA1065272A (en) | 1975-01-03 | 1975-12-31 | Treatment of dilute cyanide solutions |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS51125674A (en) |
| CA (1) | CA1065272A (en) |
| DE (1) | DE2600084A1 (en) |
| FR (1) | FR2296597A1 (en) |
| GB (1) | GB1483126A (en) |
| IT (1) | IT1052773B (en) |
| ZA (1) | ZA757840B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5342449A (en) * | 1990-12-11 | 1994-08-30 | Holbein Bruce E | Process for the decontamination of toxic, heavy-metal containing soils |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2836720C2 (en) * | 1978-08-22 | 1986-06-26 | Okubo, Katsuhiro, Tokio/Tokyo | Process for the continuous electrolytic regeneration of a washing solution containing silver cyanide which occurs during electroplating processes and a device for carrying out the process |
| GB2098238B (en) * | 1981-05-07 | 1984-10-24 | Electricity Council | An electrochemical cell |
| JPS6077937A (en) * | 1983-10-03 | 1985-05-02 | Toppan Printing Co Ltd | Metal recovering apparatus |
| DE4218916C2 (en) * | 1992-06-10 | 1996-03-21 | Heraeus Elektrochemie | Use of a grid anode for electrolytic detoxification or regeneration of an aqueous solution containing cyanide |
| DE4233721A1 (en) * | 1992-10-07 | 1994-04-14 | Ceotronics Gmbh Elektronische | Communication device for use in police motorcycles |
| US6280594B1 (en) * | 1998-12-01 | 2001-08-28 | Tateki Yamaoka | Device for producing ion water and partition wall for device for producing ion water |
| US6277266B1 (en) * | 1999-03-23 | 2001-08-21 | Tateki Yamaoka | Device for producing ion water and partition wall for device for producing ion water |
| DE102009013380A1 (en) | 2009-03-09 | 2010-09-16 | Hansgrohe Ag | Process for the decomposition of partially fluorinated and perfluorinated surfactants |
| DE102010021424A1 (en) * | 2010-05-26 | 2011-12-01 | Gerald Metge | Metallic gauze anode useful in a galvanic cell, comprises a tube made of metal thread, fabric or knitted fabric |
| CN106006946A (en) * | 2016-05-26 | 2016-10-12 | 南京大学 | Electrolytically modified quartz sand filter bed and application thereof |
| CN112830556A (en) * | 2021-01-20 | 2021-05-25 | 苏州融和福天宝环保科技有限责任公司 | Method for combined treatment of cyanide copper plating wastewater and acidic copper plating wastewater |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CH302143A (en) * | 1951-07-28 | 1954-10-15 | Bamag Meguin Aktiengesellschaf | Pre-electrode for electrolytic cells and method for producing such an electrode. |
| IT953307B (en) * | 1971-04-14 | 1973-08-10 | Hooker Chemical Corp | PROCEDURE FOR REDUCING THE CYANIDE NUTRITION OF A SOLUTION USING AN ELECTROCHEMICAL TECHNIQUE |
| FR2190743A1 (en) * | 1972-06-28 | 1974-02-01 | Studelec | Electrolytic destruction of cyanides - in waste water and industrial effluents |
| GB1415000A (en) * | 1972-12-15 | 1975-11-26 | Pacific Eng Production Co Of N | Method and apparatus for removing solids from electrolytic cells |
-
1975
- 1975-01-03 GB GB267/75A patent/GB1483126A/en not_active Expired
- 1975-12-17 ZA ZA7840A patent/ZA757840B/en unknown
- 1975-12-23 FR FR7539439A patent/FR2296597A1/en active Granted
- 1975-12-31 IT IT70233/75A patent/IT1052773B/en active
- 1975-12-31 CA CA242,861A patent/CA1065272A/en not_active Expired
-
1976
- 1976-01-02 DE DE19762600084 patent/DE2600084A1/en not_active Withdrawn
- 1976-01-05 JP JP51000408A patent/JPS51125674A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5342449A (en) * | 1990-12-11 | 1994-08-30 | Holbein Bruce E | Process for the decontamination of toxic, heavy-metal containing soils |
Also Published As
| Publication number | Publication date |
|---|---|
| GB1483126A (en) | 1977-08-17 |
| FR2296597B1 (en) | 1982-10-08 |
| DE2600084A1 (en) | 1976-07-15 |
| ZA757840B (en) | 1977-01-26 |
| FR2296597A1 (en) | 1976-07-30 |
| IT1052773B (en) | 1981-07-20 |
| JPS51125674A (en) | 1976-11-02 |
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