DE2600084A1 - METHOD AND DEVICE FOR TREATMENT OF DILUTED METAL LYANIDE SOLUTIONS - Google Patents

Description

Patent attorneys Dipl.-Ing. KWfickmann, 2bUUUo4

Dipl.-Ing. K. v7eigkmaiMN, Dii-l.-Phys. Dr. K. Fincke Dipl.-Ing. F. A. Weickmann, Dipl.-Chem. B. Huber

8 MUNICH 86, POST BOX 860 820

MÖHLSTRASSE 22, NUMBER 48 39 21/22

<983921/22>

FA 7649/243 / H / KR

The Electricity Council, 30 Millbank, London, SWIP 4RD,

England

Method and device for the treatment of diluted

Metal cyanide solutions

The invention relates to the treatment of dilute cyanide solutions.

In many technical processes, e.g. during electroplating, objects are turned into concentrated cyanide solutions immersed. Sung about after removal from the cyanide the objects must be free of cyanide contamination

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genes are flushed free. This rinsing is usually done in running water, creating aqueous effluents containing dissolved cyanide. Although the concentration of cyanide in such effluents is relatively low (typically less than 1000 mg / l), these effluents represent due to the high toxicity Even dilute cyanide solutions pose considerable problems of removal.

Furthermore, the present cyanide can be in the form of a heavy metal cyanides, i.e. of copper, zinc, cadmium etc., are present, as is the case, for example, in many electroplating solutions. Because heavy metals are toxic, they must also be removed from the effluent before it can be discharged into the sewer system.

So far it has been the normal practice to collect effluents, e.g. washing solutions from electroplating plants, in a separate facility to treat the effluent. The cyanide is usually destroyed by alkaline chlorination. This process uses alkali added to adjust the pH, followed by the addition of either gaseous chlorine or sodium hypochlorite. The treated effluent is then left to stand for about half an hour and checked for excess chlorine, the presence of which indicates complete removal of the cyanide. This is where the pH is set to precipitate heavy metals which are allowed to settle as sludge of metal hydroxides. This sludge is then removed and discarded by dumping, if necessary after dewatering.

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This effluent treatment process has a number of disadvantages. Namely, there must be a separate facility for treatment of the effluent can be built independently of the electroplating or other technical process plant. The process of treating the effluent includes delaying the discharge of the effluent for a sufficient amount of time Allow a period of time to ensure the completion of the various treatment responses. Further the necessary chemicals for the treatment process must be purchased. This treatment process also provides a sludge, the removal of which is due to Environmental considerations is becoming more and more difficult. Finally, the value of the heavy metals in the wash solution has been lost as these metals are removed as worthless hydroxide sludge.

Another method for destroying cyanides in solution is an electrochemical treatment process applied. When used as an electrolyte in an electroytic If a cyanide solution is used then the cell can use the Cyanides are oxidized to cyanates at the anode of the cell. However, cyanates are considerably less toxic than cyanides. The cyanide solutions in the wastewater, for example electroplating plants have an extremely low concentration and they tend to do so; in normal electrolytic cells are only inadequately destroyed.

In copending British Patent Application No. 44650/73 an electrolytic cell is described which has a flat or curved flat electrode in

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a liquid electrolyte. The electrode is formed from an apertured material or a material having surface irregularities. A fluidized bed of non-conductive particles is provided adjacent the surface of the electrode. The effect of the fluidized bed together with the specific shape of the electrode is to create the surface layer of the electrolyte adjacent to the electrode and causing the electrolyte to mix. This mixing of the electrolyte prevents the formation of a surface layer that is depleted in ions, until a considerably higher current density is achieved compared to that in the cell occurs without such mechanical mixing. This enables the cell to be successfully electrolysed of substances to use in dilute solutions.

The invention now provides a device for treating dilute metal cyanide solutions provided, which comprises: an electrolytic cell with a cathode and an anode, wherein the Cathode and anode have irregularly shaped effective surfaces and are thus adapted and arranged to one another are that the ratio between the effective surface of the cathode and that of the anode between 1.3: 1 and 2: 1, a bed of non-conductive particles in the cell that adheres to the effective surfaces adjacent to the cathode and the anode, means for circulating a dilute metal cyanide solution through the cell so that the electrolyte in upward

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direction flows through the bed and this swirls, and a device to flow a current between the cathode and to conduct the anode in the cell so that metal is deposited on the cathode and the cyanide on the Anode is oxidized.

In this device, the metal in the solution is deposited on the cathode of the cell while at the same time the cyanide is oxidized on the anode. Thus, the device according to the invention has the significant advantage that the heavy metals are recovered from the washing solution and that the cyanides are destroyed will. For this reason, the effective area of the cathode is greater than that of the anode, so that at the Anode a higher. Current density prevails than at the cathode. At. These conditions will cause the oxidation of the cyanide optimized at the anode and the deposition of the metal at the cathode. The anode and the cathode can be made from reticulated material can be made * In this case, the difference in effective areas may be in the way be achieved that one provides an anode with a larger open area than the cathode. The anode should made of an inert material such as platinized titanium or titanium coated with lead dioxide be. However, the cathode can just as easily be made from other materials. If e.g. copper cyanide is to be electrolyzed, then the cathode can be made of copper, if after the metal deposition then a homogeneous material is required.

The invention also provides a method for treating dilute metal cyanide solutions for

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added, which is characterized in that an electrolytic cell with a cathode and a Provides anode, the cathode and the anode having irregularly shaped effective surfaces and so adapted and are arranged to each other that the ratio between the effective surface of the cathode and that the anode is between 1.3: 1 and 2: 1, adjacent a bed of non-conductive particles in the cell on the effective surfaces of the anode and the cathode provides the dilute metal cyanide solutions to be treated circulated through the cell so that the electrolyte flows upward through the bed, with it this is whirled up, and that a current is passed between the cathode and the anode in order to generate metal on the To deposit cathode and oxidize cyanide at the anode.

For example, the invention can be used in an electroplating facility where a cyanide solution is used as a plating or electroplating electrolyte is used. The invention can then be used to clean the effluent Treat by rinsing baths to destroy the cyanides in the solution before draining into drains will. Preferably, however, the invention is used to achieve a low level of cyanide concentration maintain in a wash solution in a primary treatment or rinse bath for items to be electroplated, by recirculating the wash solution through the cell.

The device according to the invention can therefore include a treatment bath for rinsing objects,

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which are contaminated with metal cyanides. The device for .Zirkulierung is designed so that dilute metal cyanide solution from the rinsing bath through the Cell is recirculated. ■

The invention can easily be incorporated into the process line of a tech- niche process can be inserted in the objects are contaminated. In the example of the electroplating plant the plated articles are taken out of the plating solution and they become subjected to a primary rinse in the rinsing bath. The content of cyanide and metal ions in the rinsing bath becomes low held by the wash solution being recirculated through the electrolytic cell, causing the cyanide to increase Cyanate oxidizes and the metal is deposited. One Further rinsing of the items after removal from the primary rinsing bath can be carried out in the normal manner in flowing Water carried out, reflecting the low level of contaminants in the objects after Primary flushing is due. The secondary rinse water may be of sufficiently low toxicity that it can be discharged directly into drains.

The invention is explained in more detail with reference to the accompanying drawings explained. Show it:

1 shows a schematic representation of an embodiment of a treatment device according to the invention and the

Figures 2 and 3 show the anode and cathode, respectively, of the cell of the device according to Figure 1.

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The electrolytic cell 10 acts to destroy cyanides in a washing solution which is in a treatment stank 11 is included. The solution in the tank 11 is recirculated through the cell 10 by means of a pump 12. The cell 10 has an anode 13 and two cathodes 14 which are immersed in the recirculated solution in the cell will. The pump 12 from the tank 11 Pumped-in solution enters the bottom of the cell 10 and flows through a distributor plate 15. The distributor plate 15 carries a bed 16 of non-conductive particles. This bed is created by the upward flow the solution from the tank 11 is whirled up under the influence of the pump 12 or transferred into a fluidized bed. the pumped solution passes from the top of the cell 10 through a line 17 back into the treatment tank 11. The bed of particles in the fluidized state fills the spaces between the anode and the cathodes to to a level just below the outlet point of the cell leading to line 17.

The effective cathode area that is formed by the cathodes 14 is greater than the effective area that is formed by the anode 13, so that the current density is larger at the anode than at the cathode. This is conveniently achieved in such a way that the Anode 13 and cathodes 14 as nets or mesh structures 25 and 26 (which are enlarged in FIGS are shown) and by making the open area of the network 25 larger than that of the network 26. This can, if the washing solution contains metal cyanides, both the oxidation of the cyanide on the

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Anode and the deposition of the metal on the cathode can be optimized. To supply electricity to the cell is a power source 18 is connected so that an electrolysis current flows between the anode 13 and the cathodes 14.

The anode 13 and the cathodes 14 are suitably used formed from platinized titanium or titanium coated with lead dioxide. The particles of the fluidized bed 16 can be spherical particles made of glass, sand or plastics or any other material that is inert to the electrolyte. The openings in the meshes 25 and 26 of the electrodes can can be made larger than the diameter of the particles in bed 16 so that the particles will pass therethrough can. The distribution plate 15 can be formed with openings or slots of sufficiently small dimensions, so that the particles of the bed are prevented from passing through. Alternatively, the plate 15 can also be a porous one Be plate.

When the system is in operation, objects that have been treated with a concentrated cyanide solution, e.g. from a galvanic. Bath, contaminated, immersed in the tank 11 to rinse off the contaminating substances. Too strong Accumulation of cyanides in the treatment tank 11 would reduce the effectiveness of the flushing process. These however, too much accumulation is prevented in such a way that the washing solution in the tank 11 through the Cell 10 recirculates, wherein the cyanide is oxidized at the anode 13 to relatively non-toxic cyanates will. Metals, such as copper in a galvanic copper plating plant, are deposited on the cathodes 14.

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divorced. After rinsing in the tank 11, the objects can can be rinsed further in running water without the running water being too strong with cyanides or Metals is contaminated that treatment would be required before draining into the sewer system.

In a first test example, the effect of repeated rinsing of contaminated objects in the washing solution was mimicked in that an enriched, concentrated galvanic solution contained in a vessel 20 was continuously pumped into the tank 11. This solution had the approximate composition: 26 g / l copper cyanide, 35 g / l sodium cyanide, 30 g / l sodium carbonate and 45 g / l Rochelle salt. In this test example, the treatment tank was 16 inches by 18 inches by 30 inches. The total volume of the washing solution was 100 liters. The anode was formed from a titanium mesh which was coated with lead dioxide. It had an overall size of 580.6 cm /. Thus, after both surfaces of the anode 13 were effective, the effective anode area was 545.8 cm. Two copper mesh electrodes were used as cathodes 14 on each side of the anode. The size of each cathode was 677.5 cm and the open area was approximately 43%. Only one area of each cathode was effective so that the effective cathode area was 774.2 cm ² . The ratio of the cathodes to the anode area was therefore approximately 1.4: 1, which resulted in a correspondingly higher anode current density than the cathode current density.

Before starting the test run, a galvanic solution was added from the vessel 20 to the wash water in the Be-V and an open area of approximately 53 #.

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Handiungstank added so that a copper concentration of about 200 mg / 1 and a cyanide concentration of about 370 mg / l was achieved. In addition, 10 g / l of sodium sulfate was added to the solution in the treatment tank added, thereby increasing the conductivity of the washing solution and reducing the energy costs of the process became.

An energy source 18 was arranged and connected in such a way that a potential difference of? V between the anode and the cathodes have been adjusted. That tension created one. Current of 7 A, which is an anode current density of about 12 A / 0.09 m and a cathode current density of about 8.4 A / 0.09 m. The galvanic solution was pumped from the vessel 20 into the treatment tank 11 in such a way that that copper is supplied approximately in an amount of 20 mg / min and cyanide in approximately an amount of 46 mg / min became. The test was carried out for 7 hours. The copper content in the treatment tank at the start of the test was 207 mg / l and it had decreased to 163 mg / l after 7 hours. The cyanide concentration was 370 mg / l has been reduced to 298 mg / l. It can thus be seen that in this example the electrolysis not only had kept pace with the addition of copper cyanide and sodium cyanide, but that they even increased the concentrations this had decreased in the treatment tank. During the 7 hour test period, 12.8 grams of copper was removed and 26.7 grams of cyanide was destroyed, with one Electricity of 49 Ah had been used. The recovered copper was of high purity.

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In the second test example, a silver cyanide solution was used in the vessel 20 instead of copper cyanide. The solution contained 90.9 g / l silver cyanide salts, 85.86 g / l potassium cyanide and small amounts of two commercially available polishing agents. The two cathodes were made of copper mesh as in the first example, but the anode was made of a platinized titanium mesh.

The apparatus was operated for 7 hours with the solution being introduced into the treatment tank 11 at an average rate of 82 ml / hour. The power source 18 was used and the open area of the mesh electrodes was such that the anode current density was 10 A / 0.09 m and the cathode current density was 6 A / 0.09 m. During the experiment, the cyanide concentration in the treatment tank corresponded to an average of A69 ppm and the silver concentration to 146 ppm. The pH was 9.6. A total of 575 ml of solution from vessel 20 was added and 4.954 P, high purity silver was recovered and 7.973 g of cyanide was destroyed.

In a third test example, a galvanic zinc cyanide solution from an electroplating system was used. The solution contained 52.98 g / l zinc and 42 g / l cyanide. A total of 320 ml of this solution were in the course of a Put in the treatment bath for a 5-hour test. The zinc concentration was 268 ppm at the beginning of the experiment and 136 ppm at the end. The corresponding numbers for the cyanide were 343 ppm and 306 ppm. The power output for zinc recovery was 49.8% and the rate the cyanide destruction was 0.34 g / Ah.

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26Q0084

In practice it is not likely that the rate of addition the cyanide to the solution in the treatment tank remains constant. To imitate these relationships Another experiment was carried out in which the rate of addition of the strong cyanide solution was varied. In addition, two large volumes of a strong cyanide solution were added to "shock" stress to simulate.

The results obtained are summarized in the following table:

Time (h) Addition rate of the strong solution (ml / h)

Total volume of added strong solution

Zn conc. (ppm)

CN ~ conc, (ppm)

0 7

24

97 91

0680

2230

136 99

90

306

not measured

289

At this point 500 ml of the strong solution had been added and the rate of addition was then over the circulation pump also increased.

24 248 2730 354 499 29 17th 3970 264 780 49 _ 4290 3 81

At this point 200 ml of the strong solution had been added.

49 77

87

4490 109 165 6930 166 320 -14-

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The overall current efficiency for zinc deposition in the The course of 77 hours was 39% and the rate of cyanide destruction was 0.376 g CN "/ Ah.

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Claims (11)

P a t e η t a η s ρ r ü c h e 1. Device for the treatment of dilute metal cyanide solutions, characterized by an electrolytic cell (10) with a cathode (14) and an anode (13), the cathode and the anode have irregularly shaped effective surfaces (25, 26) and are adapted and arranged to one another that the ratio between the effective surface of the cathode and that of the anode between 1.3: 1 and 2: is a bed (16) of non-conductive particles in the cell adjacent to the effective surfaces of the Cathode and the anode, means (12) for circulating a dilute metal cyanide solution through the Cell in such a way that the electrolyte flows upwards through the bed to stir it up and means (18) for passing a current between the cathode and the anode in the cell to Metal to deposit on the cathode and cyanide on the To oxidize anode. 2. Apparatus according to claim 1, characterized in that the cathode and the anode as Networks or mesh bodies are formed. 3. Apparatus according to claim 2, characterized in that g e k e η η ζ e i ch η e t that the cathode and the anode Netzbzw. Have mesh openings that are larger than the particles are in the bed so that the particles can pass through. 4. Apparatus according to claim 3, characterized in that a proportion in the cathode network -16-60 9829/0833 is present on open surfaces, which is smaller than in the anode network. 5. Apparatus according to claim 4, characterized in that the cell has two network cathodes Each side of the anode contains. 6. The device according to claim 1, characterized in that it further comprises a treatment bath (11) for rinsing objects with metal cyanides are contaminated, the means for circulation being adapted to contain a dilute metal cyanide solution is recirculated from the rinsing bath through the cell or -! 7. Apparatus according to claim 2, characterized in that at least the cathode or the The anode is made of platinized titanium. 8. Apparatus according to claim 2, characterized g e k.e η η that at least the cathode or the Anode is made of titanium coated with lead dioxide. 9. Apparatus according to claim 2, characterized in that the cathode is made of copper is. 10. Process for the treatment of dilute metal cyanide solutions, characterized in that an electrolytic cell with a cathode and a -17- 80 9829/0833 7 - Anode, wherein the cathode and the anode have irregularly shaped effective surfaces and are mated and arranged so that the ratio between the effective surface of the cathode and that of the anode is between 1.3 i 1 and 2: 1, a bed of not -provides conductive particles in the cell adjacent to the effective surfaces of the anode and the cathode, the dilute metal cyanide solutions to be treated circulates through the cell so that the electrolyte flows upwardly through the bed so that it is swirled and that there is between the cathode and the anode conducts a current to deposit metal on the cathode and oxidize cyanide on the anode. 11. The method according to claim 10, characterized in that the to be treated is diluted Metal cyanide solution is recirculated through a treatment bath for rinsing objects contaminated with metal cyanides or bypasses. 609829/083 3 Blank page