CH642033A5 - Process and equipment for the treatment of waste waters containing heavy metals - Google Patents

Description

The object of the present invention is therefore the recovery of heavy metals from waste water in a closed circuit, which can be carried out in pure form reliably and without great maintenance and chemicals, with good electricity yield and with recovery of the separated heavy metals, and in which the device used is simple and clearly structured is.

This object is achieved by a method with the features specified in claim 1 and by an installation for carrying out this method.

The only figure in the attached drawing shows the flow diagram of a preferred form of the method according to the invention.

By connecting the electrolytic cell downstream of the concentration and cleaning device, it is possible to use relatively slightly modified conventional electrolytic cells with electrode arrangements, from which the deposited metals can be removed in a simple mechanical manner, which are simple and inexpensive to produce. Due to their simple design, these cells are only slightly prone to malfunction and easier to operate than the complex compact electrolysis cells.

If an ion exchange, reverse osmosis, electrodialysis, dialysis, ultrafiltration or evaporation system is used as the concentration and purification device, the operation of these simple electrolysis cells is made possible in an optimal concentration range; In particular, the embodiment of the invention, in which ion exchangers are used as concentration and cleaning devices, ensures a very economical process, since high concentrations of heavy metal ions can be used in the solution, the electrolysis of which results in highly concentrated acidic and base-containing electrolyte solutions which can be recycled to the ion exchangers for regeneration or elution. This keeps the operating costs extremely low. In the process according to the invention, ion exchangers can therefore serve on the one hand to produce a concentrated heavy metal ion solution and on the other hand to separate them from the wastewater containing further impurities, some of which are in ionic form, and thus have two functions, whereas according to the prior art they only have the prescribed maximum concentrations of heavy metals should achieve. The discharge from the ion exchangers obtained according to the invention can be kept largely free of heavy metals. In addition, using special circuits and when using certain ion exchange resins, disruptive constituents can be separated from the solution prior to electrolysis, so that the purity of the electrodeposited metals is significantly improved.

Furthermore, the method according to the invention offers a great deal of flexibility and allows the heavy metal to be removed selectively and from the officially approved values both from very dilute wastewater containing only a few ppm heavy metal and from concentrated wastewater with several 10,000 ppm heavy metal in a single process step .

Various process stages can be combined in the process according to the invention. For economical and effective operation of the electrolysis unit, it is advisable to increase the heavy metal concentration to over 1.5 g / l, in particular to 10 to 150 g / l, depending on the type of metal, if the wastewater obtained has a lower heavy metal content. This takes place in corresponding concentration and cleaning devices, such as ion exchange columns, reverse osmosis, electrodialysis, ultrafiltration, dialysis, electrolysis or evaporation devices. As a rule, however, the concentration device must selectively separate the heavy metal in such a way that the resulting portion of solution with a low heavy metal content can either be economically reprocessed either in a demineralization device, such as an ion exchange circuit, or in a reverse osmosis device or the like can be derived directly without additional treatment.

The heavy metal concentration required and desired for the electrolysis cell can be generated continuously. For this, e.g. continuously eluate from the concentration and purification device in the mass, as heavy metal is deposited on the cathode, into the electrolysis cell. Continuous concentration processes such as reverse osmosis, electrodialysis or continuous ion exchange are particularly well suited for this. An almost continuous admixture of eluate can also be achieved with the use of ion exchange columns with two columns if, in a conventional system, the column in operation brings about concentration, while the second column is continuously regenerated. Here, the second column is continuously flowed through with acidic or alkaline electrolyte, which contains little heavy metals, as a regenerating agent. In the case of continuous process control, the electrolyte provided for the regeneration is collected in a compensating vessel as an intermediate storage container and pumped from there into the regeneration and washing column of the continuous system.

When using an ion exchanger, the heavy metal contained in the wastewater can be bound to an ion exchange resin and thus separated from the other ions. The heavy metal ions are usually subsequently coated with an alkaline electrolyte, e.g. dilute sodium hydroxide solution, which is formed in the electrolytic bath during the electrodeposition of the heavy metals, or with an acidic electrolyte, e.g. Contains sulfuric acid, eluted. The eluted solution that the

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Contains heavy metal ions in concentrated form, is usually introduced continuously into an electrolysis cell. The heavy metal can be recovered electrolytically and the heavy metal concentration of the solution in the electrolytic cell can be continuously supplemented in the form of the heavy metal-containing eluate of the ion exchange column. If the electrolyte is alkaline, a weakly acidic cation exchange resin or a weakly basic anion exchange resin is usually used in the ion exchange stage. In contrast, when an acidic electrolyte is used, a strongly acidic or a weakly acidic cation exchange resin is suitable as the ion exchange resin.

The effluent from the ion exchange resin, which contains no or only a small amount of heavy metal, is expediently directed to a desalination device for water recovery. By separating the ions still present, purified water can be formed, which can be returned to the plating process and reused there as rinsing water. Of course, the process can also be derived directly.

According to the flow diagram in the figure, the essential components of the device according to the invention are a concentration and purification device 1, shown here as an ion exchange system, an electrolytic bath 2 and a device 21 for circulating the electrolyte. With A a metal refining or surface treatment plant, e.g. denotes a plating system with a plating bath, a recovery tank, a standing wash tank or a running wash tank. B is a desalination device for the recovery of industrial water by further cleaning the discharge coming from the ion exchanger, which has been largely or completely freed from heavy metal ions,

designated. This facility can e.g. an ion exchange circuit, an evaporation electrodialysis, dialysis, electrolysis, ultrafiltration or reverse osmosis device.

The ion exchange columns 5, 5 'can be installed in pairs or in multiple combinations in the concentration and purification device 1, so that continuous treatment is possible without the need to interrupt the loading of the electrolyte during the elution (regeneration). A continuous separation of the heavy metal ions from accompanying ions by adsorption and the elution of the heavy metal ions with the electrolyte simultaneously in the same ion exchange columns containing continuous fixed and floating beds made of ion exchange resin is particularly effective.

Weak or strongly acidic cation exchange resins can be used to fill the ion exchange columns 5 and 5 'for the separation or concentration of cations. Depending on the heavy metal concentration and pH of the medium, it is necessary to operate the resins either in the H form or after conditioning in the Na form. Conditioning is particularly important for weakly acidic cation exchange resins when the pH of the solution to be prepared is low, otherwise the resin's capacity for heavy metals is too low.

To remove anions or anionic complexes, weakly or strongly basic anion exchangers are used in the OH form or conditioned in the salt form (preferably chloroid or sulfate form).

Weakly acidic or basic exchangers have a relatively strong selectivity for certain heavy metals or heavy metal complexes. In some cases, however, this selectivity is not sufficient, so that it is necessary to use special chelate resins known to the person skilled in the art.

The arrangement of the electrolysis cell, the composition of the electrolyte and the electrolysis conditions are selected so that the most suitable conditions are present for the electrolytic recovery of the desired heavy metal. In a preferred embodiment of the invention, an electrolysis cell of the following type is used: The electrolysis cell 8 contains at least one cathode plate 14 in the cathode space 14 'and one anode plate 15 in the anode space 15' and a diaphragm 16 with porous walls. The electrolytic cell is connected at 38 to the power source with a rectifier. It preferably has a heating device 37.

The cathode plate 14 may be made of iron, stainless steel, aluminum or other metal suitable for the electrolytic recovery of the desired heavy metal. A normal plate electrode is preferably used, but is provided with an angle rubber strip, which is arranged on the circumference of the electrode, for better detachment of the metal coating which forms. When the deposited metal has reached a thickness of 0.2 to 1 mm, it can be easily lifted off with the help of the rubber strip and used as a new cathode instead of the original plate cathode. The metal layer then increases evenly and there are no difficulties in separating the deposited metal from the original electrode.

The anode plate 15 consists of lead or a lead alloy for an acidic electrolyte. For an alkaline electrolyte, the anode plate 15 consists of an insoluble material suitable for the electrolytic recovery of the heavy metal under consideration. The use of the acidic or alkaline electrolyte as a regenerant in the ion exchange column 5,5 'requires a high acid or alkali concentration in the anode space of the electrolytic cell and therefore a corrosion-resistant material is used for the diaphragm 16. The circulation device 21 for the electrolyte is designed such that alkaline or acidic electrolyte can circulate through the ion exchange column 5, 5 '. In this version, a pump P3 is used for the circulation. It is advantageous to regulate the pH of the catholyte by being able to return part of the anolyte to the cathode chamber.

The control device for the eluate contains a sensor 7 which indicates the end of the elution of the heavy metal from the ion exchange column 5 or 5 '. This sensor can also be used to monitor the end of the subsequent conditioning (transfer of the resin to the salt form).

The system according to the invention also has a compensating vessel 18 in which the outflow which occurs when the electrolyte is circulated from the ion exchange column 5 or 5 'is temporarily stored. A closed system for the recovery of heavy metals is obtained by using the devices described.

In order to maintain uniform electrolysis conditions in the electrolysis cell, it is advantageous to e.g. to stir by means of the circulation device 21, to filter, to clean with activated carbon and / or to control its temperature and the pH by means of the heating device 37 and measuring device 36. This can e.g. by taking a partial flow of the solution to be electrolyzed from the electrolytic cell 8 and passing it via line 23 to a special cleaning filter 24, which contains absorption material, and from there returning the cleaned solution via line 25 'to the electrolytic cell 8. This cleaning is particularly appropriate when s

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the solution to be electrolyzed strongly. organic and / or inorganic substance, which leads to disturbances in the metal deposition. In this case, activated carbon, macroporous inert absorption material based on an organic polymer or macroporous ion exchanger can be used as the absorption material, the latter being able to be regenerated with alkaline electrolyte which is formed in the same cell.

An electrolysis solution is particularly advantageous here, which in addition to high alkalinity also has a high neutral salt content. Cleaning can be done before or during the electrolysis process. If, for example, during the electrolysis from a solution that contains heavy metal in the form of organic complexes, organic substance is continuously formed by splitting the complex, then it is advisable to recycle through the cleaning filter during the electrolysis. The organic substance resulting from the heavy metal complex can be split into smaller molecules during the electrolysis process by chemical reactions, which e.g. reduce its purity by embedding it in the surface of the deposited metal. By continuously removing a certain proportion of this organic substance in the filter 24, its content in the electrolysis solution can be adjusted to such a low concentration that the metal deposition is not impaired.

A circulation circuit 23, 25 with a circulation pump P2 is provided for better mixing of the electrolysis liquid.

In the figure, a system with two ion exchange columns is shown. If only one ion exchange column or another discontinuous concentration and cleaning device, such as an evaporator system, is used, the desired heavy metal concentration in the electrolyte can be maintained by interrupting the electrolysis process when the concentration falls below this concentration and the solution containing heavy metals via the concentration and cleaning device 1 is circulated until either the desired maximum concentration is reached or the ion exchange resin is loaded when using an ion exchanger. The eluate formed during the regeneration of the ion exchange resin is either admixed with the remaining heavy metal above the permissible value until the desired maximum concentration is reached, or the concentrate or eluate is used again directly for the electrolysis. A prerequisite for this, however, is that the electrolyte solution, after it has been circulated over the ion exchangers, has been freed of heavy metal to such an extent that it can be removed after this concentration and heavy metal separation process.

For the continuous recovery of heavy metals, however, it is better to use two or more ion exchange columns 5,5 'or to use continuous ion exchange systems whose ion exchange columns contain ion exchange resin 6,6' in floating and fixed bed form and from which, depending on the loading state of the bed, batches are taken, are regenerated in external regeneration columns and, after regeneration and the washing out of excess regeneration agents, are returned in ion exchange operating columns.

It is favorable to use 3 ion exchange columns, 2 of which are connected in series and the third is regenerated or eluted with anolyte from the electrolysis cell.

The series connection of the ion exchangers in the operating state serves to load the first ion exchanger up to a total capacity, so that the highest possible heavy metal concentration in the eluate is achieved in the subsequent elution. The first ion exchanger is therefore extended until the outlet concentration of heavy metal ions is equal to the inlet concentration. The ion exchanger switched in the second stage is then brought into position 1 and the meanwhile eluted and conditioned third exchanger in position 2. The ion exchanger previously in position 2 is then regenerated with anolyte from the electrolytic cell.

It is generally necessary to switch on the concentration and cleaning device 1 if, for any reason, the heavy metal solution contained in the electrolytic cell, the heavy metal concentration of which is still above the officially approved values, has to be drained off. However, the solution can then be prepared without concentration using conventional techniques by chemical detoxification and neutralization.

Another embodiment is illustrated by electrolytic nickel recovery from rinse water containing nickel ions used in the metal surface treatment method A. Used rinsing water, which contains nickel ions and is obtained in process A, is fed into the ion exchange column 5 via a preliminary tank 40 with a pump PI and line 12. There, nickel ions are bound to the weakly acidic cation exchange resin 6, which is conditioned in the Na form. The outlet of the ion exchange column contains the sodium exchanged for nickel. It is passed via line 13 into a desalination device B and a neutral salt extraction unit B 'for the recovery of water and neutral salts. In this facility, the water is desalted and then sent to process A for reuse. If a further ion exchange column 5 'is present, the recovery operation can take place continuously, since used rinsing water containing nickel ions can flow into one ion exchange column while the other column is eluted, washed and conditioned to the sodium form after it has been loaded with nickel ions and exhausted has been.

After the ion exchange resin 6 in the ion exchange column 5 has been exhausted by nickel ions, the rinse water supply from the nickel plating into the ion exchange column 5 is interrupted. The exchange resin 6 is washed with pure water or soft water to remove Cl ", SO42" etc.

After removal of the used washing water from the ion exchange column 5.5 ', the electrolyte still present from the electrolysis cell 8 via the equalization tank 18 by means of the pump P3 via valve 20, line 9, flow meter 19, line 10 and valve 3 for eluting the nickel ions from the Pumped ion exchange resin 6 'into the ion exchange column and started the electrolysis process in the electrolysis cell 8.

The electrolysis cell 8 and the ion exchange column are connected via the lines 9 and 10, which lead to the ion exchange shear column 5 ', and line 11, which is connected to the electrolysis cell 8. The electrolysis in the electrolysis cell 8 results in a nickel deposition on the cathode plate 14 and an acidification of the solution, due to anionic concentration around the anode plate 15. Then the acidified anolyte is transported with the pump P3 into the ion exchange column 5 'via lines 9 and 10. Here, nickel ions adsorbed by the ion exchange resin 6 'are eluted by the acid in the anolyte to form nickel sulfate. The eluate is again conducted via line 11 into the electrolysis cell 8. If this operation is carried out continuously until the nickel ions adsorbed on the ion exchange resin 6 'are completely

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are eluted out, the pH value of the solution at the outlet of the ion exchange column 5 ′ gradually decreases towards the end of the elution, which is then determined with the sensor 7.

After the nickel ions are completely eluted from the ion exchange resin 6 ', the operation is diverted to the ion exchange column 5, where the nickel ions are separated. As a result, the electrolysis for nickel recovery can be carried out continuously.

Recirculated solution containing nickel ions, which remains in the ion exchange column 5 'after the nickel ion elution, is passed via line 17 and valve 22 into the compensating vessel 18. This container 18 generally has the function of holding electrolyte or eluates containing heavy metals, washing water and the like. When the system is started up, the electrolytic cell 8 and the container 18 are filled with eluate from the ion exchanger or a specially prepared electrolyte. The anolyte which is withdrawn from the anode space 15 'for the regeneration of the one exchanger runs continuously into the container 18 and is circulated from there via the ion exchanger to be eluted. Due to the heating of the solution with the heating device 37 in the electrolysis cell and the heat generated by the chemical reaction, the volume of liquid is continuously evaporated during the electrolysis process. As a result, the water level in the container 18 decreases. During backwashing and the washing processes that take place before and after the regeneration of an ion exchanger, the higher metal content of backwashing and displacing water as well as washing water is passed into the container 18. Only dilute solutions with little metal are fed into the desalination device B and neutral salt extraction unit B 'with disaster unit C and demineralization water tank 39 and / or desalination unit D.

On the other hand, the compensation vessel 18 contains nickel-free or low nickel-containing electrolyte when processed electrolyte with a low nickel or heavy metal content is passed over the ion exchanger for concentration. In this case, the heavy metal is absorbed by the ion exchange resins. When circulating via the circulation pump P3, which corresponds to that of the anolyte when eluting an ion exchanger, there is a gradual depletion of heavy metals until the desired residual metal content is reached, which should be below the value of the official guidelines.

After the elution and before restarting the ion exchange resin in the ion exchange column 5 ', the exchange resin is conditioned into the Na form. This is carried out by passing sodium hydroxide solution via line 12, the ion exchange column 5 ', line 13 and the desalination device B. If necessary, the alkaline electrolyte generated in the electrolysis cell can be used as the sodium hydroxide solution. If several electrolyte baths are arranged side by side, the alkaline electrolyte from another electrolytic cell can also be used. Conditioning is also possible with fresh water, the content of calcium and magnesium ions of which has been replaced by sodium by softening. Raw water with a high calcium and magnesium hardness is advantageous in order to obtain the highest possible concentration of sodium in the softened water used for conditioning.

If an additional desalination unit D, such as an ion exchange circulation system or the like, is available for rinsing water desalination or for desalting the outflow of the concentration and cleaning device of the recovery system, conditioning of the ion exchange is possible by adding a partial stream of the desalinated water generated there with sodium hydroxide solution and for conditioning via the ion exchange column which is not in operation. In this type of conditioning, the sodium of the sodium hydroxide is taken up by the ion exchanger to be conditioned and deionized water is formed which, in order to avoid water losses, can be returned to the rinsing water circuit of the process from which it was removed. The water supply for the desalination unit D for the regeneration and washing of the ion exchange columns 5.5 'takes place via E4. Demineralized water obtained in the various stages of the method according to the invention can be collected in the demineralization water tank 39.

If the concentration and purification device consists of at least two ion exchangers, a regenerated and conditioned ion exchanger can also be connected in series with a regenerated but not yet conditioned ion exchanger in the H + or OH ~ form. If you now load the regenerated and conditioned ion exchanger with heavy metal ions from the wastewater, the downstream regenerated ion exchanger is conditioned by the ions displaced from the upstream ion exchanger.

According to the method according to the invention, heavy metals, neutral salts and water can be recovered at the same time using a closed system with a closed circuit and catastrophe system by passing a solution containing sodium salt through line 13 into the desalination device B with a neutral salt extraction unit B ' 5 or 5 'was passed through a weakly acidic cation exchange resin 6 during the nickel ion adsorption. The resulting demineralized water can be recycled to Process A where it can be reused. The metal that was recovered in the electrolysis plant 2 can be reintroduced into the plating plant A via EL. Water that has evaporated in a closed circuit is added via E2.

If the pH value in the electrolysis cell 8 increases undesirably, the pH value can be lowered by admixing solution from the compensating vessel 18 via lines 9 and 33 to the electrolysis cell. For this purpose, a partial stream is branched off from the anolyte, which is circulated through the ion exchanger to be eluted. In this case, the ion exchanger is bypassed, since acid is consumed when the ion exchanger is eluted and therefore the eluate returning from the ion exchanger into the electrolysis cell contains less acid than the anolyte which is located in the compensation vessel 18.

A measuring device 36 is used to check the pH value, the heavy metal concentration and possibly also the organic impurities in the electrolysis cell 8. Another measuring device 34 is used to check the pH value, heavy metal content and toxin content in the disaster tank 35 of the disaster unit C, so that no treated water is drained into the receiving water. From the disaster tank 35, above all water that is produced in B in excess is discharged via E3.

To explain the method according to the invention, the quantitative information for five examples is compiled below:

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example 1

Nickel recovery from waste water with a low heavy metal content

Table I

Test conditions and results

Waste solution

Outflow that occurs when flushing in a nickel plating bath. Dissolved ions

Ni ++ = 95 ppm, Na + = 20 ppm

SO4- = 140 ppm, Cl- = 30 ppm

Ion exchange resin weakly acidic cation exchange resin (Na form)

volume

11

Ni ++ loading

90 g / 1

Electrolytic bath

51

Anode plate

Pb (2 plates)

Stainless steel cathode plate immersed part of the plate

2 dm2

Composition of the electrolyte

NÌSO4 (as Ni content) 40 g / 1

Na2S04 40 g / 1

H3BO3 40 g / 1

Vol. D. Electrolytes

61

Current density

1.25 A / dm2

Electrolyte circulation

2 1 / h pH d. Electrolytes

1.6 to 2.5 anode side

4.0 to 5.5 cathode side

Electrolysis time

48 h pH of the solution at the outlet of the

5 to 6

I on exchange column

Results

Ni deposition

121g

Current efficiency

92.5%

Example 2

Nickel recovery from waste water with a high heavy metal content

Table II

Test conditions and results

Waste solution used rinse water in a recovery tank (standing rinse tank) from

ions dissolved in a Ni plating process

Ni ++ = 4800 ppm, SO4- = 6500 ppm, Ch = 1000 ppm

Ion exchange resin the solution is drawn off from the weakly acidic ion exchange resin which

into the H form by complete elution of the Ni ++ adsorbed in Example I.

was transferred and the exchanger is washed with water. Then it will be

NaOH solution at a rate of SV = 4 for conditioning to the Na form

passed through. The resin is then used for subsequent use

washed with water for 1 hour.

Electrolytic bath

Cathode plate the nickel deposited on the cathode plate in Example 1 is removed

and processed into an electrode plate

Electrolysis time

72 h

The other conditions are the same as in Example 1

Results

State of Ni deposition

The deposition mainly consists of a nickel plate, which acts as an anode

can be used in Ni plating

Composition of the deposited

Fe 0.01% or less

Ni plate

Cu 0.001% or less

Pb 0.01% or less

Ni 99.9% or higher

Current efficiency

95%

642 033

Example 3 Copper recovery

Table III

Waste solution dissolved ions pH value flushed water from an acid pickling process Cu ++ = 60 ppm, SO4- = 150 ppm 3

Ion exchange resin volume

Rate at which the waste water flows into the ion exchange resin weakly acidic cation exchange resin (Na form) 11

SV = 20

electrolysis

Cathode plate anode plate the electrolysis takes place while Cu ++ is eluted from an ion exchange resin depleted with Cu ++ by countercurrent circulation of the electrolyte from an electrolytic bath Cu hard Pb (Sb = 3.5%)

Results

Cu deposition

Current efficiency

99.9% or higher 95%

Example 4 Copper recovery

Table IV Test conditions and results

Waste solution dissolved ions pH value flushed water from an acid pickling process Cu ++ = 60 ppm, SO4- = 150 ppm 3

Ion exchange resin weakly acidic cation exchange resin (Na form)

Volume 11

Rate at which the waste water enters the

Ion exchange resin flows SV = 15

Cu "" * Cu ++ <0.1 ppm bound Cu + * Cu = 90 g remaining in the solution after the ion exchange

Diaphragm-free electrolysis

Cathode plate Cu 1 dm2

Anode plate Pb 1 dm2

electrolytic bath 11 beaker

Electrolyte CuSCk 50 g / 1

H2SO4 50 g / 1

Temperature 25 to 30 ° C

Current density 1 A / dm2

The electrolysis takes place while Cu ++ is eluted from the ion exchange resin depleted with Cu ++ through the circulating electrolyte

Results

Cu deposition 85 g

Composition Cu at 99.9% Fe s; 0.01% Pb; 0.01%

Current efficiency 98%

642 033

OK

Waste water dissolved ions

Example 5

Zinc recovery from waste water with low zinc content

Table V

Test conditions and results

Waste water containing ZnS04 Zn ++ = 50 ppm, S04 ~ = 80 ppm

Ion exchange resin volume

Rate at which the waste water flows into the ion exchange resin bound Zn ++

weakly acidic cation exchange resin (Na form) 11

SV = 15 Zn ++ = 100 g

Electrolysis cathode plate

Use of an AI diaphragm

Anode plate electrolytic bath electrolyte composition

Temperature current-tight electrolyte circulation

Pb

11 beaker ZnSÜ4 Ah (S04) 3 H3BO3 40 ° ± 5 ° C 4 A / dm2 SV = 5

250 g / 1 30 g / 1 20 g / 1

Results of Zn deposition

Current efficiency

Composition: Zn ^ 99.9% Fejï 0.1% Cuä 0.05%

98%

When using the method according to the invention for the electrolytic recovery of chromium from waste water containing chromium, the chromium is reduced to Cr3 + ions if it is not already in this form. After the pH has been adjusted, the solution for binding the chromium ions is then passed over the ion exchange resin. After the resin has been exhausted, the bound chromium ions are eluted by passing the acidic electrolyte containing chromium sulfate and sulfuric acid into the ion exchange resin column after reduction of Cr6 +. The electrolyte is removed from the anode chamber 15 'of the electrolytic cell 8, which is separated with a diaphragm 16 into a cathode space 14' and an anode space 15 '. The chromium-laden eluate is continuously fed into the cathode chamber 14 'in order to electrolytically recover the chromium.

In the electrolytic recovery of zinc, copper, silver or gold from wastewater, which contains pyrophosphate ions or other complexing agents or which contains the heavy metal ions in the form of cyanide complexes and is formed when plating with cyanide zinc, copper, silver and gold baths, In order to avoid blocking of the anion exchanger, which takes up the anion-active complex, it is necessary to first pre-clean the solution by means of a cation exchanger. The cation exchanger removes metal that contaminates the solution. The metal complex freed from disruptive heavy metals is used for electrolysis.

The binding of the metal complexes and the separation of other anions still present is then carried out in a column with weakly basic anion exchange resin. The anion exchange resin, which is depleted by the heavy metal complex loading, is regenerated with an electrolyte containing sodium hydroxide. Because of the

35 high selectivity of the anion exchanger used, it is necessary to add a strong complexing agent such as sodium cyanide or organic complexing agents such as ethylenediaminetetraacetic acid, 40 nitrilotriacetate and the like to the regeneration solution in addition to the alkaline electrolyte or sodium hydroxide solution. The capacity and selectivity of the resins used, in particular a weakly acidic cation exchanger for cleaning or a medium-based anion exchanger for concentration, can be determined by conditioning the exchanger after elution of the heavy metals or heavy metal complexes using an alkaline electrolyte or sodium hydroxide solution in the case of weakly acidic cation exchangers using an acidic electrolyte, Sulfuric acid, hydrochloric acid in medium-based anion exchangers and using highly concentrated neutral salt solutions, such as Sodium chloride solution or sodium sulfate solution can be improved when using a strongly basic anion exchanger. If the solution to be processed contains a lot of foreign metal or a lot of neutral salt in addition to the complex-bound metal,

can be used for cleaning, i.e. to connect upstream of the concentration exchanger, a chelate resin may also be necessary in order to achieve sufficient capacity or sufficient separation or interfering substances.

For certain anionic heavy metal complexes, medium-based ion exchange resins have a significantly better capacity than strongly basic anion exchange resins under certain conditions, namely that the solution to be prepared is not too alkaline. Furthermore, certain complexes can normally be eluted better from medium-based ion exchange resins than from strongly basic ones. Strongly basic anion exchange resins in the neutral form have particularly good selectivity for certain noble metal complexes (silver and gold cyanide complexes).

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By layering both ion exchangers in a layer bed, considerable capacity improvements and also the separation of different metal complexes from one another can be achieved if regeneration is carried out alternately with an alkaline regenerant, once without and once with a complexing agent.

If the pH of the electrolyte is not sufficient to regenerate the ion exchanger, it can be adjusted accordingly by adding acidic or basic solutions. For acidic conditioning, a tank 30 containing sulfuric acid is used, from which, with a low metal content in the electrolysis cell or in the compensating vessel 18, sulfuric acid is introduced into the circuit via line 31, so that the ions can be properly eluted642 033

exchange column is possible. Accordingly, there is 32 sodium hydroxide solution in the conditioning tank, which is fed via the pump P3 and line 10 for conditioning into the eluted ion exchanger.

With the method according to the invention, heavy metals can be recovered by recycling treatment and, in addition, purified water can be obtained from effluents which contain mixed or different ions by simultaneously using a demineralization and neutral salt recovery unit for industrial water recovery. The method according to the invention thus simultaneously controls environmental pollution and avoids wasting valuable raw materials.

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Claims (19)

642 033 2nd PATENT CLAIMS 1. A process for the treatment of heavy metal-containing waste water with recovery of heavy metals, the waste water containing heavy metal and other ions being passed through a concentration and cleaning device, characterized in that the concentration and cleaning device is regenerated by the electrolyte accumulating in the electrolysis cell and introduces the eluate containing heavy metal ions into the electrolytic cell. 2. The method according to claim 1, characterized in that the eluate containing heavy metal ions is continuously introduced into the electrolysis cell and the wastewater purified from the heavy metal ions is removed to remove further impurities in a desalination device. 3. The method according to claim 1 or 2, characterized in that when the electrolysis process is interrupted with the remaining heavy metal ions of the solution present in the electrolysis plant, the concentration * and cleaning device is loaded and treated wastewater is withdrawn from the concentration and cleaning device. 4. The method according to any one of claims 1 to 3, characterized in that if the pH in the electrolysis cell increases undesirably, a partial stream of the electrolyte is returned directly from a compensating vessel to the electrolysis cell. 5. The method according to claim 1, in which an ion exchange system is used as the concentration and cleaning device, wherein the ion exchanger is also regenerated by the electrolyte accumulating in the electrolysis cell and the eluate containing heavy metal ions is introduced into the electrolysis cell, characterized in that when interrupted of the electrolysis process with the remaining heavy metal ions of the solution present in the electrolysis system loads the ion exchanger and withdraws treated wastewater from the ion exchanger. 6. The method according to any one of claims 1 to 4, characterized in that a reverse osmosis, dialysis or electrodialysis system is used as the concentration and cleaning device. 7. The method according to claim 5, characterized in that chloride and sulfate ions are washed out of the ion exchanger of the ion exchanger system by means of soft water before the start of the regeneration. 8. The method according to claim 5, characterized in that the ion exchanger of the ion exchanger system is regenerated by means of the anolyte. 9. The method according to claim 2, characterized in that the further impurities are removed by means of an ion exchange system, an evaporation system, an electrodialysis system or a reverse osmosis. 10. Plant for carrying out the method according to claim 1, characterized in that a concentration and cleaning device (1) an electrolysis plant (2) containing an electrolysis cell (8) with cathode plates (14), anode plates (15) and diaphragms (16) is connected downstream and the electrolysis system (2) is connected to the concentration and purification device (1) via a line (4), a compensation vessel (18) and a circulation device (21). 11. Plant according to claim 10, characterized in that the concentration and purification device is a reverse osmosis, dialysis, electrodialysis or ion exchange system. 12. Plant according to claim 11, characterized in that there are at least two ion exchange columns (5,5 '). 13. Plant according to claim 10 or 11, characterized in that the ion exchanger system (1) is followed by a desalination device (B) in the form of an electrodialysis, reverse osmosis, ion exchanger or evaporation system for water recovery. 14. Plant according to one of claims 10-13, characterized by a circulation circuit consisting of the electrolytic cell, a circulation pump, corresponding connecting lines and a bypass line which leads via a cleaning filter. 15. Plant according to one of claims 10-14, characterized in that the electrolysis plant (2) is an electrolysis plant with a relatively small ratio of electrode surface to cell volume. 16. Plant according to claim 10 or 15, characterized in that the anode plates (15) in the anode space (15 ') of the electrolytic cell (8) and the cathode plates (14) in the cathode space (14') of the cell are made of insoluble material and that the cathode itself has the shape of a plate and can be used again as a cathode plate after the metal deposited thereon has been detached. 17. Plant according to one of claims 10-12, characterized in that the concentration and purification device (1) is an ion exchanger and the plant comprises at least one desalination device (B) or / and (D) to in this one of Ca2 + - and to produce Mg2 + -free water which can be fed to the ion exchanger (1). 18. Plant according to one of claims 10-12 or 17, characterized in that the concentration and cleaning device (1) is an ion exchanger, that the plant has at least one desalination device (B) and / and (D) in order to obtain demineralized water therein, and that the system further comprises a conditioning tank (32) intended for receiving sodium hydroxide solution, a tank (30) intended for receiving acid and the compensating vessel (18) as a tank for receiving alkaline or acidic electrolyte as well as corresponding lines (13, 13 '). 19. Plant according to one of claims 10-13, 17 or 18, characterized in that it serves as a concentration and purification device (1) at least two ion exchange columns (5,5 ') and devices for regeneration and conditioning of the in the columns (5, 5 ') contained ion exchange resin (6 or 6') and a line for connection to the electrolytic system (2) and for repeating the conditioning. In order to avoid environmental pollution as well as for cost reasons, it has been necessary for some years to recover heavy metals from wastewater that occur during metal surface treatment in pre-rinse baths such as standing sinks and cascade cascades, if possible in a closed circuit system with a disaster system. As closed water recycling systems, not only circulation ion exchange systems, but also reverse osmosis, dialysis, electrolysis, evaporation, ultrafiltration and electrodialysis devices are used in practice. However, none of these processes enables the economical and technically simple recovery of heavy metals. A plating plant is often used to recover valuable heavy metals from electrolyte solutions 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 3rd 642033 Recovery tank used for the electrolyte solution carried out of the plating bath together with the electrodes, and a standing sink or standing sink tank. The main amount of the electrolyte solution that is carried out is recovered there. The recovered solution is then returned to the plating bath to compensate for the electrolytic solution lost through evaporation when the electrolytic solution is used at a higher temperature. If the temperature of the electrolyte is low and the evaporation loss is not too great, the recovered solution can also be concentrated by evaporation, reverse osmosis or electrodialysis to a concentrate with a composition similar to that of the electrolyte solution. Due to the decomposition of the additives in the solution and the accumulation of unwanted metals and other impurities, the extraction of the heavy metal compounds, together with the concentration of the recovered solution and its repeated use as an electrolyte, causes an earlier exhaustion of the electrolyte solution. This type of recovery has therefore proven to be disadvantageous; in any case, it is not possible to continuously produce good claddings for a long time. From Meinck, Industrieabwässer, 4th edition, 1968, pages 149, 200, 201 and 211, various methods for processing waste pickling are known. Various processes for treating waste water from the metalworking industry are known from the separate print from “Chemische Rundschau” 24, 1971, No. 23, pages 3 to 11. However, these known methods have in particular the disadvantage that the cleaning systems used have to be regenerated with expensive chemicals. In another known method for the recovery of heavy metals, the pH of the solution containing heavy metal ions is adjusted so that heavy metal hydroxides are formed. The heavy metal hydroxides are then separated off as a solid residue or sludge with dewatering. The heavy metal is then dissolved by circulating an acid electrolyte (anolyte). The heavy metal ion is extracted and the solution containing the heavy metal salt is used to re-sharpen a treatment or electrolyte bath, followed by the electrolysis. In this known process, the dissolved heavy metal is precipitated as a hydroxide and is thereby separated from the other cations and anions (SO42-, Cl ~, NO3 etc.). However, if there is a high concentration of metal ions and other ions in the solution, it is difficult to completely separate the metal ion. Often the metal hydroxide contains various contaminants that can accumulate in the electrolyte and cause a large change in its composition and severe corrosion of the anode. This means that expensive insoluble anodes e.g. made of platinum or platinum titanium etc. Another disadvantage of the known method is that additional purification processes have to be carried out and that this makes the entire recovery process complicated and expensive. Furthermore, in known processes for the electrolytic recovery of metals from solutions containing heavy metals, in particular those with low or medium concentrations of heavy metals, electrolysis cells with electrodes are used which have very large electrode areas. These systems are e.g. designed as winding electrodes, fluidized bed electrodes, fixed bed cells and the like. The ratio of electrode area to Electrode cell volume increased as much as possible. These electrodes were developed because the conventional electrolysis with plate electrodes at heavy metal concentrations of 10 to 100 mg / 1, as is very often found in waste water, has a very poor electrical efficiency and treatment effect. With such constructions, the officially prescribed limit values for the residual heavy metal contents, which for most metals are in the range of 0.5 to 3 mg / 1, can either not be achieved at all or only extremely economically. The above-mentioned electrolytic cells with very large electrode areas can partially overcome these disadvantages. However, in spite of a more favorable ratio of electrode area to electrolytic cell volume, the economy and the treatment effect of modern electrolytic cells also decrease very strongly with heavy metal concentrations in the wastewater of less than 10 mg / 1. Therefore, in the known methods, the electrolysis is not carried out up to the permissible limit values mentioned above. Rather, the electrolysis cells are followed by ion exchangers, such as weakly acidic and strongly acidic cation exchangers or weakly basic or strongly basic anion exchangers, but preferably weakly acidic and weakly basic exchangers in order to achieve the prescribed limit values. After loading the ion exchangers, they are eluted with chemicals that are supplied separately and cannot be produced in the electrolysis cells. The eluates are led into the electrolysis cells. The circuitry of the ion exchangers is only designed to achieve the prescribed maximum concentrations of heavy metal ions in the wastewater with still economical chemical expenditure. However, it does not serve to switch off high-purity metals by appropriate separation operations or concentrations in the electrolysis cell. As already stated, the modern electrolysis cells work more economically, but still do not achieve the prescribed minimum heavy metal content in waste water. The construction of these known electrodes in the form of interwoven cathodes and anodes, the use of metal particles in the fluidized bed as the cathode or the compact arrangement of very tightly fitting flat electrodes next to one another have the disadvantage of that the amount of metal to be deposited on the surface of these electrodes is comparatively small and the metal that has been deposited can generally only be detached chemically from the electrodes. On the other hand, the resulting metal layer can be removed very easily mechanically in the form of a metal plate or a metal sheet from the conventional plate electrodes. In order to enable the proposed compact electrodes to work economically, the turbulence at the electrode surface must also be increased, i.e. the mass transfer coefficients from the solution to the metal surface must be increased by more intensive solution movement. For all proposed compact electrode systems, this means that in addition to the energy required for the electrolysis, additional mechanical energy must be introduced, which in the form of pump lines to achieve high flow velocities in the winding electrode arrangements, in the form of agitator energy to generate high turbulence on the electrode surface built-in agitators or in the form of energy for moving a fluidized bed within a rotating electrolysis cell. This shows that such modern electrolysis systems are extremely complex and therefore require high investment 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 642033 most require. Furthermore, they are susceptible to faults in maintenance and operation and are difficult to operate due to the difficult removal of the deposited metals. The ion exchangers downstream of the electrolysis to remove the remaining heavy metal content must primarily in the form of selective exchangers, i.e. be operated with elution and subsequent conditioning. During elution or regeneration, the heavy metal taken up is released. The ion exchange resin is then conditioned again into a form in which it has a sufficiently high capacity and selectivity for the heavy metal ions. The regeneration is normally not carried out in countercurrent and therefore requires a large excess of regenerant. The chemicals required for this must be introduced into the process and cannot be generated in the system. Because the highly compact electrolysis systems are operated according to their task in areas of low heavy metal concentration (less than 1 g / 1) and therefore the acidic or alkaline electrolysis solutions produced in the form of by-products in the electrolysis cell have low acid and base concentrations. The ion exchangers used only serve to remove the residual metal contents; The chemical costs for their regeneration do not result in an improved economy of the electrolysis cell and also no increase in the degree of purity of the deposited metals. Your costs must be written off as running wastewater treatment costs.