CH645077A5 - METHOD FOR RECOVERY OF CYANIDES FROM CLEANING WATER CONTAINING CYANIDES. - Google Patents

Description

15 The present invention relates to a method for the recovery of cyanides from cyanide-containing rinsing water by precipitation.

In the field of electroplating, we are looking for systems and methods that are more economical and practical for the treatment and detoxification of rinsing water. The previous development in this field of electrochemistry is very complex, requires specialized workers and is associated with great costs due to the need for energy and skilled worker costs. The considerable consumption of 25 chemicals in electroplating is known, whereby sludge and residues are formed during the detoxification of the toxic components, which are rich in heavy metals and are lost in the process.

It is also known to those skilled in the art that the treatment of rinse water with cyanides primarily involves the detoxification process, i.e. the destruction of the cyanides. Another process, known as "recycling", is based on the evaporation of water using energy to concentrate the liquids, which are then reused in the corresponding baths. Processes are also known in which ion exchangers are used using chemicals, but which have been destroyed and are therefore lost, with high installation costs.

40 Several processes are known in which metal cyanides are precipitated. According to US Pat. No. 3,736,239, the precipitated cyanides remain in the corresponding baths. Cyan gases occur. According to another method (JP-OS 45-10905, published April 20, 1970) 45, the pH is shifted from the alkaline to the acidic range using hydrochloric acid, and the precipitated copper cyanide is subsequently destroyed using hydrochloric acid to form copper chloride. Cyan gases also occur. It is known from US Pat. No. 2,845,330 that copper cyanide is precipitated at pH values from 6.5 to 7.5 by adding copper sulfate to which sodium sulfite has been added. Both the pH range used and the use of sodium sulfite are unsuitable.

According to SU-PS 528 265, copper ions-S5 are used to precipitate cyanides at pH values between 7 and 7.5. At such pH values, however, hydroxides and carbonates are precipitated at the same time, which require a considerable excess of copper ions. Here too, the use of sodium sulfite is disadvantageous, copper 60 ions being used for the precipitation, for. B. of zinc cyanides leads to a mixture of cyanides, which are difficult to separate. The precipitation of cyanides from rinsing solutions with nickel salts leads to precipitated nickel cyanides, which are destroyed. Furthermore, from US Pat. No. 1,614,523 only 65 has become known a process for the production of metal cyanides.

It is the object of the invention to overcome the disadvantages of the previous treatment and / or detoxification of cyanide-containing

3rd

645 077

gene rinse water, especially z. B. the electrolytic metal deposition, to avoid and to create a method of the type mentioned with the cyanides in a simple and safe manner from the rinse water not only economically recovered, but can also be reused industrially.

To achieve the object, in the method of the type mentioned in the invention, the cyanides dissolved in the rinse water are chemically reacted by adding a quantity of a metal salt corresponding to the content of the cyanides in the rinse water with a metal component corresponding to the metal of the cyanides in the rinse water and that in the galvanic bath Insoluble cyanides are transferred, which are separated from the rinsing water by filtering or decanting.

This advantageously creates a process which not only allows the cyanides to be recovered directly from the rinsing water, but which can also enable them to be reused industrially in the galvanic process. Above all, there is no detoxification process with the loss of valuable chemical substances. With the method according to the invention, the total precipitation of the cyanides can take place, so that the entire amount of cyanide present in the rinsing water can be recovered and converted into its insoluble form.

This creates an economical and practical system for treating rinse water for the electroplating industry, with which the recovery of cyanides, i.e. e.g. Waste products from which rinse water can be obtained. After being separated from the rinse water, the cyanides can be recovered and reused. The method according to the invention is preferably used for the recovery of cyanides from cyanide-containing rinsing water of the electrolytic metal deposition.

For example, Zinc sulfate or chloride for the rinse water of a cyanide zinc bath, or e.g. B. copper sulfate or chloride for the rinse water of a cyanide copper bath added. Acidic or alkaline salts can be added at the same time, by means of which the pH of the rinsing water and the valency of the metal ions, depending on the type of metal, can be regulated in such a way that the conversion of the entire free cyanide and complex salts into the form of the simple ones Cyanides can be achieved, which are then insoluble in the rinsing water at an appropriate pH and can not develop cyano gases. All of the cyanide in the rinse water can thus transform into an insoluble salt and can be removed from the water by decanting or by filtration.

If you use e.g. B. separate rinsing baths for each metal type of the electrolytic metal deposition without it being possible for the metals to mix with one another, the precipitated cyanides can be removed by the method according to the invention after washing the insoluble precipitate in filters or by decanting with water directly in the corresponding galvanic baths can be reused. In one embodiment, the washout is e.g. until the water reaches a density of 1,000 or 0 ° Bé, whereby the precipitated cyanides can be freed from all other soluble constituents.

In one embodiment, the precipitation and / or recovery of the cyanides can also take place from a cyanide liquid which can be obtained in electrolytic processes for the metal deposition of zinc, cadmium, copper, silver, gold and their alloys.

The implementation of the method according to the invention shows e.g. the simplicity of the same for the recovery of the cyanides from rinsing water without e.g. the need for technically trained professionals and without special installations; just as unnecessary. B. the use of chemicals to destroy the cyanides. Rather, the valuable chemicals can be completely recovered from the rinse water. B. The value of the metal salts to precipitate can be two to six times lower than the value of the recovered material.

In the two examples below, e.g. the technical and economic value of the method according to the invention is shown using two embodiments.

1st case:

Cyanide zinc bath with the following composition:

60g / l zinc cyanide at Cr $ 130.00 = Cr $ 7.80

50g / l sodium cyanide at Cr $ 100.00 = Cr $ 5.00

70g / l caustic soda à Cr $ 18.00 = Cr $ 1.26

One liter of zinc bath = Cr $ 13.06

If e.g. If one liter of zinc bath is carried into the sink, the following material is required to precipitate the soluble cyanides and parts of the caustic soda: 200 g zinc sulfate at Cr $ 14.00 / kg = Cr $ 2.80

The value of the recovered material is then e.g. 120 g zinc cyanide at Cr $ 130.00 / kg = Cr $ 15.60

16 g of zinc hydroxide at Cr $ 40.00 / kg = Cr $ 0.64 recovery value = Cr $ 16.24

The result is 5.8 times the value of the recovered material compared to the material used for recovery. After this treatment, the water is free of cyanides and free of heavy metals, and only sodium sulfate and some caustic soda remain, which is easy to neutralize.

2nd case:

Cyanide copper bath with the following composition:

60 g / 1 copper cyanide at Cr $ 180.00 / kg = Cr $ 10.80

81 g / 1 sodium cyanide at Cr $ 100.00 / kg = Cr $ 8.10

15 g / l caustic soda à Cr $ 18.00 / kg = Cr $ 0.27

One liter copper bath = Cr $ 19.17

If one liter of copper bath is carried into the sink, the following is required to precipitate the soluble cyanides: 161g copper chloride at Cr $ 111.60 / kg = Cr $ 17.96 The value of the recovered material is then e.g. the following:

210 g copper cyanide at Cr $ 180.00 / kg = Cr $ 37.80

The value of the recovered material is 2.1 times higher than that of the material used for recovery. After the treatment, the water is free of cyanides and free of heavy metals, and only sodium chloride remains in a soluble form, which is not a problem for wastewater treatment.

For comparison, two examples of a commonly known process for the treatment of cyanides in water are given below with the following values for expenses for the chemical products for the destruction of the cyanides without recovery:

1st case:

For one liter of zinc bath the following is used:

360 g chlorine = Cr $ 2.88

410g caustic soda = CrS 7.38

Total = Cr $ 10.26

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

645077

4th

2nd case:

For one liter of copper bath the following is used: 430 g of chlorine = Cr $ 3.44

490 g caustic soda = Cr $ 8.82

Total = Cr $ 12.26

These expenses do not include the costs of filtration and sludge removal, installation, and expenses for the sludge landfill at appropriate locations. The above comparisons are based on international physical values that are well known. The currency information refers to the different price of the products in the different international currencies, whereby for 30 Brazilian cruziros a US dollar is set (1.00 = Cr $ 30.00). In the majority of countries e.g. Copper, zinc, cadmium, gold and cyanide imported materials, so that a loss of these products in the rinse water of the electrochemical electroplating industry leads to considerable costs.

The electroplating industry is subject to e.g. B. to comply with certain standards and conditions, such. B. Values, sharp provisions that serve to preserve and protect the environment and are monitored by control bodies that require adequate and complete treatment of chemical industrial wastewater. Because of the high toxicity of the cyanides, these controls are necessarily strictly handled.

With the method according to the invention, however, cyanide wastewater can be treated in such a way that at the same time the user can profit from the recovery of the materials, and the method can also be visually checked, whereby equipment and thus costs and also pollution can be avoided .

The invention is explained below in further examples. The following four chemical formulas show the evolution to insoluble copper cyanide (CuCN) with potassium cyanide (KCN), which is dissolved by the latter and forms the complex salt of the soluble copper cyanide, and further the formation of soluble copper cyanide complex salts (Cu (CN) 2 3 4 ) r-2 "'3" by adding copper chloride (CuCl) to insoluble copper cyanide in the waste water:

1.CuCN + KCN = K (Cu (CN) 2)

2. K (Cu (CN) 2) + KCN = K2 (CUCN) 3)

3. K2 (Cu (CN) 3) = K2 (CU (CN) 2) '

(Cu (CN) 3) 2 "

5 (Cu (CN) 4) 3 "

4. (Cu (CN) 2i3i4) 1 + n CuCl = CuCN insoluble.

In the fourth formula above, instead of copper chloride (CuCl), copper sulfate (CuS04) can be used without difficulty.

10 If you use e.g. B. for the preparation of zinc baths the insoluble zinc cyanide Zn (CN) 2 with sodium cyanide, you get the soluble complex salt of zinc cyanide, which can be precipitated with zinc sulfate in the stage of wastewater treatment according to the formula

Zn (CN) 4 + ZnS04 = 2 Zn (CN) 2

insoluble.

Is z. B. generally denoted by M a metal with an atomic weight between 60 and 200, 20 results in the recovery of the cyanides and the corresponding metals from the rinse water e.g. the following general equation:

(M (CN) 2i3f4) 1A3 ~ + nMCl = nMCN

25 M (CN) 42 "+ MS04 = nM (CN) 2.

In another embodiment of the process according to the invention, the recovery of cyanide from the rinse water can be carried out in an economically and technically valuable manner by adding metal salts together with salts and / or acids for regulating the pH of the water and together with salts, Gases and / or acids are used to correct or change the valence of the metal ions.

35 The process according to the invention can advantageously be used in a further embodiment, but also for other processes for the recovery of cyanides, as a result of which it can also be valuable in other areas of chemistry and electrochemistry. So the 40 method can be used for a rinse water liquid, such as. B. in a metal surface treatment or in the hardening of metals or in dissolved industrial waste by the rinsing liquid zinc salts, such as. Zinc sulfate can be added and the soluble cyanides can be precipitated in the form of insoluble zinc cyanide.

Claims (10)

645 077 1. A process for the recovery of cyanides from cyanide-containing rinse water by precipitation of the cyanides from the rinse water, characterized in that the cyanides dissolved in the rinse water by chemical reaction by adding an amount of a metal salt corresponding to the cyanide content in the rinse water with a metal in the rinse water and Metal components of the electroplating bath are converted into insoluble cyanides, which are separated from the rinsing water by filtering or decanting. 2. The method according to claim 1, characterized in that the cyanides are totally precipitated together with the metals bound to the cyanides by the addition of the metal salt. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that the total amount of the cyanides dissolved in the rinse water is precipitated as insoluble salt and the precipitate is washed with filtration or decantation to a density of the wash water of 1,000 or 0 ° Bé and thereby the precipitated cyanides from the soluble components are freed and cleaned so that they can be fed directly to a galvanic bath for reuse. 4. The method according to any one of claims 1-3, characterized in that metal salts in which the metal has an atomic weight above 60, and optionally salts, gases or acids are added, by which the valence of the metal ions and / or with the salts and / or change the pH of the rinsing water with the acids. 5. The method according to claim 1, characterized in that cyanides from the cyanide-containing liquid of the electrolytic metal deposition of zinc, copper, cadmium, silver or gold or their alloys are precipitated and recovered. 6. The method according to claim 1, characterized in that cyanides of the general formulas MCN or M (CN) 2 are formed and precipitated according to the following reaction equations (MCCN) ^) 1-2'3 "+ nMCl = nMCN M (CN) 42 "+ MS04 = nM (CN) 2, where M is a metal with an atomic weight between 60 and 200 and a valence of 1 or 2. 7. The method according to any one of claims 1-6, characterized in that as a precipitate copper cyanide (CuCN) in rinse water of copper baths at a pH between 1.5 and 4.0, preferably 2.0, is precipitated, with addition of sodium bisulfite (NaHS03) the pH is changed from the alkaline to the acidic range without the addition of hydrochloric acid (HCl), while the value of the copper ions can be changed. 8. The method according to any one of claims 1-6, characterized in that cyanides are precipitated from the rinse water of cadmium baths, the solution being diluted to a content of less than 17 g / 1 cadmium cyanide in a first stage and free by adding an equivalent amount of zinc salt Cyanide and the cyanide bound to the cadmium are precipitated in the form of the insoluble zinc cyanide, and that in a second stage after separating the zinc cyanide by adding sodium carbonate or sodium sulfide, the cadmium ions are precipitated from the rinsing water in the form of an insoluble cadmium salt. 9. Application of the method according to one of claims 1-8 to rinse water, which are obtained in the electrolytic metal deposition. 10. Application of the method according to one of claims 1 or 3 to rinse water, which are obtained in metal surface treatment, the hardening of metals or in the dissolution of industrial waste, zinc salts being added to the s rinsing water and the soluble cyanides being precipitated in the form of insoluble zinc cyanide.