CH618148A5 - Process for separating out heavy metal ions from the aqueous solutions of complex compounds of metal-sequestering and metal chelate-forming chemicals - Google Patents

Description

618 148

2nd

PATENT CLAIMS

1. Process for the separation of metal ions from the aqueous solutions of complex compounds of metal sequestering and / or chelating chemicals, characterized in that metal ions selected for recycling and classified as toxic for waste water treatment from groups Ib to VIII with the exception of the groups IIa and Mb of the periodic system of the elements with compounds containing organic sulfhydryl groups, in which the sulfhydryl groups are present in monomeric or polymeric form, alone or together with inorganic alkali metal sulfides and / or hydrogen sulfides, in such a way that precipitation of the metal Thio compounds with a low solubility product are formed, which are separated by simple mechanical processes, so that metal ions only remain in the miligram range per liter in the resulting aqueous residual solution.

2. The method according to claim 1, characterized in that the cleavage of the metal complex compounds of the metal cations of groups Ib, IIb, IVb and Vb of the periodic system of the elements with the exception of zinc in acidified solutions and the metal cations of the groups Illa, IVa, Va, Via, Vlla and VIII of the periodic system of elements including zinc with the sulfhydryl group-containing organic compounds alone or together with inorganic alkali sulfides and / or hydrogen sulfides in preferably alkaline solutions.

3. Process according to claims 1 and 2, characterized in that the complex compounds of the metal cations to be split up are treated with oxidizing agents before the precipitation with compounds containing sulfhydryl groups in order to reduce the sequestering and / or chelating effect of the complexing agents against the metal ions to loosen up or to put an intermediate end to the fact that the precipitation process takes place more quickly and quantitatively more extensively.

4. Process according to claims 1, 2 and 3, characterized in that in the presence of anionogenic tensioactive substances or by adding such compounds and / or higher molecular weight flocculants, the precipitation is modified with the aid of the mer capto compounds so that in the presence of these Auxiliaries Mixed metal ions and thio complexes with very low solubility in aqueous systems result in easily separable coagulates or flocculates.

5. The method according to claims 1, 2, 3 and 4, characterized in that when the metal chelate and / or sequestering agent solutions are present together with ionoge-

In the case of tensioactive substances, these are treated beforehand or together with the compounds containing sulfhydryl groups with such precipitants which contain an ion which reacts in a contradicting manner to the ionogenic group of tensioactive substances, so that the 20 bar metal precipitates as sulfide or mixed complexes. Ions cannot be resolubilized again.

6. The method according to claims 1, 2, 3, 4 and 5, characterized in that the processing of wastewater and solutions obtained in the technology, which in addition to the metal ion complex compounds and surfactants of an ionogenic nature

25 and other wastewater-related substances to be designated as toxic, such as cyanides, aldehydes, organic colloids of native or synthetic origin or other substances that can be changed by oxidation, so that the individual opera to be carried out one after the other to destroy the pollutants or to process the technical liquids -ions in the pH range required in each case are carried out in the same container in order to arrive at non-toxic residual solutions which have a less harmful effect on public waters.

It is known that certain chemical compounds with metal ions can form stable water-soluble complexes. These compounds are therefore called sequestering agents or metal chelating agents. These include, for example: cyanides, pyro- and poly-phosphates, ammonia, organic bases of the type ethylenediamine and polyalkylene-polyamines, alkanolamines and polyalkanol-polyamines, organic polyhydro-xy-carboxylic acids, oxy-polycarboxylic acids - for example

Tartaric acid, citric acid, gluconic acid and heptonic acid -, the amphoteric amino-alkylene-carboxylic acids and polycarboxylic acids of the nitrilotriacetic acid (NTA), ethylenediamine-tetraacetic acid (EDTA) and diethylene-triamine-pentaacetic acid (40 DEPTA).

These compounds form complexes 45 of the type of the formula I below or also compounds of the type II with metal ion:

I)

Na-00C-CH? CHo-CHo CHo-COONa </ \ /

N N

/ \ / \

CH2

'' Cu '

CH '

CO-0x0-CO

Chelation Binding (Coordination Links)

II)

HO-CHo- (CH) 3-CH-CO-O-Cu-O-CO-CH- (CH) 3-CH0-OH

II f II

I OH OH

OH OH

Complexation (sequestration)

In many of these complex compounds, the metal atoms can only be separated chemically with great difficulty and incompletely.

The complex compounds of such sequestering agents with heavy metals, such as, for example, copper, nickel, lead, etc., have become increasingly important in gal

3rd

618 148

vano technology, because in this way it was possible to replace the cyanide, which is very toxic in terms of work physiology and also in terms of wastewater, and e.g. T. also to produce better metal deposits from baths with such complex compounds in the electrical field.

Also in the treatment of printed circuit boards or printed circuits as well as the electroless metallization of plastic surfaces, metal chelates of the listed connection classes have gained increasing technical importance.

Furthermore, such sequestering agents are also increasingly used in alkaline cleaning agents and neutral or weakly basic rust removers, their sequestering and chelating effect being used industrially to convert metal oxides into water-soluble metal complex compounds.

When using such complex compounds within chemical surface technology, particular disadvantages and difficulties have been shown in the treatment of rinsing and waste water and also in the destruction of used baths.

Since in order to keep the water clean and within the scope of the water protection laws associated with environmental protection in the individual countries, metal ions may only be discharged into the public waters to a very limited extent and in the prescribed ppm ranges (parts per million or milligrams per liter) , there were considerable difficulties with the chemical destruction of these stable metal complex compounds.

The reversible dissociation process between metal ions on the one hand and sequestering agents on the other hand largely prevented the precipitation of the metal ions by strongly alkaline or strongly acidic puffing off of the wastewater, whereby in most cases the possibilities of precipitation of the metals as poorly soluble or water-insoluble compounds by conversion into metal hydroxides or metal sulfides only occur in very specific percentages, so that after filtration or similar separation processes there are still far too high metal ion contents in the waste water.

Even when passing through ion exchanger plants, the metal complex compounds are not or only incompletely separated, especially when higher concentrations are present.

It was therefore imperative to look for better ways of precipitating the metals as poorly soluble compounds in order to ensure a more complete elimination of the metal ions from the aqueous solutions and the waste water within economically acceptable limits. Since copper complexes in electroplating and in the manufacture of printed circuit boards, as well as in the treatment of copper workpieces, are generally subject to a very wide range of technical uses, extensive studies on the copper compound compounds of the above-mentioned connection classes were therefore carried out first Precipitation of the metal ions made.

For example, the precipitation of copper from solutions containing ammonia - where they are present as a copper tetramine complex - is already practiced by reaction with sodium sulfide to precipitate copper sulfides. However, it has been shown that even with this method only conversions of 80-90% of the complex copper are possible, whereas 10% of the original copper content still remains in the remaining filtrate water, so that this method is also in no way satisfactory.

It has now been found that heavy metal ions, such as copper, bismuth, lead, mercury, silver, can be separated and precipitated from their complex compounds much more completely if the chelate bond between metal atom and sequestering agent is first used strong oxidizing agent or by strong acidification using hydrochloric, sulfuric or nitric acid or strongly acid dissociative salts thereof and then the heavy metals with organic mercapto compounds as sulfide (mercaptide) complexes or mixed sulfide-carboxylic acid-sulfonic acid complexes precipitates.

For economic reasons, the compounds containing organic sulfhydryl groups can also be used in combination with inorganic sulfides - such as, for example, sodium sulfide, ammonium sulfide or sodium sulfhydrate - it having been found that working in strongly acidic solutions leads to much more complete precipitation of the metal thio compounds than working in alkaline solutions.

In addition, it can be demonstrated that the risk of re-complexing in a basic environment is disproportionately high for a large part of the sequestering agents mentioned above compared to working in acidic solutions.

The completeness of the precipitation of the metals from their complex compounds is of course dependent on the type of metal to be removed, on the solubility product of the precipitated sulfide or mercapto compounds and on the hydrogen ion concentration (pH value), at which the specific precipitation is carried out.

The solubility products of various metal sulfides are shown, for example, in Table I below.

Table I

Solubility products of crystalline metal sulfides at 25 ° C (after J.R. Goates, J. Am. Former Soc. 74 [1952] 835)

Compound solubility-forming affinity product of the sulfide of the metal ion kcal / mol kcal / g ion

MnS

1 • 10 ~ n

47.6

53.4

FeS

5 • 10-18

23.32

20.30

NiS

2 • 10 ~ 21

18.8

11.1

ZnS

8-10-25

47.4

35,184

CoS

8 • 10 ~ 23

21.8

12.3

C02S3

~ io-124

47.6

-29.6

CdS

7-10-27

33.6

18.58

PbS

8 • 10 ~ 28

22.15

5.81

HgS

3 • IO "52

10.22

-39.38

CuS

8 • IO "36

11.7

-15.53

Cu2S

MO "48

20.6

-12.0

Ag2S

7 • IO "50

9.56

-18.430

T12S

7-IO "20

21.0

7,755

BÌ2S3

~ 10 ~ 96

39.4

15

La2S3

2-IO "13

301.2

172.9

Ce2S3

6-IO "11

293.0

170.5

Furthermore, the inorganic or organic acids, with which the metal to be worked up or precipitated must be removed completely from the solution as far as possible, should not, in excess, cause resolubilization (for example nitric acid) and should not have any metal-sequestering effect, such as organic oxycarboxylic acids.

The completeness of the precipitation of the metal thio compounds in a strongly acidic medium can furthermore be disturbed if the organic mercapto compounds used a) themselves have a complexing effect or complex groups forming reactive groups, such as, for example, polymeric organic nitrogen groups,

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

618 148

4th

b) in the acid phase or when buffering back to neutral pH, the metal-thio complex contains solubilizing groups (such as thiourea, mercapto-ethyl-NN-dimethylamine),

c) or water-solubilizing polymeric OH groups or hydroxy carboxylic acid groups.

The best precipitants prove to be the best in this process

1. thio-monocarboxylic acids,

2. thio and dithio alkanols,

3. dithio compounds which do not contain any groups soluble in acidic medium,

4. higher molecular weight polymers with multiple sulfhydryl and carboxylic acid groups,

5. Mixture of the said mercapto compounds 1-4 with alkali sulfides or monoalkali hydrogen sulfide.

It has been found that the metals of the so-called hydrogen sulfide group, i.e. the elements of groups Ib, IIb, IVb and Vb of the periodic system of the elements with the exception of zinc, give the best precipitation results when working in the acidic phase, whereas zinc is advantageously precipitated in neutral to alkaline solution. Copper, silver and gold in particular, as cations of the complex compounds with chelating agents in a strongly acidic environment, give fairly complete cleavage results with excellent precipitability.

Conversely, depending on the valence level in which the metal is bound in a complex manner, precipitations in an alkaline environment can give good results (for example elements of the sulfur ammonium group) if one carefully buffers back to neutral to weakly acidic pH values (phosphate buffer ).

Since many metals of this group in valence stage III can already be almost completely separated from complexing substances even by strong alkali, the sulfide / mercap-to precipitation is primarily in connection with anionic surfactants for wastewater treatment and the separation of Remaining metal contents important.

The loosening of the chelate bond between the metal atom and the sequestering agent, for example when using strong oxidizing agents - such as potassium peroxide sulfate - can be demonstrated by the colorimetric determination of the metal ions.

If the metal atoms are chelated to polyamino-polycarboxylic acid salts, known colorimetric detection methods for the corresponding metals indicate strongly scattering or completely wrong, mostly far too low values for the quantitative measurement of the metal content in aqueous solution or in wastewater, whereas after Removal of the chelate bond by oxidizing agents, these colorimetric determination methods fully indicate the content of metal ions again.

This fact is important for the selection and sequence of the chemical processing method for the precipitation of the metals from solutions containing complex or chelate compounds.

In the technical use, metal complex compounds and chelates are usually associated with other chemicals in wastewater, rinse water and in the destruction of used bath fillings, e.g. tensides (surface-active substances, wetting agents), with cyanides, with oxidizing agents; mixtures of different complexing agents and chelating agents as well as different metal ions are often present side by side.

These ingredients must be taken into account when working up using the metal precipitation method described here.

For example, when cyanides are present in addition to the complex compounds, it has proven advantageous to destroy the cyanides by oxidation before the acidification process with the aid of sodium hypochlorite or acid-stabilized hydrogen peroxide solutions, the chelate at the same time Bond between the s complex compounds and the metal ions is intermediately or partially removed.

If, on the other hand, there are also anionogenic surfactants in addition to the metal complex compounds, these can be precipitated simultaneously with the metal ions using a contrary dissociating cation surfactant according to a process already protected by Swiss Patent No. 430 371, so that the possibility of possible re-solubilization of the metal ions by strongly ionically dissociating surfactants is switched off before the organic mercapto-Verbin-15 is used. If cationic surfactants or cationically dissociative etching inhibitors are present in a pickling bath that is acidic and contains complexing agents, the precipitation process can be carried out with the contra-dissociating anionic surfactants, using free tensioactive sulfonic acids or polyether carbonic acid -Tensiden the subsequent metal precipitation process is influenced very favorably with the help of mercapto compounds and in many cases leads to a substantial reduction in the amount of organic Mer-25 capto compounds required for metal precipitation.

In this treatment process, water-insoluble metal ion precipitation products are formed, which, among other things, correspond to the following general formula III:

30th

III fatty alkyl S03 ~ -; Me + j -S-alkyl or alkanol

If the metal ions are present in bivalent or polyvalent form, especially after the oxidation processes, the particularly favorable and extensive precipitation reactions with mercapto-monocarboxylic acids can be attributed to the fact that crosslinked or higher molecular weight precipitation Products of the general formula IV are formed:

40 IV (-Me + -S-alkylene-C0--0 "-Me + -S-alkylene-C00 -) x.

From the precipitation products obtained in this way, after separation by filtration or centrifugation, the metals can be converted again into the corresponding metal sulfides or metal oxides by combustion. If necessary and depending on the type of metal, they can be recovered in this way (recycling).

In the practical implementation of the method described here for the cleavage of the complex and chelate compounds of metals with simultaneous and largely complete precipitation of the metal atoms down to the microgram range per liter of waste water, the amount depends on the Precipitation process chemicals to be used according to the existing and previously measured metal concentration in the aqueous solution to be processed. The content of metal ions that have to be precipitated is determined by known and proven analysis methods, such as, for example, in copper, colorimetrically with dithizone or, depending on the nature of the metal present, with other organic colored solutions-forming agents, or most precisely by atomic absorption spectra -trography determined quantitatively.

The spectrographic methods also provide the most reliable information about the metal-ion fractions remaining in the residual water or filtrate in the 65 microgram range after the metal precipitation.

The effectiveness and technical implementation of the process claimed here for the precipitation of metals from aqueous solutions of their complex or chelate compounds should

5

618 148

In the case of copper as an example for the metals of the hydrogen sulfide group, the following procedure examples are used:

Process Example I 50 ml of an aqueous solution containing 15 g of copper-chelate complex per liter and a measured proportion of 1280 mg of CU1 per liter and a pH of 9.2 are first acidified 0.5 ml of concentrated sulfuric acid . Then 2 ml of a 45 percent sodium thioglycolate solution are introduced with thorough stirring. An intense yellow-colored precipitate forms immediately, which is filtered off after 5 minutes. The clear, colorless filtrate still contains about 0.45 mg per liter of copper, which corresponds to a precipitation rate of 99.3 percent of the original metal content.

Process Example II 50 ml of an aqueous solution of a copper EDTA chelate with 1000 mg of copper per liter and a pH of 9.45 are first mixed with colorimetrically reactive test papers (Merckoquant Cu or Quantofix Cu test paper) tested for copper ion content. There is no color reaction, the test papers do not respond to the complexed copper. Then 0.4 g of potassium peroxodisulfate are added to the solution, and the entire solution is treated at 35 ° C. for 15 minutes. The colorimetric test then shows about 1000 mg of copper per liter. The chelation is interrupted. After cooling to room temperature, 0.1 g of 90 percent dodecylbenzenesulfonic acid is then added to this solution and dissolved with thorough stirring, followed by another 0.1 g of a 50 percent sodium thioglycolate solution. A light brown, flaky precipitate forms, which is filtered off. According to the spectrographic measurement, the clear residual water as filtrate contains only 1.1 mg copper per liter. This corresponds to a copper content of 1.1 per thousand of the original amount.

If the filtrate is run over an anion exchange resin with polymeric sulfo groups, the residual copper content decreases to 0.06 mg per liter in the residual water portion.

Process Example III If one adds to a copper complex solution of 50 ml of 1.0 ml of concentrated hydrochloric acid mentioned in Example I and 0.5 ml of mercapto-ethanol is added to the solution with stirring, the result is an intensely yellow-colored precipitation, which is easy to filter off. The clear filtrate still contains about 2 mg per liter of copper ions, which corresponds to a residual proportion of 1.56 per thousand of the amount of copper originally complexed in the solution.

Process Example IV To 50 ml of a solution containing an aqueous copper-heptonate complex compound (prepared from 10 g of sodium heptonate and 5 g of copper sulfate with 5 mol of water of crystallization) and a measured copper content of 1280 mg per liter and a pH Value of 6.2, 1.0 g of dodecylbenzenesulfonic acid and then 1 ml of a 45 percent sodium thioglycolate solution are added with thorough stirring. A flaky and easily filterable, intensely yellow-colored precipitate is obtained.

The remaining water still contains 0.55 mg per liter of copper, which corresponds to a residual content of 0.42 per thousand of the original amount of copper.

An approximately equally high precipitation rate is obtained if, instead of the dodecylbenzene-sulfonic acid mentioned, it is acidified with about 1 ml of concentrated hydrochloric acid before the organic thio compound is added.

Process Example V If 50 ml of the copper-heptonate complex compound listed in Example IV with a copper content of 1280 mg per liter are added with 1 ml of concentrated hydrochloric acid or 25 percent dodecylbenzene sulfonic acid solution, then 0.5 ml is stirred Thiolactic acid, you also get an intense yellow-colored precipitation. After centrifuging off this precipitation, a clear residual water is obtained which contains about 2 mg per liter of copper ions. This corresponds to a residual content of 1.56 per thousand of the original copper content.

The same result is obtained if, instead of the thiolactic acid mentioned, 0.5 ml mercapto-ethanol is used as a precipitant.

Process Example VI 50 ml of a complex compound containing 1280 mg per liter of copper are acidified with nitrilotriacetic acid (NTA) with 1 ml of concentrated hydrochloric acid and 0.3 ml of 2,3-di-mercapto-l-propanol are then added to this solution , the copper complex precipitates as a coarse, flocculent precipitate that can be easily separated by filtration or centrifugation.

The residual water obtained contains about 0.8 mg per liter of copper ions, which corresponds to a residual fraction of 0.62 per thousand of the original amount of complexed copper.

The same result is obtained if 0.5 ml of mercapto-ethanol or free thioglycolic acid are used instead of the di-mercapto compound.

Process example VII 0.5 ml of thioglycolic acid or thiolactic acid are added to 50 ml of a copper chelate with diethylene triamine pentaacetate (DTP A) and a copper content of 1280 mg per liter after acidification with 1 ml of concentrated hydrochloric acid with good stirring a yellow-colored, finely dispersed precipitation of copper mercaptide is obtained, which can be easily separated off by filtration.

The residual water obtained contains approximately 0.55 mg per liter of copper ions, which corresponds to a residual metal content of approximately 0.42 per thousand of the original copper content.

A lower residual copper content of only 0.35 mg per liter is obtained if, instead of the thiolactic acid or thioglycolic acid, a mixed polymer of methacrylic acid and allyl mercaptan (obtained by peroxide-catalyzed mixed polymerisation of allyl disulfide and methyl methacrylate and subsequent reduction with subsequent saponification) is used. When using this polymeric flocculant containing sulfhydryl groups, more compact and low-water precipitation products are obtained, which can be more easily separated from the residual water by means of continuous centrifuges with large throughput quantities.

Process Example VIII 100 ml of a technical etching solution for non-ferrous metals, which contains 1560 mg of metallic copper per liter and in which the copper is complexed both as a copper tetramine complex and as copper citrate and which has a pH of 10.95 5 ml of concentrated sulfuric acid are added with thorough stirring so that the solution has a pH of 2.0.

5.0 ml of a mixture of 3.0 ml of a 30 percent sodium sulfide solution and 2.0 ml of a 50 percent ammonium mercaptoethanol solution are then added to this solution with stirring. A compact, dark-colored precipitate is obtained, which can easily be separated from the residual water by filtration or centrifugation.

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

618 148

6

The residual water contains 1.360 mg per liter of copper ions, which corresponds to a residual content of 0.82 per thousand of the original amount of copper.

Process example IX 50 1 of an industrial etching solution which contains about 110 g per liter of metallic copper as a copper tetramine complex compound are first diluted with 20 times the amount of water, so that 1 cubic meter of waste water with a copper content of about 5.5 g per liter. 501 concentrated hydrochloric acid and 45 l sodium thioglycolate / 45 percent solution are successively added to this solution with good stirring at room temperature.

The solution obtained is left to stand for 15 to 30 minutes for the reaction, after which the organic metal mercaptide compound is separated from the water content by means of a continuous centrifuge.

The light and clearly colored residual water still shows a residual copper content of 0.5 mg per liter according to the atomic absorption spectrographic determination, which corresponds to a residual metal content of 0.09 per thousand.

Process example X A bath intended for electroless copper plating with a content of 1 cubic meter contains 1.8 g per liter of copper ■ complexed with sodium EDTA. The bathroom still contains

Sodium hydroxide solution, formaldehyde, sodium cyanide and anionic surfactants in varying amounts.

The wastewater treatment is first carried out by oxidation of the cyanide and the formalin, which requires 101 5 15 percent sodium hypochlorite solution. After the bath content had been left to stand for the oxidative reaction for one hour, the mixture was then acidified with 38 l of sulfuric acid with good stirring, after which the copper-chelate bond was released by the oxidative pretreatment and acidification.

To precipitate the copper ions 20 1 of a 50 percent sodium sulfide solution, 4.5 1 of a fatty acyl polyamine polyhydrochloride as a 20 percent aqueous solution and 10 1 of a 45 percent sodium thioglycolate solution are then stirred in successively.

A compact, fluffy precipitate is obtained which remains in the bath for 30 minutes before the reaction takes place. The precipitate is then separated from the residual water using a filter press.

20 After this treatment, the residual water still contains 1.3 mg per liter of metallic copper, which corresponds to a residual amount of 0.7 per mille of the original copper content.At the same time, more than 90 percent of the surfactant content is also precipitated during this treatment cycle and remain 25 in addition to the copper sulfide and mercaptide in the flocculate.