WO2000064817A1

WO2000064817A1 - Waste water treatment during phosphation

Info

Publication number: WO2000064817A1
Application number: PCT/EP2000/003447
Authority: WO
Inventors: Jan-Willem Brouwer; Peter Kuhm
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1999-04-26
Filing date: 2000-04-15
Publication date: 2000-11-02
Also published as: DE19918713C2; DE19918713C5; DE19918713A1; AU4118800A

Abstract

The invention relates to a method for treating the overflow from a phosphating bath and/or rinsing water after phosphation, the phosphation having been carried out with an acidic aqueous phosphating solution containing 3 to 50 g/l phosphate ions, calculated as PO4<3->, 0.2 to 3 g/l zinc ions, optionally other metal ions and optionally, accelerators. After phosphation, the phosphating bath overflow and/or rinsing water is guided over a slightly acidic ion exchanger, after membrane filtration or without upstream membrane filtration. Said ion exchanger is preferably selective for zinc and/or nickel ions. The solution that is produced when the ion exchanger is regenerated can be re-used to supplement the phosphating solution.

Description

"Wastewater treatment in phosphating"

The invention is in the field of phosphating metal surfaces, as is carried out as a widespread corrosion protection measure in the metalworking industry such as, for example, the automobile industry and the household appliance industry, but also in part in steelworks. It relates to a method for treating the overflow of the phosphating baths and / or the rinsing water after the phosphating. In preferred embodiments, the method enables the recycling of bath ingredients into the phosphating bath, the reuse of active ingredients for the preparation of supplementary solutions for phosphating baths and the use of the solution depleted in metal ions as rinsing water.

The phosphating of metals pursues the goal of producing firmly adherent metal phosphate layers that already improve corrosion resistance and, in conjunction with paints and other organic coatings, contribute to a significant increase in adhesion and resistance to infiltration when exposed to corrosion. Such phosphating processes have long been known in the prior art. For the pretreatment before painting, the low-zinc phosphating processes are particularly suitable, in which the phosphating solutions have comparatively low zinc ion contents of e.g. B. 0.5 to 2 g / 1. An important parameter in these low-zinc phosphating baths is the weight ratio of phosphate ions to zinc ions, which is usually in the range> 12 and can take values up to 30.

It has been shown that by using polyvalent cations other than zinc in the phosphating baths, phosphate layers with significantly improved corrosion protection and paint adhesion properties can be formed. For example, find low-zinc processes with the addition of z. B. 0.5 to 1.5 g / l Manganese ions and e.g. B. 0.3 to 2.0 g / 1 nickel ions as a so-called trication process for the preparation of metal surfaces for painting, for example for the cathodic electrocoating of car bodies, wide application.

A phosphating solution contains layer-forming components such as e.g. Zinc and possibly other divalent metal ions and phosphate ions. In addition, a phosphating solution contains non-layer-forming components such as alkali metal ions to blunt the free acid and in particular accelerators and their degradation products. The degradation products of the accelerator result from the fact that it reacts with the hydrogen formed on the metal surface by the pickling reaction. The non-layer-forming components such as alkali metal ions that accumulate over time in the phosphating bath, and in particular the degradation products of the accelerator, can only be removed from the phosphating solution by removing and discarding part of the phosphating solution and replacing it continuously or discontinuously with new phosphating solution. Phosphating solution can be discharged, for example, by operating the phosphating bath with an overflow and discarding the overflow. As a rule, however, an overflow is not necessary since the phosphated metal parts discharge a sufficient amount of phosphating solution as an adhering liquid film.

After phosphating, the phosphating solution adhering to the phosphated parts, such as automobile bodies, is rinsed off with water. Since the phosphating solution contains heavy metals and possibly other ingredients that must not be released into the environment in an uncontrolled manner, the rinsing water must be subjected to a water treatment. This must be done in a separate step before being discharged into a biological sewage treatment plant, otherwise the functioning of the sewage treatment plant would be endangered.

Since both the disposal of the waste water (from the phosphating bath overflow and / or rinsing water) and the supply of the phosphating system with fresh water are cost factors, there is a need to minimize these costs. They don't Pre-published German patent application 198 13 058 describes a method for treating phosphating bath overflow and / or rinsing water after phosphating, the phosphating bath overflow and / or rinsing water being subjected to nanofiltration. The concentrate of the nanofiltration can be returned to the phosphating bath. The filtrate from the nanofiltration represents waste water, which may have to be treated further before being discharged into a biological sewage treatment plant. The unpublished German patent application 198 54 431 describes a method for saving rinsing water in the phosphating. The phosphating bath overflow and / or the rinsing water after the phosphating is subjected to a treatment process such as a reverse osmosis, an unspecified ion exchange process, nanofiltration, electrodialysis and / or heavy metal precipitation and the water phase depleted of metal ions is used as rinsing water for rinsing the phosphating metal parts is used after cleaning. DE-A-42 26 080 discloses the treatment of rinse water after phosphating by ion exchange processes. Strongly acidic cation exchange resins based on sulfonic acid groups are used. These bind all cations non-selectively. The regenerate cannot be used to supplement the phosphating solution since it contains non-layer-forming cations in addition to the layer-forming cations, which would lead to excessive salting of the phosphating solution.

The object of the invention is to provide an improved method for treating phosphate bath overflow and / or rinsing water after phosphating. It should at least be ensured that ultimately there is a waste water to be disposed of, the content of zinc and / or nickel ions of which is below the permissible waste water limit values. Instead of being disposed of by a sewage treatment plant, however, the wastewater should also be able to be used to rinse the metal parts to be phosphated after they have been degreased. The process should preferably be able to be operated in such a way that layer-forming components of the phosphating bath, in particular zinc and / or Nickel ions can be recovered and reused for phosphating purposes.

The object is achieved by a process for the preparation of a phosphating bath overflow and / or rinsing water after the phosphating, the phosphating being carried out with an acidic aqueous phosphating solution which contains 3 to 50 g / 1 phosphate ions, calculated as P0 ₄ ^{3 "} , 0.2 to Contains 3 g / 1 zinc ions, optionally further metal ions and optionally accelerator, the phosphating bath overflow and / or the rinsing water after the phosphating being passed after a membrane filtration or without an upstream membrane filtration over a weakly acidic ion exchanger.

The zinc contents are preferably in the range from 0.4 to 2 g / 1 and in particular from 0.5 to 1.5 g / l, as are customary for low-zinc processes. The weight ratio of phosphate ions to zinc ions in the phosphating baths can vary within a wide range, provided that it is in the range between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred.

In addition to the zinc and phosphate ions, the phosphating bath can contain other components which are currently common in phosphating baths. In particular, 0.01 to 2.5 g / l, preferably 0.3 to 2.0 g / l, nickel ions can also be present. In addition, the phosphating solution, as is customary for trication processes, can contain 0.1 to 4 g / l, in particular 0.5 to 1.5 g / l, of manganese ions. In addition to the zinc ions and optionally together with the nickel and / or manganese ions, the phosphating solution can also contain as further metal ions:

0.2 to 2.5 g / l magnesium (ll),

0.2 to 2.5 g / l calcium (II),

0.002 to 0.2 g / l copper (ll),

0.1 to 2 g / l cobalt (II).

For example, in addition to zinc ions, the phosphating solution contains additional ones Cations 0.1 to 4 g / l manganese ions and 0.002 to 0.2 g / l copper ions and not more than 0.05 g / l, in particular not more than 0.001 g / l nickel ions. However, if one wishes to stick to the conventional trication technology, phosphating baths can be used which, in addition to zinc ions, contain 0.1 to 4 g / l manganese ions and additionally 0.1 to 2.5 g / l nickel ions. The form in which the cations are introduced into the phosphating baths is in principle irrelevant. It is particularly useful to use oxides and / or carbonates as the cation source. Because of the risk of salting up the phosphating baths, salts of acids other than phosphoric acid should preferably be avoided.

In phosphating baths which are said to be suitable for different substrates, it has become customary to use free and / or complex-bound fluoride in amounts of up to 2.5 g / l of total fluoride, of which up to 750 mg / l of free fluoride, each calculated as F ^" , In the absence of fluoride, the aluminum content of the bath should not exceed 3 mg / l. In the presence of fluoride, higher levels of AI in the complex formation are tolerated, provided the concentration of the non-complexed AI does not exceed 3 mg / l.

In addition to the layer-forming divalent cations, phosphating baths generally also contain sodium, potassium and / or ammonium ions to adjust the free acid.

Phosphating baths that are used exclusively for the treatment of galvanized material do not necessarily have to contain a so-called accelerator. However, accelerators, which are required for the phosphating of non-galvanized steel surfaces, are also often used in technology for the phosphating of galvanized material. Accelerating phosphating solutions have the additional advantage that they are suitable for both galvanized and non-galvanized materials. This is particularly important when phosphating car bodies, as these often contain both galvanized and non-galvanized surfaces. In the prior art, different accelerators are available for phosphating baths. They accelerate the formation of layers and facilitate the formation of closed phosphate layers, since they react with the hydrogen generated during the pickling reaction. This process is referred to as "depolarization". The formation of hydrogen bubbles on the metal surface which disrupt the formation of the layer is thereby prevented. whose by-products or degradation products (reaction products with hydrogen) can penetrate the membrane, thereby ensuring that these by-products and degradation products of the accelerator do not accumulate in the phosphating bath, but are at least partially discharged from the system via the filtrate from the membrane filtration.

Those accelerators which are used as secondary or

Degradation products form either water or monovalently charged ions, one

Can penetrate the nanofiltration membrane. For example, the

Phosphating solution contain one or more of the following accelerators:

0.3 to 4 g / l chlorate ions

0.01 to 0.2 g / l nitrite ions

0.1 to 10 g / l hydroxylamine

0.001 to 0.15 g / l hydrogen peroxide in free or bound form

0.5 to 80 g / l nitrate ions.

In the depolarization reaction on the metal surface, chlorine ions form chloride ions, nitrite ions nitrate ions and ammonium ions, ammonium ions from nitrate ions, ammonium ions from hydroxylamine and water from hydrogen peroxide. The anions or ammonium ions formed can pass through a nanofiltration membrane, so that in the process according to the invention they are at least partially discharged from the phosphating bath overflow or from the rinsing water after the phosphating. Together with or instead of chlorine ions, hydrogen peroxide can advantageously be used as the accelerator. This can be used as such or in the form of compounds which form hydrogen peroxide under the conditions of the phosphating bath. However, polyvalent ions should preferably not be formed as by-products in this case, since these form part of a

Return of the concentrate of the nanofiltration in the phosphating bath would be enriched. Therefore, alkali metal peroxides are particularly suitable as an alternative to hydrogen peroxide.

An accelerator which is also preferably to be used in the process according to the invention is hydroxylamine. If this is added to the phosphating bath in free form or in the form of hydroxylammonium phosphates, hydroxylammonium nitrate and / or hydroxylammonium chloride, only degradation or by-products are created which can penetrate a nanofiltration membrane.

In the prior art, different membrane types are available for nanofiltration or reverse osmosis. Since phosphating baths and also the corresponding rinsing water react acidic, the membrane used should be acid-stable. For example, inorganic membranes such as. B. ceramic membranes. Organic polymer membranes can also be used. A polyamide membrane is particularly suitable as a nanofiltration membrane.

The process according to the invention can be operated in such a way that the phosphating bath overflow and / or the rinsing water after the phosphating is passed directly (optionally after removal of sludge and / or organic constituents) via the weakly acidic ion exchanger. As an alternative to this, the phosphating bath overflow and / or the rinsing water after the phosphating (likewise if appropriate after the removal of sludge and / or organic constituents) can be subjected to membrane filtration in the form of nanofiltration or reverse osmosis. The permeate (filtrate) of the membrane filtration used is then passed through the weakly acidic ion exchanger directed. The weakly acidic ion exchanger selectively removes metal ions, which are valuable substances from a phosphating solution, from the permeate of the membrane filtration. On the one hand, this increases the certainty that the wastewater limit values for these cations are observed. Furthermore, these cations can be used again for the purposes of phosphating after regeneration of the ion exchanger.

If one of the membrane filtration processes mentioned is used before the ion exchange, the process is preferably carried out in such a way that the retentate of the membrane filtration is returned to the phosphating solution. As a result, part of the layer-forming cations present in the overflow of the phosphating bath or in the rinsing water is already returned to the phosphating solution. This leads to a more economical way of operating the phosphating bath, since fewer ingredients have to be added again.

Regardless of whether the phosphating bath overflow and / or the rinsing water after the phosphating is passed directly to the ion exchanger or whether one of the membrane filtration processes mentioned is used beforehand, it is preferred to use the phosphating bath overflow and / or the rinsing water after the phosphating of sludge and / or free organic ingredients. This prevents the filtration membranes or the ion exchanger from blocking. Sludge can be removed, for example, by bag filtration. The filter Lofclear 523 D from Loeffler GmbH is suitable as a filter here. It removes 95% of the particles smaller than 1.5 μm and 99.9% of the particles smaller than 5.5 μm. Organic constituents in the phosphating bath (for example organic accelerators and / or their decomposition products or organic polymers possibly present in the phosphating bath) can be removed by activated carbon or by synthetic resins. The type Lofsorb LA 40 E-3-01 from Loeffler GmbH is suitable as activated carbon. Lewatit VP 0C 1066 or Dowex OPTL 285, for example, can be used as organic resins to remove organic constituents. For example, a Desal DK membrane is suitable for the nanofiltration step. At a pressure difference of 7 bar and a temperature of 35 ° C and a volume ratio of concentrate: filtrate = 1: 1, it delivers a membrane flow of the order of 35 to 40 l per m ² and hour. For example, a Filmtec SW 30 membrane from Rochem can be used for the step of reverse osmosis. At a pressure difference of 25 bar and a temperature of 45 ° C, with a volume ratio of concentrate: filtrate = 5: 1, it results in a membrane flow of about 30 l per m ² and hour.

A weakly acidic ion exchanger is preferably a type which is selective for zinc and / or nickel ions. In contrast, monovalent cations should be bound as little as possible. Those weakly acidic ion exchangers which carry chelating iminodiacetic acid groups are particularly suitable for this. A suitable product is Lewatit TP 207 from Bayer.

The process is preferably operated in such a way that the weakly acidic ion exchanger is regenerated after loading with a strong acid. The selectively bound cations zinc and / or nickel are eluted here and can be used again for the purposes of phosphating. By using the method according to the invention, these cations do not have to be disposed of as sludge containing heavy metals, but can be used again for phosphating, if appropriate after suitable treatment. This saves resources. It is particularly preferred to use such an acid for the regeneration of the loaded weakly acidic ion exchanger which is a valuable substance for the phosphating solution. Phosphoric acid is particularly suitable. Nitric acid can also be used if the phosphating solution is to contain nitrate ions as accelerators or as co-accelerators.

The regenerate can then be used again immediately or after supplementation with further active ingredients to supplement a phosphating solution. It is particularly preferred in this case to mix the regenerate with additional zinc and / or To add nickel ions and other active ingredients of a phosphating solution, that a conventional supplementary solution for a phosphating bath is created. This supplementary solution can then be used as usual to supplement the phosphating bath.

It is particularly preferred to carry out the regeneration of the loaded weakly acidic ion exchanger in two or more fractions. A regenerate is obtained as the first fraction, which contains the main part of the zinc and / or nickel ions. This regenerate is returned to the phosphating solution or used as the starting material for the preparation of a supplementary solution for the phosphating solution. Solutions are obtained as the second fraction and possibly as further fractions which only have comparatively low contents of zinc and / or nickel. These regenerates are preferably collected and used as the first fraction for the regeneration of a further loaded weakly acidic ion exchanger. A solution is then obtained as the first fraction which contains the main part of the zinc and / or nickel ions. The regeneration of the loaded weakly acidic ion exchanger in cascade form is therefore preferably carried out.

The solution depleted in cations, which leaves the weakly acidic cation exchanger in its loading phase, can, depending on the ingredients, be sent to a simplified wastewater treatment or be fed directly into a biological sewage treatment plant. However, it is more economical to use this solution as rinse water for the metal parts to be phosphated after they have been degreased. This embodiment of the method according to the invention has the additional advantage that flushing water is saved. Embodiments

example 1

Contains rinse water after phosphating

Zn ²⁺ : 115 mg / l

Mn ²⁺ : 59 mg / l

Ni ²⁺ : 57 mg / l

H ₂ P0 ₄ ^" : 1500 mg / l

he 300 mg / l

Na ⁺ : 430 mg / l organic components: 10 mg C / l

Sludge 0.05 g / l

Treatment of rinsing water: 400 l / h

A. Sludge removal by bag filtration Filter: Lofclear 523 D from Loeffler GmbH Particle size sludge removal

<1.5 micron 95%

<2.5 micron 99%

<5.5 micron 99.9%

ß. Removal of organic components by activated carbon or synthetic resins (e.g. Lewatit VP 0C 1066 or Dowex OPTL 285)

Charcoal: Lofsorb LA 40 E-3-01: 22 filter cartridges from Loeffler GmbH retention of organic components: 35-45% C. Nanofiltration rinse water

Operating conditions:

Desal DK membrane

Pressure difference: 7 bar

Temperature: 35 ° C

Membrane flow: 35-45 l / m ^{2 ■} h

Volume ratio: concentrate / filtrate: 1: 1

Result:

Concentrate filtrate

Zn ²⁺ (mg / l) 330 (mg / l) 2.4 (mg / l)

Mn ²⁺ (mg / l) 118 (mg / l) 0.6 (mg / l)

Ni ²⁺ (mg / l) 114 (mg / l) 0.6 (mg / l)

Na ⁺ (mg / l) 470 (mg / l) 390 (mg / l)

H ₂ PO ₄ - (mg / l) 2160 (mg / l) 840 (mg / l)

ClO ₃ ^' (mg / l) 250 (mg l) 150 (mg / l)

Cr (mg / l) 375 (mg l) 225 (mg / l)

D. Residual removal of Zn and Ni by selective cation exchangers

Selective cation exchanger:

Adsorber resin: Lewatit TP 207 (40 I) (Bayer): selective for Zn + Ni

Filtrate: nanofiltration

Preparation of filtrate nanofiltration by Lewatit TP 207 (mono-sodium form)

(see C) Filtrate nanofiltration after processing with TP 207 pH 3.6 3.6

Zn 2.4 mg / l <0.1 mg / l

Ni 0.6 mg / l <0.1 mg / l

Waste water limit values for Zn (2 mg / l) and Ni (0.5 mg / l) can be maintained using selective cation exchangers.

E. Regeneration of selective cation exchanger TP 207 (loaded with Zn + Ni) by HCI,

Regeneration HCI, 5%: 2 bed volumes (80 I)

Zn Conc. Regenerate: 20 g / l Ni conc. Regenerate: 5 g / l

F. Preparation of regenerate selective cation exchanger TP 207 by nanofiltration

Recycle regenerate (E) in concentrate nanofiltration (C)

Concentrate concentrate filtrate

Nanofiltration (C) Nanofiltration Nanofiltration

(I m ³ ) after addition after addition

Regenerate E (801) Regenerate E (801)

Zn ²⁺ (mg / l) 330 1787 12.0

Mn ²⁺ (mg / l) 118 109 0.6

Ni ²⁺ (mg l) 114 476 2.5

Na ⁺ (mg l) 470 435 370

H ₂ PO ₄ - (mg / l) 2160 2000 820

ClO ₃ ^" (mg / l) 250 231 135

Excess CI ^" is converted into permeate ratio Zn + Ni / Cl in the regenerate 1: 2 ratio Zn + Ni / Cl in the concentrate 1: 1.79 ratio Zn + Ni / Cl in the permeate 1: 167

After concentration 1: 1

Concentrate filtrate

+ Regenerate

Zn ²⁺ (mg / l) 3570 21.0

Mn ²⁺ (mg / l) 220 1.1

Ni ²⁺ (mg / l) 950 4.0

Na ⁺ (mg / l) 470 400

H ₂ PO ₄ - (mg / l) 2837 1276

ClO ₃ ^" (mg / l) 292 169

CI ^" (mg / l) 5063 3038

Ratio Zn + Ni / Cl in the concentrate 1: 1, 12 ratio Zn + Ni / Cl in the permeate 1: 122

Nanofiltration makes it possible to greatly reduce the excess anion in the regenerate, so that the regenerate can be reused in the phosphating.

Example 2

Rinse water after phosphating contains:

Zn ²⁺ 1 10000 mmgg // ll organic components: 10 mg C / l

Mn ²⁺ 50 mg / l

Ni ²⁺ 49 mg / l

Na ⁺ 130 mg / l

H ₂ P0 ₄ ^" 1500 mg / l

N0 ₃ - 300 mg / l

Treatment of rinsing water (400 l / h)

A. Sludge removal by bag filtration

Filter: Lofclear 523 D from Loeffler GmbH

Particle size sludge removal

<1.5 micron 95%

<2.5 micron 99%

<5.5 micron 99.9%

B. Removal of Zn and Ni by selective cation exchangers

Selective cation exchanger:

Adsorber resin: Lewatit TP 207 (Bayer)

Mono-sodium form: selective for Zn + Ni 2 columns with 40 I resin in series

After treating 10 m ^{3 of} rinsing water (1000 g Zn ²⁺ / 490 g Ni ²⁺ ), column 1 was regenerated with 120 IH ₃ P0 ₄ - 40% (= approx. 160 kg H ₃ PO4 - 40%) (= approx. 64 kg

nn = not proven

Fraction 1 can be used to prepare a new supplement. Fractions 2 + 3 can be reused for the next regeneration.

C. Preparation of Supplementary Solution

Fraction 1 contains (1 kg):

Zn 15.0 g

Ni 7.5 g

H ₂ 0 744.5 g

Encore:

1) 5.0% ZnO is dissolved in the regenerate; then cooling to 40 ° C

3) 2.3% MnC0 ₃

4) 2.0% H ₂ SiF ₆ - 34% Composition of the new supplement solution (1.25 kg):

Zn 55.0 g = 44.0 g / kg

Mn 11.0 g = 8.8 g / kg

Ni 7.5 g = 6.0 g / kg

H3PO4 291.5 g = 233.2 g / kg

H ₂ SiF ₆ 6.8 g = 5.4 g / kg

H ₂ 0 878.2 g = 702.5 g / kg 1250 g

Claims

claims

1. Process for the preparation of phosphating bath overflow and / or rinsing water after phosphating, the phosphating being carried out with an acidic aqueous phosphating solution which contains 3 to 50 g / l phosphate ions, calculated as P0 ^{3 "} , 0.2 to 3 g / l zinc ions , optionally contains further metal ions and optionally accelerator, the phosphating bath overflow and / or the rinsing water after the phosphating being passed after a membrane filtration or without an upstream membrane filtration over a weakly acidic ion exchanger.

2. The method according to claim 1, characterized in that the phosphating bath overflow and / or the rinsing water after the phosphating is subjected to a membrane filtration in the form of a nanofiltration or a reverse osmosis and the permeate of the membrane filtration is passed over a weakly acidic ion exchanger.

3. The method according to claim 1 or 2, characterized in that the phosphating bath overflow and / or the rinsing water after phosphating is freed of sludge and / or organic components before the phosphating bath overflow and / or the rinsing water after phosphating after membrane filtration or without upstream membrane filtration is passed over a weakly acidic ion exchanger.

4. The method according to one or more of claims 1 to 3, characterized in that the weakly acidic ion exchanger is selective for zinc and / or nickel ions.

5. The method according to claim 4, characterized in that the weakly acidic ion exchanger carries chelating iminodiacetic acid groups.

6. The method according to one or more of claims 1 to 5, characterized in that the weakly acidic ion exchanger is regenerated after loading with a strong acid.

7. The method according to claim 6, characterized in that the regenerate is reused immediately or after supplementation with active ingredients to supplement a phosphating solution.

8. The method according to claim 6 or 7, characterized in that the regeneration takes place in two or more fractions, wherein the regenerate obtained as the first fraction is reused immediately or after addition with active ingredients to supplement a phosphating solution and that as a second and / or subsequent fraction Regenerate obtained is used as the first fraction for the regeneration of a further weakly acidic ion exchanger loaded in the process according to one or more of claims 1 to 5.

9. The method according to one or more of claims 1 to 5, characterized in that the solution obtained after passing the weakly acidic ion exchanger is used as rinsing water for the metal parts to be phosphated after their degreasing.

10. The method according to claim 2, characterized in that the retentate of the membrane filtration is returned to the phosphating solution.

11. The method according to one or more of claims 1 to 10, characterized in that the phosphating solution additionally contains 0.01 to 2.5 g / l of nickel ions.