DE10256884A1 - Process for phosphating metal surfaces with improved phosphate recovery - Google Patents

Abstract

When phosphating metal surfaces, rinsing water after phosphating is returned to a cleaning solution or rinsing water before phosphating. At least a part of the latter is removed, a precipitation reagent for heavy metal cations is added, and the solution is subjected to membrane filtration. From the largely heavy metal-free retentate of membrane filtration, cleaning anions, in particular phosphate ions, are recovered via anion exchange, reverse osmosis or precipitation reaction and, if necessary, reused.

Description

The invention is in the field the phosphating of metal surfaces, as used as a common corrosion protection measure in the metal processing industry such as the automotive industry and the household appliance industry, but is also partially carried out in steel mills. It affects one Process for improved recovery of active components that were previously used the waste water was discharged. In a preferred embodiment the procedure is additional so much wastewater saved that Process works almost wastewater-free.

The phosphating of metals followed the target on the metal surface to produce firmly grown, crystalline metal phosphate layers, the for corrosion resistance improve and in conjunction with paints and other organic Coatings for a significant increase in adhesion and resistance against infiltration when exposed to corrosion. Such Phosphating processes have long been known in the prior art. For the Pretreatment before painting is particularly suitable for low-zinc phosphating processes, where the phosphating solutions comparatively low levels of zinc ions of e.g. B. 0.5 to 2 have g / l.

It has been shown that through the use of polyvalent cations other than zinc in the phosphating baths phosphate layers trained with significantly improved corrosion protection and paint adhesion properties can be. For example, find low-zinc processes with the addition of z. B. 0.5 to 1.5 g / l manganese ions and z. B. 0.3 to 2.0 g / l of nickel ions as a so-called trication process for preparing metal surfaces for painting, for example for the cathodic electrodeposition of car bodies, wide Application.

A phosphating solution contains layer-forming components such as. Zinc and possibly other divalent metal ions and phosphate ions. Moreover contains a phosphating solution non-layer-forming components such as accelerators in particular and their degradation products. The degradation products of the accelerator are created in that this with the hydrogen formed by the pickling reaction on the metal surface responding. Those that accumulate over time in the phosphating bath non-layer-forming components such as alkali metal ions and in particular the degradation products of the accelerator can the phosphating solution can only be removed by: part of the phosphating solution discharges and discards and continuously, or discontinuously by new ones phosphating replaced. phosphating can be carried out, for example, that the Phosphating bath with an overflow operates and the overflow rejects. There is usually an overflow but not necessary, because of the phosphated metal parts sufficient amount of phosphating solution as an adherent liquid film is carried out.

After phosphating, the on the phosphated parts such as automobile bodies adhering phosphating solution rinsed with water. Because the phosphating solution Contains heavy metals and possibly other ingredients that The flushing water must not be released into the environment in an uncontrolled manner be subjected to a water treatment. This has to be done in one separate step before discharge into a biological sewage treatment plant take place, otherwise the functionality of the sewage treatment plant endangered would.

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. The EP-A-414 301 relates to a wastewater-free process for producing phosphate coatings on metal surfaces by means of aqueous zinc phosphate solutions containing iron (II) and nitrate ions. The phosphating bath is followed by a rinsing bath cascade consisting of at least 2 rinsing baths, low-salt, preferably salt-free water is fed into the last rinsing bath, the water overflow is led into the preceding rinsing bath or the phosphating bath, and at least as much low-salt or salt-free water is withdrawn from the phosphating bath that it which can absorb rinsing water enriched with phosphate from the cascade. However, it cannot be avoided here that undesirable ingredients, such as degradation products of the accelerator, accumulate in the phosphating bath.

WO 99/48819 describes a process for the preparation of 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 / l phosphate ions, calculated as PO ₄ ^3- , 0.2 to 3 g / l zinc ions, optionally containing further metal ions and accelerators, characterized in that the phosphating bath overflow and / or the rinsing water is subjected to nanofiltration. The layer-forming cations of the phosphating process accumulate in the retentate of nanofiltration. The retentate is therefore preferably returned to the phosphating solution directly or after enrichment with further active ingredients. The permeate from nanofiltration can be used as rinsing water after cleaning the parts to be phosphated before phosphating. This document therefore already describes extensive recycling of recyclable materials from the rinsing water into the phosphating solution and a method for saving fresh water and thus also to reduce the amount of waste water. A further development of this method is in the unpublished German patent application DE 101 42 933 proposed. According to this teaching, premature blocking of the nanofiltration membrane is prevented, for example, by acidifying the rinsing water before the nanofiltration, preferably with phosphoric acid. The phosphate ions partially get into the permeate of the membrane filtration. These can be reused by raising the pH of the permeate to such an extent that it can be used to supplement the cleaning solutions before phosphating.

DE 198 54 431 teaches that the rinsing water after phosphating by reverse osmosis, ion exchange processes, nanofiltration, electrodialysis and / or heavy metal precipitation can be worked up so that the water phase depleted in metal ions can be used as rinsing water for rinsing the metals after cleaning and before phosphating.

Extension measures the lifespan of cleaning solutions using membrane processes has long been state of the art. in this connection are contaminated, partly together by membrane filtration with surfactants, separated from the cleaning solution and water as well as builder salts returned to the cleaning solution. Such procedures are For example, described in more detail in the following literature: N. Rajagopalan, T. Lindsey and J. Sparks, “Recycling of Aqueuos Cleaning Solutions with Membrane Filtration: Issues and Practice ", Met. Finish (1999), 97 (3), pp. 39-40, 42-44, 46-51.

Such procedures lead Water and some of the valuable substances in the cleaning solution this back, Recyclable materials of the phosphating solution, the in the cleaning solution have been received, but are lost.

The prior art therefore contains Numerous suggestions for saving rinse water and recycling Recyclable water after phosphating in the phosphating solution. Through general procrastination while of practical operation and in particular through the cascade-like transfer of dishwater from subsequent rinsing stages in upstream rinse levels and into the cleaning solution However, active ingredients in the phosphating solution reach the first rinse water or up to the cleaning solution. Especially with spraying systems can be due to incorrectly set Nozzles phosphating solution by over-spraying in the first rinse water and thus also be entered indirectly into the cleaning solution.

This can be done, for example be found that the pH value of the first rinse water is reduced by the entry of the acidic phosphating solution. You can also in the alkaline cleaning solution and subsequently also enrich zinc ions in the first rinse water, which are removed when cleaning galvanized surfaces. Zinc ions a resource for is the phosphating solution.

The unpublished German patent application 102 36 293 is the task in the cleaning solution and / or in the first rinse water Active ingredients of the phosphating can be traced back into the phosphating solution. By appropriate process management should be additional preferably a further saving of rinsing water is made possible, so that the phosphating process can be operated almost wastewater-free.

This is achieved through a process for phosphating metal surfaces, the metal surfaces in Spraying and / or dipping processes

• a) cleans with at least one cleaning solution,
• b) rinsing with at least a first rinse water,
• c) phosphated with a phosphating solution which contains 3 to 50 g / l phosphate ions, calculated as PO ₄ ³ , 0.2 to 3 g / l zinc ions, optionally further metal ions and optionally accelerator, and
• d) rinsing with at least a second rinse water and taking one
• e) continuously or discontinuously at least a portion the first rinse water transferred into the cleaning solution, thereby characterized that you can continue
• f) at least part of it continuously or discontinuously the cleaning solution and / or part of the first rinse water with a first cation exchanger treated that is selective for Zinc, nickel and / or manganese ions,
• g) this first cation exchanger after loading with a Acid under Receiving a first regenerate regenerated and
• h) at least part of the first regrind is transferred into the phosphating solution.

This document further discloses that cleaning anions such as phosphate ions can be recovered from the solution obtained after sub-step f). These can either be reused for cleaning purposes or converted into other products, such as fertilizers for agriculture. Because of the cation exchange step f), the recovered phosphate-containing valuable substances contain only such small amounts of heavy metals that they do not interfere with further use. However, this presupposes that sub-step f) according to the above Procedure is carried out. The ion exchanger provided there has the disadvantage that traces of surfactant and / or oil are retained on the exchange resin in the feed to the ion exchanger. When the loaded exchanger is regenerated, the surfactants and / or the oil are released again and thus reach the regenerates in an enriched form. In this way, the regenerates are contaminated and can no longer be used or can only be reused after a high level of cleaning.

The present invention provides against it the task of processing cleaning or rinsing solutions in such a way that cleaning active Anions such as phosphate ions can also be recovered can, if you do without the cation exchanger step.

This task is solved by a method for phosphating metal surfaces, wherein one the metal surfaces by spraying and / or immersion

• a) cleans with at least one cleaning solution,
• b) after cleaning with at least a first rinse water rinsed,
• c) phosphated with a phosphating solution which contains 3 to 50 g / l phosphate ions, calculated as PO ₄ ³ , 0.2 to 3 g / l zinc ions, optionally further metal ions and optionally accelerator, and
• d) after phosphating with at least a second rinse water rinses and being one
• e) continuously or discontinuously at least a portion of the second rinse water in the first rinse water or transferred to the cleaning solution, thereby characterized that you can continue
• f) at least part of it continuously or discontinuously the cleaning solution , and / or takes part of the first rinse water, with a precipitating reagent which forms compounds which are difficult to dissolve with heavy metal cations, and then g) subjected to membrane filtration, whereby one contains first retentate and a first permeate.

If there is "at least" a cleaning solution or of "at least" one rinse water it is said that instead of a single one Cleaning or rinsing stage several cleaning or rinsing stages connected in series can be provided. In practice, this is quite common. For the present Invention means this that the measures described in each case at least one of these cleaning or rinsing stages be made. The phrase "part of the cleaning solution" or "part of the first Rinsing water "means that not the entire first cleaning solution or the entire first rinse water undergoes the treatment mentioned. Rather one takes a part of each and leads him to the treatment mentioned: This can be, for example around the overflow act out of the cleaning solution or the first rinse water led out becomes.

The sub-step e) is preferably carried out Proportion of the second rinse water not directly in the first rinse water or in the cleaning solution, but separates polyvalent cations from this portion of the second rinse water preferably largely from. Therefor you can, for example, the proportion of the second rinse water Undergo nanofiltration and convert it into a permeate and a retentate split. The polyvalent cations are enriched in the retentate, that from the phosphating solution were transferred to the second rinse water. The retentate leads one preferably either directly or after further work-up into the phosphating solution back and closes thereby largely the cycle of multivalent cations. The permeate which contains nanofiltration the biggest part the phosphate ions from the second rinse water. If you acidify the portion of the second rinse water before nanofiltration with phosphoric acid, what to prevent membrane blockage is advisable, additional Phosphate ions in the second rinse water. Also these are largely found in the permeate. By transferring the Permeates in the first rinse water or in the cleaning solution these phosphate ions ultimately enter the treatment cycle according to the inventive method.

Before going into the sequence of processes according to the invention, the phosphating solution which can be used in sub-step c) is first described in more detail:
The zinc contents are preferably in the range from 0.4 to 2 g / l 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 it is in the range between 3.7 and 30. A weight ratio between 10 and 20 is particularly preferred.

The phosphating bath can besides the Zinc and phosphate ions contain other components as they are currently are common in phosphating baths.

Phosphating solutions which contain further mono- or divalent metal ions, which experience has shown to have a favorable effect on the paint adhesion and the corrosion protection of the phosphate layers thus produced, are preferably used. Accordingly, the phosphating solution according to the invention preferably additionally contains one or more of the following cations:
0.1 to 4 g / l manganese (II),
0.1 to 2.5 g / l nickel (II),
0.2 to 2.5 g / l magnesium (II),
0.2 to 2.5 g / l calcium (II),
0.002 to 0.2 g / l copper (II),
0.1 to 2 g / l cobalt (II).

For example, the phosphating solution contains zinc ions in addition as additional 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, especially not more than 0.001 g / l Nickel ions. wishes however, the conventional To hold trication technology, phosphating baths can be used be that except Zinc ions 0.1 to 4 g / l manganese ions and additionally 0.1 to 2.5 g / l nickel ions contain. In what form the cations are introduced into the phosphating baths in principle is 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 should preferably be salts other acids as phosphoric acid or nitric acid be avoided.

For phosphating baths for different substrates it should be suitable, it is common become free and / or complex bound fluoride in amounts up to 2.5 g / l total fluoride, of which up to 750 mg / l free fluoride, each calculated as F to add. In the absence of fluoride the aluminum content of the bath should not exceed 3 mg / l. At, present Due to the complex formation of fluoride, higher Al contents are tolerated, provided the concentration of the uncomplexed Al does not exceed 3 mg / l.

Except for the layer-forming divalent Cations contain phosphating baths usually additionally Sodium, potassium and / or ammonium ions to adjust the free Acid.

Phosphating baths, exclusively the Treatment of galvanized material does not necessarily have to serve contain a so-called accelerator. Accelerator at the phosphating of non-galvanized steel surfaces are required but also often in technology used in the phosphating of galvanized material. accelerator containing phosphating have the added benefit that she as well as galvanized as well for non-galvanized materials are suitable. This is particularly the case with the Phosphating of car bodies is important, as these are often both contain galvanized and non-galvanized surfaces.

In the prior art there are different types of phosphating baths Accelerators available. They accelerate the formation of layers and facilitate the formation of closed ones Phosphate layers, since they coincide with that which occurs during the pickling reaction React hydrogen. This process is referred to as "depolarization" Formation of hydrogen bubbles on the metal surface will disrupt layer formation thereby prevented. Within the scope of the method according to the invention accelerators are preferred whose by-products or degradation products (Reaction products with hydrogen) a nanofiltration membrane - penetrate can. This ensures that itself these by-products and degradation products of the accelerator are not in the phosphating bath accumulate.

Particularly suitable are those accelerators which, as by-products or degradation products, form either water or monovalently charged ions which can penetrate the nanofiltration membrane. For example, the phosphating solution can 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 in free, ionic or bound form
0.001 to 0.15 g / l hydrogen peroxide in free or bound form
0.5 to 80 g / l nitrate ions.

Together with or instead of chlorate ions can advantageously use hydrogen peroxide as an accelerator become. This can be used as such or in the form of connections be hydrogen peroxide under the conditions of the phosphating bath form.

A likewise preferably to be used The accelerator is hydroxylamine. If you put this in free form or in the form of hydroxylammonium phosphates, hydroxylammonium nitrate and / or hydroxylammonium chloride to the phosphating bath also only degradation or by-products that have a nanofiltration membrane can penetrate.

Metal surfaces to be phosphated are common with oil or fat coated. That oil or fat has to go through the cleaning solution be removed before phosphating. Therefore enriches with time oil or grease in the cleaning bath and by dragging in the first too dishwater on. These not water soluble Impurities can either in the cleaning solution be emulsified or at least partially float on it. In sub-step g) of the method according to the invention, these are by membrane filtration such as nanofiltration or preferably ultrafiltration removed. Suitable membrane types For this Membrane filtration steps are introductory, for example contain the cited reference from Rajagopalan.

Heavy metal cations in the cleaning solution or the first rinse water would pass into the permeate together with phosphate ions in the membrane filtration step g) and be reused later hinder the formation of phosphate ions. This is prevented by adding a precipitation reagent to the removed part of the cleaning solution and / or the first rinsing water in sub-step f), which forms poorly soluble compounds with heavy metal cations. As a result, the heavy metal cations are precipitated or at least converted into a colloidal form. You will then no longer be able to penetrate the membrane in step g) and contaminate the phosphate-containing permeate. The term “poorly soluble compounds” is understood to mean that these compounds have such a low solubility that, according to the solubility product, less than 10 mg / l of heavy metal ions remain dissolved and can pass into the permeate of the membrane filtration g).

It is preferable to provide that he in sub-step f) the removed part of the cleaning solution and / or of the first rinse water with an acid, for example with hydrochloric acid before the precipitation reagent admits. By adding acid the strong alkaline pH of the cleaning solution should be 10 or lowered below. However, it is not necessary set a pH below 7.

In step f), a precipitation reagent is preferably used which contains a sulfur compound with sulfur in a negative oxidation state (ie from -1 or -2). This can be, for example, inorganic or organic sulfides. For example, a product can be used that is marketed by the Gütling company under the name Katoplex. The use of such sulfur compounds in processes for treating waste water is in the DE-A-30 22 679 described.

To destroy excess precipitation reagent, especially of sulfur compounds, which in the partial step g) in the permeate Membrane filtration, you can use this permeate Add oxidizing agent. For example, hydrogen peroxide is used for this suitable.

That in the permeate of membrane filtration g) phosphate contained is preferably recovered by that he the permeate obtained in sub-step g) via a selective anion exchanger conducts the anions of polyvalent acids, especially phosphate ions, binds selectively. Is this selective anion exchanger with anions polyvalent acids, For example, phosphate ions can be loaded with a strong alkali such as caustic soda or potassium hydroxide. The Regenerate contains the polyvalent anions, especially the phosphate ions. It can can be used as raw material for the production of a cleaning solution. In the simplest Trap this can mean that he this second regenerate is partially or completely transferred to the cleaning solution. The Regenerate can also be discharged from the system and become one differently formulated cleaning solution.

In this way, cleaning will be effective Anions of polyvalent acids recovered for example phosphates, borates and / or silicates. On the one hand, this closes the recycling cycle for these anions. On the other hand, this prevents such Anions get into the wastewater, from which they are removed would. As a selective anion exchanger is, for example, a resin (e.g. cross-linked polystyrene) suitable as the functional groups quaternary amino groups wearing.

Accordingly, according to the above embodiment, cleaning-effective anions are removed from the treated part of the cleaning solution and used again for cleaning purposes before, if desired, the part of the cleaning solution is freed from monovalent cations and anions. As an alternative to this, in particular the phosphate ions can be removed from the permeate of membrane filtration g) and sent for further use. At least two embodiments are available for this:
The first embodiment consists in subsequently precipitating the phosphate ions as calcium and / or iron phosphates from the permeate obtained in sub-step g). This can be done, for example, by contacting the portion of the cleaning solution with a slurry of calcium hydroxide and / or iron hydroxide, thereby binding the phosphate ions to the hydroxide and separating the solid. A cheaper alternative to the precipitation is to add an aqueous solution of water-soluble calcium and / or iron (III) salts to the proportion of the cleaning solution and to precipitate the poorly water-soluble phosphates of the cations mentioned, optionally together with the hydroxides additionally formed. If the permeate has a pH above 7 after the sub-step g), hydroxides form automatically. This leads to the formation of easily separable solid flakes. Furthermore, the proportion of the cleaning solution - if desired after prior acidification, for example with hydrochloric acid - can be mixed with a solution of iron (III) salts, for example iron (III) chloride, and an alkaline pH value can be set by adding an aqueous calcium hydroxide slurry. This also leads to the formation of easily separable solid flakes.

A further embodiment of the phosphate removal consists in that the permeate obtained in sub-step g) is then passed through a container which contains solid calcium hydroxide, iron hydroxide, or a mixture of calcium hydroxide and iron hydroxide. These solid hydroxides bind the phosphate ions. They can be available as a fixed bed or as a fluidized bed. Because of the better handling for this alternative method, solid, preferably crystalline or partially crystalline, iron hydroxide is preferred. For example, the iron hydroxide known as “ferrrihydrite” can be used. When the phosphate-containing permeate comes into contact with this solid, the phosphate ions become like an anion exchange bound the solid.

Due to the heavy metal precipitation in sub-step f), the calcium and / or iron phosphate-containing solids formed according to the above process variants only contain such small proportions of other heavy metals or hydrocarbons that they do not have to be disposed of as waste, but as valuable materials, for example in agriculture, the cement industry or wastewater treatment (further phosphate binding) can be used. This makes it possible to recycle the phosphate ions contained in the wastewater from phosphating processes, including the associated cleaning steps, instead of disposing of them costly in the form of waste materials. The method according to the invention thus represents an alternative to the non-prepublished patent application cited in the introduction DE 102 36 293 described methods.

The solution remaining after the phosphate ions have been bound by the selective anion exchanger still contains the monovalent cations and anions of the cleaning solution or the first rinsing water and undissolved ions or molecules of the phosphating solution which have entered the first rinsing water or the cleaning solution via the second rinsing water , This solution is preferably worked up in such a way that these monovalent ions are also removed and ultimately demineralized water is obtained. This can be used as rinsing water after phosphating or for other purposes. This will - as already in the unpublished DE 102 36 293 described - also the water cycle largely closed. So you not only recover the phosphate ions, you also save fully demineralized water.

The procedure is preferably such that either the permeate of the membrane filtration g) which has been freed of phosphate ions by the selective anion exchanger is either
h) first treated with a second, strongly acidic cation exchanger and then with a second, strongly basic anion exchanger, or first with a second, strongly basic anion exchanger and then with a second, strongly acidic cation exchanger to obtain deionized water, or
h ') is subjected to a reverse osmosis, demineralized water being obtained as the third permeate and a third retentate being obtained as a concentrate, which is disposed of. In this case, largely demineralized water is obtained as the permeate, while the retentate (concentrate) contains the enriched monovalent cations and anions and is discharged from the system as (only) waste water.

Leads you have to go through sub-step h) as an ion exchanger step loaded cation and anion exchangers are regenerated. The Cation exchangers are preferably regenerated with hydrochloric acid Anion exchanger with sodium hydroxide solution. The regenerates obtained here one mixes for mutual neutralization. This regenerate are disposed of. They represent the only wastewater in this embodiment leaves the water cycle of the overall process. Compared to the total volume of the water cycle this represents only a very small proportion so that the It is justified to state that the Process sequence according to the invention can be operated largely wastewater-free. If the regenerate can not contain fluoride ions they are introduced directly into the sewer network. Fluoride ions should for environmental reasons precipitated and disposed of separately, for example by precipitation in Form of calcium fluoride.

The second rinse water obtained after the phosphating is preferably worked up by one of the methods known in the prior art. For example, this can be done by ion exchange, as described in WO 00/64817 or in the training DE 100 56 629 is described. The layer-forming cations are recovered during the regeneration of the cation exchangers and can be used again for the phosphating.

In the context of the overall process according to the invention, however, a processing of the second rinse water by nanofiltration is preferred, as is the case, for example, in the unpublished German patent application DE-A-101 42 933 is described. Accordingly, one preferably proceeds in such a way that one

• i) continuously or discontinuously Proportion of the second rinse water undergoes nanofiltration, whereby a second retentate and get a second permeate,
• k) the second retentate is transferred into the phosphating solution and
• l) the pH of the second permeate by adding a strong one Lye increased and subsequently the second permeate either in the cleaning solution or preferably in the first rinse water transferred.

The second permeate is preferably transferred to the first rinse water after the pH has been raised to about 7 to 8. To compensate, a portion of the first rinse water is transferred to the cleaning solution. This proportion is preferably supplemented with surfactant and lye, for example sodium hydroxide solution, so that a cleaning solution with a pH in the range from 9 to 12 is obtained which has a sufficient surfactant content. In this way, the losses of the cleaning solution are compensated, which result from the fact that part of the cleaning solution is discharged in sub-step f). The second rinse water can be supplemented with the largely demineralized water which is used in the further processing of the above described Cleaning solution arises. This largely closes the water cycle.

As in DE-A-101 42 933 It is preferable to acidify the portion of the second rinse water by adding phosphoric acid before subjecting it to nanofiltration. This gives a strongly acidic retentate in which the layer-forming cations of the phosphating solution are enriched. In order not to lower the pH value too much or to increase the content of "free acid" too much when this retentate is returned to the phosphating solution, it is preferable to raise the pH value of the second retentate so that it is in the phosphating solution can be transferred, for example to the range 2.5 to 3. The pH of the second retentate is preferably raised by adding at least one neutralizing compound of zinc, nickel and / or manganese before the second retentate is added to the The oxides and carbonates are particularly suitable as such compounds with a neutralizing effect. For reasons of simple handling, they are preferably used as an aqueous slurry.

In the sequence of processes according to the invention can also be provided that the phosphated metal surfaces after rinsing with the second rinse water undergoes post-passivation. To do this, bring them with a passivation solution in contact. Post-passivation solutions of this type are state of the art known. It is within the scope of the sequence of processes according to the invention preferable to use a post-passivation solution that only Contains components, which are also used in a phosphating solution. This allows the recycling cycle to be kept closed and the Reduce the amount of waste. A post-passivation solution is particularly suitable as detailed in WO 00/73536 is described.

One preferably sees in the sequence of processes according to the invention so before that the phosphated in step c) and rinsed in step d) another step

• m) passivated by using a aqueous solution in Brings contact, the only divalent or multivalent, cations Contains nickel ions and wherein the anions are selected are more complex from nitrate ions, fluoride ions, phosphate ions and anions Fluorides of B, Ti and Zr and after
• n) rinsing with at least a third rinse water.

The post-passivation solution preferably provides a solution of nickel dihydrogen phosphate and contains 50 to 500 mg / l nickel ions and 200 to 1,500 mg / l phosphate ions. Both nickel ions as well Dihydrogen phosphate ions are valuable substances in a phosphating solution. These valuable substances accumulate in the third rinse water and can from over there the second rinse water by processing it over Cation exchange or nanofiltration can ultimately be transferred to the phosphating solution.

Accordingly, one can see in the sequence of processes according to the invention preferably further before that continuously or discontinuously a portion of the third rinse water transferred into the second rinse water and the third rinse water supplemented by adding fresh water. In particular, this can largely be the case demineralized water can be used in that described above complete processing of part of the cleaning solution. Also using a post passivation solution and a third rinse water can So the water cycle and the material cycle are largely closed become. this leads to to a saving of raw materials and reduces the accumulating Amount of waste and waste water. The sequence of methods according to the invention accordingly shows special economic and ecological Advantages on.

Phosphating: Granodine ^R 952: tri-cation phosphating (Henkel KGaA), accelerated nitrite

Post-passivation: Nickel phosphate passivation according to WO00 / 73536 Preparation / reuse of rinsing water: a) Reuse of rinsing water after re-passivation as rinsing water after phosphating (no treatment): 0.2 m ³ / h

b) nanofiltration of the rinse water after phosphating (a): removal of Zn, Mn and Ni

Composition of rinsing water: see a)
Operating conditions nanofiltration:
Desal DK membrane (Osmonics)
Pressure difference: 8 bar
Temperature: 35 ° C
Membrane flow: 15 l / m ² h
Volume ratio retentate / permeate: 1/10
Add HP ₃ O ₄ - 75% to the rinse water: 4.0 g / l
Add ZnCO ₃ to the retentate: 1.5 g / l
Add NaOH - 30% to the permeate: 8.0 g / l

Composition of retentate / permeate after nanofiltration: Table b1:

• 1. Return retentate into the phosphating bath: reuse zinc, manganese, nickel and phosphate for the production of phosphate layers
• 2. Reuse of the permeate as rinsing water after degreasing. Composition of the rinsing water after degreasing Table b2:
  
  Increased concentration compared to the permeate due to over-spraying from phosphating
• 3. Reuse of the rinse water b2 for degreasing after adding 5.0 g / l NaOH, 30% + 1.0 g / l nonionic surfactant 'Composition of the degreasing solution: Table b3:
  

c) Ultrafiltration of the overflow degreasing (b3): removal of hydrocarbons (= KW)

Composition of degreasing solution: see b3
Operating conditions ultrafiltration:
Membrane: Koch HFM-251 (PVDF)
Pressure difference: 2 bar
Temperature: 29 ° C
Membrane flow: 100 - 200 l / m ² · h

Heavy metal removal by adding in working container Ultrafiltration:

• - HCl, 30%, pH 9.3 adjustment
• - 4th ml / l Katoplex: product from Gütling

Composition permeate after ultrafiltration:

Excess sulfide was oxidized with N ₂ O ₂ , 30%, 25 mg / l.

Retentate must be disposed of: contains hydrocarbon ("KW") and heavy metals

d) Processing permeate ultrafiltration: removal of PO ₄

1. Selective anion exchanger

Adsorber resin: Lewatit MP 500
OH ^- form selective for HPO ₄ ^2- / PO ₄ ^3-
2 columns with 20 l resin in series

Operating conditions: 200 l / h Composition drain:

After processing 0.5 m ³ (1000 g PO ₄ ):
Regeneration column 1 with 60 l NaOH, 4% (3 fractions of 201)
Fraction 1 (20 l) contains:
PO ₄ : 50 g / l

Fraction 1 is used as a raw material for the production of degreasing products. Fractions 2 + 3 will be at the next Regeneration used: fractional regeneration.

2. Precipitation of PO ₄ by FeCl ₃ / Ca (OH) ₂

• - encore HCl, 30%: up to pH 5
• - Add FeCl ₃ , 40%: 1.0 g / l
• - Add Ca (OH) ₂ : up to pH 7.5 - 9.0

Composition of wastewater after precipitation: PH value: 7.5 - 9.0 PO ₄ : <10 ppm NO ₃ : 415 ppm F: 34 ppm Cl: not measured Ca: not measured Composition of sludge after precipitation: Ca: 21.8% Fe: 4.9% PO ₄ : 33.6%

This sludge is not classified as hazardous waste and can be reused in agriculture or the cement industry.

e) Generation of demineralized water using a conventional ion exchanger system (cation + anion exchanger): removal of the rest of the cations + anions, composition of the Lewatit MP 500 drain: see d)

After mixing and adding CaCl ₂ / Ca (OH) ₂ , the regenerates can be introduced into the wastewater system after filtering the bag with Lofclear 523 D (Hayward) (pH 6-9).

Alternative for e): reverse osmosis

Claims (10)

Process for phosphating metal surfaces, the metal surfaces being sprayed and / or dipped a) cleaned with at least one cleaning solution, b) rinsed after cleaning with at least a first rinse water, c) phosphated with a phosphating solution which is 3 to 50 g / I contains phosphate ions, calculated as PO ₄ ³ , 0.2 to 3 g / l zinc ions, optionally further metal ions and optionally accelerator, and d) after phosphating with at least one second rinse water and wherein e) continuously or discontinuously at least one Share of the second rinse water in the first rinse water or in the cleaning solution, characterized in that f) at least part of the cleaning solution and / or part of the first rinse water is continuously or discontinuously removed, mixed with a precipitation reagent that is difficult to dissolve with heavy metal cations Forms connections, and danac h g) subjected to membrane filtration, giving a first retentate and a first permeate. A method according to claim 1, characterized in that in step f) the removed part of the cleaning solution and / or of the first rinse water with an acid before the precipitation reagent admits. Method according to one or both of claims 1 and 2, characterized in that the precipitation reagent contains a sulfur compound with sulfur in a negative oxidation state. Method according to one or more of claims 1 to 3, characterized in that one obtained in sub-step g) first permeate mixed with an oxidizing agent. Method according to one or more of claims 1 to 4, characterized in that obtained in sub-step g) first permeate over leads a selective anion exchanger, the anions more polyvalent acids binds selectively. A method according to claim 5, characterized in that you can do that about the selective permeate first permeate passed in any Order over a strongly acidic cation exchanger and a strongly basic Anion exchanger conducts. A method according to claim 5, characterized in that you can do that about the first permeate of a reverse osmosis passed the selective anion exchanger subjects. A method according to claim 5, characterized in that the selective anion exchanger regenerated with a strong alkali and the regenerate obtained as a raw material for Cleaner products reused. A method according to claim 5, characterized in that he from the first permeate phosphate ions obtained in sub-step g) fails as calcium and / or iron phosphates or by sticking them to solid Calcium hydroxide, iron hydroxide or a mixture of calcium hydroxide and binds iron hydroxide. Method according to one or more of claims 1 to 9, characterized in that in step e) the proportion of the second rinse water undergoes nanofiltration, whereby a second retentate and contains a second permeate and the second permeate is transferred into the first rinse water or into the cleaning solution.