EP1567689A1

EP1567689A1 - Method for phosphatizing metal surfaces with improved phosphate recovery

Info

Publication number: EP1567689A1
Application number: EP03795846A
Authority: EP
Inventors: Jan-Willem Brouwer; Peter Kuhm; Iradj Peirow
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 2002-12-05
Filing date: 2003-11-26
Publication date: 2005-08-31
Also published as: WO2004050949A1; AU2003298143A1; RU2005121129A; DE10256884A1

Abstract

The novel method for phosphatizing metal surfaces is characterized by guiding a wash fluid after phosphation into a cleaning solution or recovering a wash liquid before phosphation. At least a part of said wash liquid is removed, mixed with a precipitant for heavy metal cations and the solution is subjected to filtration, preferably membrane filtration. Cleansing anions, especially phosphate ions, are recovered from the substantially heavy metal-free filtration permeate via anion exchange, reverse osmosis or precipitation and are optionally reused.

Description

"Process for phosphating metal surfaces with improved phosphate recovery"

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 automotive industry and the household appliance industry, but also in part in steelworks. It relates to a process for the improved recovery of active components that were previously discharged via the wastewater. In a preferred embodiment of the process, so much wastewater is additionally saved that the process works almost wastewater-free.

The aim of phosphating metals is to create crystalline metal phosphate layers that are firmly adhered to the metal surface, which in themselves 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 / l.

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 of manganese ions and z. B. 0.3 to 2.0 g / l of nickel ions as a so-called trication process for the preparation of 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 as well as phosphate ions. In addition, a phosphating solution contains non-layer-forming components, such as accelerators in particular 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, which 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 discharging 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, as 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. 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 the rinse water enriched with phosphate can absorb 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 treatment of phosphating bath overflow and / or rinsing water after the phosphating, the phosphating using a 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 further metal ions and accelerators, characterized in that the phosphating bath overflow and / or the rinsing water contain a Nanofiltration is subjected. 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 for reducing the amount of waste water. A further development of this method is proposed in the unpublished German patent application DE 101 42 933. 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 in such a way that the water phase depleted in metal ions can be used as rinsing water for rinsing the metals after cleaning and before phosphating can.

Measures to extend the lifespan of cleaning solutions using membrane processes have long been state of the art. Membrane filtration removes contaminants from the cleaning solution, sometimes together with surfactants, and returns water and builder salts to the cleaning solution. Such processes are described in more detail, for example, in the following literature reference: N. Rajagopalan, T. Lindsey and J. Sparks, "Recycling of Aqueuos Cleaning Solutions with Membrane Filtration: Issues and Practice", Met. Finish (1999), 97 (3), SS 39-40, 42-44, 46-51. Although such processes return water and some of the valuable substances in the cleaning solution to them, valuable substances in the phosphating solution that have entered the cleaning solution are lost.

The prior art thus contains numerous suggestions for saving rinsing water and for recycling valuable materials from the rinsing water after the phosphating in the phosphating solution. However, due to general carryover during practical operation and in particular due to the cascade-like transfer of rinsing water from subsequent rinsing stages into upstream rinsing stages and into the cleaning solution, active ingredients in the phosphating solution reach into the first rinsing water or into the cleaning solution. In the case of spraying systems in particular, phosphating solution can be introduced into the first rinse water and thus indirectly into the cleaning solution due to incorrectly set nozzles. This can be determined, for example, by lowering the pH of the first rinse water by introducing the acidic phosphating solution. In addition, zinc ions can accumulate in the alkaline cleaning solution and subsequently also in the first rinse water, which are detached during the cleaning of galvanized surfaces. Zinc ions are a valuable substance for the phosphating solution.

The German patent application 102 36 293, which has not been published beforehand, has the task of returning phosphating agents which have reached the cleaning solution and / or the first rinsing water to the phosphating solution. Appropriate process control should preferably also allow further savings in rinsing water, so that the phosphating process can be operated almost wastewater-free.

This is achieved by a process for phosphating metal surfaces, the metal surfaces being sprayed and / or immersed a) cleaned with at least one cleaning solution, b) rinsed with at least a first rinse water, c) phosphated with a phosphating solution which is 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 optionally accelerators, and d) rinsing with at least one second rinse water and wherein e) continuously or batchwise at least a portion of the first rinse water is transferred to the cleaning solution, characterized in that f) continuously or batchwise at least a portion of the cleaning solution and / or a portion of the first rinse water is treated with a first cation exchanger which is selective for Zinc, nickel and / or manganese anions, g) regenerating this first cation exchanger after loading with an acid to obtain a first regenerate, and h) converting at least part of the first regenerate 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) is carried out according to the method described above. 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.

In contrast, the present invention has the task of working up cleaning or rinsing solutions in such a way that cleaning-active anions such as phosphate ions can also be recovered even if one does without the cation exchanger step.

This object is achieved by a method 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, the 3 to 50 g / l phosphate ions, calculated as PO ₄ ³ -, 0.2 to 3 g / l zinc ions, optionally further metal ions as well optionally contains accelerator, and d) after the phosphating rinsing with at least one second rinse water and wherein e) continuously or discontinuously at least a portion of the second rinse water is transferred into the first rinse water or into the cleaning solution, characterized in that f) continuously or discontinuously removes at least part of the cleaning solution and / or part of the first rinse water, mixed with a precipitation reagent which forms compounds which are difficult to dissolve with heavy metal cations, and then g) subject to filtration, giving a first permeate. This filtration can be carried out as a "dead end" filtration, in which all the liquid is filtered, a filter cake being built up on the filter. The filtrate is referred to here as "permeate" because of the uniformity of the designations. The resulting filter cake can increase the separation properties of the filter. Or one uses cross-flow filtration over a membrane, in which only part of the liquid passes through the membrane as permeate and another part remains as retentate. A membrane filtration is preferably used as the filtration in this step, and contains a first retentate and a first permeate.

If “at least” a cleaning solution or “at least” one rinsing water is used, this means that instead of a single cleaning or rinsing step, several cleaning or rinsing steps connected in series can be provided. In practice, this is quite common. For the present invention, this means that the measures described are in each case carried out on at least one of these cleaning or rinsing stages. The phrase "part of the cleaning solution" or "part of the first rinse water" means that not all of the first cleaning solution or all of the first rinse water is subjected to the treatment mentioned. Rather, a portion of each is removed and fed to the treatment mentioned: this can be, for example, the overflow that is led out of the cleaning solution or the first rinse water.

Preferably, in part step e) the portion of the second rinse water is not led directly into the first rinse water or into the cleaning solution, but polyvalent cations are separated as much as possible from this portion of the second rinse water. The proportion of the second rinse water, for example a nanofiltration, can be used for this undergo and split it into a permeate and a retentate. The retentate contains the multivalent cations that have been transferred from the phosphating solution into the second rinse water. The retentate is preferably returned either directly or after further working up to the phosphating solution, thereby largely closing the cycle of polyvalent cations. The permeate of the nanofiltration contains most of the phosphate ions from the second rinse water. If the portion of the second rinse water is acidified with phosphoric acid before nanofiltration, which is advisable to prevent membrane blocking, additional phosphate ions get into the second rinse water. These are also largely found in the permeate. By transferring the permeate into the first rinse water or into the cleaning solution, these phosphate ions ultimately end up in the treatment cycle in accordance with the method according to the invention.

Before going into the process sequence 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

In addition to the zinc and phosphate ions, the phosphating bath can contain other components which are currently customary 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 (ll),

0.2 to 2.5 g / l calcium (II),

0.002 to 0.2 g / l copper (ll), 0.1 to 2 g / ICobalt (II).

For example, in addition to zinc ions, the phosphating solution contains 0.1 to 4 g / l of manganese ions and 0.002 to 0.2 g / l of copper ions as additional cations and not more than 0.05 g / l, in particular not more than 0.001 g / l, of 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 advisable to use oxides and / or carbonates as the cation source. Because of the risk of salting in the phosphating baths, salts of acids other than phosphoric acid or nitric acid should preferably be avoided.

In the case of phosphating baths which are said to be suitable for different substrates, it has become common 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-, add. In the absence of fluoride, the aluminum content of the bath should not exceed 3 mg / l. In the presence of fluoride, higher Al contents are tolerated as a result of the complex formation, 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 education closed phosphate layers, since they react with the hydrogen generated during the pickling reaction. This process is referred to as "depolarization". This prevents the formation of hydrogen bubbles on the metal surface which interfere with the layer formation. In the process according to the invention, preference is given to accelerators whose by-products or degradation products (reaction products with hydrogen) can penetrate a nanofiltration membrane This ensures that these by-products and degradation products of the accelerator do not accumulate in the phosphating bath.

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 / I chlorations

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 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.

Another accelerator to be preferably used 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.

Metal surfaces to be phosphated are usually coated with oil or fat. This oil or fat must be removed by the cleaning solution before phosphating. Therefore, over time, oil or fat accumulates in the cleaning bath and, due to dragging, also in the first rinse water. These non-water-soluble impurities can either be emulsified in the cleaning solution or at least partially float on it. In sub-step g) of the invention In the process, these are removed by membrane filtration, such as, for example, nanofiltration or preferably ultrafiltration. Suitable membrane types for this membrane filtration step are contained, for example, in the Rajagopalan literature cited at the beginning.

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 hinder a later reuse of the 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 preferably provided that an acid, for example hydrochloric acid, is added to the removed part of the cleaning solution and / or the first rinsing water in step f) before adding the precipitation reagent. The strong alkaline pH of the cleaning solution should be reduced to 10 or below by adding the acid. However, it is not necessary to 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 (i.e. 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 described in DE-A-3022 679.

To destroy excess precipitation reagent, in particular sulfur compounds, which got into the permeate of the membrane filtration in sub-step g), this permeate can be mixed with an oxidizing agent. For example, hydrogen peroxide is suitable for this. The phosphate contained in the permeate of membrane filtration g) is preferably recovered by passing the permeate obtained in sub-step g) over a selective anion exchanger which selectively binds anions of polyvalent acids, especially phosphate ions. If this selective anion exchanger is loaded with anions of polyvalent acids, for example phosphate ions, it can be regenerated with a strong alkali such as sodium or potassium hydroxide solution. The regenerate contains the polyvalent anions, especially the phosphate ions. It can be used as a raw material to make a cleaning solution. In the simplest case, this can mean that some or all of this second regrind is transferred to the cleaning solution. However, the regrind can also be discharged from the system and reformulated into a different cleaning solution.

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

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 consists in adding an aqueous solution of water-soluble calcium and / or iron (III) salts to the proportion of the cleaning solution and the poorly water-soluble phosphates formed cations mentioned, if appropriate together with 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 are bound to the solid in the manner of an anion exchange.

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 method described in the introductory cited unpublished patent application DE 102 36 293.

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 of the first rinsing water and ions or molecules of the phosphating solution which have not been removed and which pass into the first rinsing water or into the cleaning solution via the second rinsing water have arrived. 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. As a result, as already described in the unpublished DE 102 36 293, the water cycle is also largely closed. So you not only recover the phosphate ions, you also save fully demineralized water.

The procedure is preferably such that the permeate from the membrane filtration g) which is freed of phosphate ions by the selective anion exchanger is either h) first 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 treated with a second, strongly acidic cation exchanger to obtain demineralized water, or h ') is subjected to 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.

If sub-step h) is carried out as an ion exchanger step, the loaded cation and anion exchangers must be regenerated. The cation exchanger is preferably regenerated with hydrochloric acid, the anion exchanger with sodium hydroxide solution. The regenerates obtained here are mixed for mutual neutralization. These regenerates are disposed of. They represent the only wastewater that leaves the water cycle of the overall process in this embodiment. In comparison to the total volume of the water cycle, this represents only a very small proportion, so that the statement is justified that the process sequence according to the invention can be operated largely free of waste water. If the regenerates do not contain fluoride ions, they can be fed directly into the sewer network. For environmental reasons, fluoride ions should be precipitated and disposed of separately, for example by precipitation in the 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 further training according to DE 100 56 629. 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 described, for example, in the unpublished German patent application DE-A-101 42 933. Accordingly, the procedure is preferably that i) continuously or discontinuously a portion of the second rinse water

Undergoes nanofiltration, whereby a second retentate and a second permeate are obtained, k) the second retentate is transferred into the phosphating solution and I) the pH of the second permeate is increased by adding a strong alkali and then the second permeate either in the cleaning solution or preferably transferred to the first rinse water.

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 obtained in the further processing of the cleaning solution described above. This largely closes the water cycle.

As described 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 of a neutralizing compound of zinc, nickel and / or manganese before the second retentate is transferred to the phosphating solution. Oxides and carbonates are particularly suitable as such compounds having a neutralizing effect. For reasons of easy handling, these are preferably used as an aqueous slurry.

In the sequence of processes according to the invention it can further be provided that the phosphated metal surfaces are subjected to a post-passivation after rinsing with the second rinsing water. To do this, they are brought into contact with a post-passivation solution. Post-passivation solutions of this type are known in the prior art. In the course of the sequence of processes according to the invention, it is preferable to use a post-passivation solution which contains only those components which are also used in a phosphating solution. This allows the recycling cycle to be kept closed and the amount of waste to be reduced. A post-passivation solution as described in more detail in WO 00/73536 is particularly suitable.

It is therefore preferably provided in the sequence of processes according to the invention that the metal surfaces phosphated in sub-step c) and rinsed in sub-step d) are passivated in a further step m) by contacting them with an aqueous solution which is the only two or contains polyvalent cations of nickel ions and the anions are selected from nitrate ions, fluoride ions, phosphate ions and anions of complex fluorides of B, Ti and Zr and then n) with at least a third rinse water.

The post-passivation solution is preferably a solution of nickel dihydrogen phosphate and contains 50 to 500 mg / l of nickel ions and 200 to 1 500 mg / l of phosphate ions. Both nickel ions and dihydrogen phosphate ions are valuable substances in a phosphating solution. These valuable substances accumulate in the third rinsing water and can ultimately be transferred from there to the phosphating solution via the second rinsing water by treating it via cation exchange or nanofiltration.

Accordingly, the sequence of processes according to the invention preferably further provides that a portion of the third rinse water is added continuously or discontinuously the second rinse water is transferred and the third rinse water is supplemented by adding fresh water. For this purpose, in particular the largely demineralized water can be used, which is obtained when a part of the cleaning solution is completely worked up as described above. The water cycle and the material cycle can therefore be largely closed even using a post-passivation solution and a third rinse water. This leads to a saving of raw materials and reduces the amount of waste and waste water. The sequence of processes according to the invention accordingly has particular economic and ecological advantages.

Examples:

Phosphating: Granodine ^R 952: tri-cation phosphating (Henkel KGaA), nitrite accelerated post-passivation: nickel phosphate passivation according to WO00 / 73536

Treatment / 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 rinsing water after phosphating (a): removal of Zn, Mn and Ni

Composition of rinsing water: see a)

Operating conditions nanofiltration: Desal DK membrane (from Osmonics) pressure difference: 8 bar temperature: 35 ° C membrane flow: 15 l / m ² -h volume ratio retentate / permeate: 1/10 addition of H ₃ PO ₄ - 75% in 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 of retentate to the phosphating bath: reuse of zinc, manganese, nickel and phosphate to produce phosphate layers

2. Reuse of the permeate as rinsing water after degreasing

Composition of the rinse water after degreasing Table b2:

Increase in concentration compared to the permeate by 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:

(Increasing the Zn concentration by pickling zinc from galvanized steel)

c) Ultrafiltration of the degreasing overflow (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 to the ultrafiltration container:

HCI, 30%, pH 9.3 adjustment

4 ml / l Katoplex: product from Gütling

Composition permeate after ultrafiltration:

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

Retentate must be disposed of: contains hydrocarbons ("KW") and heavy metals d) Processing permeate ultrafiltration: removal P0 ₄

1. Selective anion exchanger

Adsorber resin: Lewatit MP 500

OH- form selective for HPO ₄ ² - / PO ₄ ³ -

2 columns with 20 I resin in series. Operating conditions: 200 l / h

Process composition:

After processing 0.5 m ³ (1000 g PO ₄ ):

Regeneration column 1 with 60 I NaOH, 4% (3 fractions of 20 I)

Fraction 1 (20 l) contains: PO ₄ : 50 g / l

Fraction 1 is used as a raw material for the manufacture of degreasing products. Fractions 2 + 3 are used in the next regeneration: fractionated regeneration.

2. Precipitation P0 ₄ by FeCI ₃ / Ca (OH) ₂

Add HCI, 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: 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)

Adsorber resin: cation exchanger: SP 112, 20 I resin

Anion exchanger: MP 500, 20 I resin Operating conditions: 200 l / h

Composition of drain: deionized water <10 μS-crrr ¹

Regeneration: Cation exchanger: 6% HCI (40 1)

Anion exchanger: 4% NaOH (40 I)

After mixing and adding CaCl ₂ / Ca (OH) ₂ , the regenerates can be introduced into the waste water system after filtering the bag with Lofclear 523 D (Hayward) (pH 6-9). Alternative for e): reverse osmosis

Claims

claims

1. 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 / l phosphate ions, calculated as PO ₄ ³ -, 0.2 to 3 g / l zinc ions, optionally containing further metal ions and optionally accelerators, and d) rinsing after phosphating with at least one second rinse water and wherein e) continuously or discontinuously at least a portion of the second rinse water is transferred into the first rinse water or into 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 which contains heavy metal cations forms poorly soluble compounds, and dan ach g) subjected to a filtration, whereby a first permeate is obtained.

2. The method according to claim 1, characterized in that a membrane filtration is carried out in sub-step g) as filtration, wherein a first retentate and a first permeate are obtained.

3. The method according to one or both of claims 1 and 2, characterized in that in step f) the removed part of the cleaning solution and / or the first rinse water is mixed with an acid before adding the precipitation reagent.

4. The method according to one or more of claims 1 to 3, characterized in that the precipitation reagent contains a sulfur compound with sulfur in a negative oxidation state.

5. The method according to one or more of claims 1 to 4, characterized in that the first permeate obtained in sub-step g) with a Oxidizing agent added.

6. The method according to one or more of claims 1 to 5, characterized in that the first permeate obtained in sub-step g) is passed over a selective anion exchanger which selectively binds anions of polyvalent acids.

7. The method according to claim 6, characterized in that the first permeate passed through the selective anion exchanger is passed in any order over a strongly acidic cation exchanger and a strongly basic anion exchanger.

8. The method according to claim 6, characterized in that the first permeate passed over the selective anion exchanger is subjected to a reverse osmosis.

9. The method according to claim 6, characterized in that the selective anion exchanger is regenerated with a strong alkali and the regenerate obtained is used as a raw material for cleaning products.

10. The method according to claim 6, characterized in that one precipitates as calcium and / or iron phosphates from the first permeate obtained in sub-step g) or binds them to solid calcium hydroxide, iron hydroxide or a mixture of calcium hydroxide and iron hydroxide.

11. The method according to one or more of claims 1 to 10, characterized in that the portion of the second rinse water is subjected to a nanofiltration in sub-step e), containing a second retentate and a second permeate, and the second permeate in the first Rinsing water or transferred to the cleaning solution.