Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2000-08-03
2002-10-15
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S805000, C210S806000, C118S603000
Reexamination Certificate
active
06464879
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of phosphatising metal surfaces, such as is performed as a widely used corrosion protective measure in the metal processing industry, such as the automobile industry and the domestic appliance industry, but also sometimes in steelworks. It relates to a process for treating the overflow from phosphatising baths or the wash water after phosphatising. The process simplifies effluent treatment and enables, in a preferred embodiment, recycling of the bath constituents to the phosphatising bath.
BACKGROUND OF THE INVENTION
The phosphatising of metals is aimed at producing metal phosphate layers which penetrate the metal surface in order to improve the existing corrosion resistance and, in combination with lacquers and other organic surface coatings, contributes to a substantial increase in adhesion and in the resistance to creepage under corrosive conditions. These types of phosphatising processes have been known for some time in the prior art. Low-zinc phosphatising processes in which the phosphatising solutions have comparatively low concentrations of zinc ions of e.g. from 0.5 to 2 g/l, are suitable in particular for preliminary treatment prior to lacquering. An important parameter in these low-zinic phosphatising baths is the ratio by weight of phosphate ions to zinc ions which is generally in the region of greater than 12 and may have values of up to 30.
It has been shown that phosphate layers having greatly improved corrosion protective and lacquer adhesive properties may be produced by also using polyvalent cations other than those of zinc. For example, low-zinc processes with the addition of, e.g., from 0.5 to 1.5 g/l of manganese ions and, e.g., from 0.3 to 2.0 g/l of nickel ions, as the so-called tri-cation process, are widely used for preparing metal surfaces for lacquering, for example for the cathodic electrodeposition lacquering of car bodies.
A phosphatising solution contains layer-producing components, such as zinc ions, and optionally other divalent metal ions, as well as phosphate ions. In addition, a phosphatising solution contains non-layer-forming components, such as in particular accelerators and the degradation products thereof. The degradation products of the accelerator are produced when this reacts with hydrogen formed at the metal surface by the pickling reaction. The non-layer-forming components which accumulate in the phosphatising bath over time such as alkali metal ions and, in particular, degradation products of the accelerator, may only be removed from the phosphatising solution by removing and discarding some of the phosphatising solution and continuously or batchwise replacing this with fresh phosphatising solution. Phosphatising solution may be removed, for example, by providing the phosphatising bath with an overflow and discarding the overflowing solution. However, an overflow is not generally required because an adequate amount of phosphatising solution is removed as a liquid film adhering to the phosphatised metal parts.
After the phosphatising process, the phosphatising solution adhering to the phosphatised parts, for example car bodywork, is washed off with water. Since the phosphatising solution contains heavy metals and optionally other components which cannot be released into the environment in an uncontrolled manner, the wash water has to be subjected to a water treatment process. This has to be performed in a separate step prior to introduction to a biological water treatment plant since otherwise the ability of the water treatment plant to function correctly would be at risk.
Since both the waste disposal of effluent (from the phosphatising bath overflow and/or wash water) and also the provision of the phosphatising plant with fresh water represent cost factors, there is a requirement to minimise these costs. DE-C-44 20 760 describes a process and a plant for regenerating or concentrating spent surfactant-containing iron phosphatising baths. This does not therefore refer to a zinc phosphatising process as described above in which crystalline zinc-containing phosphate layers are produced on the treated metal surfaces. Rather, this process describes an iron phosphatising process in which amorphous layers of iron phosphate and iron oxide are produced on iron surfaces. If surfactants are added to the iron phosphatising solution, then these also act as cleansers. In the document mentioned, the regeneration of this type of surfactant-containing iron phosphatising solution is achieved by ultrafiltration. This is performed in such a way that the surfactants are largely retained as the retentate. The permeate contains the metal ions and has to be disposed of The other components of the iron phosphatising solution may be added to the surfactants retained in the retentate and these are then returned to the phosphatising bath. Some of the active substances in the iron phosphatising solution may be recycled by this process and the quantities of effluent and fresh water involved are minimise.
EP-A-414 301 relates to an effluent-free process for producing phosphate coatings on metal surfaces using aqueous zinc phosphate solutions which contain iron(II) and nitrate ions. In this case, the phosphatising bath is connected in series with a wash bath cascade consisting of at least two wash baths. Low-salt, preferably salt-free water, is fed into tile last wash bath, each water overflow is introduced into the preceding wash bath or the phosphatising bath and at least enough low-salt or salt-free water is withdrawn from the phosphatising bath for it to be able to accept phosphate-enriched wash water from the cascade. However, this cannot prevent undesired components, such as degradation products of the accelerator, accumulating in the phosphatising bath.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for treating phosphatising bath overflows and/or wash water after phosphatising, which at least enables simplified effluent treatment. The process is intended to be operated, if possible, in such a way that at least partial recycling of the components to the phosphatising bath is possible without large amounts of degradation products of the accelerator being returned to the phosphatising bath. Furthermore, it is intended that the process, if required, will provide treated water for the wash cascade.
DETAILED DESCRIPTION OF THE INVENTION
This object is achieved by a process for treating phosphatising, bath overflow and/or wash water after phosphatising, wherein phosphatising is performed using an acid aqueous phosphatising, solution which contains from 3 to 50 g/l of phosphate ions, calculated as PO
4
3−
, from 0.2 to 3 g/l of zinc ions, optionally further metal ions and accelerator, characterised in that the accelerator is an organic molecule or molecular ion having, a molecular weight of at least 80 g/mol and that the phosphatising bath overflow and/or the wash water is subjected to ultrafiltration.
The zinc concentration is preferably in the range from 0.4 to 2 g/l and in particular from 0.5 to 1.5 g/l as is conventional for the low-zinc process. The ratio, by weight, of phosphate ions to zinc ions in the phosphatising, baths may vary over wide limits provided it is in the range between 3.7 and 30. A ratio, by weight, of between 10 and 20 is particularly preferred.
The phosphatising bath may contain other components apart from zinc and phosphate ions, such as are currently conventional in phosphatising baths.
Preferably, phosphatising solutions are used which contain mono- or di-valent metal ions which, as is known from experience, have a beneficial effect on the adhesion of lacquer and on the corrosion protective effect of the phosphate layers produced therewith. Accordingly, the phosphatising solution according to the present invention preferably also contains one or more of the following cations:
from 0.1 to 4 g/l of manganese(II),
from 0.2 to 2.5 g/l of magnesium(II),
from 0.2 to 2.5 g/l of calcium(II),
from 0.002 to 0.2 g/l of copper(II),
from 0.1 to 2
Brouwer Jan-Willem
Kuhm Peter
Vier Jens
Cecil Terry K.
Drodge Joseph W.
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
Ortiz Daniel S.
LandOfFree
Treatment of phosphatizing waste water does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Treatment of phosphatizing waste water, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Treatment of phosphatizing waste water will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2999373