WO1993004779A1

WO1993004779A1 - Method of rinsing cleaned, degreased metal surfaces

Info

Publication number: WO1993004779A1
Application number: PCT/EP1992/001902
Authority: WO
Inventors: Wolfgang Hater; Lutz Hüsemann
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1991-08-29
Filing date: 1992-08-20
Publication date: 1993-03-18
Also published as: DE4128648A1

Abstract

The invention concerns a method of rinsing metal surfaces which have previously been cleaned and degreased with an aqueous cleaning fluid. The rinse water is recycled after ion separation and removal of other substances using activated charcoal. In a particularly simple and universally applicable embodiment of the method proposed, the used rinse water is first treated with activated charcoal and only then passed through an ion-exchange column.

Description

"Process for rinsing degreased and cleaned metal surfaces"

The invention relates to a method for rinsing metal surfaces previously degreased and cleaned with aqueous cleaning media. The used rinse water is recycled after the separation of ions and the separation of other ingredients using activated carbon.

Aqueous degreasing and cleaning media for metallic surfaces are widely used in industrial manufacturing and finishing processes. In many cases, following the cleaning process, the cleaned metal surfaces have to be rinsed in order to remove adhering residues of the used cleaning medium, which would impair the subsequent processing steps. Due to the carryover of the cleaning bath, the rinsing water contains the usual cleaning components (cress J. et.al .: "Cleaning technical surfaces", Contact & series

Studium, volume 264, p. 5 ff., Expert-Ve lag, 1988) also the washed-off soiling of the cleaning solution, namely synthetic and vegetable oils and fats, waxes, chips,

Pigments, dust, heavy metal ions etc., in one

Concentration range usually between 0.01 and 10 g / 1.

The concentration ratios of the individual

Rinse water ingredients to each other can be any. The used rinsing water is therefore not sufficiently pure for further use, so that large amounts of waste water are generated. On the other hand, wastewater-free operation is desirable for economic and ecological reasons. With known methods, however, this is only achieved in an inadequate manner and with too much effort.

The process of replacing the evaporation losses in the process bath with rinsing water is known (Galvanotechnik 81.12 (1990), 4286). It is also known to use stand-alone or economy sinks (Galvanotechnik 78.2 (1987), 378 and 81.12 (1990), 4286), cascade technology (Galvanotechnik 81.5 (1990), 1630), individually or in combination (Galvanotechnik 77.2 (1986 ), 294) to significantly reduce the consumption of flushing water. A disadvantage of the methods, however, is the space requirement and the additional costs. In many areas, in particular in which a high surface cleanliness must be achieved, a water overhang arises despite the use of these processes, which must be eliminated.

It is also known to treat the used rinsing water with ion exchangers alone or in combination with the water-saving rinsing techniques mentioned (Galvanotechnik 73.8 (1982), 843; Galvanotechnik 73.8 (1982), 832), in particular for rinsing water from chromating processes (DE 2758960) in connection with a return of the rinse water to the chromating bath. However, the regenerability of the adsorber resins is severely impaired by oils and surfactants (Hartinger L .: Taschenbuch der Abwasserverarbeitung, Volume 2, p. 90, Carl-Hanser-Verlag, 1977). In addition, recycling processes by evaporation are described in the literature (MetallOberface 31.9 (1977), 386, DE 2729006). Disadvantages are the relatively high energy, space and investment requirements as well as the limited effectiveness, particularly in the case of solutions containing surfactants, due to carryover into the condensate.

The use of membrane processes such as reverse osmosis (US 3973987) and electrodialysis (Galvanotechnik 81.12 (1990), 4286) requires considerable investments. In addition, the performance of these techniques is significantly reduced by so-called membrane-damaging substances. The mechanisms of membrane damage are not yet well known.

The method mentioned in the first paragraph is known from DE 25 27 853 B2. In the process, metals are degreased, rinsed, phosphated and then rinsed again. The used rinsing water is drawn off from the rinsing stages. The anions contained in it are precipitated with calcium hydroxide, the sludge formed is separated off and the desludged solution is passed over a surfactant adsorber. Here, a regenerable exchanger system is preferably used. However, a filter made of activated carbon can also be used. Since the rinse water to be treated is that of the last rinse stage, care must be taken that the phosphating is carried out with a solution which is essentially free of components which give water-soluble salts when the solution is neutralized with calcium hydroxide. Another disadvantage of this process is the high sludge volume as well the complex process engineering due to the necessary sludge separation.

Following the last rinsing process, in this process the workpiece is burned off with demineralized water, which is stored in an isolated circuit, e.g. can be regenerated by reverse osmosis or ion exchange.

The object of the invention is to provide a simple and universally applicable method of the type mentioned.

This object is achieved in that the rinsing water used is first treated with active carbon and only then with an ion exchanger. The invention lies in the selection of the special combination of the two process steps in the specific order from the large number of possible preparation processes and their combinations.

The sequence of the two process steps is particularly important and essential to the invention. In the first step, oils and surfactants are separated. In the second step, cations and / or anions are removed. This means that there is a technically easy-to-carry out process with which wastewater-free rinsing is achieved. Compared to known processes, the investment costs are very low, so that the process is also suitable for small plants. It can also be adapted to changing water quality requirements by appropriate design. Another advantage is the ability to regenerate the adsorption media (with regard to activated carbon: Perrich JR: Activated Carbon Adsorption for Waste Water Treatment, p. 155 ff., CRC press, 1981; with regard to ion exchangers: Hartinger L .: Taschenbuch der Wastewater Treatment, Volume 2, p. 88 ff., Carl-Hanser Verlag, 1977). In an advantageous embodiment of the invention, it is proposed that the rinsing water be subjected to a coarse filtration before the treatment with activated carbon in order to separate undissolved contaminants. This removes chips, metal debris, pigments, dust ^, etc.

The one treated with activated carbon is preferably filtered

Rinse water before the ion exchange in order to separate residues of activated carbon. Incidentally, the activated carbon is preferably used in granular form.

A mixed bed exchanger containing a cation and anion exchanger is preferred for ion exchange. However, a simple cation or anion exchanger can also be used.

It is also proposed that the used rinsing water be passed through columns containing activated carbon or ion exchangers, in particular from the bottom up. The loading of the ion exchanger in the upstream is e.g. in Galvanotechnik 73.8 (1982), page 843.

In order to achieve larger throughputs, preferably 2 to 6, in particular 2 to 4, columns are connected in parallel. This also has the advantage of being able to change columns while the system is in operation. This is particularly important for production systems and continuous operation.

A further advantage of the process according to the invention results from the possibility that the treated rinsing water is additionally or completely reprocessed into ultrapure water and the partial streams obtained are used in different ways Places in the rinsing process. The treated rinsing water is preferably passed through a fine filter (microfilter) before being treated to ultrapure water. The preparation can take place, for example, by membrane filtration. Retentate and per eat are then returned to the rinsing process at various points.

It contributes to the security of the process if one

Conductivity and / or the COD value of the processed

Flushing water continuously measures and monitors. With that the

Function of the ion exchanger or activated carbon adsorber monitored.

The method according to the invention can be used particularly advantageously in combination with the water-saving flushing techniques known per se and mentioned above.

A system for carrying out the method according to the invention is described below by way of example with reference to the single FIG. 1.

The used rinsing water is conveyed from a collecting tank 1 by a pump 2 through a microfilter 3 into one of the two active carbon adsorbers 4. The column 4 is flowed through from bottom to top. A further microfilter 5 is connected downstream, so that the subsequent mixed bed ion exchanger 6 is not contaminated by entrained carbon particles. The exchanger is also flowed through from bottom to top. A third microfilter 7 follows. The quality of the regenerated rinsing water obtained is monitored at reference number 8 by continuous conductivity measurement. The cleaned rinsing water is finally temporarily stored in a second reservoir 9. In order to be able to change the columns while the system is in operation, 2 columns are installed, which can be operated optionally. This is particularly important for production plants. Any number of columns 4, 6 can be connected in parallel for larger plants or throughputs.

Here, too, it is particularly important and essential to the invention in which order the columns are arranged. First, the activated carbon adsorber 4 and then the mixed bed ion exchanger 6 must be flowed through.

In another example, test results for the method according to the invention are presented.

The tests were carried out on aqueous solutions, each with an alkaline or neutral cleaner. The alkaline product VR 5353-6 contains silicate, borate, carbonate and phosphate and nonionic surfactants as builder components. The neutral cleaner VR 5271-1 is composed of salts of inorganic and organic acids as well as non-ionic surfactants.

Aqueous solutions of the products in a concentration of 0.1 g / 1 were added to 0.04 g / 1 of a cutting oil (Shell KS 212) or a mineral oil (Pioneer TYPE 4556) and emulsified using a rotor-stator stirrer.

The content of inorganic salts in the solutions was determined by conductivity, the content of organic components by COD (chemical oxygen demand).

In the experiments, the batch solution was pumped through a column filled with 120 ml of activated carbon and a column containing 60 ml of ion exchanger. Two came commercially available mixed bed exchangers and activated carbon with a grain size of 1.5 mm (commercial product from Merck) are used. The operating temperature in all tests was 3 ° C, the volume flow 5 l / h.

Table 1 shows the conductivity and COD values of the batch solutions and the regenerates after a flow of 5 l. Examples 1 and 2 (without ion exchanger) show that a satisfactory regeneration of the rinsing solution alone is not possible with an activated carbon treatment. In the process according to the invention, however, both organic and inorganic ingredients are largely removed from the rinse water.

Table 2 shows the results of a load test in which 50 l of the solution were regenerated in the test apparatus without changing the adsorption media. The tests were carried out under otherwise the same conditions as tests 3 and 4 (Table 1).

Table 1

No. Cleaner Oil Nischbett- COD conductive exchanger (■ 9/1) (μS / c «)

Continuation of table 1

No. cleaner oil mixed bed COD conductivity exchanger (■ 9/1) (μS / ca)

* less than detection limit

II -

Table 2

* less than detection limit

Claims

- 12-patent claims

1. A method for rinsing metal surfaces previously degreased and cleaned with aqueous cleaning media, the used rinsing water being recycled after separation of ions and separation of other ingredients by means of activated carbon, characterized in that the used rinsing water is first treated with activated carbon and only then with an ion exchanger treated.

2. The method according to claim 1,

_ d a d u r c h g e k e n n z e i c h n e t that the rinse water is subjected to a coarse filtrate on to remove undissolved contaminants before treatment with activated carbon.

3. The method according to claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the rinsing water treated with activated carbon is filtered before the ion exchange.

4. The method according to any one of claims 1 to 3, d a du r c h ge k e n n z e i c h n e t that activated carbon is used in granular form.

5. The method according to any one of claims 1 to 4, characterized in that a mixed bed exchanger containing cation and anion exchangers is used for ion exchange.

6. The method according to any one of claims 1 to 5, so that the used rinsing water is passed through columns containing activated carbon or ion exchangers, in particular from bottom to top.

7. The method of claim 6, d a d u r c h g e k e n n z e i c h n e t that 2 to 6, in particular 2 to 4 columns are connected in parallel.

8. The method of claim 7, d a d u r c h g e k e n n z e i c h n e t that one changes between the columns connected in parallel.

9. The method according to any one of claims 1 to 8, d a d u r c h g e k e n n z e i c h n e t that the treated rinsing water completely or partially treated to ultrapure water and the partial streams obtained at various points returned to the rinsing process.

10. The method according to claim 9, d a d u r c h g e k e n n z e i c h n e t that the treated rinsing water before reprocessing to Reiπstwasser through a fine filter (microfilter).

11. The method according to any one of claims 1 to 10, characterized in that the conductivity and / or the COD value of the treated rinsing water is continuously measured and monitored.

12. The method according to any one of claims 1 to 11, d a d u r c h g e k e n e i c h n e t that it is used in combination with water-saving flushing techniques.