DE2527346A1 - PROCEDURE FOR CONTINUOUS REMOVAL OF IRON SALT POLLUTING GALVANIZATION BATHS - Google Patents

Description

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Process for the continuous elimination of electroplating baths contaminating iron salts

The invention relates to a method for the continuous removal of fouling galvanizing baths Iron salts, especially for ammonium chloride and zinc chloride baths that are used in the electroplating of metal parts be used under the action of heat.

Before iron-containing metal parts are actually electroplated, they must be cleaned. These Treatment takes place in two stages, with the first stage metal parts using hydrochloric acid or sulfuric acid be stripped and in the second section the surfaces of the metal parts in a generally concentrated form Solution of ammonium chloride and zinc chloride treated existing bath. With this in general as a fluid bath designated bath it is possible on the one hand the oxidation

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of the parts and, on the other hand, the final deposition of zinc on the respective metal part during the treatment assist in a bath of molten zinc.

The iron (II) content in the fluid bath increases as a function of the number of parts treated and the bath must therefore be drained from time to time and replaced with a fresh bath be replaced. This type of handling is on the one hand expensive, on the other hand it involves draining a heavily zinc-containing one Solution required which complies with the applicable statutory Regulations must be treated accordingly in order to avoid disturbances in the runoff of dissolved zinc salts. Until now is to neutralize such solutions, the procedure is to precipitate iron and zinc hydroxides in the form of sludge which, however, requires a lot of space and the elimination of which poses new problems when draining.

A new process has now been found that is continuous Allows removal of iron salts.

The invention accordingly relates to a method for removing iron salts in pretreatment baths for surfaces of metal parts are included, which one Subjected to electroplating treatment with the action of heat and is characterized by the following process steps :

a) Feeding the solution to be cleaned into a device in which the iron salts while maintaining the pH of the Bath and under the action of an oxidizing agent in iron (III) salts being transformed,

b) removing the precipitate obtained by direct filtering, optionally after a flocculation treatment, and

c) reintroducing the purified solution into the treatment bath, the percentage of the reintroduced amount being so regulated is that the iron content of the treatment bath or flowing bath does not exceed a predetermined value, so that one

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Easy-to-filter precipitate of iron (III) hydroxide is obtained.

In the drawing, a system for carrying out the method according to the invention is shown schematically.

It is known to separate iron salts and zinc salts by precipitating iron (III) hydroxide in an acidic medium at a pH between 3 and 4 , the zinc hydroxide remaining in solution. Under these conditions, however, the precipitate of iron-III-hydroxide occurs in the form of flakes, which can only be separated with difficulty by decanting.

However, if one takes the precautionary measure according to the method of the present invention takes to limit the content of iron (III) in the starting solution, so can the 'obtained precipitate on iron (III) hydroxide by a simple direct filtration, for example using sand or gravel remove.

In a given fluidized bath, one first carries out the oxidation of iron (II) to iron (III) using an oxidizing agent which is free of other mineral elements, for example using hydrogen peroxide. Ozone, Chlorine etc .. Flow baths usually have a VpH value, which is maintained during the oxidation, so that only iron (III) hydroxide precipitates and no other hydroxides, such as zinc hydroxide precipitate in colloidal form, which cannot be decanted.

The iron (III) hydroxide is then left in an exchanger tower flocculate and filter this to remove the ferric hydroxide straight through sand. The purified solution obtained in this way is fed back into the flowing bath, with the percentage the amount fed back in is regulated so that the iron content of the bath does not exceed a specified maximum value.

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_ 4 steps.

It has been found that in practice a value of 100 mg per liter leads to quite good results.

The filter is regularly washed under positive pressure with water and compressed air after the in the exchanger tower and in the The fluid bath solution contained in the filter has been separated out beforehand *

The sludge containing iron (III) obtained in this way only takes in has a small volume and can be easily loaded with a suitable conventional device such as a filter press, a belt-shaped Dehydrate the filter or a centrifuge. The mud is completely neutral and non-toxic and leaves can be deposited in the normal waste disposal areas without damage.

The following is an exemplary embodiment based on the drawing of the method according to the invention are described.

The liquid to be treated from the flowing bath is pumped into a container 1 in amounts of approximately 10 m / h, in order to achieve a to be able to carry out rapid treatment; for example, a continuous treatment of 4 hours is used every two days carried out.

The solution then passes through a mixing device 2, in which at 2 an oxidizing agent 3, for example hydrogen peroxide is introduced and which is provided with a control device 4 for the pH value. Then the solution is left in a Wash tower 5 go through, in which the flocculation of the ferric hydroxide takes place, which with the supply of air 6 under a much higher pressure than the ambient pressure, for example runs at about 5 bar for 1m / h to support the oxidation. The next step consists of

5Q9885 / 1124 - 5 -

filtering on sand or gravel 7, with the ferric hydroxide is deposited.

The purified solution of the fluidized bath is stored in a subsequent container 8 and fed back to the container 1. A densimeter 9 enables the concentration of ammonium chloride and zinc chloride to be measured in the floating bath. So that the original Bath 1 does not leach out, is a dry metering device 10 for the appropriate amounts of ammonium chloride and zinc chloride provided for the particular composition of the flowing bath with which the original composition of the floating bath is kept constant.

In one embodiment, 50 liters of a fluid bath were used treated with the following composition:

NH ₄ Cl : 280 g / l ZnCl ₂ : 420 g / l pH : 3.2 Fe ^{2 +} : 100 mg / 1

The oxidation is carried out with the help of 1.5 g of hydrogen peroxide carried out at 100% and the solution is passed progressively through an exchange column containing one liter of pozzolana with grains of a grain size between 5 and 10 mm, and a filter column pass through which 2 l of sand with contains a grain size between 1 and 2 mm.

The filtered liquid only contains 0.2 to 0.3 mg / 1 iron. After passing through 200 1 solution of the bath water is allowed to flow through the columns at a low throughput to remove the concentrated solvent contained therein and then washes the columns with a countercurrent flow. From the regained A dried lump of water is extracted

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fr

250 cxsTf which contains 5 g of iron.

The process described above can be carried out continuously but cleaning can also be carried out intermittently, depending on the iron content.

With the procedure described above it is possible to do the regular Avoid draining the floating bath as well as detoxifying the fluid, which otherwise necessarily occurs before each Drain must be done.

There is another advantage of the method described above in a significant improvement in the treatment of the respective metal parts, which is based on the much lower iron content of the floating bath is based.

Claims;
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509885/1124

Claims (8)

Claims 1. Method of removing iron salts in pretreatment baths for surfaces of metal parts that are subject to electroplating treatment Should be subjected to the action of heat, characterized by the following process steps: a) Feeding the solution to be cleaned into a device in which the iron salts while maintaining the pH of the Bath and converted into iron (III) salts under the action of an oxidizing agent, b) removing the precipitate obtained by direct filtering, if necessary after a flocculation treatment, and c) returning the purified solution to the treatment bath, the percentage of the amount returned is regulated so that the iron content of the treatment bath or The floating bath does not exceed a specified value, so that a precipitate of iron (III) hydroxide that is easy to filter is obtained receives. 2. The method according to claim 1, characterized in that substances are used as the oxidizing agent that are free of mineral elements. 3. The method according to claim 1 or 2, characterized in that the oxidizing agent is hydrogen peroxide, Ozone or chlorine is used. 4. The method according to one or more of claims 1 to 3, characterized in that the pH is on a value is held at which only the ferric hydroxide precipitates, preferably in a range from pH 3 to 5. The method according to one or more of claims 1 to 4, characterized in that the percentage 509885/1124 of the solution fed back into the fluidizing bath is regulated in such a way that the content of Fe ⁺ ions in the treatment bath does not exceed a value of 100 mg / l. 6. The method according to one or more of claims 1 to 5, characterized in that the by Oxidation of precipitated iron (III) hydroxide after flocculation in deposited in an exchanger tower by direct filtering using sand or gravel. 7. The method according to one or more of the claims 1 to 6, characterized in that the process is optionally carried out continuously or batchwise will. 8. The method according to one or more of claims 1 to 7, characterized in that the method is applied to the regeneration of a bath with ammonium chloride and zinc chloride. 50988b / 1 124