EP1277849A1 - Flux composition, which removes iron from flux baths - Google Patents

Abstract

Flux salt composition contains zinc chloride, alkali metal chloride, one or more alkalizing components and one or more components which oxidize iron (II) to iron (III). An Independent claim is also included for a process for operating a flux bath. Preferred Features: The composition contains 25-70, especially 50-70 wt.% zinc chloride, and 20-90, especially 30-50 wt.% alkali metal chloride. The alkali metal chloride is ammonium chloride. The alkalizing component is zinc oxide, lithium, sodium and/or potassium hydroxide, or zinc carbonate. The oxidizing component is potassium permanganate, zinc peroxide and/or zinc chlorate.

Description

The invention relates to a flux salt composition for Flux baths, a particularly simple reprocessing and Fermentation is accessible.

To achieve a high quality zinc coating go through the workpieces to be galvanized before hot-dip galvanizing several process steps. After a degreasing stage for removal of organic impurities and a subsequent Pickling step for the acidic removal of oxidic impurities, After rinsing, the workpieces pass through a pretreatment stage in a flux bath containing the fluxing agent solution. The purpose of this bath is to set the workpieces on the way to Zinc bath and to protect against corrosion during drying.

Fluxmittel solutions are aqueous salt solutions with a salt content of 300 to 500 g / l. Main components of these flux salts are zinc chloride and ammonium chloride. In addition, various alkali and alkaline earth metal chlorides (for example KCl, NaCl, MgCl ₂ , CaCl ₂ ) may be present to a limited extent. In the case of low-smoke flux salts, in particular salt mixtures, which however are rarely used because of the lower pickling effect, the proportion of ammonium chloride is largely replaced by KCl.

During dry galvanizing, the flux salt is removed by immersing the Workpiece in the fluxing agent solution applied to the galvanizing. Even when drying occurs through the formation of Hydroxozic acids have a certain pickling effect. When dipping the dried flux salt melts into the zinc kettle brought. It is important for the effectiveness of flux salts that their melting point is well below the temperature of the Zinc bath (about 450 ° C) is, so they quickly their pickling effect can unfold. The pickling effect is based on the release of hydrochloric acid, which is preferred in the temperature range from 250 to 320 ° C of ammonium chloride. This hydrochloric acid causes the dissolution of oxidic impurities.

In the fluxing agent disturbing substances accumulate during operation by introduction. Even with careful operation of the degreasing a carryover of organic substances in the subsequent pickling and further into the flux bath can not be completely avoided. Of greater importance, however, is the imported iron from the pickling baths. In the pickling, the iron accumulates in the form of FeCl ₂ and, the iron contents can be in the order of 100 to 160 g / l. To a lesser extent, alloying constituents of the steel grades used are also brought into solution during pickling. The entry of iron salts, hydrochloric acid, pickling inhibitors and alloying ingredients in the subsequent flux bath is highly dependent on the flushing technique used, but can not be completely avoided even at high flushing.

As a further source of impurities, the pickling effect the flux salt itself a role. In the flux bath is hydrochloric acid contained in different proportions, whereby iron and alloying elements removed in small quantities from the galvanizing become.

Iron, which with the flux salt in the galvanizing boiler Hot dip galvanizing is introduced, reacts with the elemental Zinc and forms hard zinc (iron-zinc mixed crystals), which in the Zinc kettle precipitates as a solid. From 1 g of iron arise about 25 g of hard zinc (Böhm, 1974 "Wastewater technology in hot-dip galvanizing plants" 12 (1974) No. 11, 235-239). The zinc losses are so considerably, so that the iron content in the flux bath is not 10 g / l should exceed (Maaß, Peißker manual "hot-dip galvanizing", 2. Aufl. German publishing house for basic industry, Leipzig 1993, p. 72). So far, however, the flux salts were often only with iron contents of 80 to 100 g / l, in extreme cases only exchanged at 150 g / l. At high iron concentrations comes In addition to zinc losses, it has an adverse effect on the Galvanizing. Hard zinc crystals in the molten zinc swim, sit on the surface of the galvanizing and then appear as so-called pimples in appearance. Next Pimples can also cause other flaws. So can by the presence of fine hard zinc crystals the viscosity The zinc melt locally be increased so much that the Pulling the workpieces out of the zinc kettle Galvanizing fault like streaks and so-called curtains. Introduced pickling acid also causes a stronger in the flux bath Dissolution of iron and thus increased hard zinc formation in the zinc kettle. Altfluxe can acidify more than 10 g / l and thus have a pH of less than 1.

The concentration of entrained organic matter Degreasing and pickling in the flux bath is generally low and does not lead to quality degradation in galvanizing. However, the organic substances are in the zinc kettle with the existing Reactants (for example, zinc, chlorine, ammonium) implemented in an uncontrolled manner so that pollutant-containing reaction products (partly dioxin-containing) may arise in the larger quantities to malfunction in the exhaust air purification lead (blockage of the filter) and recovery of the deposited Make filter dusts difficult or impossible.

Contaminated flux baths must therefore be replaced regularly with the iron content leading to replacement in the factories the galvanizing industry in many areas varies (40 to over 80 g / l). Only a small part of the ingredients could in the past in the recovery of such Altfluxe be recovered while the vast majority Share had to be disposed of as hazardous waste. This procedure The prior art is generally based on the fact that in In a multi-step process, first the pH value is set to one value between 3.5 and 4, then by hydrogen peroxide addition, the bivalent iron present in the flux bath Iron (III) hydroxide is precipitated, and then in a due the tricky consistency of these iron hydroxide flakes consuming and lengthy process from the fluxing agent solution Filtration is separated. This procedure can only one Part of the fluxing agent solution can be used again. A variant this process, in each case only part of the fluxing agent solution being treated in a separate facility will be in DE-20 29 580 C3 described. The basic disadvantages, namely the low degree of recycling and the complex Procedures and exposure of the staff to toxic and However, corrosive chemicals are not dissolved. As described in the Process the flux salt recovery is low, Many galvanizing companies refrain from recycling the Fluxes solution and prefer disposal of the whole Fluxmittel solution, if the iron content of the fluxing agent solution has risen to a defined maximum. hereby is a significant environmental impact of heavy metal salts inevitable.

An alternative method is described in DE-38 14 372 A1 described. After this procedure, the flux bath is continuous or discontinuously taken a certain amount, the made alkaline in a separate reactor with a caustic and provided with an oxidizing agent to ferric (II) To oxidize iron (III). This iron is in a preferably hydrochloric acid ion exchanger bound and after separation as reextraction acid laden with iron returned to the pickling tank. The iron-purified flux solution is returned to the flux bath after this procedure. This method has the disadvantage that it is expensive and expensive and no removal of entrained organic contaminants guaranteed.

A method by which the active substances contained in the Altfluxen practically completely recovered and the impurities, especially iron and organic impurities, quantitative can be separated has been proposed in the prior art. According to the principle of recycling by external Workup is obtained with this method from the Altfluxen a mint conditioner solution used in galvanizing shops is used again. Organic contaminants are destroyed, or concentrated in a precipitation sludge, its quantity and risk potential Other methods of the prior art are significant lower. For procedural reasons, this procedure however, only use Altflux solutions with iron contents up to 20 g / l, which requires a more frequent flux bath change is what is due to the economic and environmental benefits of complete recycling of Fluxsalzes the small Pollutant content of the waste sludge and the considerably increased Galvanizing quality is overcompensated. In the process becomes the Altflux in several steps first Hydrogen peroxide and ammonia added to precipitate iron, then by means of potassium permanganate addition, the organic Pollution destroyed. After filtering off the Eisenhydroxidschlamms is containing manganese (II) with hydrogen peroxide oxidized to brownstone and separated by filtration, with which finally received a mint Fluxmittel solution becomes.

However, this prior art method is also multi-level and above all reliant on the Altfluxe centrally reconditioned at the expense of high transport costs and in liquid form back to the galvanizing plants must be delivered.

Under the impression of environmental protection reasons increasing encapsulation of galvanizing plants and the tendency of galvanizers, the recycling of the flux agent solution on its own Therefore, the object of the present invention is to perform to provide flux salt composition which a simple reprocessing of the fluxing agent solution in one Step and not to external central reprocessing facilities instructed. This allows the flux also in Markets are used for conventional recycling for transport costs are not achievable, for example Overseas countries.

The above object is achieved by a Deicing fluxing salt composition for flux baths containing Zinc chloride and alkali metal chloride, characterized that they contain at least one or more alkalizing ingredients and one or more in aqueous solution iron (II) to Contains iron (III) oxidizing constituents.

This is usually done by reprocessing in one step in the galvanizing the preferred method of pH adjustment with ammonia water and oxidation with hydrogen peroxide simplified. At the same time is used by the Flux salt the chemical composition of the fluxing agent solution kept constant. The setting of the zinc chloride / ammonium chloride ratio by adding zinc chloride powder after a few weeks of operation can also be omitted. Three steps are replaced by one step and considerably simplify the management of the business.

To set the desired ratio of zinc chloride to alkali metal chloride to form a eutectic (low-melting) Fluxsalzmischung to ensure the galvanizing, contains a preferred embodiment of the invention Flux salt composition 10 to 80 wt .-%, preferably From 25 to 70% by weight, more preferably from 50 to 70% by weight Zinc chloride based on the salt content of the flux salt.

In addition, the flux salt composition should be 20 to 90% by weight, in particular 30 to 75 wt .-%, more preferably 30 to 50 wt .-% of alkali metal chloride based on the salt content of the fluxing salt.

Because of its additional pickling effect by release of HCl in the galvanizing bath, ammonium chloride is particularly preferred here.

As the alkalizing the flux salt composition of the invention especially zinc oxide, alkali metal hydroxides, especially lithium, sodium and / or potassium hydroxide, Metal carbonates, in particular zinc carbonate or a Combination thereof included, in a preferred embodiment 1 to 20 wt .-%, preferably 2 to 10 wt .-%, particularly preferably 3 to 7 wt .-% zinc oxide based on the flux salt.

As the oxidizing component is alkali metal permanganate, especially Potassium permanganate is beneficial because it contains both iron and also can oxidize organic contaminants and resulting Manganese (II) as manganese dioxide by methods known per se removable, but it can also metal peroxides and / or metal chlorates such as zinc peroxide or zinc chlorate as oxidizing ingredients are used.

The amount of permanganate contained ideally results from the stoichiometric need for oxidation everything contained Iron (II) to iron (III). That is why a salary of 0.1 to 15 wt .-%, preferably 0.5 to 10 wt .-%, particularly preferably From 1 to 5% by weight of alkali metal, in particular potassium permanganate, based on the fluxing salt in the fluxing salt composition of great advantage.

Another preferred embodiment of the present invention relates to a fluxing agent used to treat ferrous metal surfaces used before galvanizing and containing a fluxing salt of the above composition. In particular, this fluxing agent solution should have a concentration of less than 40 g / l, preferably less than 30 g / l and especially preferably less than 25 g / l iron, since a high Iron content, as stated above, to hard zinc formation and reduced Quality of galvanizing leads.

Likewise, the reaction temperature exceeds in the reprocessing of the Altfluxes due to the exothermic oxidation of Iron (II) to iron (III) the optimum range when the iron (II) content of the Altfluxes is above 35 to 40 g / l and it must be used coolers. This is the reprocessing sensibly at temperatures below 60 to 70 ° C carried out because above this temperature by evaporation of water Problems in the galvanizing plants occur.

In operation of the flux bath for the treatment of ferrous metal surfaces before galvanizing, a preparation of from the normal operation by Eiseneinschleppung iron-containing Fluxbädern (Altfluxen) includes, is inventively the Zinc chloride alkali metal chloride ratio and the pH to Iron precipitation and the oxidation of iron (II) to iron (III) by continuous or discontinuous addition of a Flux salt composition as described in one step. This simplifies the procedure compared to the The method described in the prior art considerably and can also decentralized in galvanizing plants also by untrained Staff are made.

The flux salt composition can be used to operate the flux bath in solid form and also dissolved in water before being added become. An optimal effect is achieved when going to operation the flux bath with the addition of the flux salt the pH of the flux bath in a range of 3.0 to 4.5 preferably from 3.3 to 4.0, more preferably at 3.8, in the solution galvanized iron (II) to iron (III) oxidized and fails. It is for the reasons described above this is advantageous for an iron content of the Altfluxes of 5 to 40, preferably 10 to 30, particularly preferably 15 to 25 g / l.

The addition of permanganate can lead to manganese over time in the Altflux accumulate. This manganese should be used from time to time Example by Komproportionierung with potassium permanganate or by oxidation with hydrogen peroxide or otherwise be precipitated and removed.

EXAMPLES Example 1:

A standard flux was selected, which is sufficient in practice is proven, has good buffering effect and a pH guaranteed from 3 to 3.8. This flux is at the galvanizing plants well introduced and recognized.

Under consideration of all possible chemical influences and risk assessment was as oxidizing agent according to the invention Potassium permanganate selected, which is added to the flux.

To determine the necessary potassium permanganate concentration and ultimately, the flux concentration to be applied became standard values used by an average galvanizing plant.

Defaults:

Flux bath size: 20 m ³ , corresponds to about 24 t; Annual throughput of galvanized material, about 10 000 t; Flux salt consumption, about 1.5 kg / t galvanizing material = 15 t flux per year, annual iron introduction up to 20 gFe / l, ie iron content to be oxidized 400 kg / year; Lugging loss 0.5 m ³ per week.

For a large-scale application, a mix of 2% Potassium permanganate chosen.

The flux salt had the following composition (% by weight): 54% Zinc chloride (crystalline) 5% Zinc oxide solid 40% ammonium chloride 2% potassium permanganate

This will change the iron levels over the course of a few months Operating time pressed to zero, then with potassium permanganate excess to achieve a demanganization of the flux bath.

Example 2:

In zinc chloride operation, a batch of 500 kg of the flux was added prepared according to Example 1 and taken therefrom samples to to test the mode of action on a laboratory scale.

Laboratory approach:

1 l of an Altfluxes were examined according to the following parameters: ZnCl ₂ 23.8% NH ₄ Cl 8.1% Fe 2.1% = 26.75 g / l Mn 200 ppm HCl 0.3% pH <1.0 density 1.274 g / ml

This flux bath turned out to be the experimental procedure ideal, because in particular the ratio of zinc chloride to Ammonium chloride deviated strongly from the optimum.

Before starting the Fluxeinsatzes was with 10 ml of 50% NaOH the pH of the flux bath set to 3.0.

25 ml were removed from this adjusted flux formulation (corresponding to A1 in Table 1), which corresponds to the weekly escape loss of 0.5 m ^{3 of} a standard 20 m ³ bath.

The 25 ml removed were again supplemented by 25 ml of a fluxing agent solution according to the invention according to Example 1 with a concentration of 400 g flux / l or 400 kg / m ³ , a usual working concentration in a galvanizing plant, and stirred for about 1 hour.

After a few seconds, there was an intense brown color and after completion of the stirring process to a very fast Decantation. The pH increases from 3.0 to 3.8.

After one day, a sample was taken and the iron reduction and the composition of the flux components tested (see A2 in Table 1). The sample of Altfluxlösung was with a few drops of HCl and the pH value again 2.8 to 3.0 to simulate HCl entrainment.

This procedure was carried out a total of four times to to simulate the four-week driving style of a bath. To each cleaning batch was analyzed (A2 to A5 in Table 1) to control iron removal.

Summary of results:

The pH increased from about 3.0 with each addition of flux to about 3.8. This is an optimal value for ferric hydroxide precipitation.

The zinc chloride ammonium chloride composition did not changed significantly.

For samples A4 and A5 of Table 1, one recognizes a slight Improvement of zinc chloride / ammonium chloride ratio.

The iron values fell from 26.75 g / l to 20.4 g / l. Related to the load of 480 kg of iron to be removed annually 127 kg of iron have been deposited per month. Considering of freshly infiltrated iron, about 2 g / l and month, the bath would be with consistent application of the de-icing Fluxes iron free in 5 months. During this time, the manganese content rises to 1000 ppm.

This content could be eliminated by free formation of MnO ₂ with free KMnO ₄ at the latest.

The iron and manganese-free bath may then be e.g. with for a year Conventional flux salt operated. From an iron content, preferably 20 g / l, the de-ironing step can be repeated be recorded.

Also conceivable is a driving style, which is a month of ironing and then two months driving with conventional Flux salt comprises. The manganese increase is due to discharge again reduced.

The insights gained allow everyone the freedom to dose the flux inserts exactly to the needs of each galvanizing plant. Measurement protocol of the flux bath analyzes. A 1 A 2 A 3 A 4 A 5 ZnCl ₂ 303 303 292 303 290 g / l NH ₄ Cl 102 102 103 105 107 g / l Fe 26.7 25.5 23.9 22.6 20.4 g / l Mn 200 220 240 340 380 ppm density 1,274 1.270 g / ml TOC 100 110 ppm

Claims (15)

A defluxing flux salt composition for flux baths containing zinc chloride and alkali metal chloride, characterized in that it contains at least one or more alkalizing constituents and one or more aqueous solution of iron (II) to ferric oxidizing constituents. Flux salt composition according to claim 1, characterized in that it contains 10 to 80 wt .-%, in particular 25 to 70 wt .-%, particularly 50 to 70 wt .-% zinc chloride, based on the salt content of the flux salt. Flux salt composition according to claim 1 or 2, characterized in that it contains 20 to 90 wt .-%, in particular 30 to 75 wt .-%, very particularly 30 to 50 wt .-% of alkali metal chloride, based on the salt content of the flux salt. A flux salt composition according to claim 3, characterized in that the alkali metal chloride is ammonium chloride. Flux salt composition according to one of Claims 1 to 4, characterized in that the alkalizing constituent comprises metal oxides, in particular zinc oxide, alkali metal hydroxides, especially lithium, sodium and / or potassium hydroxide, metal carbonates, in particular zinc carbonate or a combination thereof. Flux salt composition according to claim 5, characterized in that it contains 1 to 20 wt .-%, in particular 2 to 10 wt .-%, particularly 3 to 7 wt .-% zinc oxide based on the flux salt. Flux salt composition according to any one of claims 1 to 6, characterized in that the oxidizing constituent comprises alkali metal permanganate, metal peroxides and / or metal chlorates, in particular potassium permanganate, zinc peroxide and / or zinc chlorate. Flux salt composition according to claim 7, characterized in that it contains 0.1 to 15 wt .-%, in particular 0.5 to 10 wt .-%, particularly 1 to 5 wt .-% alkali metal, in particular potassium permanganate, based on the Flux salt contains. Flux agent solution for the treatment of ferrous metal surfaces before galvanizing, containing a flux salt composition according to one of claims 1 to 8. Fluxmittel solution according to claim 9, characterized in that the iron content has a concentration of less than 40 g / l, in particular less than 30 g / l, especially less than 25 g / l. A method for operating a Fluxbades according to claim 9 or 10 for the treatment of ferrous metal surfaces prior to galvanizing, comprising a treatment of normal operation by Eiseneinschleppung iron-containing fluxing solutions, characterized in that the zinc chloride-alkali metal chloride ratio and the pH to Iron precipitation and the oxidation of iron (II) to iron (III) by continuous or discontinuous addition of a flux salt composition according to one of claims 1 to 8 in one step. A method according to claim 11, characterized in that the fluxing salt composition is dissolved in water prior to addition. Process according to Claim 12, characterized in that the pH of the flux bath is adjusted in a range from 3.0 to 4.5, in particular from 3.3 to 4.0, very particularly 3.8, in the solution by galvanizing occurring iron (II) is oxidized to iron (III) and precipitates. A method according to any one of claims 11 to 13, characterized in that the fluxing salt composition is added at an iron content of the Altfluxes of 5 to 40, especially 10 to 30, especially 15 to 25 g / l. A process according to any one of claims 11 to 14, characterized in that accumulating manganese in the Altflux precipitates and removes, in particular, as manganese dioxide.