Method and device for preparing the bath compositions within hot-dip galvanising lines

Abstract

The present invention relates to a method and a device for preparing bath compositions within hot-dip galvanizing plants, in particular a flux bath, wherein process fluid of the flux bath is transferred in batch operation into at least one separate precipitation bath, in which ammonia (NH3) and hydrogen peroxide (H2O2) are alternately added to the process fluid until no pH change or decrease is measurable when hydrogen peroxide is added.

Description

Brief description of the invention

[0001] The present invention relates to a method and a device for preparing bath compositions within hot-dip galvanizing plants, in particular the flux bath.

[0002] The method according to the invention is used in particular in baths of hot-dip galvanizing plants, in which metallic, especially ferrous, components are treated in baths, in the so-called immersion process, using flux.

[0003] In conventional hot-dip galvanizing processes, which typically include degreasing, pickling, flux treatment, a drying step, and galvanizing (with the possibility of intermediate rinsing steps), impurities accumulate due to the preceding steps. These carryovers can negatively impact galvanizing quality and zinc consumption. Therefore, attempts are made to eliminate the impurities through precipitation reactions. Furthermore, the disposal of these impurities is often costly and environmentally problematic.

[0004] Precipitation plants are known from the prior art that operate with a continuous volume flow, in which process fluid is fed from the flux bath into a settling tank with overflow and, after the addition of ammonia and hydrogen peroxide, is then returned to the flux bath.

[0005] The disadvantage of these methods is that it is not apparent to the user whether the precipitation reaction has worked and / or is complete. Furthermore, other contaminants that occur during the hot-dip galvanizing process remain.

[0006] German patent DE 20 2020 106 580 U1 describes a device in which flux is continuously or batch-wise extracted from the flux bath via a pressure line into a reaction vessel where ammonia, hydrogen peroxide, and pickling agent are added to the liquid. The treated liquid is then returned to the flux bath via a mixer, a filter, and a buffer.

[0007] The disadvantage of this method, as described above, is that it is unclear whether precipitation has been (completely) achieved. Even though zinc stripper has already been used, some contaminants remain.

[0008] Another disadvantage of the processes and systems in the prior art is that the initial concentration of iron in the flux must be known, otherwise there is a risk of overdosing the hydrogen peroxide component. As a rule, the systems in the prior art are highly susceptible to malfunctions because the mostly superstoichiometric additions of hydrogen peroxide and ammonia in the upstream and downstream lines lead to post-reactions. Furthermore, in flow-through systems, only partial precipitation of the iron usually occurs, meaning that it is returned to the flux bath.

[0009] The object of the present invention is therefore to provide a method which completely removes contaminants, in particular iron, iron ions and iron compounds, from the flux bath and, moreover, allows the recovery of the components from the flux bath and other accompanying processes, whereby the remaining residue that has to be disposed of is environmentally unproblematic or is eliminated.

[0010] The present invention therefore relates to a method for preparing bath compositions within hot-dip galvanizing plants, in particular a flux bath, wherein process fluid of the flux bath is transferred in batch operation to at least one separate precipitation bath, in which ammonia (NH₃) and hydrogen peroxide (H₂O₂) are alternately added to the process fluid until no further pH change is measurable upon addition of hydrogen peroxide. Alternatively or additionally, no pH change may occur in the corresponding reaction time of hydrogen peroxide (H₂O₂) in the precipitation bath. The addition is preferably carried out such that a) In a process solution in the precipitation bath with a pH value below 4.00 (pH < 4.00), ammonia (NH₃) is added in a first step, continuing until the pH value preferably reaches 4.00 to 5.50, particularly preferably 4.00 to 4.20. After reaching the corresponding pH value, hydrogen peroxide (H₂O₂) is added in a second step until the pH value of the process solution in the precipitation bath is reduced to 2.00 to 3.90, preferably to 3.50 to 3.90; or b) in the case of a process solution in the precipitation bath with a pH value above 4.00 (pH ≥ 4.00) hydrogen peroxide (H 2 O 2 ) is added in a first step until the pH value of the process solution in the precipitation bath has been reduced to 2.00 to 3.90, preferably to 3.50 to 3.90.In a second step, ammonia (NH3) is added, and this is added until the pH of the process solution preferably reaches 4.00 to 5.50, particularly preferably 4.00 to 4.20; . the steps of adding ammonia or hydrogen peroxide are repeated until there is no change in pH at H 2 O 2 -addition is no longer measurable. In a particularly preferred form, the first step and / or the second step of adding ammonia or hydrogen peroxide are carried out in several sub-steps to avoid overdosing. Between the sub-steps or the addition of hydrogen peroxide (H 2 O 2 ) or ammonia (NH₃) 3 ) a preferred aspect is a reaction time which is preferably between 20 seconds (sec) and 400 seconds, particularly preferably between 30 seconds and 200 seconds.

[0011] In one embodiment, the iron hydroxide sludge that settles out within the precipitation bath upon the addition of ammonia and hydrogen peroxide to the process solution is further processed by filtering it and preferably returning the resulting filtrate to the flux. A filter cake formed during filtration is preferably rinsed in a further step using compressed air and / or water, thereby washing out zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl) from the filter cake, which then pass into the filtrate.

[0012] In a further aspect of the present invention, the filter cake is treated in a further step with hydrochloric acid, whereby iron chloride (FeCl 2 ) is formed, which can be introduced into the iron (old) pickling solution, wherein the filter cake is preferably treated directly in the acidic iron old pickling solution or dissolved in it.

[0013] In a further embodiment of the invention, a zinc pickling solution can be introduced into the precipitation bath, preferably during the filling process. This process is particularly preferably preceded by the addition of filter dust from a galvanizing process to dissolve zinc chloride (ZnCl₂), zinc oxide (ZnO), and ammonium chloride (NH₄Cl) from the filter dust. The zinc oxide (ZnO) contained in the filter dust neutralizes the residual acid content in the zinc pickling solution, which positively influences and reduces the ammonia consumption resulting from the subsequent precipitation process.

[0014] Furthermore, the present invention relates to a device for preparing bath compositions within hot-dip galvanizing plants, in particular a flux bath, comprising a) at least one precipitation bath into which process fluid from the flux bath can be fed; b) at least one container for ammonia (NH3) which is connected to the precipitation bath via a supply line; c) at least one container for hydrogen peroxide (H2O2) which is connected to the precipitation bath via a supply line; d) at least one container for zinc pickling solution which is connected to the precipitation bath via a supply line; and e) at least one container for filter dust from a galvanizing process which is connected to the container for zinc pickling solution via a feed line, so that the filter dust can be introduced into the zinc pickling solution.

[0015] The apparatus further comprises a filter press into which precipitated sludge from the precipitation bath is transferred, the filter press preferably being designed such that it has at least one drainage channel through which the filtrate formed within the filter press can be conveyed into at least one filtrate container. The filter press may also preferably a) have at least one pressure sensor capable of measuring increasing resistance within the filter press; b) include at least one valve at the inlet; and / or c) have at least one compressed air supply and / or water supply.

[0016] In a further embodiment, the device comprises at least one container for used iron pickling solution, which is connected to a container for the filter cake generated in the filter press, so that ferrous chloride (FeCl₂) is recovered from the filter cake and preferably used to utilize the residual acid content in the used iron pickling solution. By using the filter cake in the used iron pickling solution, its concentration of valuable substances, namely the ferrous chloride content, is increased, and at the same time the free hydrochloric acid content, which is problematic for further use, is reduced.

[0017] The device may preferably include at least one control element which a) the volume of process fluid transferred from the flux bath to the precipitation bath; b) the amount of ammonia (NH3) added to the precipitation bath as a function of the pH change, preferably controlling the maximum addition amount and / or the amount per step; c) the amount of hydrogen peroxide (H2O2) added to the precipitation bath as a function of the pH change, preferably controlling the maximum addition amount and / or the amount per step; d) the amount of zinc (Zn) pickling solution introduced; e) the reaction time of ammonia (NH3) and hydrogen peroxide (H2O2) within the precipitation bath; f) the number of addition cycles of ammonia (NH3) and hydrogen peroxide (H2O2); g) the addition duration of ammonia (NH3) and hydrogen peroxide (H2O2); h) the termination of the complete precipitation process due to the absence of a pH change during the addition of hydrogen peroxide; and / or i) regulates the post-treatment of the precipitated sludge or filter cake.

[0018] Furthermore, at least one sensor for pH measurement may be provided in one aspect, which is arranged in such a way that it can determine the pH value of the process liquid within the precipitation bath.

[0019] In one embodiment, the precipitation bath can include at least one valve, preferably a bypass valve, and at least one pump, either on the precipitation bath or in a line, which directs the process fluid from one point within the precipitation bath to at least one other point within the precipitation bath in order to create mixing. Alternatively or additionally, at least one pump can also be provided that generates movement of the process fluid.

[0020] Furthermore, the present invention also relates to a computer program product with a storage medium on which a computer program is stored that can perform the method described above.

[0021] In one aspect of the invention, the computer program product performs a method comprising the following steps: a) Filling the precipitation bath with a predetermined quantity of zinc-containing hydrochloric acid; b) Transferring a defined quantity of flux from the flux bath to the precipitation bath; c) Continuously monitoring the pH of the liquid obtained in the precipitation bath; d) Selectively adding ammonia or hydrogen peroxide to the precipitation bath until a predefined pH value is reached, wherein ammonia is added until a pH of 4.0 is reached, followed by the addition of hydrogen peroxide pH 4.0 to the precipitation bath (2) until the pH falls below 3.9, with a reaction time of 10 seconds (sec) to 600 seconds between chemical changes; e) Repeating step d) until no pH change is reached.-change is determined during the addition of hydrogen peroxide; f) Transfer of the treated flux from the precipitation bath to a filter press, wherein the precipitated components of the flux are retained in the filter medium and the purified flux is preferably transferred to a collection vessel with filtrate.

[0022] In a preferred aspect, the liquid within the precipitation bath is further mixed by a bypass mode.

[0023] In a further embodiment, it may also be provided that the reaction times and / or the quantity of the intervals of additions are determined by an analysis of the pH reaction curve.

[0024] In addition, in another aspect of the invention, the purified flux, for example from a collection container with the filtrate, can be returned to the flux bath.

[0025] The present invention is characterized by the embodiments in the claims and is further described by the details in the following description, examples and drawings. Description of the drawings

[0026] Fig. 1 Schematic representation of an apparatus according to the invention and of a method, wherein a subset of the process solution is transferred from the flux bath to a precipitation bath, where it is treated with hydrogen peroxide and ammonia. Furthermore, zinc pickling solution, to which filter dust has previously been added, is fed into the precipitation bath. The resulting filter cake is transferred to a filter press, where the filtrate is collected and the remaining filter cake, after rinsing with water and / or compressed air, is introduced into the iron pickling solution. The filtrate from the filter press is returned to the flux bath. Reference sign

[0027] 1 Flux bath 2 Precipitation bath 3 Hydrogen peroxide 4 Ammonia 5 Zinc pickling solution 6 Filter dust 7 Ferrous hydroxide sludge 8 Filter press 9 Filtrate 10 Ferrous pickling solution 11 Hydrochloric acid / ferrous chloride solution legend

[0028] valve Sensor / pH measurement Transfer of components Addition of zinc chloride Mixing cycle Compressed air flushing Water flush Dissolution of precipitated sludge Detailed description of the invention

[0029] The present invention relates to a method and a device for preparing bath compositions within hot-dip galvanizing plants, in particular the flux bath.

[0030] In the following, the articles "ein" and all derivatives thereof, as used here, should generally be understood as "ein / e / es or more", unless otherwise specified or the singular form is evident from the context.

[0031] Where the terms "contains", "has", "possesses" and the like are used in the description or claims, these terms shall be understood in the same way as the terms "possessing" or "comprising", i.e., not exhaustively, unless explicitly stated otherwise.

[0032] The terms "bath," "baths," or "container(s)" used below generally refer to basins that can be filled with liquid, preferably process fluid, and into which at least one component can be immersed. For this reason, these are usually basins or baths open at the top. While we generally refer to multiple baths, it can also refer to a single basin or bath divided into individual sections, each containing its own process fluid. In such a case, each section would correspond to a separate bath. In some cases, however, the baths or containers may also be closed.

[0033] The term "component(s)" refers to metallic components of any kind, preferably components made of ferrous or iron-based material, in particular components made of steel, such as blanks, sections, structures, and / or finished workpieces. The term "component" also includes, in the following, groupings and / or assemblies of components of different or the same type and / or of different or the same material that can undergo joint treatment in one or more process baths and / or steps. These groupings can, in some cases, also be assembled using suitable aids such as crossbeams, workpiece carriers, or similar devices.In the flux bath (1), a previously degreased and pickled ferrous component is treated with a flux, which typically comprises an aqueous solution of inorganic chlorides, especially zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl). The flux serves, among other things, to finely clean the component surface and to improve the wetting of the component surface during subsequent steps, such as galvanizing. The flux, which is also referred to as the process fluid, usually has a composition comprising the following components: zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl).Furthermore, other components such as alkali salts, alkaline earth salts and / or metal salts may be included, such as tin chloride (SnCl2), bismuth chloride (BiCl3), antimony chloride (SbCl3) and / or aluminum chloride (AlCl3), but not limited to the above list.

[0034] In the process according to the invention, the process fluid of the flux bath (1) is processed in batch operation, i.e., during ongoing operation. This ensures that contaminants, such as iron ions (Fe²⁺ / ³⁺), are continuously removed from the bath. A specific volume of process fluid is extracted from the respective bath and fed to a separate bath, basin, and / or container or separate area. This so-called batch volume can comprise a different quantity of process fluid depending on the bath volume; however, the quantity is selected such that the process in the bath is not disrupted by the extraction of the process fluid. In a preferred embodiment, 300 to 800 liters (1), particularly preferably 500 liters of process fluid, are extracted and introduced into a separate basin, hereinafter referred to as the precipitation bath (2).In the precipitation bath (2) the process fluid is treated and prepared by adding ammonia (NH 3 ) (4) and hydrogen peroxide (H 2 O 2 ) (3).

[0035] The duration and / or quantity of ammonia (NH₃) (4) and hydrogen peroxide (H₂O₂) (3) added is determined according to the invention by means of pH measurement. Here, the pH fluctuation within the process fluid of the precipitation bath (2) caused by the addition of hydrogen peroxide (H₂O₂) (3) is measured. The reason for the pH fluctuation is the iron chloride, which is contained in solution within the process fluid of the flux bath (1) and is converted to iron(III) hydroxide by the addition of hydrogen peroxide (H₂O₂) (3). Hydrochloric acid (HCl) is also produced in this reaction, which lowers the pH, as shown in the following equation: FeCl₂ + ½ H₂O₂ + 2 H₂O = Fe(OH)₃ + 2 HCl.

[0036] As long as ferric chloride (FeCl₂) is in solution in the process fluid, the pH value consequently drops upon the addition of hydrogen peroxide (H₂O₂) (3). Using suitable pH measurements that record the fluctuations or changes in pH, it can therefore be determined whether the iron in solution has been completely precipitated. If the pH value changes due to the alternating addition of hydrogen peroxide (H₂O₂) (3) and ammonia (NH₃) (4) to the process fluid of the precipitation bath (2) upon H₂O₂ addition, the alternating addition of the two components is repeated until no further change is measurable upon H₂O₂ addition. It is essential for the process that the precipitation process is only considered complete when no change in pH value can be detected during the hydrogen peroxide addition (H₂O₂ addition) and / or the associated reaction time.If this is the case, all the iron chloride in the precipitation bath has been converted into iron hydroxide.

[0037] The respective addition of ammonia (4) or hydrogen peroxide (3) can comprise several sub-steps. In these sub-steps, for example, a specific quantity and / or a specific period of time of hydrogen peroxide (3) is added. The number of sub-steps, for example, for the hydrogen peroxide addition (3), can be arbitrarily high. The same applies to the addition of ammonia (4). In a preferred embodiment, several sub-steps of the addition are used to raise the pH value using ammonia (NH₃) (4) or to lower the pH value using hydrogen peroxide (H₂O₂) (3) in order to achieve the desired pH values. The reaction of the substances contained in the process fluid with the added components, i.e.,Ammonia (4) or hydrogen peroxide (3) requires a certain amount of time, the so-called reaction time, so a specific interval should be observed between the individual additions of hydrogen peroxide (H₂O₂) (3) and ammonia (NH₃) (4). This reaction time ensures that the reaction of the two components with the process fluid is complete. The reaction time and the number of (partial) steps depend on the volume of the precipitation bath (2), the iron concentration, the amount of each component added (H₂O₂ and NH₃), and / or the degree of mixing of the process fluid in the precipitation vessel. In a preferred embodiment, a control element detects the completion of the precipitation process by the absence of a pH change during the hydrogen peroxide addition. Alternatively or additionally, the completion of the precipitation process can also be detected by the absence of a pH change within the reaction time following the hydrogen peroxide addition.If this is the case, the iron chloride present in the process solution has been converted into iron hydroxide. Control can be achieved, for example, by specifying the maximum addition quantity of hydrogen peroxide (H₂O₂), the maximum dosing time (including reaction time) of hydrogen peroxide (H₂O₂), the number of addition cycles of hydrogen peroxide (H₂O₂), and / or the addition quantity of hydrogen peroxide (H₂O₂) within the individual substeps, but is not limited to the preceding list. The reaction time of hydrogen peroxide (H₂O₂) (3) or ammonia (NH₃) (4) within the process solution, i.e., the duration of the reaction of one of the components with the process solution in the precipitation bath (2), is, according to one aspect of the invention, between 10 and 600 seconds, preferably between 20 and 400 seconds, and particularly preferably between 30 and 200 seconds. The precipitation bath (2) further preferably comprises 200 l to 5000 l, particularly preferably 500 l to 1000 l.A key aspect of the present invention is that hydrogen peroxide (H₂O₂) (3) or ammonia (NH₃) (4) are alternately introduced into the process fluid of the precipitation bath. Preferably, the addition is further carried out in partial steps, in which smaller quantities of the components are repeatedly added to the process fluid. If the entire quantity of ammonia (NH₃) or hydrogen peroxide (H₂O₂) for the precipitation or oxidation of the iron is added immediately, i.e., after the stoichiometric consumption – 0.609 g of 100% ammonia (NH₃) for 1 g of iron (Fe) and 0.304 g of 100% hydrogen peroxide (H₂O₂) – only partial precipitation of the iron within the process fluid is observed. Therefore, a single addition of the components to the precipitation bath does not achieve the precipitation of all the iron within the process solution.It has been found that alternating between the addition of ammonia (NH3) or hydrogen peroxide (H2O2) with smaller amounts of the components and / or in partial steps leads to complete precipitation of the iron within the process solution. Therefore, in a preferred aspect of the present invention, after filling the precipitation bath (2) with process fluid from the flux bath (1), the pH value in the process fluid within the precipitation bath (2) is increased to 4.00 to 5.50, preferably to 4.00 to 4.20, using ammonia (NH3) (4). Once the pH value reaches the desired level, hydrogen peroxide (H2O2) (3) is added, preferably lowering the pH value to 2.00 to 3.90, and more preferably to 3.50 to 3.90.The addition of ammonia (NH₃) (4) and hydrogen peroxide (H₂O₂) (3) is repeated until no further changes in the addition and reaction time can be observed with hydrogen peroxide (3). If the initial pH of the process fluid transferred from the flux bath (1) is above 4.00, hydrogen peroxide (H₂O₂) (3) is added first, followed by ammonia (NH₃) (4), i.e., in reverse order of the added components. By determining the pH changes with hydrogen peroxide addition, and thus the presence of iron in solution, a stoichiometric addition of hydrogen peroxide (H₂O₂) (3) and ammonia (NH₃) (4) is possible.Furthermore, the advantage of such a process is that the initial concentration of iron dissolved in the process solution in the flux bath (1) is not relevant and does not need to be known, since the addition of hydrogen peroxide (H 2 O 2 ) (3) and ammonia (NH 3 ) (4) takes place according to the actual consumption or the corresponding presence of iron in solution.

[0038] In a further aspect of the present invention, the settled iron hydroxide (7a) is then processed in a subsequent filtration process by passing it through a filter press (8), preferably a chamber filter press, using a pump. The filter press (8) is preferably equipped with filter cloths that retain the precipitated iron hydroxides. The filtration within the filter press (8) yields a filtrate (9) that no longer contains iron (filtrate = 0 g / l Fe). In one embodiment, the filtrate (9) can then be conveyed via a drain channel within the filter press (8) into a filtrate container, which stores the flux for later recirculation or other use. Alternatively, the filtrate (9) can also be directly returned to the flux bath (1). The transfer of the filtrate (9) into the filtrate container or the process bath is preferably carried out using suitable pumps.

[0039] In one embodiment, the filter press (8) is continuously supplied with liquid throughout its operation, preferably via the filtrate container and, during emptying, via the precipitation tank. This continuous supply of liquid to the filter press (8) throughout the precipitation process ensures a uniform filter cake formation and protects the filter plates and filter cloths of the filter press (8).

[0040] In the filter press (8), a filter cake containing iron hydroxide builds up within the precipitation bath (2) as the amount of precipitate increases. This increasing filter cake leads to increasing resistance within the filter press (8). In one aspect of the invention, a pressure sensor is arranged in the feed line of the filter press (8) or in the press itself, which registers the pressure generated by filling the press with iron hydroxide. If a pressure of 1 to 10 bar, preferably 3 to 8 bar, and particularly preferably 5 to 7 bar, is measured, the filter press (8) is emptied. Alternatively, instead of or in addition to the pressure reading, time-controlled emptying can be performed.

[0041] To obtain a nearly pure filter cake consisting of iron hydroxide and / or to prevent excessive removal of filtrate (9), i.e., process fluid containing the flux salts, a valve located upstream of the filter press (8) can be closed, and the filter press (8), and thus the filter cake, can be treated with compressed air and / or water. Such rinsing of the filter cake allows the flux components zinc chloride and ammonium chloride, contained in the residual moisture of the filter cake or precipitate sludge, to be washed out, thereby reducing the residual moisture content of the filter cake. The washed-out components zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl) can then be returned to the flux bath (1).By treating the filter cake or precipitate sludge with a preferably compressed air-water-compressed air rinse, only small amounts of zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl) remain. The compressed air rinse preferably lasts from 1 to 30 minutes, preferably from 5 to 15 minutes. For the most effective compressed air rinse, the filtrate outlets of the filter press (8) are preferably closed when a predetermined pressure is reached and / or after a predefined period. Subsequently, one filtrate outlet at a time is opened and pressurized with compressed air, while the other filtrate outlets remain closed, thus rinsing each filter chamber individually. The compressed air rinse operates at a pressure of 5 to 10 bar, preferably 6 to 8 bar, in one aspect.The treatment time of the compressed air rinsing per filtrate outlet within the filter press (8) is preferably 5 seconds to 120 seconds, more preferably 30 seconds to 60 seconds. In one aspect of the invention, the compressed air rinsing is carried out before and / or after the water rinsing. As with the compressed air rinsing, in another aspect of the present invention, the water rinsing is carried out separately for each filter chamber. The volume of water required for the water rinsing depends on the size of the filter press (8) and the desired purity level of the precipitated sludge. In a preferred embodiment, the volume of water for rinsing the precipitated sludge is matched to the evaporation losses of the flux bath and is 100 liters to 2,000 liters, more preferably 300 liters to 1,000 liters. If rinsing is carried out per chamber, the amount of water per filtrate outlet is preferably 5 liters to 50 liters, more preferably 20 liters to 35 liters.At the end of the filter cake post-treatment, and when no more liquid flows from the filter press (8), the compressed air supply is stopped and the filter press (8) is opened, allowing the filter cake to be conveyed, preferably via a hopper, into a collection container. The filter cake is collected there and can be disposed of accordingly. One advantage of this post-treatment of the filter cake is that a contaminant-free iron hydroxide sludge (7b) is produced, which is not relevant to accidents and therefore does not require separate disposal documentation. Another advantage of returning the compressed air- and / or water-rinsed filtrate (9) to the flux bath (1) is that evaporation losses within the flux bath (1) can be compensated for. At 45°C, these evaporation losses amount to approximately 300–1,000 liters per day, depending on the bath surface area. Consequently, such recirculation also saves water.

[0042] The filter cake, which contains iron hydroxides, can also be used to recover ferric chloride (FeCl₂), which can be used, for example, in iron pickling. In this process, the iron hydroxide in the filter cake is dissolved using hydrochloric acid (11), which can be obtained, for example, from the waste iron pickling solution. This reaction produces ferric chloride: 2 Fe(OH)₃ + 4 HCl = 2 FeCl₂ + 5 H₂O + % O₂.

[0043] By treating the filter cake in this way, it is possible to reduce or even eliminate the disposal costs otherwise incurred during the precipitation process, as the specified limit parameters for the disposal of the waste iron pickling baths are met even after the precipitated sludge has been redissolved. Returning the precipitated sludge to the waste iron pickling baths increases their concentration of valuable substances, in this case iron chloride (FeCl₂), and further reduces the remaining residual acid content.

[0044] Based on the precipitation reactions, the components obtained or the process solution can be returned to the original process cycle, namely the flux bath (1). In addition to the above-mentioned oxidation of the iron chloride with hydrogen peroxide (H₂O₂) (3) within the precipitation bath (2) (see above), the addition of ammonia (NH₃) (4) neutralizes the acid, forming ammonium chloride (NH₄Cl), which is one of the components of the flux bath (1), as shown in the following equation: HCl + NH₃ = NH₄Cl

[0045] In a further aspect of the present invention, zinc chloride (ZnCl₂) can also be recovered from the zinc pickling solution (5). The zinc pickling solution (5), also called stripper, is preferably introduced into the precipitation bath (2) during the filling process.

[0046] Furthermore, in another embodiment, the residual acid content of the zinc pickling solution (5), which is typically ≤ 50 g / l HCl, is used to extract the zinc chloride, zinc oxide, and ammonium chloride components contained therein from the filter dust (6). This filter dust consists of approximately 1 / 3 wt.% each of the components ZnCl₂, NH₄Cl, and ZnO. Filter dust (6) is generated by the flue gases produced during the galvanizing process at the boiler. Upon addition of the hydrochloric acid (HCl) from the zinc pickling solution (5), zinc oxide (ZnO) additionally forms zinc chloride (ZnCl₂). The acid is also neutralized. An advantage of recovering the components from the filter dust (6) is that its disposal was usually subject to a cost, which is now eliminated.A further advantage of using filter dust (6) in the precipitation reaction of the precipitation bath (2) is that the aforementioned neutralization of the zinc pickling solution (5) by means of filter dust (6) results in a higher pH value of the process liquid within the precipitation bath (2) than without the addition of filter dust (6). Consequently, the consumption of ammonia (NH3) (4) in the subsequent precipitation process is lower when the filter dust is added. For example, the pH value of the process solution within the precipitation bath (2) without neutralization of the zinc pickling solution (5) with filter dust is 3.07. With the addition of the filter dust (6) and the neutralization of the zinc pickling solution (5), the process solution can, for example, reach a pH value of 3.82. Due to the neutralization using filter dust (6) and the addition of the zinc pickling solution (5), the amount of ammonia (NH 3 ) (4) added is consequently lower to pH 4.00 to 5.50.

[0047] In summary, by processing almost all components of the flux bath (1), only the consumption of the burnt-off flux salts through zinc ash formation during the galvanizing process needs to be compensated for. This is particularly advantageous because, in conventional processes, components, especially zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl), have to be replenished at considerable expense.

[0048] The present invention further relates to a device for preparing a flux bath (1) within a hot-dip galvanizing plant, comprising a flux bath (1) from which a specific volume (batch) of the process fluid is extracted by means of suitable lines and at least one pump and directed into at least one precipitation bath (2). At least one control element regulates the volume of process fluid that is directed from the flux bath (1) into the precipitation bath (2). In addition to the process fluid, other liquids and / or materials, such as powders, can be added to the precipitation bath (2), which is a basin or bath that can be open or closed. According to the invention, ammonia (NH₃) (4) and hydrogen peroxide (H₂O₂) (3) are added to the process fluid directed into the precipitation bath (2) from corresponding containers.To determine the amount of each component added, the pH of the process fluid is measured using suitable sensors. For this purpose, the pH sensor is preferably located within the precipitation bath (2) and / or the bypass line of the precipitation bath (2) to directly measure the pH within the process fluid. The pH measurement and monitoring are performed throughout the entire process. If the pH probe detects a pH below 3.90, ammonia (NH₃) (4) is added from a container to the process fluid in the precipitation bath (2) using at least one control element until the pH is raised to between 4.00 and 5.50, preferably to between 4.00 and 4.20.When the pH reaches the corresponding target value, the at least one control element triggers the addition of hydrogen peroxide (H₂O₂) (3) from an H₂O₂ container, preferably lowering the pH to 2.00 to 3.90, and more preferably to 3.50 to 3.90. The at least one control element also regulates the addition quantities in liters and / or the addition duration of the components ammonia (NH₃) (4) and hydrogen peroxide (H₂O₂) (3). Furthermore, it regulates the reaction time, i.e., the time interval between the addition of one of the two components and the reaction to it. Finally, the control element regulates the number of partial addition steps of ammonia (NH₃) (4) and hydrogen peroxide (H₂O₂) (3) to prevent overdosing or underdosing of the components within the precipitation bath.Furthermore, in a particularly preferred embodiment, the control element determines the termination of the precipitation process by the absence of a pH change during the addition of hydrogen peroxide. Alternatively or additionally, the absence of a pH change is also checked during the reaction time of the hydrogen peroxide (H₂O₂) (3) in the process solution in the precipitation bath. To raise the pH using ammonia (NH₃) (4) and / or lower the pH using hydrogen peroxide (H₂O₂) (3), the addition of hydrogen peroxide (H₂O₂) (3) and the addition of ammonia (NH₃) (4) are preferably carried out in several steps to achieve the previously described preset pH values ​​for the hydrogen peroxide (H₂O₂) addition (3) and the ammonia (NH₃) addition (4), respectively. The precipitation bath (2) further preferably comprises 200 l to 5000 l, particularly preferably 500 l to 1000 l.

[0049] The two containers, which comprise ammonia (NH 3 ) (4) and hydrogen peroxide (H 2 O 2 ) (3), preferably also have sensors that determine the fill quantity of the components, i.e., with which it is particularly preferably possible to check whether the containers are empty or nearly empty.

[0050] According to the invention, the device further comprises a container for the zinc pickling solution (5), which can be open or closed, wherein the zinc pickling solution (5) is fed into the precipitation bath (2) by means of a pump. Furthermore, according to the invention, filter dust (6) is transferred from a separate container into the container for the zinc pickling solution (5).

[0051] The reaction times and / or previously described chemical reactions are improved and ensured by adequate mixing, particularly within the precipitation bath (2). For this purpose, the process liquid within the precipitation bath (2) is extracted from the bottom region using a valve, preferably a bypass valve, and at least one suitable pump, and directed to at least one other location, preferably just below the liquid level, within the precipitation bath (2), thereby generating more thorough mixing of the process liquid.

[0052] The precipitated sludge generated within the precipitation bath (2), in the form of iron hydroxide, preferably iron hydroxide flakes and / or iron hydroxide particles, is transferred to a filter press (8), preferably a chamber filter press. The transfer is preferably carried out by means of at least one pump, particularly preferably a sludge pump. The filter press (8) is preferably designed such that it has at least one outlet channel through which the filtrate (9) formed within the filter press (8) can be conveyed into at least one filtrate container.

[0053] In one aspect of the invention, the filter press (8) comprises at least one pressure sensor which measures the increasing resistance within the filter press. When a certain pressure is reached within the filter press (8), a signal is transmitted to at least one control element to empty the filter press (8). Alternatively or additionally, a timed emptying can be programmed using a control element. To prevent excessive removal of filtrate (9) and flux components, i.e., process fluid and feed chemicals, and to produce a precipitation sludge that is as free of contaminants as possible, a valve is arranged upstream of the filter press (8) in one embodiment of the present invention, which can be closed as needed. The valve is preferably an electrically controlled solenoid valve or a manual shut-off valve.After this is closed, in a preferred embodiment the filter press (8) is rinsed by means of a compressed air supply and / or a water supply. A control element regulates the duration and / or the amount of rinsing. For this purpose, a sensor can also be arranged at the outlet of the filter press (8), i.e., preferably at the overflow, which is at least one drain channel, to measure whether filtrate (9) is obtained from the filter press (8) during rinsing. If no more liquid leaves the filter press (8), the compressed air supply is stopped. In a particularly preferred embodiment, valves are arranged inside the filter press (8) upstream of the individual chambers and filtrate outlets, which make it possible to open the filtrate outlets and thus the filter chambers individually.This ensures that each filter chamber and its associated filtrate outlet always receives the same backwash pressure, unlike in a series circuit where the first outlets receive a higher pressure than the last. In a preferred embodiment, the water supply also has a valve for each filter chamber and filtrate outlet, through which the respective filter chamber can be controlled. This can be the same valve used for compressed air backwashing. The filter cake formed within the filter press (8) can then preferably be conveyed into a collection container via a funnel located below the filter press (8).

[0054] According to the invention, the filtrate (9) is returned from the filtrate container to the flux bath (1) by means of a pump.

[0055] In a further aspect of the invention, the filter cake is supplied with hydrochloric acid, preferably iron pickling solution (10), from at least one suitable container within the collection vessel or within a separate bath, so that iron chloride (FeCl₂) can be recovered. The iron chloride formed can be collected in a container or fed directly to the iron (Fe) pickling solution via suitable lines. Alternatively, the precipitated sludge can also be dissolved directly in the iron pickling solution.

[0056] In this context, feeding or returning refers to the transport of a liquid and / or component to another location, such as a different bath or container. This is generally accomplished using suitable inlet or outlet lines, valves, and pumps. These conform to established designs and are therefore not described in detail.

[0057] Furthermore, in one aspect of the invention, level sensors are arranged in at least one of the baths or containers to ensure that no overfilling occurs and, optionally, to monitor the pump runtime. Alternatively or additionally, at least one leakage probe can be provided to signal any leakage of liquids.

[0058] In a preferred aspect of the invention, a collection tray is located below the device, which collects any liquids that may have leaked out.

[0059] The control element preferably comprises at least one computing module, such as a computer, and / or a programmable logic controller (PLC), which may include one or more transmission modules and thus receive, collect, and transmit information, and / or control components such as valves and pumps, either wired or wirelessly. The at least one computing module and / or the at least one programmable logic controller may further comprise one or more internal and / or external memory units. The at least one control element may also preferably perform at least one step of the method described above. Suitable control elements are known from the prior art and may include such elements; therefore, further details are not provided here.The at least one control element can include a computer program product, described later in this document, which coordinates and executes the control of the processes within the bath preparation system. For this purpose, the at least one control element preferably includes at least one terminal device, such as an operator panel, a PC, or similar, on which the user has access to a visualization module that displays the parameters and / or states of the device's components, such as valves, taps, pumps, and others. The device can be operated either automatically and / or manually. Both operating modes are preferably secured by safety interlocks.

[0060] In manual operation, individual valves and pumps can preferably be controlled manually. This control can be achieved using at least one control element, which sends a signal to the corresponding actuator, or by manually operating the respective actuator. In a preferred configuration, the filtrate pump and the associated filtrate valve preferably remain in automatic control mode to prevent the filtrate collection tank from overflowing. Furthermore, the filter press preferably also remains in automatic operation to ensure an optimal and reliable filtration process.

[0061] In contrast to manual operation, in automatic operation all process-relevant interfaces, i.e. all actuators, such as pumps, levers, taps, valves or similar, as well as sensors, such as pH probe, flow sensor, level monitoring sensor and / or others, are automatically controlled by at least one control element depending on the current device state and / or the data received from the device components, the actuators and / or sensors are evaluated.

[0062] Alternatively, an operation can be provided that is partly automated and partly manual.

[0063] In a particularly preferred embodiment of the present invention, the device comprises the following components: a) at least one precipitation bath (2); b) at least one filter press (8); c) at least one collection tank for the iron hydroxide; d) at least one chemical dosing system; e) at least one hydraulic control system; and f) at least one control element.

[0064] The chemical dosing system is preferably a dosing device which can dispense chemical components, in particular ammonia (4) and hydrogen peroxide (3), in predetermined quantities and at predetermined times to the at least one precipitation bath (2).

[0065] The hydraulic control system includes, in particular, actuators such as pumps, gates, taps and / or valves, which serve to control the fluid flow.

[0066] The present method and apparatus are ideal from an environmental perspective compared to the prior art, as they produce few to no contaminants and many relevant substances for the flux bath (1) can be recovered and recycled. Furthermore, the placement of sensors at relevant positions within the apparatus ensures ease of use, enabling the operator to directly detect potential disturbances in the precipitation reactions.

[0067] Furthermore, a control system was developed to ensure the smooth operation of the process, which produces few to no contaminants and partially returns substances to the flux bath. This system can be implemented by the control element and can regulate and control the process.

[0068] By implementing the method in a computer system, at least some of the steps belonging to the method are carried out by a processor through the execution of instructions. In a further embodiment, instructions or a part of the instructions for executing the described method and / or for implementing the described method in a system can be stored on a non-transitory, computer-readable data carrier.

[0069] In this context, the at least one control element can comprise a multitude of identical and / or different modules. Modules are also referred to as "components" or "functional units." Furthermore, modules and / or components can also be "computer-executed" and / or "computer-implemented." The modules are implemented within a computer system, which typically includes a processor and memory. Generally, a module is a component of a system that performs specific operations to implement a particular functionality. Examples of functionalities include receiving measured values ​​(such as image data) or calculating the field using a computation module. However, the modules can also possess other functionalities described in the embodiments of the method above.

[0070] The term "module" here encompasses a tangible entity that is physically constructed, permanently configured (e.g., hardwired), or temporarily configured (e.g., programmed) to operate in a particular way or to perform certain operations described herein. In embodiments where the modules are temporarily configured (e.g., programmed), not every module needs to be configured or instantiated at every moment. For example, a general-purpose processor may be configured to execute different modules at different times. In some embodiments, a processor implements a module by executing instructions that implement at least part of the module's functionality. Optionally, memory may store the instructions (e.g.,(as computer code) which are read and processed by the processor and cause the processor to perform at least some operations involved in implementing the functionality of the module.

[0071] Additionally or alternatively, a memory, which may comprise one or more memory devices, can in one embodiment store data that is read and processed by the processor to implement at least part of the module's functionality. In another embodiment, the memory can comprise one or more hardware elements capable of storing information accessible to a processor. In one embodiment, the memory can be at least partially integrated into the processor, located on the same chip as the processor, and / or be a physical element separate from the processor.

[0072] In one embodiment, the at least one processor executes instructions stored in memory that perform operations involved in implementing the functionality of a specific module. The at least one processor can also operate in such a way that the performance of the relevant operations is supported in a cloud computing environment or as Software-as-a-Service (SaaS). For example, at least some of the operations involved in implementing a module can be performed by a group of computers accessible via a network, such as the internet, and / or via one or more appropriate interfaces, such as application programming interfaces (APIs). Optionally, some of the modules can be executed in a distributed manner across multiple processors.In one embodiment, the at least one processor can be located at a single geographic location or distributed across multiple geographic locations. Furthermore, in one embodiment, data can be uploaded to cloud-based servers. In some embodiments, modules can provide information to other modules and / or receive information from other modules. Accordingly, such modules can be considered communicatively coupled. If several such modules are present simultaneously, communication can be achieved through signal transmission. In embodiments where modules are configured or instantiated at different times, communication between such modules can be achieved, for example, by storing and retrieving information in memory structures that multiple modules can access.In one embodiment, a module can perform an operation and store the output of this operation on a storage device with which it is communicatively coupled. Another module can then access the storage device at a later time to retrieve and process the stored output.

[0073] In this context, the present invention further relates to a computer program product comprising a storage medium on which a computer program is stored that can coordinate and control the bath preparation method described above. In a preferred embodiment, the computer product is loaded directly into the internal memory of a digital computer and comprises software code sections with which the steps of the method described herein are executed when the product is running on a computer.The term computer program product here includes a computer program stored on a medium, such as RAM, ROM, CD, devices and similar equipment; an embedded system as a comprehensive system with a computer program, such as an electronic device with a computer program; a network of computer-implemented computer programs, such as server systems, client systems, cloud computing systems and the like; and / or computers on which a computer program is loaded, running, stored, executed or being developed.

[0074] Although the methods disclosed herein may be described and presented with reference to certain steps performed in a specific sequence, it is understood that these steps may be combined, subdivided, and / or rearranged to form an equivalent method without deviation from the teachings of the embodiments. Accordingly, unless expressly stated herein, the sequence and grouping of the steps do not constitute a limitation of the embodiments. Furthermore, for the sake of clarity, the methods and mechanisms of the embodiments are in some cases described in the singular. However, unless otherwise stated, some embodiments may include multiple iterations of a method or multiple instantiations of a mechanism.For example, if a processor is disclosed in one embodiment, the scope of that embodiment should also cover the use of multiple processors. Certain features of the embodiments, which may have been described in the context of separate embodiments for clarity, may also be provided in various combinations within a single embodiment. Conversely, various features of the embodiments, which may have been described in the context of a single embodiment for reasons of space, may also be provided separately or in any suitable subcombination.

[0075] In another embodiment, the methods and programs can be executed with various computer system configurations. These computer systems include, but are not limited to, cloud computing, client-server models, grid computing, peer-to-peer, handheld devices, multiprocessor systems, microprocessor-based systems, programmable consumer electronics, minicomputers, and / or mainframes. Additionally or alternatively, some of the embodiments can be performed in a distributed computing environment where the tasks are carried out by remote processing devices connected via a communication network. In a distributed computing environment, program components can be located on both local and remote computers and / or storage devices.Additionally or alternatively, some of the implementations can be carried out in the form of a service such as Infrastructure-as-a-Service (laaS), Platform-as-a-Service (PaaS), Software-as-a-Service (SaaS) and / or Network-as-a-Service (NaaS).

[0076] In the following, a preferred embodiment of the method will be presented, which can coordinate and control the bath preparation using a computer program product.

[0077] In a first step, the precipitation bath (2) is filled (filling phase). Preferably, a predetermined quantity of zinc-containing hydrochloric acid is first introduced into the at least one precipitation bath (2). Subsequently, flux is transferred from the flux bath (1) into the precipitation bath (2) until a predetermined reactor volume is reached in the precipitation bath (2).

[0078] In another aspect, a circulation phase can preferably be provided. Here, the pump operation is adapted in such a way that it contributes to improving or generating mixing dynamics within the at least one precipitation bath (2) in bypass mode.

[0079] Furthermore, in one embodiment, pH monitoring and chemical dosing are performed in a further step. Continuous pH monitoring is preferably carried out via at least one integrated pH probe in the filling line. The chemical dosing of ammonia (4) or hydrogen peroxide (3) into the precipitation bath (2), in particular 18% ammonia solution or 35% hydrogen peroxide, is carried out by selective dosing, preferably via precision dosing pumps with flow measurement. In a preferred aspect, the addition of ammonia (4) or hydrogen peroxide (3) takes place at controlled intervals with predetermined pause times between doses to achieve complete precipitation of the iron within the flux in the precipitation bath (2). In a preferred embodiment, ammonia is added until a pH value of 4.0 is reached.When this value is reached, hydrogen peroxide at pH 4.0 is automatically added to the precipitation bath (2) until the pH falls below 3.9. If a corresponding drop is measured, the ammonia dosage is resumed. In a particularly preferred embodiment, a predefined pause, the so-called reaction time, is observed between the addition of hydrogen peroxide (H₂O₂) (3) or ammonia (NH₃) (4). This is preferably between 10 and 600 seconds, and particularly preferably between 30 and 200 seconds.

[0080] The amount of ammonia (4) or hydrogen peroxide (3), the pause times and / or the number of intervals of additions are determined by an analysis of the pH reaction curve.

[0081] After completion of the precipitation, which was achieved when no further change in pH could be measured during the addition of hydrogen peroxide (3), the treated flux is transferred from the precipitation bath (2) to the filter press (8), whereby the bound iron or iron compounds are retained in the filter medium and the purified flux can be transferred, for example, to a collection container with filtrate (9).

[0082] Subsequently, it may be provided that the purified flux is returned from the collection container with the filtrate (9) to the flux bath (1).

[0083] In addition, further steps, such as a backwashing process of the filtrate, the use of the zinc pickling solution (5), the introduction of filter dust (6), the use of processed zinc ash as an alternative input material, as previously described for the process, can also be used in the computer-implemented control.

[0084] The innovative system comprising process, device, and computer program offers several technical advantages over the prior art. A key aspect is volume optimization. Using the system described herein, the processing volume can be reduced to a maximum of 500 liters, compared to conventional systems with 1,000 liters. Furthermore, efficient processing of smaller volumes with proportional chemical dosing is possible, and the system's minimized fluctuations in the flux bath level are particularly advantageous for smaller tanks.

[0085] Another advantage of this system is that safety has been improved compared to the current state of the art. This is achieved in particular through an intelligent locking system, which, among other things, controls overflow.

[0086] Precise measurement and control of ammonia and hydrogen peroxide additions reduces chemical consumption, as the pH of the precipitation process is monitored in real time. Furthermore, the minimized chemical use results in reduced environmental impact.

[0087] The material recovery and recycling described herein, in which zinc-containing pickling solution is used to recover zinc chloride and ammonium chloride, a direct replenishment of essential flux bath components lost during normal galvanizing processes, and a significant reduction in the need for flux additives, lead to an improved environmental balance in addition to the reduced disposal volume of zinc-containing pickling solutions.

[0088] The system represents a significant advance in the technology for maintaining galvanizing flux baths, offering improvements in operational efficiency, chemical consumption, environmental impact and process economics through innovative control and process integration.

[0089] These and other embodiments of the present invention are disclosed in and encompassed by the description and examples. Further literature on known materials, processes, and applications that can be used in accordance with the present invention can be accessed from public libraries and databases, for example, using electronic devices. A more complete understanding of the invention can be obtained by referring to the following examples, which are provided for illustrative purposes and are not intended to limit the scope of the invention. Examples Example 1: Precipitation reaction within the precipitation bath

[0090] In a particularly preferred embodiment, a pH value of 4.00 is specified for the addition of hydrogen peroxide (3) (H₂O₂) and a pH value of 3.90 for the addition of ammonia (NH₃) (4). Consequently, at a pH value of 3.90, the control system ensures that ammonia (NH₃) (4) is added to the precipitation bath (2). Conversely, reaching a pH value of 4.0 causes the control system to initiate the addition of hydrogen peroxide (3) (H₂O₂) to the process solution in the precipitation bath (2). The duration of the addition of hydrogen peroxide (H₂O₂) (3) or ammonia (NH₃) (4) is 30 seconds in each case, with a dosing rate of 1 l / min and a process fluid flow rate of 500 l / min for the respective metering pumps. The reaction time of ammonia (NH₃) (4) was set to 30 seconds and the reaction time of hydrogen peroxide (H₂O₂) (3) to 100 seconds. In one experiment, the process solution in the precipitation bath (2) had a pH value of 3.82 after a mixing time of 180 seconds.The controller then triggered the addition of ammonia (NH3) (4). In one aspect, the ammonia (NH3) (4) was added in several steps to achieve a pH of ≥ 4.0. In this case, there were 8 steps of ammonia (NH3) addition (4), in which a partial amount of ammonia (NH3) (4) was added to reach a pH of ≥ 4.0. The addition of ammonia (NH3) (4) resulted in a pH of 4.01. The controller then switched and triggered the addition of hydrogen peroxide (H2O2) (3). Here, too, several additions (steps) of hydrogen peroxide (H2O2) (3) occurred until a pH of 3.90 was reached. In this case, 4 partial steps of hydrogen peroxide (H 2 O 2 ) addition (3) were required to achieve a pH of 3.90.The alternating addition of H₂O₂ and NH₃ was carried out 10 times until the pH value no longer changed upon the addition of hydrogen peroxide (H₂O₂) (3) and remained at 3.95. The constant value clearly indicated that the iron in the solution had precipitated, whereupon the device initiated the emptying process via the downstream filter press (8).

[0091] If the pH value was initially above 4 (pH > 4.00), the first step involved the addition of hydrogen peroxide (3) followed by alternating addition of ammonia (4) (process liquid pH < 3.90) taking into account the adjustable reaction times.

[0092] To achieve the desired pH values, 4.00 and 3.90, using ammonia (4) and hydrogen peroxide (3), respectively, several partial steps of adding hydrogen peroxide (H₂O₂) (3) or ammonia (NH₃) (4) may be necessary, i.e., repeated sequential additions of ammonia (4) or hydrogen peroxide (3). The complete precipitation cycle is only achieved when the iron has completely precipitated and no further pH change is observed during or after the addition of hydrogen peroxide (H₂O₂) (3). Example 2: Rinsing the filter cake (ferrous hydroxide sludge) (7b)

[0093] After completion of a filter press cycle, i.e., after the filter press (8) was full, the filter cake was rinsed with water to remove the impurities contained in the residual moisture in the form of zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl). The results showed that backwashing with water successfully washed zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl) out of the filter cake, but no iron or iron compounds were recovered. The higher the volume of water, the greater the proportion of recovered components (ZnCl₂ and NH₄Cl). Furthermore, the combination of compressed air and water rinsing resulted in the complete removal of both components from the filter cake. Example 3: Recycling of the iron hydroxide sludge (filter cake) into the iron pickling solution

[0094] In continuous operation, the hot-dip galvanizing of components generates approximately 400 kg / week of iron hydroxide sludge (7b) at ≤ 2 g / l Fe in the flux bath (1). This corresponds to 20.0 t / year of precipitated sludge with a flux bath connection. The following substances are specified as limit parameters for the disposal of used iron pickling baths (for second-grade iron pickling baths): NH₄⁺: 500 mg / l; Zn: 5 g / l. If these parameters are exceeded, penalty surcharges are levied during disposal, or the waste is reclassified (e.g., third-grade iron pickling baths). Both generally result in higher disposal costs. The disposal costs for second-grade iron pickling baths are currently approximately €85 / t. Experiments involving the addition of a rinsed and an unrinsed filter cake to the old iron pickling solution (10) showed that the re-dissolution of the filter cake in the iron pickling solution is possible, since the residual acid converts the iron hydroxide into iron chloride and thereby increases the iron concentration.However, when using unrinsed iron hydroxide sludge (7b), the specified limit parameters were exceeded, resulting in higher disposal costs. When introducing rinsed filter cake into the old iron pickling solution (10), the disposal parameters could be met.

Claims

1. Method for preparing bath compositions within hot-dip galvanizing plants, in particular a flux bath (1), wherein process fluid of the flux bath (1) is transferred in batch operation into at least one separate precipitation bath (2), in which ammonia (NH3) (4) and hydrogen peroxide (H2O2) (3) are alternately added to the process fluid until no pH change is measurable during the hydrogen peroxide addition (3) and / or the associated reaction time of hydrogen peroxide (H2O2) (3) in the precipitation bath (1).

2. The method according to claim 1, wherein a) in a process solution in the precipitation bath (2) with a pH value below 4.00 (pH < 4.00), ammonia (NH3) (4) is added in a first step, this being carried out until the pH value preferably reaches 4.00 to 5.50, particularly preferably 4.00 to 4.20, after reaching the corresponding pH value, hydrogen peroxide (H2O2) (3) is added in a second step until the pH value of the process solution in the precipitation bath (2) has been reduced to 2.00 to 3.90, preferably to 3.50 to 3.90;or b) in a process solution in the precipitation bath (2) with a pH value above 4.00 (pH ≥ 4.00), hydrogen peroxide (H2O2) (3) is added in a first step until the pH value of the process solution in the precipitation bath (2) has been reduced to 2.00 to 3.90, preferably to 3.50 to 3.90, followed in a second step by the addition of ammonia (NH3) (4), which is supplied until the pH value of the process solution has preferably reached 4.00 to 5.50, particularly preferably 4.00 to 4.20; The steps of adding ammonia (4) or hydrogen peroxide (3) are repeated until no further change in pH is measurable upon addition of H2O2 and / or in the associated reaction time of hydrogen peroxide (H2O2) (3) in the precipitation bath (1).

3. The method according to claim 2, wherein the first step and / or the second step of adding ammonia (4) or hydrogen peroxide (3) comprises several sub-steps.

4. Method according to any one of claims 1 to 3, wherein the reaction time between the addition of hydrogen peroxide (H2O2) (3) or ammonia (NH3) (4) is preferably between 10 seconds (sec) and 600 seconds, and particularly preferably between 30 seconds and 200 seconds.

5. A method according to any one of claims 1 to 4, wherein a) the precipitated sludge settled by the addition of ammonia (4) and hydrogen peroxide (3) to the process solution is further treated within the precipitation bath (2) by filtering it and preferably returning a filtrate (9) generated therefrom to the flux bath (1); b) a filter cake formed during filtration is rinsed by means of compressed air and / or water rinsing, whereby zinc chloride (ZnCl2) and ammonium chloride (NH4Cl) are washed out of it and pass into the filtrate (9); c) the filter cake is further treated with hydrochloric acid, whereby ferric chloride (FeCl2) is formed, which can be introduced into the iron pickling baths (10), wherein the filter cake is preferably treated directly in an acidic iron pickling bath (10); d) a zinc pickling solution (5) is introduced into the precipitation bath (2), preferably during the filling process;and / or e) filter dust (6) from a galvanizing process is transferred into the zinc pickling solution (5) to release zinc chloride (ZnCl2), zinc oxide (ZnO) and ammonium chloride (NH4Cl) from the filter dust (6).; 6. Device for the preparation of bath compositions within hot-dip galvanizing plants, in particular a flux bath (1), comprising: a) at least one precipitation bath (2) into which process fluid from the flux bath (1) can be fed; b) at least one container for ammonia (NH3) (4) which is connected to the precipitation bath (2) via a feed line; c) at least one container for hydrogen peroxide (H2O2) (3) which is connected to the precipitation bath (2) via a feed line; d) at least one container for zinc pickling solution (5) which is connected to the precipitation bath (2) via a feed line; and e) at least one container for filter dust (6) from a galvanizing process which is connected to the container for zinc pickling solution (5) via a feed line, so that the filter dust (6) can be fed into the container for zinc pickling solution (5).

7. Device according to claim 6, wherein the device further comprises at least one control element which controls: a) the volume of process fluid transferred from the flux bath (1) into the precipitation bath (2); b) the amount of ammonia (NH3) (4) added to the precipitation bath (2) as a function of the pH change; c) the amount of hydrogen peroxide (H2O2) (3) added to the precipitation bath (2) as a function of the pH change; d) the amount of zinc (Zn) pickling solution introduced; e) the reaction time of ammonia (NH3) (4) and hydrogen peroxide (H2O2) (3) within the precipitation bath (2); f) the duration of the addition of ammonia (NH3) (4) and hydrogen peroxide (H2O2) (3) to the precipitation bath (2); g) the number of cycles of ammonia (NH3) (4) and hydrogen peroxide (H2O2) addition (3); h) the termination of the complete precipitation process by lack of pH change during the hydrogen peroxide addition and / or the associated reaction time of hydrogen peroxide (H2O2) (3);and / or i) regulates the post-treatment of the precipitated sludge or filter cake.; 8. Device according to claim 6 or 7, wherein at least one sensor for pH measurement is arranged such that it can determine the pH value of the process liquid within the precipitation bath (2).

9. Device according to one of claims 6 to 8, further comprising a filter press (8) into which precipitation sludge from the precipitation bath (2) is transferred, wherein the filter press (8) is preferably designed such that it has at least one drainage channel through which the filtrate (9) formed within the filter press (8) can be conveyed into at least one filtrate container.

10. Device according to claim 9, wherein the filter press (8) a) has at least one pressure sensor which can measure an increasing resistance within the filter press (8); b) includes at least one valve at the inlet; and / or c) has at least one compressed air supply and / or water supply.

11. Device according to one of claims 6 to 10, wherein this comprises at least one container for iron pickling solution (10) which is connected to a container for the filter cake generated in the filter press (8) so that iron chloride (FeCl2) can be recovered from the filter cake and preferably transferred to the iron pickling solution (10).

12. Computer program product comprising a storage medium on which a computer program is stored that can perform the method according to any one of claims 1 to 5.

13. Computer program product according to claim 12, wherein the program product performs the method by the following steps: a) filling the precipitation bath (2) with a predetermined quantity of zinc-containing hydrochloric acid; b) transferring a defined quantity of flux from the flux bath (1) into the precipitation bath (2); c) continuously monitoring the pH of the liquid obtained in the precipitation bath (2); d) selectively adding ammonia (4) or hydrogen peroxide (3) to the precipitation bath (2) until a predefined pH value is reached, wherein ammonia is added until a pH value of 4.0 is reached and hydrogen peroxide pH 4.0 is subsequently added to the precipitation bath (2) until the pH value falls below 3.9, and wherein a reaction time of 10 seconds (sec) to 600 seconds is observed between chemical changes; e) Repeat step d) until there is no pH.-change is determined more during the addition of hydrogen peroxide; f) Transfer of the treated flux from the precipitation bath (2) into a filter press (8), wherein the precipitated components of the flux are retained in the filter medium and the purified flux is preferably transferred into a collection container with filtrate (9).

14. Computer program product according to claim 12 or 13, wherein the mixing of the liquid within the precipitation bath (2) is carried out by a bypass mode.

15. Computer program product according to one of claims 12 to 14, wherein the reaction times and / or the quantity of the intervals of additions are determined by an analysis of the pH reaction curve.

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