EP3904563A1 - Dissolving device, dissolving basket, galvanic system and method for dissolving zinc - Google Patents

Abstract

The invention relates to a dissolving device for dissolving metallic zinc in an electrolyte, in particular an alkaline zinc electrolyte, which comprises a dissolving section which is provided for equipping with at least one dissolving basket. During operation, the dissolving basket is filled with metallic zinc and the electrolyte initially at least partially flows through it in the vertical and then in the horizontal direction Method of dissolving zinc.

Description

Technical area

The invention relates to a release device with a release basket for receiving zinc elements and for an electrolyte to flow through them. The invention also relates to an electroplating system with such a release device and a method for releasing zinc.

State of the art

In the galvanic deposition of zinc from alkaline zinc baths, insoluble anodes are usually used in the zinc deposition baths, and the zinc is added to the bath in dissolved form as Zn (II). In order to regulate the zinc content of the zinc plating bath, electrolyte is usually removed from the bath and fed into a separate zinc dissolving device. In this zinc dissolving device, metallic zinc is anodically dissolved to form Zn (II) in the electrolyte, and the electrolyte thus enriched with Zn (II) is returned to the treatment bath.

Due to the negative redox potential, zinc dissolves exothermically in the alkaline electrolyte with the evolution of hydrogen. However, this reaction is kinetically inhibited due to the relatively high hydrogen overvoltage on the zinc surface. In addition, passivation of the zinc surface can occur, which further slows down the rate of dissolution of the zinc (rate of dissolution of the zinc).

The prior art attempts to solve this problem by bringing zinc into direct contact or electrically conductive contact with a material that has a lower overvoltage for hydrogen, such as steel, in order to increase the zinc dissolution rate. To this end, for reasons of cost, steel baskets are usually filled with pieces of zinc and immersed in the alkaline electrolyte. The zinc pieces can be designed as spheres, hemispheres or pellets, for example.

In addition to the anodic oxidation of the zinc, a cathodic reduction of protons to hydrogen takes place on the steel baskets. The reaction equations can be formulated as follows, for example:

(1) Zn (0) → Zn (II) + 2 e ^-

(2) 2 H ⁺ + 2 e ^- → H ₂

respectively.

2 H ₂ O + 2 e ^- → H ₂ + 2 OH ^-

With these zinc dissolving methods, sufficient flooding of the zinc pieces is also required in order to avoid passivation of the zinc surface (see e.g. R. Ludwig, R. Holland: Zinc Generator Tanks for the Alkaline Cyanide-Free Zinc Plater, Metal Finishing, 1998, Vol. 6, pp. 106-112 ).

In known zinc dissolving systems, the electrolyte is introduced from the treatment bath into a dissolving device with a basket-like dissolving container (dissolving basket) in such a way that the electrolyte passes through the dissolving basket in a horizontal direction flows. The zinc-enriched electrolyte is then fed back into the zinc plating bath in order to replace the zinc consumed in the electrodeposition process and to maintain the target value for the zinc content in the zinc plating bath.

An essential parameter for the constant regulation of the zinc content in the electrolyte is the variable size of the dissolution rate of the zinc to be dissolved. The amount of zinc to be dissolved is regulated by changing the anode surface, i.e. the surface of the zinc in contact with the electrolyte. This is done by changing the fill level of the electrolyte in the zinc dissolving device or on the dissolving basket by changing the zinc surface that is in contact with the electrolyte by pumping in or out or by immersing or lifting the dissolving basket. However, due to the necessary structural measures for changing the filling level or a corresponding lifting device for immersing or lifting the release basket or several release baskets, the release device is spatially relatively large and also expensive.

In addition, it is known that the dissolution rate is influenced by other factors, in particular the speed at which the electrolyte flows onto the zinc surface, the dirt in the dissolving baskets and the oxidation of the zinc surface. With the current state of the art, however, these factors are not or only insufficiently taken into account for regulating the release rate.

Subject of the invention

The invention aims to provide a release basket for receiving zinc elements and a release device with which a refined influencing and / or regulation the dissolution rate is made possible while at the same time increasing the efficiency of the dissolution system.

For this purpose, the invention provides a release basket with the features according to claims 1-5 and a release device with the features according to claims 6-13. The invention also relates to an electroplating system with such a release device and a method for releasing zinc.

The dissolving basket according to the invention has a housing which is provided for receiving pieces of zinc, preferably in the form of spheres, hemispheres, pellets or other shapes and through which the electrolyte flows during operation. At a first end section of the housing, a feed section is provided which is designed in such a way that, when the dissolving basket is in use, an electrolyte introduced into the housing by means of the feed section has or forms a flow direction component in the dissolving basket that is initially at least partially aligned in a vertical direction. In particular, the feed line section can be attached to the upper or lower end of the housing.

This configuration requires that the electrolyte introduced into the housing flows in the dissolving basket from bottom to top, or alternatively from top to bottom. The flow direction component can be partially inclined in relation to a vertical direction, or the flow can initially take place vertically and then be deflected laterally or radially. This can be done in particular by means of a tube which is attached vertically in the release cage and provided with radial openings. The electrolyte flows vertically into the pipe from the feed section and exits the radial openings, so that the vertical flow changes into a horizontal flow from the inside to the outside.

With the aid of a release basket according to the invention and the release device according to the invention, a targeted, uniform flow around the zinc pieces is made possible. On the one hand, this leads to a more uniform dissolving rate over the entire filling height of the dissolving basket with a constant flow rate, since the occurrence of poorly exposed sections, as can occur in the course of operation in the prior art, is avoided.

In addition, by setting the flow rate, a targeted control of the release rate is made possible. For this purpose, for example, with the aid of a controllable pump that conveys the electrolyte from the zinc deposition bath to the dissolving device and thus to the dissolving basket, the flow rate of the electrolyte through the dissolving basket can be regulated directly. Furthermore, a plurality of dissolving baskets can be used, and the electrolyte flow is switched on or off or regulated individually for each basket in order to obtain a desired total flow rate.

It has been shown that with the procedure according to the invention, a laminar flow can be formed in the dissolving basket, and the flow taking place over the entire zinc anode surface significantly improves the amount of zinc dissolving per unit amount of electrolyte. Therefore, the size (installation space) of the release basket and the release device can be kept relatively small compared to the prior art. Likewise, in order to achieve a certain dissolution rate, significantly less zinc can be kept in the dissolving basket or in the entire dissolving device.

Another advantage has been shown that a cleaning effect can be significantly improved during the process. A targeted and intensive flow removes dirt and degradation products that have accumulated in the dissolving basket.

With regard to the cleaning effect, the release basket preferably has a substantially basket-shaped or cage-shaped shape, so that dirt particles can settle through the openings in the bottom of the basket or cage outside the basket in areas provided for this purpose.

Furthermore, the loosening device preferably has a calming area downstream of the actual loosening area, in which dirt particles whirled up or suspended by the flow during the zinc loosening can settle.

Brief description of the drawings

Fig. 1

shows a cross-sectional view of a first embodiment of a release device according to the invention showing the individual chambers.

Fig. 2

FIG. 11 shows another cross-sectional view of the FIG Fig. 1 shown release device with representation of the individual connections, the partition walls and the flow principle in schematic form.

Fig. 3

shows a perspective and a side view of a release basket according to the invention, which is used in the release device according to FIG Fig. 1 +2 is used.

Detailed description Release device

The structure of the release device (100) is described below with reference to the FIGS Figures 1 and 2 embodiment shown in more detail.

The release device (100) is designed to operate in conjunction with a galvanic zinc plating bath (not shown). It is preferably a bath that uses an alkaline zinc electrolyte. The electrolyte is typically removed from the zinc deposition bath (not shown) and is to be enriched with zinc in the dissolving device and then returned to the zinc deposition bath. This can be done, for example, continuously while the deposition bath is in operation, in order to keep the zinc concentration in the zinc deposition bath within a specified working range.

The release device (100) comprises at least one release section (110) which is provided for receiving one or more of the release baskets (10) described below and in which the actual release process takes place.

Preferably, the release device further comprises, as in FIG Figure 1 shown, a sludge chamber (120) arranged in the vertical direction below the release section (110), a calming section (130) arranged adjacent to the release section (110) and an exchange section (140) arranged adjacent to the calming section (130).

During operation, the electrolyte is introduced into the dissolving section (110) and enriched with Zn (II) by anodic dissolution of the zinc pieces contained in the dissolving baskets (10). In the process, dirt particles and degradation products present in the zinc pieces can be exposed, which settle in the sludge chamber (120). The electrolyte enriched with Zn (II) then reaches the calming section (130), in which any suspended dirt particles can settle as a result of the flow. The electrolyte then enters the exchange section (140) and is returned from there to the zinc plating bath.

Release section

The release section (110) preferably comprises one or more chambers (110a) - (110x), each of which is arranged adjacent to one another or in several rows. The chambers (110a) - (110x) are each separated from one another by a partition. Each of the chambers is provided for receiving an individual dissolving basket, and the dissolving baskets can be removed from the respective chamber.

The number of chambers is not particularly limited and can be selected appropriately depending on the bath volume and throughput or on the amount of zinc to be dissolved. It can be, for example, between 1 and 100, preferably 3 to 50, in particular 5 to 20. The chambers can be arranged in a row or in several rows.

Since the release baskets are thus arranged in separate chambers, the amount of hydrogen produced is kept low in the event of an emergency standstill due to the comparatively small amount of electrolyte in each chamber, and thus the risk of hydrogen deflagration is minimized. The chambers can also be emptied independently of one another in an emergency standstill of the release device (100) or also outside of the operation of the release device (100). This prevents or minimizes the further development of hydrogen, but also the oxidation processes between the electrolyte and the anodes.

An emergency drain (117) is also preferably provided, which can be opened, for example, in the event of a power failure, in order to remove the electrolyte from the chambers (110a) - (110x). For this purpose, a currentless openable valve is used on the emergency drain (117), which opens with a previously defined time delay if necessary.

The chambers (110a) - (110x) have feed lines (111a) - (111x) for the electrolyte to be enriched with zinc, each of which ends at a feed line opening (112a) - (112x). The feed line opening is opened upwards in the vertical direction in order to conduct the electrolyte through the dissolving baskets described below.

The feed lines are each provided with a shut-off valve so that the electrolyte supply in the chambers can be individually regulated or switched on and off. In this way, for example, the rate of zinc dissolution can be regulated, for example by only having the electrolyte flow through some of the chambers.

Furthermore, the electrolyte flow rate in the supply lines can preferably be regulated. This can be done, for example, with the aid of the pump (s) provided for the electrolyte supply (not shown) and / or via the shut-off valves (not shown).

Dissolving basket

The release basket (10) is intended to receive the zinc pieces to be released and, during operation, the electrolyte flows through it, which exits vertically upwards from the feed opening (112a).

The dissolving basket is preferably made at least partially from a metal which, under the dissolving conditions, has a lower hydrogen overvoltage than zinc and is in contact with the zinc pieces. This allows a local element to form, with the zinc pieces acting as the anode and the metal as the cathode:

(1) Zn (0) → Zn (II) + 2 e ^-

(2) 2 H ₂ O + 2 e ^- → H ₂ + 2 OH ^-

The metal is preferably iron or an iron alloy such as, in particular, steel. In a particularly preferred embodiment, the surface of the metal is provided with a thermally sprayed iron layer to further improve the dissolution rate, as in FIG EP 3,222,757 described.

The dissolving basket can be made entirely of the metal. Alternatively, only parts of the basket (e.g. the side wall) can consist of the metal, or the basket can also be made of a different material and is provided with an insert made of the metal.

Furthermore, the release basket is preferably like a basket or cage and is open at the top so that zinc pieces can be easily refilled. The shape of the cross section is not particularly limited and may, for example, be substantially round, rectangular, or square. The bottom is provided with openings so that impurities and sludge can escape downwards, in particular into the sludge chamber (120) described below.

In a preferred embodiment, the release basket (10) comprises a housing (11) with a base plate (11a) (first end section), a circumferential side wall (11b) and an upper section (11c) (second end section). When the release basket (10) is in use, the bottom plate (11a) faces downward and the side wall (11b) extends in a vertical direction.

The side wall (11b) of the dissolving basket (10) is provided with a large number of passages (11b-1) so that the electrolyte can flow in or out of the housing (11) of the dissolving basket (10) from the side.

The bottom plate (11a) of the dissolving basket (10) has a feed section (12) which forms a through opening which is essentially centrally arranged in the plan view of the dissolving basket (10) and is opposite the feed opening (112a). The electrolyte fed in via the feed opening (112a) is introduced into the dissolving basket (10) through this passage opening.

Furthermore, a large number of outlet openings (11a-1) are provided on the base plate (11a), through which a sludge formed when dissolving zinc in the electrolyte is disposed under the dissolving section (110) and thus also under the dissolving basket (10) Mud chamber (120) can reach. The sludge that has accumulated can thus be easily removed from a dirty area of the release device. A filtration can therefore be omitted, even if it is conceivable that such a filtration is provided in addition.

In the case of a purely vertical flow, depending on the flow rate and shape / size of the zinc pieces, the zinc pieces located further down may act as a flow obstacle, so that the flow of the zinc pieces is reduced from bottom to top. This can lead to a stronger passivation of zinc pieces lying on top, which are less exposed to the flow, and thus to a reduction in the rate of dissolution.

To avoid this effect, in a particularly preferred embodiment, a tube (15) is integrated in the release cage on the feed section (12), which tube extends in the housing (11) preferably centrally along the vertical alignment of the side wall (11b) of the housing (11). The tube (15) has a multiplicity of radial openings (15a) through which the electrolyte guided through the tube (15) can flow out radially. In this way, a uniform flow of the zinc pieces over the entire vertical axis of the dissolving basket ensured from the inside to the outside.

The electrolyte flow also has a cleaning effect in that it washes away impurities or passivating oxides that form during the dissolution process from the zinc surface. Most of the particles released in this way settle downwards and thus get into the sludge chamber described in the following section. Depending on the flow rate, a certain proportion of particles can also remain suspended and are retained in the calming compartment described below.

The outlet openings (11a-1) in the bottom of the dissolving basket prevent the settling particles from remaining in the dissolving basket as sludge. This significantly reduces the maintenance effort.

Mud chamber

A sludge chamber (120) is preferably attached in the vertical direction below the release section (110), and thus also below the release basket (10). The sludge chamber (120) extends along the entire dissolving section (110) and can thus be used by several dissolving baskets if several dissolving baskets are required due to the required amount of zinc.

The sludge produced during the dissolving process can enter the sludge chamber (120) through the outlet openings (11b-1) of the base plate (11a) of the dissolving basket. To remove the sludge that has accumulated in the sludge chamber (120), a cleaning opening (125) is provided for cleaning the sludge chamber.

Calming section

Adjacent to the release section (110) there is preferably a calming section (130) which is designed such that the multiple chambers (110a) - (110x) of the release section (110) share the calming section (130).

Due to the flow and the evolution of hydrogen in the dissolving section, the electrolyte typically contains dispersed gas (hydrogen and / or air bubbles) and possibly also impurity particles. By lingering in the calming section (130), these are removed by means of outgassing or sedimentation, or they are deposited on the bottom of the calming section (130).

In particular, the electrolyte enriched with dissolved zinc flows over a first partition (115) formed between the release section (110) and the calming section (130) and thus flows into the calming section (130). The calming section (130) is delimited by the partition (115) provided between the calming section (130) and the release section (110) and a barrier (135) which extends parallel to the first partition (115).

An overflow weir (116) is preferably provided on the first partition (115) on the side facing the calming section (130). The overflow weir acts as a flow sheet for the electrolyte to facilitate outgassing and to reduce any foam formation.

The overflow weir (116) forms an angle to the vertically oriented first partition wall (115), for example in the range of approx. 30-60 °. As a result of this arrangement, the electrolyte entering the calming section (130) becomes the calming section when it passes from the release section (110) (130) calms down, and an increased uptake of gas on entry into the calming section (130) is prevented.

Exchange section

An exchange section (140) is preferably provided adjacent to the calming section (130). In the embodiment shown, these sections are separated from one another by a second partition (135), the upper edge of which acts as an overflow weir.

In addition, a shielding wall (141) can be attached parallel to the second partition (135), so that a passage (142) is created between the second partition (135) and the shielding wall (141). In the vertical direction, the shielding wall (141) extends higher than the barrier (135), so that the electrolyte that passes from the calming section (130) into the exchange section (140) in a lower section of the exchange section (140) passes through an area between the barrier (135) and the opening provided in the shielding wall (141) passes through.

In the exchange section (140) there is also an outlet channel connection (143) with which the zinc-enriched electrolyte can be removed from the dissolving device by means of a pump (not shown) and returned to the zinc deposition bath via an optionally interposed filter device.

Furthermore, the exchange section (140) can be provided with an inlet (144) for the direct supply of electrolyte from the zinc deposition bath. In this way, for example, in the event that the dissolving section is switched off, for example due to an emergency, the electrolyte circulation between the dissolving device and the zinc deposition bath can be maintained. The zinc concentration can also be used if necessary can be reduced in the exchange compartment in order to set a certain setpoint.

In this embodiment, a changeover valve (not shown) is preferably also provided, with which the electrolyte removed from the zinc deposition bath can optionally be fed to the inlets of the release section (111a) - (111x) or via the inlet (144) directly into the exchange compartment.

Suction device

For the suction of hydrogen or other gases, the release device also preferably has a suction device with one or more suction channels (150), which is preferably attached above the calming section (130) and can thus suck out several adjacent areas of the release device.

In order to increase the suction effect, the release device is preferably provided with a cover which, for example, can be composed of a plurality of cover elements. For example, the release section in the filling area above the release baskets can be provided with one or more hinged lids (160), and the replacement compartment can be covered with a plurality of removable lids (170). The suction then takes place from the gas space formed by the cover above the release device.

Zinc dissolving process

The zinc dissolving process according to the invention is carried out with the dissolving device according to the invention in connection with a galvanic zinc deposition bath. Preferably an alkaline zinc or zinc alloy bath (e.g. Zn / Ni) is used.

When the release device (100) is in operation, the release baskets (10) are filled with metallic zinc, preferably in the form of pellets, spheres or hemispheres. The electrolyte to be enriched with zinc is removed from the zinc deposition bath and introduced into a respective chamber (110a) - (110x) via the supply lines (111a) - (111x) with the aid of one or more pumps (not shown). The electrolyte flow rate is regulated with the aid of the pump (s) and, if necessary, the valves attached to the supply lines. It is also possible to use only some of the release chambers and to switch off the rest or not to equip them with release baskets (10).

The electrolyte flows into the tube (15) of the dissolving basket (10) arranged in the respective chamber and exits in the radial direction through the radial openings (15a) of the tube (15). In this way, the zinc pieces are exposed to a uniform lateral flow along the entire length of the dissolving basket. This prevents passivation of the zinc surface and improves the uniformity of the dissolution rate of the entire amount of zinc in the dissolving basket.

As stated above, the zinc pieces preferably form a local element with the metal of the container, so that the zinc goes into solution as Zn (II), while the hydrogen evolution mainly takes place on the metal. The electrolyte thus enriched with zinc, which typically contains hydrogen bubbles and possibly also air and / or dispersed dirt particles, then flows over the first partition (115) and, after flowing over the overflow weir (116), reaches the calming section (130) of the release device (100). By lingering in the calming section, gases and particles can separate out.

The electrolyte then flows over the second partition (135) and is introduced into the exchange section (140) through the passage (142) provided between the second partition (135) and the shielding wall (141) and is pumped out from there by means of a pump. The zinc-enriched electrolyte pumped out of the exchange section (140) is returned to the zinc plating bath.

With the help of the switching valve (not shown), the electrolyte removed from the zinc deposition bath can also be fed directly into the exchange section (144) via the inlet (144), bypassing the dissolving and calming section. This may be necessary, for example, in order to maintain the electrolyte circulation in the event of an interruption of the zinc dissolution process, or in order to reduce the zinc concentration in the exchange section (140) to a desired target value.

Claims (15)

A dissolving basket (10) for dissolving metallic zinc in an alkaline electrolyte, comprising: a housing (11) for receiving pieces of zinc, preferably in the form of spheres, hemispheres or pellets, a feed section (12) provided at a first end section (11a) of the housing (11) which is designed in such a way that, when the dissolution basket is in use, an electrolyte introduced into the housing (11) by means of the feed section (12) in the dissolution basket (10) initially has or forms at least partially aligned flow direction component in a vertical direction. Dissolving basket (10) according to claim 1, which consists at least partially of iron or steel, the surface preferably having a thermally sprayed iron layer. Dissolving basket (10) according to claim 1 or 2, further comprising a tube (15) which is fluidly connected to the feed section (12) and which runs at least in sections in the housing (11), it being preferred that the tube (15) has a plurality of radial openings (15a), so that the electrolyte can flow out of the tube in a horizontal direction from the inside to the outside. Dissolving basket (10) according to one of the preceding claims, wherein the first end section (11a) forms an underside of the housing (11) when the dissolving basket is in use. Dissolving basket (10) according to claim 4, wherein the first end section (11a) has a plurality of outlet openings (11a-1), it being preferred that the outlet openings (11a-1) are designed in such a way that, during a process of dissolving zinc in an electrolyte resulting sludge can escape through the outlet openings (11a-1). Dissolving device (100), in particular for dissolving zinc in an electrolyte, comprising: a release section (110) which is provided for equipping with at least one release basket (10) according to one of the preceding claims, wherein the release section (110) has a supply opening (112a) which is designed such that an electrolyte introduced into the release section (110) by means of the supply opening (112a) has a flow direction component in the release basket (10) which is initially at least partially aligned in a vertical direction or train. The release device (100) according to claim 6, further comprising a mud chamber (120) which is arranged below the release section (110). Release device (100) according to claim 6 or 7, further comprising a calming section (130), wherein the release section (110) and the calming section (130) are separated by a first partition (115), it being preferred that the first partition (115) ) like that is designed so that the electrolyte located in the release section (110) can flow over the first partition (115), an overflow weir (116) being provided on the first partition (115) on the side facing the calming section (130), it being preferred that the overflow weir (116) forms an angle in the range of 30-60 ° to the vertically oriented first partition wall (115). Release device (100) according to one of claims 6-8, further comprising an exchange section (140) with an outlet line, the exchange section (140) being separated from the calming section (130) by a second partition wall (135), it being preferred that the second partition (135) is designed such that the electrolyte located in the calming section (130) can flow over the second partition (135). Release device (100) according to one of claims 6-9, wherein the release section (110) has one or more chambers (110a-110x) for receiving a release basket (10), which are preferably each arranged adjacent to one another. Release device (100) according to claim 10, wherein each of the plurality of chambers (110a) - (110x) has a supply line (111a) - (111x) for supplying the electrolyte, it being preferred that the supply lines can be opened or closed individually. Release device (100) according to one of claims 6-11, further comprising an emergency drain (117) which is arranged such that an electrolyte located in the release section (110) can be drained from the release device (100), it being preferred that the Emergency drain (117) has a valve that can be opened without current, preferably with delayed actuation. Dissolving device (100) according to one of Claims 6-12, further comprising a suction device with one or more suction channels (150) in order to suction off the hydrogen or other gases formed during zinc dissolution. Electroplating plant for galvanic zinc deposition, which comprises at least one zinc deposition bath and a dissolving device (100) according to one of Claims 6-13. A method for dissolving zinc in an electrolyte, comprising the steps of: - Provision of a release device (100) which is equipped with at least one release basket (10) which is filled with zinc pieces, preferably in the form of spheres, hemispheres or pellets; - Introducing the electrolyte into the dissolving basket (10) and bringing it into contact with the zinc pieces in such a way that the electrolyte has or forms a flow direction component initially at least partially oriented in a vertical direction, which subsequently preferably merges in a horizontal direction from the inside to the outside.

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