ES2290783T3 - INSTALLATION FOR DEPOSITS OF ZINC. - Google Patents

Abstract

Apparatus for the deposition of zinc or zinc alloys comprises: (a) a tank (14) subdivided by a separator, made of a open porous material, into cathodic and anodic compartments; (b) the component (18) is immersed in a aqueous electrolyte (16), with an alkaline pH, contained in the cathodic compartment and containing some zinc ions, and possibly some ions of a metal other than zinc,; (c) an aqueous electrolyte, with an alkaline pH, contained in the anodic compartment and surrounding an anode of an insoluble metal.

Description

Installation for zinc deposit.

The present invention relates to electrolytic installations of zinc deposits or alloys of Zinc greater than 70% zinc on one piece.

Patent application of WO 01/96631 of the inventors William Eckles and Robert Frischauf of Taskem INC. give to know a procedure for the electrolytic alkaline deposit of zinc-nickel using a perfluorinated membrane for cation exchange. An exchange membrane of cations do not allow the passage of ions more than in a single sense, from the anolyte to the catholyte under the effect of the field electric. Only the cations accompanied by their water Solvation can migrate towards the catholyte. On the contrary, the Anions present in the catholyte cannot migrate to the anolyte. These membranes are fragile and particularly expensive. its use in industrial facilities imposes many precautions so that the tanks or electrolysis devices do not damage the wall of said membranes.

The technique developed in WO Patent 01/96631 also generates the accumulation in the catholyte of the undesirable anions such as sulfates, carbonates and ions hydroxyl Sulfates come from the bathroom feed in nickel by nickel sulfate and carbonates are caused by soda absorption of ambient carbon dioxide. Ions hydroxide come from the water reduction reaction caused mainly due to the lack of faradic performance in the cathode of the zinc or alloy zinc deposit. This argumentation of the concentration in hydroxyl ions causes premature degradation of the organic additives present in the deposit baths that leads to a decrease in cathodic bath performance and a degradation of the appearance of the treated parts.

In this way, a decrease in the productivity over time. That is why to get the same coating thickness in a nickel zinc bath, it need a deposit duration of two hours thirty minutes after one year of operation while installation makes this deposit at the beginning of its commissioning in a Hour and thirty minutes.

To recover the initial productivity, it is necessary to decarbonate, desulphate and cut the bathroom to reduce the concentration of hydroxyl ions that is greater than 160 g / L After 4 months of operation. Cutting operation it consists in the elimination of a fraction of the bathroom (approximately 10 to 20%) and renewal for the new electrolyte (containing the optimal concentration of hydroxyl ions). These stages are expensive in investment and energy.

The present invention reduces these inconvenience Maintains productivity throughout the weather. Thanks to the transfer of the anions to the anolyte allows to reduce the frequency of the operations of decarbonation and desulphation. In addition it is no longer necessary cut the bathrooms because of excess salinity.

The object of the invention is therefore a installation for the deposit of zinc or higher zinc alloys  70% mass zinc with at least one other metal chosen from iron, cobalt, nickel and manganese on one piece comprising:

a) a tank subdivided by a non-separator electricity conductor in a cathodic compartment and a anodic compartment.

b) the piece is submerged in an aqueous catholyte of alkaline pH contained in the cathodic compartment and comprising zincato ions and eventually at least ions of another metal other than zinc, and

c) an alkaline pH aqueous anolyte contained in the anodic compartment and surrounding an insoluble metal anode within the anolyte, characterized in that

d) the separator is made of a material With open pores. It is understood by open pores or porosity open to all pores that communicate with the surface of the material.

An open pores material such as polytetrafluoroethylene or a polyolefin preferably of polypropylene but also polyethylene or a porous ceramic, are water permeable materials, much less expensive than ion exchange membranes much more resistant due to understand that preferably resistant materials will be chosen at alkaline pH. While the separator is a pore material open, has not been unexpectedly proven a step of the another metal more precious than zinc and especially nickel at anolyte, but especially anions sulfates, carbonates and hydroxyls, sulfate from nickel sulfate added to catholyte, the carbonate from carbonation of soda by air and hydroxyl ions from the reaction of reduction of water to the cathode caused mainly by the lack of faradic performance at the cathode of the zinc or zinc deposit Alloyed that until this moment they accumulated in the catholyte, they pass to the anolyte. Thanks to the absence of product accumulation of emigration from the anolyte to the catholyte, productivity is maintains over time.

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Thanks to the absence of accumulation of emigration products from the anolyte to the catholyte, the Productivity is maintained over time.

Preferably, the anodic compartment communicates with a desulfatador that can be a cold hold which causes the crystallization of sulfates or in which you can add a sulfate precipitation agent such as a salt Barium It is enough then to return the treated anolyte in this way to the anodic compartment. It can be considered that the anodic compartment becomes the most prominent part of the installation.

Figure 1 shows the transfers of different species comparatively across a membrane of cation exchange and porous separator as described In the invention.

A separator according to the invention exceeds following tests:

1. The average pore diameter should be located between 10 nm and 50 µm and preferably between 10 nm and 5 \ mum.

The average pore diameter is determined by mercury porosimetry with the aid of a type apparatus Micromeritics 9310, according to the principle defined in point 3.

2. Immersed in a vat containing a 120 g / L NaOH aqueous solution the separator to be checked for way that delimits in the tank two compartments are poured into one of them 20 mL / L of a solution colored in violet 8% by weight of nickel comprising weight:

36.2% nickel sulfate hexahydrate,

15% tetraethylenepentamine,

rest up to 100% water.

If one day later the solution in the compartment that has not received the violet colored solution no It has violet coloring the separator is satisfactory.

3. The porosity of the material will be chosen from way that allows a good electrical conductance of the set. For this purpose, the assembly described in Figure 2 will be used. first time it is considered an assembly not equipped with separator that comprises a referenced pure nickel anode (1) and a cathode of referenced steel (2). The whole submerged in a bathroom electrolytic (3) whose composition is defined in the following paragraph 2. A current density of 2 A / dm 2 is applied between the anode and the cathode, the voltage at the terminals of the rectifier: this voltage will be assumed x (in volts). In a second stage the anode will be isolated in an anodic compartment (5) filled with a solution of NaOH at 140 g / L equipped with a separator porous (4) as described in the invention. One is applied current density of 2 A / dm 2 between the anode and the cathode, The voltage measured at the terminals must be less than x + 5 volts. He Proven separator is satisfactory.

With regard to point 3 another test practice can be done in a way that chooses porosity of the material used especially if it is a ceramics.

This test consists in measuring the diameter of the pores and also the open porosity of ceramics by introduction  of mercury under increasing pressure from 0.0048 to 205.885 Mpa in the sample and record the volume of mercury that has penetrated the pores The diameter of the pores explored is between 300 µm and 0.006 µm. The pressure applied is related to the diameter of the pores by the Washburn equation (a continuation)

D = 4 \ gamma \ cos \ \ theta \ / p

Where d: equivalent pore diameter in millimeters γ surface tension of mercury (in N.m-1),:: contact angle in degrees and p: pressure applied in Pa.

The measured porous volume is brought to the volume apparent of the sample and the percentage provides the value of the open porosity

The open porosity of the material should be between 10 and 60% and preferably between 20 and 50% and more preferably between 30 and 40%.

According to an embodiment of the installation according to the invention the anodic compartment communicates with a alkali metal persulfate container. Adding the anolyte of sodium or potassium persulfate, cyanides that can destroy could eventually form when the catholyte comprises a complexing agent of a metal especially under the form of a polyalkylamine.

Preferably the pH of the anolyte is alkaline and greater than 12, although in certain cases it may be included especially between 8 and 12.

The invention relates to an installation for the electrolytic treatment of zinc and alloyed zinc on a Steel or iron alloy piece. The system can be applied with alkaline electrolytes that have a pH greater than 12. The deposit bath may contain zinc ions and organic additives. The steel or iron alloy piece is placed as a cathode. An "anodic assembly" is in contact with the bathroom. He "anodic assembly" may include an anolyte, a composite anode by an insoluble metal in the anolyte and a container whose wall of contact with the catholyte is constituted by a porous vessel or by a porous membrane Organic additives may be able to destroyed by electrolytic oxidation in contact with the anode. He "anodic assembly" can prevent electrolytic decomposition of organic additives. The "anodic assembly" must contain a conductive liquid that is the one designated as anolyte. He "anodic assembly" is composed on the outside by a glass porous or porous membrane. The anolyte is then contained in the volume displaced by the porous vessel or the porous membrane. He insoluble metal used in the anode can be submerged in the anolyte On the other hand the electrolytic bath can comprise different metal ions that can be deposited via electrolytic on a piece of steel with zinc ions. By For example, additional metal ions may include ions nickel, manganese, iron, cobalt and any other combination of these metals. On the other hand, organic additives can be potentially oxidized in contact with the anode. The descomposition of organic additives form by-products that are factors of decreased cathodic performance. The anode can be consisting of any metal or metalloid that can serve as anode in a caustic solution. The anolyte can be soda or solution Potash

The tank can be made in any organic plastic resistant to electrolytic baths and anolyte, for example polypropylene, and non-conductive of the electricity.

The porous vessel or the porous membrane of the "anodic mounting" can be any porous membrane of mineral or organic composition on condition that it resists chemically the alkalinity of the two anodic compartments and cathodic and this for temperatures that can reach 60 ° C. its Texture must be permeable to water. The methods of obtaining the Porous walls are multiple. They can be cited as examples not exhaustive: woven, sintered or expanded membranes. He pore diameter is between 10 nm and 50 µm and preferably between 10 nm and 5 µm.

The thickness of the porous membrane or separator It depends on the "anodic assembly" used. The thickness can be fine between 0.1 and 2 mm thanks to the mechanical reinforcement of the supports. In the case of the attached figure 3, the thickness will be very 0.1 mm variable up to 1 cm since the porous membrane cannot Have no support.

- Porous mineral membranes: They are ceramic that contain oxides of elements such as silicon, aluminum, titanium, zirconium or other components contained in clays natural

They can be prepared as follows. Be use, for example, as a constitution material a suspension  alumina combined with specific additives such as plasticizers or deflocculants.

The paste obtained in this way will be shaped by molding or extrusion and drying under temperature conditions and relative humidity controlled.

The ceramic formed in this way suffers a high temperature treatment from 1300 to 1500 ° C depending on conditions of controlled increase and decrease of temperature.

They can be parallelepipedic or tubular. It is also possible to use materials concave or small crucible, as shown in figure 3, or elements blueprints.

- Organic porous membranes: There are numerous plastics that resist in alkaline medium. They can be chosen, by example, polytetrafluoroethylene (PTFE or Dupont Teflon), polyethylenes or polypropylenes among the most common.

You can cite the example of using a porous Teflon membrane with a thickness of 0.43 mm, a weight of 510 g / m 2 and an air permeability of L / dm 2 / min at 196 Pa or from 30 m 3 / h / m 2 to 196 Pa of the Mortelecque Society with the reference TC 110. This porous membrane is cut and mounted on The walls with a board. This same material can be welded. also around a cylindrical support.

The anolyte of the anodic compartment can comprising a conductive salt or a solution base such as a aqueous alkaline solution of potash or soda. These solutions alkalines may have varying concentrations within a range of values from one mole to 20 moles / L of hydroxide, with a preferred concentration of 10 moles / L of hydroxide. The anolyte preferred may be a solution of sodium hydroxide between 50 and 760  g / L, and better between 50 and 250 g / L.

The anode of the "anodic mount" can be consisting of a metal or metalloid capable of functioning as anode in an electrolytic bath and must be stable in a solution caustic "Stable in a caustic solution" means that the anode must not decompose, deteriorate or erode in said solution. Metals can be used among the examples of nickel, Cobalt, iron, chromium and their alloys. For example steel and ferrous alloys Other metals or metalloids can also be used on the condition that they are able to function as anode and that are stable in a caustic solution.

The anode can be a metal or a metalloid solid or a metal deposited by electrolysis on a substrate. For example, the anode can be nickel, a nickel alloy or of nickel deposited on a substrate. The substrate can be a metal such as steel, copper or aluminum or plastic. An example of Nickel alloy is hastelloy, which is composed of 55% of nickel and 45% chromium. Nickel and nickel alloys can be electrolytically deposited on a substrate using a Watts type electroplating bath for nickel or alloys, or They can be deposited from chemical nickel.

Similarly, the anode can be cobalt or cobalt deposited by electrolysis on a substrate how are you alloys The anode can also be mild steel, alloy steel, iron alloy or an iron-chromium alloy such as stainless steel. The anode building material It is not restrictive. You can use, for example, deposits electrolytic or electrochemical on the anode. They can be used noble metals deposited electrolytically on a substrate metallic, for example platinum or iridized titanium. Considerations practices such as the cost of stability in caustic solution determine the choice of material to use for the anode.

The electroplating bath can be a solution aqueous alkaline whose content in hydroxide salt or metal salt Alkaline is between 50 and 250 g / L. Among the examples of hydroxides or alkali metal salts may be mentioned the sodium hydroxide, potassium hydroxide, sodium carbonate and carbonate potassium The bath is prepared by dissolving it in the aqueous solution of the alkaline compound.

The electroplating bath can comprise also a controlled amount of zinc ions. The source of the Zinc ions for electroplating bath can be any salt of soluble zinc in an alkaline medium. You can cite, for example, zinc compounds capable of being added to the bath of electroplating: zinc oxide or soluble zinc salt such as zinc sulfate, zinc carbonate, zinc sulfamate and acetate zinc. The concentration of zinc ions in the electroplating bath it can be from 1 to 100 g / L (1000 ppm to 100,000 ppm) preferably between 4 and 50 g / L (4,000 to 50,000 ppm). A ph 14 zinc species dominant in the bathroom is the zincato ion. The bathroom can contain also a controlled amount of metal ions that are not ions of zinc According to the invention these additional metals they can be of any metal ion that can be, effectively, deposited by electrolysis with zinc on a piece in the form of cathode in an alkaline electroplating bath. Among the examples of these metal ions can be cited the metal ions of transition such as nickel, manganese, iron, cobalt and ions combinations of these ions. Other metal ions not indicated which can be deposited with zinc ions on the cathode in An alkaline plating bath can also be used and they fall within the spirit of the invention.

Additional metal ions can be also only nickel ions, the source for nickel ions in the plating bath can be any nickel compound capable of being solubilized in aqueous alkaline solution forming complex. Examples of nickel compounds are salts organic and inorganic nickel, such as nickel sulfate, nickel carbonate, nickel acetate, nickel sulfamate and nickel formate. The concentration of nickel ions (or other metal) in the plating bath can be 0.1 to 50 g / L, preferably within a range of values between 0.1 and 3 grams / L.

Metal ions may also include any metal ion The electroplating bath can comprise, for example, a mixture of zinc ion and iron ion, a mixture of zinc ion, nickel ion and iron ion. The sources for these ions Additional metallic, for electroplating bath, can be any metal compound that can be soluble in a solution aqueous alkaline The concentration of metal ions in the bath Electroplating can be approximately 0.1 to 10 g / L (approximately 100 to 10,000 ppm), preferably within a range of values from 0.1 to 3 g / L (100 to 3,000 ppm).

The electroplating bath may contain also, in addition to zinc and additional metal ions, such as minimum additive commonly used in the bathrooms electroplating, zinc and zinc alloy, which improve the appearance of the deposit. These organic additives can be used to improve the physical characteristics of the electrolytic deposit and the complex characteristics of the bathroom.

The additive can be of any type of organic product capable of exerting an effect on the deposit electrolytic zinc or its alloys. The additive is potentially capable of electrolytically decomposing into anode and of producing a degradation product that will affect the process of electrolytic treatment. These degradation products can seriously affect the electrolytic procedure for example inhibiting the speed of deposit, producing a deposit "veiled or matt", increasing the toxicity of the electrolytic bath  or causing the precipitation of insoluble species.

Therefore, organic additives agree with the invention and potentially capable of being broken down into the anode will not be decomposed using the "Assembly Anodic ". The" Anodic Assembly "of the invention prevents electrolytic decomposition avoiding or minimizing the contact of Organic additives in the anode. One of the organic additives potentially capable of being broken down at the anode can Understand an amine Amines are potentially oxidizable in cyanide in the vicinity of the anode. Among the examples of amines cyanide oxidizable aliphatic amines can be included from the polymerization of alkyleneimines, such as polyethyleneimines with molecular weights between 100 and 100,000 g / mol and soluble in the bathroom. For example, you can use the polyethyleneimines whose molecular weight is between 150 and 2,000 g / mol. These polyethyleneimines are known commercially with the name Lugalvan G15, G20, G35 of the BASF firm.

Other aliphatic amines can also be used such as monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and hepaethylene octamine. A function of these aliphatic polyalkylamines is to form complexes of the metal ions in the alkaline zinc bath. Your concentration can vary from 2 to 70 g / L.

Other type of organic additives capable of being electrolytically decomposed in the anode is the product of the imidazole reaction and an electrophilic monomer such as epichloridrine

Among the other types of organic additives liable to be electrolytically decomposed at the anode it find quaternary ammonium polymers, such as polymers from the synthesis of dichlorethyl ether on the urea condensates on dimethylaminopropylamine, marketed under the name Mirapol WT by Rhodia. These molecules, in contact with the anode, can degrade, decrease the deposit speed and cause veiled deposits.

Another type of additive capable of being decomposed electrolytically at the anode is a complex former such as gluconate or tartrate. These organic additives can be oxidized at the anode and can produce oxalate. It is evident that the technician in the field can use other organic additives in the electrolytic bath such as brighteners and formers metal complexes that can decompose or not electrolytically at the anode. A known complex former is for example the Quadrol (THEED) of BASF. The Quadrol (THEED) is the N, N, N ', N', - tetrakis (2-hydroxypropyl) -ethylenediamine.

The invention is essentially characterized by continuous purification of the electrolytic bath. The concentration of anions, such as sulfates, carbonates and hydroxyls, grows in zinc or zinc alloy baths by carbonation of the alkaline medium, but also for the maintenance in salts of the metals that must undergo electrolysis and by the fact the water reduction reaction in the cathode caused mainly due to the lack of faradic performance in the cathode of the zinc or alloy zinc deposit. It is usual to consider as inconvenience and penalizers of performance and appearance, the Total salt concentrations expressed beyond 190 g / L of its sodium salts (for example Na2CO3 and Na_ {SO} {4}). Also a concentration higher than 150 g / L of soda leads to the degradation of organic products and penalizing defects for performance and appearance.

Thanks to the present invention, the anions are attracted by the anode and concentrated in the anodic compartment. Its extraction can be done continuously or by fractionation of the bathroon. The precipitation in cold between 3ºC and 6ºC or precipitation by adding a cation insolubilizer such as barium. The technician can also resort to specialized sub-treatments in Recycling of industrial rejections.

The anolyte can accidentally be loaded with organic compounds. These compounds can oxidize at the anode and accumulate in the anolyte. Its in situ treatment can be done by regular maintenance of an oxidizing solution, such as sodium persulfate. In the case of oxidation to cyanide, persulfate destroys the cyanide generated at the anode.

Other salts and oxidizers may be convenient. for the invention and the examples cited are not limiting.

The present invention and its advantages will appear more clearly based on the drawings attached to the description,  in which:

Figure 1 is a schematic representation of a nickel zinc electrolytic bath with an agreement installation with the invention

Figure 3 is a schematic representation of "Anodic Assembly" in a treatment tank electrolytic.

It is evident to technicians in the field that the container and the anodic compartment can have several different settings. For example, Figure 3 shows that the container (42) can be a folding bag (44) suspended in the catholyte (46) of the tank (48). At least part of the bag (44) or preferably all of said bag (44) may be constituted by a porous membrane. A piece of cathode (52) is arranged in the catholyte (46). A metal anode (54) is arranged in the anolyte (56) that is contained in the bag (44).

According to another aspect of the invention, a container can comprise a common wall with the tank and can be constituted by a porous membrane. A piece of cathode is arranged in the catholyte and a metal anode is arranged in the anolyte

In another aspect of the invention, a container Can comprise a cylinder. The cylinder can be composed of a mouth (84) and a cylinder body. The cylinder can be positioned within the catholyte contained in the tank. At least one part of the cylinder and preferably in the entire body of the It may itself constitute a porous vessel or a porous membrane. The mouthpiece may include an anolyte junction for entry and a union of the anolyte at the exit. The joints allow the anolyte circulate in the container. An anode is arranged in the container and is attached to the outside. A piece of cathode is arranged in the catholyte

Other containers and configurations of compartments can be used by the person skilled in the art. In the invention the cathode part can be any type of part of steel or ferrous alloy typically used in electroplating In the example in the figure, a steel insert.

In another aspect of the invention, a conduction out of the anodic compartment leads to a buffer tank by under which a duct goes to a cryogenic desulfator from the top of which a conduit leads to the bucket bucket or storage From the bottom of the bucket bucket comes a conduit equipped with a pump that carries part of the anolyte that has been treated in the desulfatador to an inlet conduction in the anodic compartment. A container of sodium persulfate allows by automatic feeding add sodium persulfate to the Cuba buffer, it should be understood that this could also be added sodium persulfate directly in the anodic compartment.

The invention will be illustrated by the examples. following. These examples show the advantages of using of "anodic assembly" with porous membrane in zinc baths Alkaline and zinc alloy. These examples have been indicated as illustration and are not limiting to the invention.

Example one

The bucket is made of polypropylene. An aqueous bath of 15 liters of zinc-nickel containing 120 g / L of alkaline sodium hydroxide containing 10 g / L zinc, 1.5 g / L of nickel, 20 g / L tetraethylenepentamine (TEPA) and 2 g / L Quadrol (THEED). An "anodic assembly" (described in Figure 1) with a porous membrane on one side containing 500 ml of a solution of 150 g / L of sodium hydroxide is placed in the bath of zinc-nickel The porous PTFE membrane used It is marketed by Mortelecque under the designation TC 110.

This porous membrane is PTFE and therefore Resists the alkaline medium.

This porous PTFE membrane has a diameter half of the pores equal to 5 µm.

It is immersed in a tank, containing a solution aqueous NaOH 120 g / L, the porous membrane in PTFE so that delimit two compartments in the bucket, pouring into one of them 20 mL / L of a solution colored in violet at 8% by weight nickel comprising in weight:

- 36.2% nickel sulfate hexahydrate

- 15% tetraethylene pentamine

- the rest up to 100% is water.

A day later the compartment solution that has not received the solution colored in violet has no color Violet.

The application of a current between the anode separated from the bath by the porous PTFE membrane and a piece a clad steel located on the cathode in the bathroom zinc-nickel generates an overvoltage of less than one volt with respect to an assembly not provided with the separator.

A metal anode has been submerged in the anodic compartment. The anodic metal is composed of a chemical nickel deposit containing 10% phosphorus on steel. A current of (5A) is passed in the 15L cell for 75 h. After regular maintenance of nickel, zinc, soda and organic additives consumed by electrolysis, performance Cathodic has remained at more than 80% at 1.2 A / dm 2. Has not been appreciated erosion of the chemical nickel deposit in the anode. Without "anodic assembly" cathodic performance would have fallen to 63% as indicated below:

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Cathodic performance of the deposit of zinc-nickel obtained with porous membrane after 25 Ah / L:

one

Cathodic performance of the deposit of zinc-nickel obtained without porous membrane after 25 Ah / L:

2

Example 2

The tank is made of polypropylene. An aqueous bath of 8000 L of zinc-nickel containing 120 g / L of sodium hydroxide (alkaline) containing 10 g / L of zinc, 1.5 g / L of nickel, 20 g / L tetraethylenepentamine (TEPA), 2 g / L Quadrol (THEED) has been set up for the test. An anodic montage consisting of 60 elements, such as those described in the figure 5A, is placed in the bathroom. The set of these elements is filling of a solution of sodium hydroxide of 150 g / L from a buffer cuvette equipped with a pump. A composite metal anode Stainless steel is submerged in each of the compartments anodic The separator is a ceramic that meets the criteria following:

-

The Ceramic is resistant to alkaline medium.

-

He average pore diameter is equal to 1.5 µm.

-

Be immerse the pottery in a bowl containing an aqueous solution of NaOH 120 g / L. It is poured into one of the two compartments delimited in this way 20 mL / L of a solution colored in 8% by weight violet nickel comprising by weight:

-

36.2% nickel sulfate hexahydrate

-

15% of tetraethylenepentamine

-

he rest up to 100% is water.

A day later the solution in the compartment that has not received the solution colored in violet has not been colored in violet.

-

The application of a current between the anode separated from the bath by the ceramic and a piece to be coated in steel placed in the form of cathode in the zinc-nickel bath generates a one volt overvoltage with respect to an assembly not equipped with separator.

-

The open porosity of the ceramic measured by mercury intrusion to Pressure is 35%.

The bath described is subjected to electrolysis during 1000000 Ah. In the course of this electrolysis the content of sulfates in the bath has increased from 2 to 15 g / L, the content of carbonate is increased from 0 to 8 g / L and the concentration in soda is has maintained at 105 g / L. The cathodic performance of the bathroom has continued constant with a value of 80% at 1 A / dm 2. Appearance of the deposit on the pieces is constant, that is, bright and no veiled or matt areas. Therefore productivity has been kept.

Example 3

(Comparative)

The assembly has been reproduced identically from example 2 but in this case the ceramic has been replaced by a perfluorinated cation exchange membrane facilitated by the Dupont company with the reference Nafion 424. The bathroom has been subjected to electrolysis for 10,000,000 Ah. In the course of this electrolysis the sulphate content in the bath has increased by 2 g / L to 25 g / L, carbonate content has increased from 0 to 30 g / L and the soda content has increased from 115 to 160 g / L. Performance Bath cathodic has decreased from 80% to 60% to 1 A / dm 2. He appearance of the deposit on the pieces has degraded going on to have a matte and veiled appearance. Therefore productivity has diminished. Therefore it is necessary to carry out an operation of desulphation and decarbonation, as well as an operation of cutting the bathroom so that the concentrations of sulfate, carbonates and soda in the bathroom, returning to recover a identical productivity to the initial one.

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Example 4

In this example the "anodic assembly" has been filled with a solution of 150 g / L of soda in water. The metal Anodic is composed of metallic nickel. A cell identical to that of Example 1 has operated at 5A for 6 h. The nickel anode had a thin conductive layer of nickel oxide and nickel hydroxide  that has not hindered the electrolytic procedure. There hasn't been Weight loss at the anode. The cathodic performance of the bath has been maintained with a value of 80% at 1 A / dm 2.

Example 5

The "anodic assembly" of example 1 has been filled with a 20% solution by weight of liquid caustic soda at fifty%. The metal anode was constituted by a steel plate electrolytically nickel plated from a Watts type bath, a 5A electrolysis for 90 h has been carried out at 7V. With a regular maintenance of nickel, zinc, soda and organic additives consumed by electrolysis, cathodic performance has remained stable at 80% at 1 A / dm 2. There has been no loss of weight at the anode.

Example 6

(Comparative)

A 2L bath of electrolysis has been subjected to electrolysis zinc nickel containing 30 g / L of polyethyleneimine (TEPA) during 160 Ah, with a nickel anode directly in the bathroom. The analysis has determined 508 ppm of cyanide as a degradation product and the cathodic yield has decreased to less than 50% for 2 A / dm 2.

Example 7

The "anodic assembly" of example 1 has been filled with a solution of 150 g / L of potash, the metal being Anodic in the anolyte a mild steel. The bathroom that was used as in example 1 has been electrolysis at 5A for 6 h. There has been a slight loss of anode weight. After the No trace of cyanide was detected.

Example 8

The "anodic assembly" of example 1 is filled with a solution of 150 g / L of soda. The anode metal is cobalt. The 15 l alkaline nickel zinc bath contains 20 g / L of polyethyleneimine and is subjected to electrolysis for 30 Ah. After of 30 Ah, the cathodic yield remains stable at 60% at 2 A / dm 2  and there has been no weight loss at the anode.

Example 9

An alkaline zinc bath has been prepared without cyanide with 10 g / L of zinc, 130 g / L of soda, 8 ml / L of a brightener and approximately 5 g / L sodium tartrate. The electrolysis has been conducted without "anodic mounting" with a Simple anode of mild steel. After 100 Ah per liter, it has A white precipitate formed in the bath. The precipitate is from sodium oxalate produced by anodic oxidation. The precipitate of Oxalate interferes with brightness and causes a deposit of matte zinc and rough. The use of an "anodic assembly" with an anode of nickel prevents oxidation of tartrate in oxalate and therefore eliminates both the defect of the appearance of the deposit caused by the precipitation of oxalates.

Example 10

An alloy bath zinc-iron containing 20 g / L zinc, 300 ppm of iron and 130 g / L of soda and 50 g / L of triethanolamine (TEA), with the purpose of complexing the iron has undergone electrolysis over a period of 100 Ah / L. Anodic oxidation of ASD causes degradation products that can interfere with the Treatment of bathroom rejections. The use of a "mount anodic "with a pure nickel anode prevents oxidation of the TORCH.

As shown in the examples above and in accordance with the invention, a installation and a procedure with which zinc and zinc alloy can be safely deposited on a substrate using an electrolytic bath that particularly contains polyalkanimines This can be achieved without anodic corrosion and without generating anodic decomposition products on the cathodic side of the electrolytic treatment bath. You can use a bathroom electrolytic comprising supplementary organic additives and organic additives described in the above.

Claims (12)

1. Installation for electrolytic tank of zinc or zinc alloys at least with another metal chosen between iron, cobalt, nickel and manganese on one piece, comprising: a) a tank (64) subdivided by a separator (70) in a cathodic compartment and an anodic compartment b) the piece is submerged in an aqueous catholyte (16) alkaline pH contained in the cathodic compartment and comprising zincato ions and eventually ions of the other metal other than zinc, and c) an aqueous anolyte (28) of alkaline pH, contained in the anodic compartment and surrounding a metal anode (30) insoluble in the anolyte (28), characterized in that d) the separator (26) is made in a open pores material and passes the following three tests:

one)

The pore diameters have a dimension between 10 nm and 50 µm.

2)

Be immerse in a bowl containing an aqueous solution of NaOH of 120 g / L the separator to be checked so that it delimits in tank two compartments, 20 mL / L of a solution is poured into one of them colored in violet at 8% by weight of nickel comprising weight:

-

36.2% nickel sulfate hexahydrate,

-

15% of tetraethylenepentamine,

-

rest up to 100% water,

one day later the compartment solution that has not received the solution colored is not colored in violet, and

3)

Provides an undervoltage lower than 5 volts

2. Installation according to claim 1, characterized in that the separator is made of a material with open pores whose pore diameters have a dimension between 10 nm and 5 µm. 3. Installation according to claim 1 or 2, characterized in that the separator is made of a porous ceramic with an open porosity comprised between 10 and 60%. 4. Installation according to claim 3, characterized in that the open porosity is between 20 and 50%. 5. Installation according to claim 1 or 2, characterized in that the separator is made of polytetrafluoroethylene or polyolefin, such as polypropylene or polyethylene. 6. Installation according to one of the preceding claims, characterized in that the anodic compartment communicates with a desulfator (108). 7. Installation according to one of the preceding claims, characterized in that the anodic compartment or a cuvette communicating with it communicates with an alkali metal persulfate container (118). 8. Installation according to one of the preceding claims, characterized in that the alkaline pH is greater than 12. 9. Installation according to one of the preceding claims, characterized in that the catholyte comprises a complexing agent of a metal. 10. Installation according to one of the preceding claims, characterized in that the catholyte and / or the anolyte contain 50 to 250 g / L alkali metal hydroxide. 11. Installation according to one of the preceding claims, characterized in that the catholyte contains Zn, expressed in metallic zinc, with a content of 4 to 50 g / L. 12. Installation according to one of the preceding claims, characterized in that the catholyte contains the other metal with a content between 0.1 g / L and 50 g / L.