Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/18—Regeneration of process solutions of electrolytes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/06—Filtering particles other than ions
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/22—Electroplating: Baths therefor from solutions of zinc
  • C25D3/24—Electroplating: Baths therefor from solutions of zinc from cyanide baths
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc

Definitions

• the invention relates to the use of soluble quaternary ammonium compounds for the regeneration of a zinc nickel electrolyte by removal of cyanide ions.
• the present invention relates to a process for the regeneration of a zinc nickel electrolyte, in which soluble quaternary ammonium compounds are added to the zinc nickel electrolyte, whereby the cyanide ions, which are present as Tetracyanonickelkomplex can be removed.
• the deposition of zinc nickel alloy coatings with a proportion of 10-16 wt.% Nickel causes a very good corrosion protection on components made of ferrous materials and is therefore of great importance for technical corrosion protection.
• the deposition can be carried out from weakly acidic or strongly alkaline electrolytes.
• weakly acidic or strongly alkaline electrolytes are preferred. These are distinguished from the weakly acidic processes by a much more uniform layer thickness distribution. This property is particularly noticeable in complex three-dimensional geometries of the components to be coated.
• a minimum layer thickness must be adhered to the component. This is usually 5 microns.
• Zinc is an amphoteric metal and is present therein as zincation, Zn [(OH) 4 ] 2- .
• nickel is not amphoteric and therefore can not be complexed by hydroxide ions.
• Alkaline zinc nickel electrolytes therefore contain special complexing agents for nickel. Preference is given to using amine compounds such as triethanolamine, ethylenediamine or homologous compounds of ethylenediamine, for example diethylenetriamine, tetraethylenepentamine and the like.
• Zinc nickel alloy electrolytes are operated with insoluble anodes.
• the use of soluble zinc anodes is not possible because zinc is amphoteric and therefore chemically dissolves in a strongly alkaline solution. The use of soluble zinc anodes would therefore lead to a strong zinc increase in the electrolyte.
• this amphoteric behavior is used to supplement the zinc content in the electrolyte.
• zinc pieces are dissolved in the electrolyte in a separate zinc solution container.
• This zinc-enriched electrolyte is then replenished to the deposition electrolyte to the extent that the zinc is consumed in the deposition.
• the supplementation is usually carried out by continuous, automatic analyzes and dosing pumps controlled on the basis thereof.
• nickel Since nickel is not amphoteric and does not dissolve in the strongly alkaline electrolyte, it is suitable as an anode material for insoluble anodes. At the nickel anode, the main reaction is the formation of oxygen. Apart from nickel, other metals such as iron, stainless steel, cobalt or alloys of the metals mentioned are also suitable.
• galvanically nickel-plated steel anodes with nickel deposits of about 30 microns. The deposited nickel is supplemented in the form of suitable supplementary solutions containing nickel salts with high water solubility. Nickel sulfate solutions are preferably used for this purpose.
• the cyanide content in the zinc nickel electrolyte is very disadvantageous.
• the accumulation of cyanide in a zinc nickel alloy electrolyte can adversely affect the composition and visual appearance of the deposit.
• a milky-fogged deposit may occur. This can be partially corrected by higher dosage of brighteners again. This measure is but with an increased Consumption of brighteners and thus additional costs associated with the deposition.
• the anode used is a platinized titanium anode.
• the anolyte is acidic and contains sulfuric acid, phosphoric acid, methanesulfonic acid, amidosulfonic acid and / or phosphonic acid.
• EP 1 702 090 B1 claims a method which provides for the separation of the cathode and anode compartments through an open cell material.
• the separator is made of polytetrafluoroethylene or polyolefin, such as polypropylene or polyethylene.
• the pore diameters have a dimension between 10 nm and 50 ⁇ m.
• ion exchange membranes where the charge transport through the membrane is carried out by the exchange of cations or anions, it can be carried out with the use of open-cell separators only by the electrolyte transport through the separator. Complete separation of the catholyte from the anolyte is not possible. It can therefore not be completely prevented that amines reach the anode and are oxidized there.
• the anode and cathode compartments are separated there by a filtration membrane.
• the size of the pores of the filtration membrane is in the range of 0.1 to 300 nm.
• a certain transfer of electrolyte from the cathode to the anode space is deliberately accepted.
• zinc nickel electrolytes do not work satisfactorily when membrane processes accordingly EP 1 344 850 or EP 1 292 724 be used.
• These brighteners obviously require anodic activation to produce their full effect. This reaction is ensured when using filtration membranes. However, this also means that the formation of cyanides can not be completely avoided.
• DE 10 2008 058 086 A1 claims a method for depositing functional layers from acidic or alkaline zinc or zinc alloy baths.
• the method includes a step of providing separation of cyanide ions by means of ion exchangers.
• any ion exchange resin capable of binding cyanide ions is suitable.
• an ion exchange resin which can attach cyanide ions to the anchor groups, inter alia, strongly basic anion exchangers are mentioned which have quaternary ammonium ions as functional groups. It is described that the subsequent regeneration of such anion exchangers is difficult and for a not even complete regeneration concentrated sodium chloride solutions have to be used.
• the object underlying the present invention is therefore to provide a means and a simplified method for the regeneration of a zinc nickel electrolyte by removing the cyanide ions.
• cyanide ions that have formed in a zinc nickel electrolyte can precipitate selectively in the form of a cyanide-containing precipitate when one or more soluble quaternary ammonium compounds are added to the zinc nickel electrolyte be added. Further studies have shown that the soluble quaternary ammonium compounds, in the sense of ion pair formation, react selectively with the tetracyanoxide anions present in the electrolyte and precipitate as a sparingly soluble product.
• the cyanide-containing reaction product can be easily removed by, for example, filtration from the electrolyte.
• the present invention is particularly against the background of the teaching of the above-mentioned DE 10 2008 058 086 A1 Surprisingly, because it describes that only the cyanide ions bind to the ion exchanger used. This is confirmed by the embodiments describing the regeneration of a zinc-nickel alloy bath with a strongly basic ion exchanger.
• a tetracyanonickel anion complex does not react with the strongly basic ion exchanger, but only the cyanide ions. It is explicitly described that the nickel concentration in the electrolyte remains constant.
• Regeneration literally means “restoration”.
• the term “regeneration” refers to the recovery of a zinc nickel electrolyte in its trouble-free state by the removal of cyanide ions which have formed during the operation of the electrolyte.
• any soluble quaternary ammonium compound can be used according to this invention.
• a quaternary ammonium compound is "soluble" in the sense of this invention if it has a solubility in the zinc nickel electrolyte of at least twice the molar amount in which the cyanide concentration calculated as tetracyanone nickel complex is present. In order to lower the cyanide concentration as much as possible, it is possible to use the soluble quaternary ammonium compound in excess of the cyanide concentration. It is therefore preferred if the solubility of the quaternary ammonium compound in the zinc nickel electrolyte is 10 times the molar amount of the molar amount of Tetracyanonickelkomplex calculated based on the cyanide concentration.
• the soluble quaternary ammonium compound preferably corresponds to the general formula [R 1 R 2 R 3 R 4 N] + X - , where R 1 to R 4 are identical or different and are C 1-24 -alkyl or -alkenyl, which may be mono- or polysubstituted by oxygen may be interrupted or substituted by hydroxyl or with an optionally substituted by one or more halogen atoms or C 1-8 alkyl radicals substituted aryl radical, or R 1 to R 4 by ring closure of three radicals 5- or 6 -membered heterocyclic rings, such as pyridine or thiazoline, form, which in turn are optionally mono- or polysubstituted by C 1-4 alkyl or C 1-4 alkenyl, which optionally carry an aryl radical, which in turn with halogen, Amino or dimethylamino may be substituted, and X - for hydroxide, sulfate, halide, such as chloride, bromide or
• quaternary ammonium compounds are commercial products.
• trialkylamines and alkyl halides e.g. Alkyl chloride, alkyl bromide or alkyl iodide.
• the quaternary ammonium compounds thus formed have chloride, bromide or iodide as counterion.
• alkylating agents and dialkylsulfates such as Dimethyl sulfate or diethyl sulfate used.
• the quaternary ammonium compounds are then obtained as alkyl sulfates, e.g. Methylsulfate or ethylsulfate.
• the quaternary ammonium compounds can be used in the form obtained in the alkylation of tertiary amines for the precipitation of tetracyanonickel complexes according to the invention. However, it is preferred to use the ammonium compounds as hydroxide or sulfate salts. In order to prevent accumulation of, for example, halogen ions in the zinc nickel electrolyte, it is preferred to use quaternary ammonium halides before their use in quaternary Convert ammonium hydroxides. The conversion can be carried out by reactions known to the person skilled in the art.
• halide salts to hydroxide salts may be by anion exchange using basic ion exchangers or by double reaction with an alcoholic solution of sodium or potassium hydroxide.
• Quaternary ammonium compounds are also commercially available in the form of their hydroxide compounds. These may be neutralized with any acid, if necessary, to form quaternary ammonium compounds with any anion X - .
• the zinc-nickel electrolyte regenerated according to the present invention is an aqueous electrolyte and typically has a zinc ion concentration in the new batch in the range of 5 to 15 g / l, preferably 6 to 10 g / l calculated as zinc, and a nickel ion concentration in the range of 0 , 6 to 3 g / l, preferably 0.6 to 1 g / l, calculated as nickel.
• the zinc and nickel compounds used for the production of the zinc nickel electrolyte are not particularly limited.
• the zinc nickel electrolytes contain an amine compound as a complexing agent for nickel.
• This amine compound is, for example, triethanolamine or ethylenediamine or homologous compounds of ethylenediamine, such as diethylenetriamine and tetraethylenepentamine.
• the complexing agent or mixtures of these complexing agents is / are usually employed in a concentration ranging from 5 g / l to 100 g / l, preferably 10 to 50 g / l, more preferably 20 g / l.
• the zinc nickel electrolyte is strongly basic.
• NaOH or KOH can be used, particularly preferably NaOH.
• a zinc nickel bath contains 80 to 160 g / l of sodium hydroxide. This corresponds to an approximately 2-4 molar solution.
• the zinc nickel electrolyte may also contain various additives commonly used to deposit zinc nickel alloys. These are, for example, aromatic or heteroaromatic compounds as brighteners, such as benzylpyridinium carboxylate or pyridinium-N-propane-3-sulfonic acid.
• the quaternary ammonium compound is preferably added to the zinc nickel electrolyte as an aqueous solution. Depending on the technical availability but also the use of a methanolic solution is possible. The addition of the quaternary ammonium compound in solid form is also possible.
• a partial volume of the electrolyte to be treated is removed and treated in a treatment vessel with the previously calculated amount of quaternary ammonium compound as a precipitant. The required amount of quaternary ammonium compound results from the cyanide concentration in the zinc nickel electrolyte.
• the precipitated reaction product can be separated, preferably by filtration, and the purified electrolyte can be returned to the production bath.
• the volume of the withdrawn partial electrolyte is calculated so that the production with the zinc nickel bath does not have to be interrupted.
• an alkaline zinc nickel bath usually a regular carbonate removal by strong cooling and Crystallization of the sodium carbonate performed.
• cyanide removal by ion pairing is associated with this carbonate freezing.
• the precipitated ion pair can thus be separated together with the Natriumcarbonatschlamm and fed to a disposal.
• phase separation by conventional means for phase separation, as they are known in the electroplating technique (for example, oil separator) possible. Furthermore, it is also possible to remove ion pairs, which do not form directly in a depositable form, by treatment of the electrolyte with activated carbon.
• the determination of the cyanide was carried out with the cuvette test LCK 319 for slightly releasable cyanides of Fa. Long.
• the quaternary ammonium compound used was benzyltriethylammonium chloride.
• 4.5 g of benzyltriethylammonium chloride were added to 600 ml of the zinc nickel electrolyte at 20 ° C. and stirred for 2 hours. After a further 20 hours, it was filtered off. In the filtrate a residual content of 82 mg / l cyanide was found. The cyanide concentration was thus reduced by 90%.
• Example 2 As in Example 1, 7.8 g / l zinc and 1.1 g / l nickel were measured in the filtrate. The decrease of the nickel value corresponds to the decrease in the accuracy of analysis as Tetracyanonickelanion.
• the quaternary ammonium compound used was benzyltributylammonium chloride.
• To 600 ml of the zinc nickel electrolyte were added 20 ° C 2.9 g of benzyltributylammonium chloride and stirred for 2 hours. After a further 20 hours, it was filtered off. In the filtrate, a residual content of 31 mg / l cyanide was found. The cyanide concentration was thus reduced by 96%.
• 7.8 g / l of zinc and 1.1 g / l of nickel were measured. The decrease of the nickel value corresponds to the decrease in the accuracy of analysis as Tetracyanonickelanion.
• test sheet Starting from the edge of the low current density range up to about 80% of the test sheet, the test sheet showed a semigloss, stainless steel-like appearance. The remaining 20% of the test sheet was dull gray.

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• 2010
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