CS263985B1 - A method of treating spent copper etching baths - Google Patents

Abstract

The essence of the solution is that the spent bath in which the copper content was reduced by direct electrolysis to 1-5 g / cm 3 is subjected to the following electrolysis in the absence of air, whereby the etching bath is passed through a porous cathode of carbonaceous or graphite felt. The procedure can be used to dispose of spent copper etching baths.

Description

The invention relates to a process for the electrolytic treatment of exhausted copper-containing etching baths in complex form.

The active component of the etching solutions are copper ions which, when etched, react with the copper metal to form copper ions, which are back oxidized by atmospheric oxygen or an oxidant present in the solution. An essential part of etching solutions are complexing agents that bind both monovalent and divalent copper in soluble form (ammonia or soluble amines) .In use, the copper content in the etching solution increases, the etching rate decreases and copper compounds may fall out if the etching capacity of the bath is exceeded The etching solutions used cannot be discharged into the waste due to the toxicity of copper and ammonia and, in addition, would result in the loss of valuable raw materials.Therefore, procedures have been devised to either remove most of the copper from the depleted bath and components to the extent that the resulting solutions can be discharged into waste water.

A process has been proposed (Ger. Offen. No. 2,651,675) to add insoluble copper compounds from the exhausted etching bath which is filtered off by addition of hydrochloric acid, and a new bath is prepared by addition of ammonia. The disadvantage of the process is the difficult filterability of the suspension and the necessity of further processing of the obtained precipitates into metallic copper to another commercially desired form of copper.

Further, extraction methods have been proposed (eg, US Pat. No. 4,083,758), according to which the cupric salt is transferred to the organic phase and the aqueous solution can be used to prepare a new bath. CuCL · is first precipitated from the organic phase, which is then taken up with concentrated sulfuric acid into a solution from which copper metal is precipitated by electrolysis.

It is considerably simpler to reduce the copper content by direct electrolysis, for example in an electrolyzer. By this method, the copper concentration in the depleted bath can be reduced from the original 100 to 150 g / dm ³ to 1 to 5 g / dm ³ , which is customary for newly prepared baths. The solutions obtained by this electrolysis can be reused for etching after the missing components have been added. Multiple regeneration of etching baths containing only copper amocomplexes, ammonia and ammonium chloride was verified experimentally.

However, baths containing monovalent copper oxidants (such as sodium trichloroacetate) or other substances (eg formic acid) which react upon etching and electrolysis to produce products (carbonates, sodium chloride) reducing the rate of copper etching in the regenerated bath cannot be regenerated by direct electrolysis.

The etching baths containing substances preventing the electrolytic regeneration can be treated according to the process according to the invention, the object of which is a method of treating depleted copper etching baths in which the copper is contained in a complex form.

SUMMARY OF THE INVENTION The present invention relates to a process in which a spent etching bath in which the copper content has been reduced by electrolysis to 1-5 g / dm ^{3 is} subjected to subsequent electrophysis in the absence of air, flowing through the porous cathode of carbon or graphite felt. almost quantitatively removed. The resulting solutions containing NH 3 Cl, NH 3 and only traces of copper (about 1 mg / dm ³ ) can be used in other industrial processes, for example in the production of soda by the Solvay process.

Electrolysis is carried out in the absence of air into the cathode space to avoid cathodic reduction of air oxygen, which would reduce the current yields on copper. Flushing the cathode space with an inert gas (e.g. nitrogen) and separating its gas space from the atmosphere with a water seal is suitable.

Advantageously, the copper deposited in the porous cathode can be removed by allowing a small amount of the first electrolysis solution (containing 1 to 5 g Cu / dm ³ ) heated to about 50 ° C to flow through the porous cathode in an electroless-free state. excreted copper easily dissolves. A relatively small amount of the resulting solution (about 0.01 to 0.05 m ³ per 1 m ^{3 of the} solution electrolyzed with a porous cathode) containing about 100 g of Cu / dm ³ can be connected to depleted baths entering the 1st electrolysis.

The advantage of the proposed process is that it solves the disposal of exhausted etching baths, which cannot be used for the preparation of the regenerated bath for the first electrolysis and cannot be used in other production nor discharged into waste water.

Example 1

A depleted etching bath of 1 dm · ⁵ containing 135 g Cu / dm ³ was electrolyzed in a plate cathode electrolyzer except for the final composition:

1.3 g Cu / dm ³ ,

240.0 g NH ³ Cl / dm ³ a

10.0 g NH 3 / dm ³ .

This solution was electrolyzed with a 5 mm thick graphite felt cathode and an area of 30 cm ² at a current density of 0.1 A per cm ² . The electrode compartments were separated by an ion exchange membrane, and the anode was a platinized titanium sheet. Electrolysis was carried out with air, the electrolyte was pumped through the cathode at a rate of 9.6 cm ³ / s. After 25 min. electrolysis decreased copper content only to 30 mg / dm ³ , so copper was removed inadequately,

3 3

Example 2

Electrolysis of the same solution was carried out under the same conditions, but air access was prevented by closing the cathode compartment and separating it from the atmosphere by a water seal. After 28 min. electrolysis decreased the copper content to 0.6 to 1.3 mg / dm ³ . Example 3

Electrolysis was performed in a similar way as

5 in Example 2, however, a carbon felt cathode was used and the cathode space was purged with nitrogen. The copper concentration reached 1 mg / dm ³ at a current of 4.8 A in 25 min, at a current of 3 A in 30 min. and at a current of 1.5 A in 56 min.

At the end of every fifth electrolysis, an etching bath containing 5 g of Cu / dm ³ heated to 50 ° C was pumped through the porous cathode. Quantitative dissolution of copper occurred within 6 to 10 min.

Claims (3)

Process for the treatment of depleted copper etching baths in which copper is bound in a complex form, in which the copper content is first reduced by electrolysis to 1-5 g / dm ³ , characterized in that the solution is subjected to electrolysis after this electrolysis In the absence of air electrolysis, the solution is sieved through a graphite or carbon felt cathode. 2. The method of claim 1, wherein: SUMMARY OF THE INVENTION that oxygen is prevented from entering the solution by purging the cathode space with an inert, oxygen-free gas. 3. A method according to claim 1 or 2, characterized in that the copper deposited in the porous cathode during electrolysis is removed after the electrolysis is finished by suction of the etching solution from the first electrolysis or another etching solution heated to min. Deň: 29 ° C.