RU2591025C1 - Method of electric membrane regeneration of solution for removal of chromium coatings - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrolytic metallurgy and can be used on sections of galvanic chromium plating. Method of regenerating solution for removal of chromium coating containing hydroxide and sodium chromate involves electrochemical processing regenerated solution in two-chamber electrolyser with cation-exchange membrane and three-chamber electrolyser with cation-exchange and anion-exchange membranes in the following sequence: at first in anode chamber two-chamber electrolysis cell, then in the middle chamber of three-chamber electrolysis cell, then in cathode chamber of a two-chamber electrolysis cell and the cathode chamber of three-chamber electrolysis cell. Method enables to obtain a solution for removal of chromium coatings of initial composition and a solution of chromic acid which can be used in chromium plating or chromate treatment.

EFFECT: invention provides ruled out abrupt current drop soon after its turning-on for electrochemical processing, which enables regeneration of solution in a stable mode until completion.

1 cl, 2 ex

Description

The invention relates to electroplating, in particular, to methods for the regeneration of a solution based on sodium hydroxide (100-200 g / l), used for anodic removal of chromium coatings from chrome-plated steel parts and from suspension devices, and can be used in plating chromium plating shops.

During the anodic removal (dissolution) of the chromium coating, chromate ions accumulate in the electrolyte. Therefore, the spent solution containing hydroxide and sodium chromate must be neutralized by neutralizing the alkali contained in it and then treating it with some reducing agent to convert chromate ions to trivalent chromium ions, followed by the addition of an alkaline reagent to precipitate chromium hydroxide. In order to reduce the consumption of chemicals and the amount of waste generated, it is advisable to replace the disposal of spent solutions with regeneration, that is, removal of most of the chromate ions accumulated in it from the spent solution and increasing the concentration of sodium hydroxide to the initial level.

A known method for the regeneration of acidic chromate-containing solutions by electrochemical processing in the anode chamber of an electrolyzer with a cation exchange membrane [Kruglikov S. S. Removal of metal cations from chromaer-based solutions by mermbrane electrolysis. Metal Finishing, vol. 107, # 11, November 2009, p. 13-1; RF patent 2481424, s. from 07/28/2011, publ. 05/10/2013]. In this method, the regeneration process includes removing accumulated zinc ions from the regenerated solution by transferring them from the regenerated solution — anolyte through a cation exchange membrane to a catholyte — auxiliary sulfuric acid solution, as well as anodic oxidation of trivalent chromium ions to chromate. A regenerated solution is an anolyte from which most of the zinc ions contained in it are removed and the initial concentration of chromate ions is restored.

      The technical task of the developed method is, on the contrary, the removal of chromate ions from the regenerated solution. In view of this, the closest to the problem to be solved and the technical essence is a method of purifying a chromium electrolyte from iron ions and other cationic contaminants [RF Patent 2481425, з.28.07.2011, publ. 05/10/2013]. In this method, chromate ions during electrolysis pass from the middle chamber to the anolyte. However, when implementing this method, solutions at all stages of the multi-stage regeneration process must have an acid reaction, which ensures sufficient electrical conductivity of both the solutions themselves (catholytes and anolytes) and the membranes separating them. Attempts to regenerate a strongly alkaline solution of removing chromium coatings using this method were unsuccessful due to a sharp drop in current as a result of a multiple increase in the resistance of the electrolyzer shortly after turning on the current.

In the proposed method, the task of eliminating a sharp drop in current shortly after the start of electrolysis is solved by carrying out the regeneration process by electrochemical processing of the regenerated solution in the chambers of a two-chamber electrolyzer with a cation-exchange membrane and a three-chamber electrolyzer with a cation-exchange and anion-exchange membranes in the following sequence: first, in the anode chamber of the two-chamber electrolyzer the middle chamber of the three-chamber electrolyzer, then in the cathode chamber of the two-chamber electrolyzer and to in the three chamber chamber electrolyzer.

As a result of regeneration, a solution of sodium hydroxide of the initial composition (100-150 g / l) and a by-product of a solution of chromic acid (25-50 g / l), which can be used to prepare and adjust the chromium electrolyte, passivation solutions, etc. are obtained. An important feature the proposed method is the absence of a sharp drop in current shortly after its inclusion, which allows you to continue the regeneration process in a stable mode until its completion.

The invention is illustrated by the following examples.

Example 1

The chrome plating remover in the bath (4) contains 100 g / l sodium hydroxide and 10 g / l chromic anhydride. Regeneration was carried out for 15 hours and a stable DC voltage of 18 V. The current strength in the circuit during electrolysis was 15-18 A, gradually increasing from the initial to the final value. At the end of the regeneration process, a removal solution was obtained with a concentration of sodium hydroxide of 140 g / l and a residual concentration of chromic anhydride of 2 g / l, returned to the removal bath (4), and a solution of chromic acid in a container (10) containing 25 g / l of chromic anhydride .

Example 2

The chrome plating remover in the bath (4) contains 120 g / l sodium hydroxide and 20 g / l g / l chromic anhydride. Regeneration was carried out for 25 hours at a stable voltage of 17 V. The current strength in the circuit was 20–25 A, gradually increasing from the initial to the final value. At the end of the regeneration process, a solution was obtained with a concentration of sodium hydroxide of 150 g / l and a residual concentration of chromic anhydride of 3 g / l, returned to the chromium removal bath (4), and a solution of chromic acid with a concentration of chromic anhydride of 40 g / l.

Claims (1)

The method of regenerating a solution for removing chromium coatings containing hydroxide and sodium chromate, including the electrochemical treatment of the solution in the anode chamber of a two-chamber electrolyzer with a cation-exchange membrane and then in the middle chamber of a three-chamber electrolyzer with a cation-exchange and anion-exchange membranes, characterized in that after the said treatment in the middle chamber, the solution treated in the cathode chamber of a two-chamber electrolyzer with a cation exchange membrane and in the cathode chamber of a three-chamber electrolyzer with a cathode ono-exchange and anion-exchange membranes.