JPH0144117B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for removing only chromium compounds present in trace amounts in an alkaline electrolyte aqueous solution using a chelate resin without changing the pH and electrolyte concentration of the electrolyte aqueous solution. Regarding.

Conventionally, the removal of trace amounts of chromium compounds has been widely carried out in wastewater treatment, etc., but in both cases PH
The properties of the aqueous solution after removing the chromium compounds change significantly with the addition of chemicals. Furthermore, when the aqueous solution is alkaline, trivalent chromium compounds can be removed by precipitation, but the removal is limited to a few ppm.

However, when a system in which a chromium compound is present in an alkaline electrolyte aqueous solution is electrolyzed, problems such as a change in the electrolytic overvoltage may occur. For this reason, the chromium compound must be removed over time, but in the commonly used chromium removal method, changes in the pH and electrolyte concentration of the electrolyte aqueous solution cannot be avoided. In particular, trivalent and hexavalent chromium compounds often coexist in electrolyte aqueous solutions, and the solubility of hexavalent chromium compounds is high, so there has been no method to sufficiently remove chromium compounds without changing the composition and physical properties of electrolyte aqueous solutions. .

In view of the above circumstances, the present inventors conducted extensive research and found that Cr, which is generally used in a neutral or acidic state,
We have discovered that it is possible to remove chromium compounds in an alkaline electrolyte aqueous solution to an extremely low concentration without changing the pH or electrolyte concentration of the aqueous solution by using a chelate resin for removing Cr. The gist is that an alkaline aqueous electrolyte solution containing a chromium compound is passed through a chelate resin that has been treated with an aqueous solution having the same electrolyte concentration and pH as the aqueous alkaline electrolyte solution containing a chromium compound, and a trace amount of the chromium compound is removed. A method for removing chromium compounds in an electrolyte aqueous solution is provided.

The present invention will be explained below.

As the chelate resin used in the present invention, those having an aminocarboxylic acid as a coordination group (for example,
Dowex A-1), some have polyamine as a coordinating group, others have glyoxal bishydroxyanyl, iminocarboxylic acid, iminodicarboxylic acid, dithiocarbamic acid, thiol, etc. or a metal salt thereof as a coordinating group, but there are others. Chelate resins that incorporate divalent or higher transition heavy metals can also be used.

The above-mentioned chelate resin is generally synthesized in a pure water solution, and after a desalting operation is carried out, it is kept in pure water.
Therefore, if it is used as it is to remove chromium compounds from an alkaline electrolyte aqueous solution, the pH and electrolyte concentration of the electrolyte aqueous solution will change after the chromium compounds are removed. Therefore, the chelate resin is washed with an aqueous solution having the same pH and electrolyte concentration as the aqueous electrolyte solution, and then used to remove chromium compounds from the aqueous electrolyte solution containing chromium compounds. This operation makes it possible to remove chromium compounds without changing the pH and electrolyte concentration.

There are various methods for removing chromium compounds using chelate resin, but usually the chelate resin is packed into a packed tower and the chromium compound-containing electrolyte aqueous solution (hereinafter referred to as the liquid to be treated) has the same pH and electrolyte concentration. Washing is performed by flowing an aqueous solution in advance, and then the chromium compound is removed by flowing a liquid to be treated.

The above method can be used in systems that remove and reuse trace amounts of chromium compounds eluted into liquid in plants using equipment made of chromium alloy materials, but especially in electrolytic tanks used for heavy water concentration. This is an excellent method for removing chromium compounds from electrolyte aqueous solutions. By this method, the electrolyte aqueous solution can be easily reused, and by removing chromium compounds, there is no change in overvoltage during electrolysis, making it possible to efficiently concentrate heavy water.

EXAMPLES The present invention will be specifically explained below by way of examples, taking as an example the removal of chromium compounds from the electrolyte of a heavy water electrolytic concentrator.

Example 1 Using an iminocarboxylate type chelate resin,
The chromium compounds in the alkaline electrolyte aqueous solution were removed by the following procedure. First, the above chelate resin with a sedimentation capacity of 68 ml was packed into a glass column with an inner diameter of 30 mm, and washed with 730 ml of light water. Then add this to PH: 12.5 and alkaline concentration:
8.4 wt% heavy water/(heavy water + light water): 280 ml of a 93.2 wt% heavy water solution was passed as a cleaning liquid at a flow rate of 600 ml/hr to wash the resin.

This chelate resin has the same pH and electrolyte concentration as the above cleaning solution containing a total chromium concentration of 0.2 ppm,
and electrolyte aqueous solution with heavy water concentration as the liquid to be treated.
2400 ml of liquid was passed through at a flow rate of 600 ml/hr. The pH, electrolyte concentration, and heavy water concentration before and after chelate resin treatment remained unchanged, and only the total chromium content decreased to 0.096 ppm.

Example 2 An electrolyte aqueous solution with a chromic acid concentration of 3.36 ppm (chromium equivalent) was used as the liquid to be treated at a flow rate of 600 ml/hr.
The procedure was the same as in Example 1 except that 2720 ml was passed through. As a result, the pH and electrolyte concentration of the treated solution before and after treatment remained unchanged, and only the chromic acid concentration (in terms of chromium) decreased to 0.05 ppm.

Claims (1)

[Claims] 1. A trace amount of chromium compound in the electrolyte aqueous solution is removed using a chelate resin treated with an aqueous solution having the same electrolyte concentration and pH as the alkaline electrolyte aqueous solution containing the chromium compound. A method for removing chromium compounds from an electrolyte aqueous solution. 2. The method for removing chromium compounds in an electrolyte aqueous solution according to claim 1, wherein the chelate resin is a chelate resin having an iminocarboxylate, an iminodicarboxylate, a dithiocarbamic acid, or a thiol as a functional group. 3. The method for removing chromium compounds in an electrolyte aqueous solution according to claim 1, wherein the alkaline electrolyte aqueous solution containing a chromium compound is a heavy aqueous solution.