Electrolyte for electrochemical decontamination and preparation method and application thereof

Abstract

An electrolyte for electrochemical decontamination and a preparation method and application thereof. The electrolyte is an aqueous solution including the following solutes: phosphoric acid, oxalic acid, citric acid, tartaric acid, hydrogen peroxide and glacial acetic acid. The electrolyte has a good decontamination effect and allows for fast decontamination and is obtained by reasonably combining different types of solutes and controlling the levels of the solutes and resulting secondary waste solution and residues are easy to treat. The electrolyte is suitable for overall or local electrochemical decontamination of radioactively contaminated stainless steel scrap.

Claims

1. An electrolyte for electrochemical decontamination, wherein the electrolyte for electrochemical decontamination is an aqueous solution comprising the following solutes by mass: 45% to 80% by mass of phosphoric acid, 5 g/L to 10 g/L of oxalic acid, 1 g/L to 10 g/L of citric acid, 1 g/L to 2 g/L of tartaric acid, 1 g/L to 5 g/L of hydrogen peroxide, and 5 g/L to 10 g/L of glacial acetic acid.

2. The electrolyte for electrochemical decontamination according to claim 1, wherein the electrolyte for electrochemical decontamination comprises 50% to 70% by mass of the phosphoric acid, 5.5 g/L to 8 g/L of the oxalic acid, 2 g/L to 7 g/L of the citric acid, 1.5 g/L to 2 g/L of the tartaric acid, 2 g/L to 4 g/L of the hydrogen peroxide, and 6 g/L to 10 g/L of the glacial acetic acid.

3. The electrolyte for electrochemical decontamination according to claim 1, wherein the electrolyte for electrochemical decontamination comprises 60% by mass of the phosphoric acid, 6 g/L of the oxalic acid, 5 g/L of the citric acid, 2 g/L of the tartaric acid, 2.5 g/L of the hydrogen peroxide, and 10 g/L of the glacial acetic acid.

4. A preparation method of the electrolyte for electrochemical decontamination according to claim 1, comprising the following step: mixing the phosphoric acid, the oxalic acid, the citric acid, the tartaric acid, the hydrogen peroxide and the glacial acetic acid with water to obtain the electrolyte for electrochemical decontamination.

5. A preparation method of the electrolyte for electrochemical decontamination according to claim 2, comprising the following step: mixing the phosphoric acid, the oxalic acid, the citric acid, the tartaric acid, the hydrogen peroxide and the glacial acetic acid with water to obtain the electrolyte for electrochemical decontamination.

6. A preparation method of the electrolyte for electrochemical decontamination according to claim 3, comprising the following step: mixing the phosphoric acid, the oxalic acid, the citric acid, the tartaric acid, the hydrogen peroxide and the glacial acetic acid with water to obtain the electrolyte for electrochemical decontamination.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) The present disclosure provides an electrolyte for electrochemical decontamination, which is an aqueous solution including the following solutes: phosphoric acid, oxalic acid, citric acid, tartaric acid, hydrogen peroxide and glacial acetic acid.

(2) In the present disclosure, the electrolyte for electrochemical decontamination includes 45% to 80%, preferably 50% to 70%, more preferably 55% to 65% by mass of phosphoric acid. In the present disclosure, the phosphoric acid is a moderate-strength inorganic acid and can cause different degrees of corrosion to metal materials, thereby being conducive to removing a contamination layer on the surface of radioactively contaminated stainless steel scrap.

(3) In the present disclosure, the electrolyte for electrochemical decontamination includes 5 g/L to 10 g/L, preferably 5.5 g/L to 8 g/L, more preferably 6 g/L of oxalic acid. In the present disclosure, the oxalic acid is capable of well complexing with metal ions such as iron ion and chromium ion, promoting continuous anodic dissolution of metals and preventing cathodic reduction thereof, thus being conducive to decontamination reaction.

(4) In the present disclosure, the electrolyte for electrochemical decontamination includes 1 g/L to 10 g/L, preferably 2 g/L to 7 g/L, more preferably 5 g/L of citric acid. In the present disclosure, the citric acid is capable of well complexing with iron ions, thereby further promoting the dissolution of iron, the principal component in stainless steel.

(5) In the present disclosure, the electrolyte for electrochemical decontamination includes 1 g/L to 2 g/L, preferably 1.5 g/L to 2 g/L, more preferably 2 g/L of tartaric acid.

(6) In the present disclosure, the electrolyte for electrochemical decontamination includes 5 g/L to 10 g/L, preferably 6 g/L to 10 g/L, more preferably 10 g/L of glacial acetic acid. In the present disclosure, the glacial acetic acid and the tartaric acid are highly corrosive to stainless steel and can facilitate the removal of the contamination layer on the surface of radioactively contaminated stainless steel scrap.

(7) In the present disclosure, the electrolyte for electrochemical decontamination includes 1 g/L to 5 g/L, preferably 2 g/L to 4 g/L, more preferably 2.5 g/L of hydrogen peroxide. In the present disclosure, the hydrogen peroxide has strong oxidizing property and is conducive to the removal of the contamination layer on the surface of radioactively contaminated stainless steel scrap.

(8) In the present disclosure, a solvent of the electrolyte for electrochemical decontamination is water. The water is not particularly limited herein, and commonly used water in the art can be used.

(9) The present disclosure provides a preparation method of the electrolyte for electrochemical decontamination described above, including the following step: mixing phosphoric acid, oxalic acid, citric acid, tartaric acid, hydrogen peroxide and glacial acetic acid with water to obtain the electrolyte for electrochemical decontamination.

(10) The method of mixing is not particularly limited herein, and a mixing method which is well known to a person skilled in the art and can enable complete dissolution and full mixing of different raw materials can be used. Reagents for preparing the electrolyte are preferably industrial pure reagents.

(11) The present disclosure further provides application of the electrolyte for electrochemical decontamination described above in decontamination of radioactively contaminated stainless steel scrap. In a specific embodiment of the present disclosure, the application is preferably as follows: adding the electrolyte for electrochemical decontamination to an electrolytic tank, immersing a portion to be decontaminated of radioactively contaminated stainless steel scrap in the electrolyte for electrochemical decontamination, and connecting the stainless steel to an anode for electrolysis. In the present disclosure, the electrolysis occurs under the following conditions: a voltage, preferably a pulsed voltage which preferably has a strength of 24 V; an electric current density, preferably 0.5-2 A/cm.sup.2; and electrolysis time, preferably 120 seconds.

(12) During electrochemical decontamination of radioactively contaminated scrap metals by the method provided in the present disclosure, little decontamination solution may be left when equipment stops running, and minimal secondary waste solution may be generated. In the present disclosure, after the decontamination is completed, the electrolyte cannot be reused and thus turns to waste electrolyte. The major components of the waste electrolyte are substances such as phosphoric acid and oxalic acid, i.e., main components for preparing iron phosphate. The waste electrolyte is preferably subjected to glass solidification. The specific method of the glass solidification is not particularly limited herein, and a method well known to a person skilled in the art can be used.

(13) The technical solutions in the present disclosure will be clearly and completely described below in conjunction with the examples of the present disclosure.

(14) Pollution episodes of radioactively contaminated stainless steel sheets used in the examples are as follows: α contamination: 100 Bq/cm.sup.2, and βcontamination: 2000 Bq/cm.sup.2.

Example 1

(15) Electrochemical decontamination was performed on radioactively contaminated stainless steel scrap by using the electrolyte for electrochemical decontamination provided in the present disclosure. The used electrolyte was composed of 60wt % of phosphoric acid, 5 g/L of oxalic acid, 2 g/L of citric acid, 1 g/L of tartaric acid, 2.5 g/L of hydrogen peroxide, and 5 g/L of glacial acetic acid, and water as a solvent.

(16) An appropriate amount of the electrolyte was added to an electrolytic tank. A portion to be decontaminated of a radioactively contaminated stainless steel sheet was immersed in the electrolyte for electrochemical decontamination, and the stainless steel sheet was connected to an anode for electrolysis under the conditions of a pulsed voltage of 24 V and an electric current density of 0.5-2 A/cm.sup.2 for 120 seconds. The decontaminated stainless steel sheet was then rinsed with deionized water. It was measured that the stainless steel sheet had a weight loss of 6.4 mg/cm.sup.2. The surface radioactive levels of the stainless steel sheet were measured as follows: α contamination below a detection line, and β contamination <0.2 Bq/cm.sup.2, which met the requirement of reuse.

(17) The resulting waste solution and residues from the electrolysis were fed into a glass solidification system for the preparation of iron phosphate glass.

Example 2

(18) Electrochemical decontamination was performed on radioactively contaminated stainless steel scrap by using the electrolyte for electrochemical decontamination provided in the present disclosure. The used electrolyte was composed of 45% of phosphoric acid, 5 g/L of oxalic acid, 10 g/L of citric acid, 2 g/L of tartaric acid, 2.5 g/L of hydrogen peroxide, and 5 g/L of glacial acetic acid, and water as a solvent.

(19) The operation method for electrolytic decontamination was the same as that in Example 1. It was measured that the stainless steel sheet had a weight loss of 8.0 mg/cm.sup.2. The surface radioactive levels of the stainless steel sheet were measured as follows: α contamination below a detection line, and β contamination <0.2 Bq/cm.sup.2, which met the requirement of reuse.

(20) The resulting waste solution and residues from the electrolysis were fed into a glass solidification system for the preparation of iron phosphate glass.

Example 3

(21) Electrochemical decontamination was performed on radioactively contaminated stainless steel scrap by using the electrolyte for electrochemical decontamination provided in the present disclosure. The used electrolyte was prepared from 50% of phosphoric acid, 10 g/L of oxalic acid, 6 g/L of citric acid, 1/L of tartaric acid, 5 g/L of hydrogen peroxide, and 10 g/L of glacial acetic acid, and water as a solvent.

(22) The operation method for electrolytic decontamination was the same as that in Example 1. It was measured that the stainless steel sheet had a weight loss of 5.7 mg/cm.sup.2. The surface radioactive levels of the stainless steel sheet were measured as follows: α contamination below a detection line, and β contamination <0.2 Bq/cm.sup.2, which met the requirement of reuse.

(23) The resulting waste solution and residues from the electrolysis were fed into a glass solidification system for the preparation of iron phosphate glass.

(24) The foregoing are merely descriptions of preferred embodiments of the present disclosure. It should be noted that a person of ordinary skill in the art can make several improvements and modifications without departing from the principle of the present disclosure, and such improvements and modifications should be deemed as falling within the protection scope of the present disclosure.