PROCESS FOR TREATING WASTE LIQUIDS OF ACID DECONTAMINATION AGENTS

Abstract: A new process for treating waste liquids of acid decontamination agent is disclosed which comprises the steps of neutralizing a waste liquid of acid decontamination agents with an alkali, filtering out suspended matter from the neutralized waste liquid using a filter, removing inhibitors from the filtered waste liquid by adsorption with activated charcoal, removing radioactive ions from the waste liquid treated by activated charcoal with a chelate resin, concentrating the chelate resin-treated waste liquid by evaporation, and bituminizing the concen­ trate obtained in the preceding step.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT : The present invention relates to a process for treating waste liquids of acid decontamination agents which result from washing equipment contaminated by radioactivity with a cleaning fluid. A method is known for decontaminating contaminated equipment using an organic acid such as oxalic acid and citric acid as a cleaning fluid. The waste liquid of such an acid decontamination agent is usually disposed of after solidification by cementation because of their radioactivity. However, it is desirable that such waste liquids of acid decontamination agents be solidified by bituminization (asphalt solidification) capable of more effective volume reduction. Unfortunately, bituminization is impracticable for waste liquids containing organic acids (such as oxalic acid and citric acid), inhibitors, LiOH, and radioactivity for the reasons mentioned below. (1) Since these waste liquids contain inhibitors which bring about foaming during evaporation and concentration, the separation of radioactivity by an evaporator becomes less effective. (2) The waste liquids also contain organic acids which promote corrosion of the evaporator. (3) The waste liquids have high radioactivity which contaminates the evaporator and bituminizing apparatus and also creates a danger of exposure during operation. OBJECT AND SUMMARY OF THE INVENTION : The present invention has been made in view of the prior art technology mentioned above. It is an object of the present invention to provide a process for treating waste liquids of acid decontamination agents by bituminization. This process is defined in claim 1. BRIEF DESCRIPTION OF THE DRAWING : FIG. 1 is a schematic diagram showing an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS : The process of the present invention starts with neutralizing a waste liquid of acid decontamination agents with an alkali, thereby adjusting its pH value to 6.5 ∼7.5. The alkali that can be used for neutralization includes, for example, NaOH, KOH, and LiOH. The neutralized waste liquid is subsequently filtered for removal of suspended matter. This step may be done using a bobbin-shaped filter or a membrane filter that is capable of filtering out particles of about 1 to 10 µm in diameter. The filtered waste liquid free of suspended matter is subsequently treated with activated charcoal for removal of inhibitors. Activated charcoal derived from coconut or coal would suit this step. The inhibitor-free waste liquid is freed of ionic radioactive materials (⁵⁸Co, ⁶⁰Co, ⁵⁴Mn, ⁵⁹Fe, etc.) with a chelate resin. The chelate resin includes, for example, a compound of the formula below which is formed by introducing imino-diacetate groups into styrene-divinylbenzene copolymer, and a compound of the formula below which is formed by introducing polyamine groups into styrene-divinylbenzene copolymer. (Here, n is an integer.) The chelate resin reacts with ionic radioactive materials as illustrated below. where R denotes the skeleton of the chelate resin, and M²⁺ denotes a radioactive ion. The waste liquid which has undergone the above-mentioned steps for neutralization and the removal of suspended matter, inhibitors, and ionic radioactive materials can be readily concentrated by any existing evaporator because it is no longer corrosive and foaming and has an extremely low level of ionic radioactivity. The resulting concentrate can be bituminized in a usual way to reduce its volume to a great extent. Embodiment An embodiment of the present invention will be described with reference to the schematic diagram shown in FIG. 1. In FIG. 1, there is shown a waste liquid tank 2 to store a waste liquid of acid decontamination agents containing organic acids (citric acid and oxalic acid, for example), inhibitors, LiOH, and radioactive materials. To this waste liquid is added NaOH from an alkali tank 1 by means of a supply pump 3, so that the waste liquid is adjusted to approximately pH 7. This neutralization step makes the corrosive organic acids harmless. During the neutralization, the waste liquid in the waste liquid tank 2 is stirred by a waste liquid transfer pump 4, with a valve 5 opened and another valve 6 closed. The pH of the waste liquid is controled by regulating the supply pump 3 according to signals from a pH meter 7. When the neutralization of the waste liquid is completed, the valve 5 is closed and the valve 6 is opened and the neutralized waste liquid is transferred to a cartridge-type filter 8 (with an effective mesh of about 0. 5 µm) for removal of crud and suspended matter. The filtered waste liquid is subsequently transferred to an activated charcoal column 9 (containing 50 ℓ of activated carbon for 300 ℓ/hr of waste liquid) for removal of inhibitors which may cause the waste liquid to foam. The waste liquid is finally transferred to a chelate resin column 10 (containing 50 ℓ of chelate resin for 300 ℓ/hr of waste liquid) for removal of ionic radioactive materials. (The chelate resin may be the one that is formed by introducing imino-diacetate groups into the styrene-divinylbenzene copolymer produced by Takeda Seiyaku Co., Ltd.) The waste liquid which is now free of suspended matter, foaming components, radioactivity, and corrosive substances after having undergone the above-mentioned steps, is sufficiently concentrated by a conventional evaporator 11. The concentrate is then bituminized at 200°C by means of a bituminizing apparatus 12 and becomes a bituminized solid 13. The process of the present invention compares favorably with the conventional cementation process as shown below. Foaming in evaporator Corrosiveness Radioactivity Exposure dose Volume of solidified mass Cost Present invention None None 1 1 1 1 Conventional process Yes Yes 1000 10 4 2 The process of the present invention permits waste liquids of acid decontamination agents to be disposed of by bituminization capable of volume reduction to a great extent. Therefore, it produces a pronounced industrial effect.

Claims: A process for treating a waste liquid containing organic acid decontamination agents, comprising the steps of adding an alkali into a waste liquid containing organic acid decontamination agents so as to neutralize the waste liquid, filtering out suspended matter from the neutralized waste liquid by means of a filter, removing inhibitors from the effluent out of the filter by adsorption with activated charcoal, removing, by means of a chelate resin, ionic radioactivity from the effluent from which inhibitors have been removed, concentrating by evaporation the effluent out of the chelate resin bed, and solidifying the concentrate obtained in the preceding step with asphalt. A process for treating a waste liquid containing organic decontamination agents as set forth in Claim 1, wherein one member selected from the group consisting of sodium hydroxide, potassium hydroxide, and lithium hydroxide is used as an alkali. A process for treating a waste liquid containing organic decontamination agents set forth in Claim 1, wherein the pH of the liquid is adjusted to between 6.5 and 7.5 by neutralization.

Inventors: KAKIMOTO, AKIRA, MATSUMOTO, HIROYO, NAKAYASU, IWAO, YONEKURA, KAZUO
Applicants: MITSUBISHI JUKOGYO KABUSHIKI KAISHA
Application year: 1988
Main classification: G21F9
IPC codes: G21F9