Removal of 137Cs from contaminated soil using pilot electrokinetic decontamination equipment
Abstract
The removal efficiencies of 137Cs for 10 days were 50 -70%. The removal efficiencies according to the elapsed time after 10 days were reduced. When an electric current density of 25 -75 mA/ cm2, sulfuric acid, nitric acid, acetic acid as electrolyte, a 0.5 -2.0 cm/min hydraulic conductivity of soil were applied, respectively, the time required for the removal efficiency of 137Cs to reach 80% was 20 -30 days. For improving removal efficiency of 137Cs from contaminated soil, it is necessary to increase an electric current density using sulfuric acid as an electrolyte and to decrease hydraulic conductivity of soil in the soil cell.
Keywords
Download Options
Introduction
The contaminated soil around the underground radioactive waste solution tank of the TRIGA reactor has a slightly high hydro-conductivity and has been mainly contaminated with 137Cs due to corrosion of a connection pipe over the past 30 years. Recently, a soil washing method has been applied to remove 137Cs from the radioactive soil, but it appears that the removal efficiency of 137Cs from fine soil is lower and a lot of reagent effluent was generated [1,2,3]. An electrokinetic (EK) decontamination method provides a high removal efficiency of 137Cs and generates a little waste effluent. It was suggested that an EK decontamination method is a suitable technology for the removal of 137Cs from soil in consideration of the soil characteristics near the TRIGA reactor [4].
Most recently, EK field has been developed to enhance the remediation of contaminated soils [5,6,7]. Many extraction solutions such as diluted salt or diluted acid only dissolve a limited portion of the liable metals and metalloids in contaminated soils [8]. Recent studies reported that the EK, as an assisted method, was effective on promoting the release of heavy metals from solid-phase components and reducing the usage of washing solution [6,9]. The EK process involves introducing EK by inserting the electrodes into the contaminated soils [10].
Once the EK remediation process is over, extraction and removal of heavy metal contaminants are accomplished by electroplating at the cathode, precipitating at the cathode, pumping water near the cathode or anode, or reacting with ion exchange resins [11]. The efficiency of the EK method can be enhanced by coupling with other remediation technologies such as oxidation-reduction, bioremediation, permeable reactive barrier, and so forth [12,13]. While previous studies have shown that EK technique is effective for remediation of Cs in low-permeability soil such as clays [14, 15], a number of recent studies have also investigated the performance of EK remediation for Cs contaminated sandy soil around nuclear facilities in South Korea [16,17].
EK involves using a direct or alternating current with electrodes inserted into contaminated soils. When a low intensity electric field is applied, H+ is generated around the anode electrode through the effect of water electrolysis. As a result, more metals are demobilized under the acid condition around the anode electrode [18]. In addition, enhanced mobilization processes occur in soils resulting in the transport of metal ions from the anode to the cathode electrode [19]. Water present in soil is able to move towards the cathode through soil pores by electroosmosis while cations move to the cathode through electromigration [20]. The migration of ions makes it possible for the subsequent removal of soluble metals or immobilization with oxides, hydroxide and carbonates during the phytoremediation [21]. However, the detailed mechanisms of releasing/mobilization of metals/metalloids with EK coupled with phytoremediation are not clearly understood.
In this study, pilot EK decontamination equipment suitable for the geological characteristics of the TRIGA reactor site was developed for the removal of 137Cs from contaminated soil. The influences in which the hydraulic conductivity of soil in the soil cell, the electric current between electrodes, and the electrolyte in chambers reach the removal efficiency of 137Cs from soil were investigated experimentally using the manufactured pilot EK decontamination equipment in order to obtain a high removal efficiency of 137 Cs during a short period.
Conclusion
To ensure a high -quality product, diagrams and lettering MUST be either computer -drafted or drawn using India ink. The removal efficiencies of 137Cs from contaminated soil in manufactured pilot EK decontamination equipment were proportional to the elapsed time. The removal efficiencies of 137Cs for 10 days were 50 -70%. In addition, the removal efficiencies according to the elapsed time after 10 days were reduced. When an electric current density of 25, 50, and 75 mA/cm2 was applied, the time required for the removal efficiency of 137Cs to reach to 80% was 25, 20, and 15 days. In addition, when sulfuric acid, nitric acid, acetic acid a s an electrolyte in the chambers was applied, the time required for the removal efficiency of uranium to reach 80% was 30, 25, and 20 days. Moreover, when a 0.5, 1.0, and 2.0 cm/min hydraulic conductivity of soil in the soil cell was applied, the time required for the removal efficiency of 137Cs to reach 80% was 20, 25, and 30 days.
