Development of electrokinetic-flushing technology for the remediation of contaminated soil around nuclear facilities

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Abstract

The effects of a flushing by a pump on an electrokinetic-flushing remediation of contaminated soil were estimated. The soils were sampled from the sites around nuclear facilities which were built on a high hydro-conductivity of sandstone. An electrokinetic-flushing equipment with a pump was manufactured to estimate the effect of a flushing on an electrokinetic-flushing remediation. In order to select an optimal reagent suitable to the characteristics of a soil near nuclear facilities, 4 experiments were executed with 4 candidate reagents selected from 12 reagents and the results of the experiments are as follows. The removal efficiencies of cobalt and cesium from the contaminated soil with the acetic acid were the highest, which were 92.1% and 83.1%, respectively. The effluent solution volume generated from an electrokinetic remediation was very smaller and it was 5% below that from a soil washing. Next, the results from a comparison of an electrokinetic-flushing remediation and an electrokinetic remediation revealed that the removal efficiencies of Co2+ and Cs+ by an electrokinetic-flushing remediation for 5 days were increased by 25% and 35% when compared to those by the electrokinetic remediation, but the effect of a flushing by the electrokinetic-flushing equipment started to decrease after 5 days. The removal efficiencies of Co2+ and Cs+ by an electrokinetic-flushing remediation for 15 days were increased by 6.8% and 7.7% when compared to that by an electrokinetic remediation. Namely, the higher the hydro-conductivity of a soil was, the larger the effect of a flushing was on an electrokinetic-flushing remediation.

Introduction

South Korea has many nuclear power plants and a research reactor. As such, the soil around these nuclear facilities can become contaminated with radionuclides from a long-term operation of these facilities. The electrokinetic process holds great promise for a remediation of polluted soils, as it has a high removal efficiency and is time effective for a low permeability. An electrokinetic remediation can be used to treat soils contaminated with inorganic species and radionuclides [1], [2]. The main mechanisms of a contaminant’s movement in an electrical field involved in electrokinetic technology are an electromigration of ionic species and electroosmosis. Electromigration probably contributes significantly to the removal of contaminants, especially at high concentrations of ionic contaminants and/or a high hydraulic permeability of a soil [3]. The cathode reaction should be depolarized to avoid the generation of hydroxides and their transport in a soil. The selected liquids, also known as purging solutions, should induce favorable pH conditions in a soil, and/or interact with the heavy metals, so that these heavy metals are removed from a soil [4]. Most radioactive facility sites have been contaminated by the leakage of radioactive waste-solution due to the corrosion of concrete and pipes by a long-term operation of waste-solution tanks and connection pipes, set up in the underground around nuclear power plants.

Electroosmosis moves a pore solution in response to an electric field, typically towards a cathode because of the negative surface charge of a soil. The magnitude of the transport velocity due to an electromigration and electroosmosis is directly related to the electric potential gradient. Therefore remediation efficiency can be improved through an increase of the electric potential gradient by a pumping. Recently, researchers have been investigating whether this method can be used to remove subsurface contaminants and they have compiled the published research on the use of electrokinetic techniques to decontaminate fine-grained soils, and discussed some of the problems that occur during this process [5], [6], [7]. An electrolytic reactor was used for a greywater reuse [8]. An electrokinetic remediation has been applied to remove heavy metals from mine trailing soils [9]. Recently researchers have tried to develop soil washing techniques in which soil-bound contaminants are transferred to a liquid phase by a desorption and solubilization. Several washing solutions have been investigated, such as water, acids, bases, chelating agents, alcohols and other additives [10], [11]. In practice, acid washing and a chelator soil washing are the two most prevalent removal methods [12], [13], [14].

The research reactor in Seoul, South Korea is under decommissioning work. Because the research reactor was constructed on a hard sandstone rock like the other Korea nuclear power plants, the contaminated soil around the research reactor contains a lot of sand and it has a higher hydro-conductivity. It has been supposed that an electrokinetic-flushing remediation is a suitable technology in consideration of the soil characteristics near the nuclear facility, which has merits of both an electrokinetic remediation and a soil flushing method.

The object of this study was to estimate the effect of a flushing by a pump on an electrokinetic-flushing remediation. The electrokinetic-flushing equipment with a pump was manufactured. In order to select an optimal reagent suitable to the soil characteristics, four experiments were executed with four candidate reagents using the electrokinetic equipment. In order to estimate the effect of a flushing by a pump on an electrokinetic-flushing remediation, different hydro-conductivities of soils were decontaminated with different injection flushing rates using the electrokinetic-flushing equipment.

Section snippets

Description of a soil

South Korea currently has about 20 nuclear power plants and a research reactor. Because most nuclear facilities in Korea have been constructed on a hard sandstone rock, the contaminated soil around a nuclear facility contains a lot of sand, and it has a higher hydro-conductivity. Experimental soil was extracted from the site around the research reactor, since it might be partially contaminated with 60Co and 137Cs. But a soil which was not contaminated was excavated and was artificially

The selection of an electrolyte reagent suitable for an electrokinetic remediation

Table 2 shows the removal efficiencies of Co2+ and Cs+ and the effluent volume as experiment results under different experiment conditions. Fig. 4 shows a variation of the electrolyte flow rate versus the remediation time at the cathode compartment during Tests I–IV. The electrolyte flow rate from the soil cell was reduced with the remediation time. Movement of the pore solution was mainly due to an electroosmosis. When EDTA was used as an electrolyte reagent, the average electrolyte flow rate

Conclusion

Electrokinetic-flushing equipment with a pump was manufactured to investigate the effect of a flushing on an electrokinetic-flushing remediation. In order to select an optimal flushing reagent suitable for the radioactive soil characteristics, four experiments were executed with four candidate-flushing reagents and the results of the experiments are as follows:

  • (a)

    The removal efficiencies of cobalt and cesium from the contaminated soil with the acetic acid were highest, which were 92.1% and 83.1%,

References (26)

  • K. Reddy et al.

    J. Hazard. Mater.

    (2001)
  • C. Chaiyaraksa et al.

    Chemosphere

    (2004)
  • B. Sun et al.

    Environ. Pollut.

    (2001)
  • A. Barona et al.

    Environ. Pollut.

    (2001)
  • S. Tampouris et al.

    J. Hazard. Mater.

    (2001)
  • Y. Yang et al.

    Chemosphere

    (2001)
  • J. Virkutyte et al.

    Sci. Total Environ.

    (2002)
  • S. Pamukcu et al.

    Environ. Prog.

    (1992)
  • K. Reddy et al.

    J. Geotech. Geoenviron. Eng.

    (2003)
  • F. Braud et al.

    Int. J. Environ. Anal. Chem.

    (1998)
  • S.O. Kim et al.

    Water Air Soil Pollut.

    (2001)
  • M.M. Page et al.

    J. Environ. Eng., ASCE

    (2002)
  • C.H. Shin et al.

    J. Ind. Eng. Chem.

    (2007)
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