A Study on the Performance of Flocculating agent for Radioactively Contaminated Soilby Soil Washing Process
SunIl Kim and JongSoon Song*Department of Nuclear Engineering, Chosun University
309 Pilmun-daero, Dong-gu, Gwangju 61452, Republic of Korea

Key words; Soil Washing, Flocculating Agent, Soil remediation

Abstract

Radioactive substances that are discharged in the process of nuclear power plant Decommissioning or
facility maintenance cause soil pollution. Such soil pollution requires decontamination in order to ensure
people’s residence and reuse of land as an industrial site. Among the various soil restoration technologies,
this paper selected soil washing technology, which has actual example of being used on soils polluted byradioactive substances in and out of the country. Soil washing process uses cleansing agent to weaken thesurface tension of soil and Cs in order to separate soil and Cs. In order to enhance efficiency of process byreusing the cleansing water in soil washing process, Sedimentation agent was used in the cleansing water toperform the experiment for studying the performance of removing micro-soil and Cs. Also, Cs removal
experiment results using ICP-OES and rate of combination between Cs and soil using Visual MINTEQ
Code were found out in order to compare Cs and micro-soil removal performance in cleansing water.

1. Introduction
Radioactive substances are discharged in theprocess of nuclear power plant Decommissioning andfacility maintenance. Major substances of such
discharged
radioactivesubstanceswheredecontamination by soil pollution ought to beconsidered include Cs-137 and I-131.
Among these, Cs-137 should be considered withpriority, because Cs-139 is water-soluble and highlytoxic, producing harmful effects when it enters thebody through breathing or consumption. Technologythat has actually been used to remove Cs includes soilwashing, soil cleansing, and current electricity, andthe technology which decontaminates a wide range ofsoil in a short period of time and shows a relatively
high decontamination efficiency is the soil washingprocess [1].
Soil washing process uses appropriate cleansing
agent to weaken the surface tension of soil and Cs inorder to separate the soil and Cs. The major factor
that determines decontamination efficiency is theselection of cleansing water. While thedecontamination process which uses acidic cleansing
water weakens surface tension greater than the onethat uses water, therefore separating Cs and soil withhigh efficiency, it produces much acid effluent. Using
water instead of acidic cleansing water, which
produces great amount of effluent, and reusing
cleansing water using sedimentation agent may
ensure a more economical and efficient process. In

order to enhance the efficiency of soil washingprocess, which uses water as the cleansing water, byreusing the cleansing water, this study used
sedimentation agent to perform the experiment for
testing the removal performance of micro-soil and Cs
that are included in the cleansing water. Also, inorder to compare the experiment results through
ICP-OES, it used Visual MINTEQ Code to compare
the removal performance of Cs and micro-soil incleansing water.
2. Soil Washing Process
2.1 Soil Remediation techniques
In general, soil restoration technology largely
consists of Physicochemical, biological, and thermal
process as shown in Table 1. Among the soil
restoration technologies, biological process, wheremuch time is required in case of pollution byradioactive substance, as well as thermal process,where the efficiency of removing radioactive
substance is low, is not appropriate to be used.
Therefore, soil restoration technologies for removing
radioactive substances are Physicochemical processes
with methods that can process heavy metals, such as
soil washing, current electricity, and heap-leaching[2].

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japanwater to conduct the experiment on Cs and soil
removal performance.

Table 1. Soil remediation techniques
Classification

Techniques

FeatureSoil-washing

Electro-kinetic
Physicochemicaltreatment
Soil-flushing· Easy to use incombination with otherprocesses· Soil remediation timeis generally shortand efficiency is highHeap-leaching

Biodegradation
Biologicaltreatment

Land farming

Naturalattenuation

Thermaldesorption
Thermaltreatment

Vitrification

Pyrolysis· Efficiency in terms ofheavy metals is
generally low· Requires time equal tohalf-life of nuclear
species to exhibit
decontamination
efficiencyforradioactivematerials· High decontamination
efficiency
forradioactive
nuclear species but noreduction of waste
volume· Secondary waste suchas ash, etc.

2.2 Soil washing techniques
Among
Physicochemicalsoil
remediation
technologies, soil washing process shows highdecontamination efficiency within a relatively shortperiod of time, therefore having actual cases of being
utilized in soil polluted by radioactive substances.
Actual domestic case example includes the case of
Korea Atomic Energy Research Institute (KAERI)
for decontaminating the soil near TRIGA
Mark-Ⅱ&Ⅲ that included Co-60 and Cs-137 [3].
Foreign case includes the case of Oak Ridge National
Lab using soil washing for Cs-137 [4].
Soil washing process largely consists of Size
Reduction Equipment, Screening Equipment,
Separation Equipment, Cyclone Equipment, andWaste Water Treatment Equipment.
As shown above, a large quantity of cleansing water
is required in order to remove Cs in soil. In theprocess, reusing the waste water from Waste Water
Equalization Tank by circulating it without
discharging it will lead to a more efficient soil
washing process. For efficient reuse of cleansingwater, sedimentation agent was put into the cleansing

3. Experimental Method
To reuse the cleansing water for soil washingprocess, Sedimentation agent (J-AF, JeonTechCo.,Ltd.) was used to perform the experiment on
micro-soil and Cs removal performance. In naturalenvironment in general, Cs is strongly united withsoil with small particle size. In order to create anenvironment where Cs is mostly adsorbed on soil
with small particle size, the soil was separated using
filter into approximately 38μm, and the filtered soil
was dried for 20 minutes using vacuum drier. Also, inorder to ensure that the soil and Cs can sufficiently beunited, 1g of filtered soil was prepared with Cs
concentrations of 0.1, 1, 2, 5 and 10mmolee and thenstirred at 250rpm for 24 hours. CsNO 3 was used as Cs
specimen, temperature was 23℃, and pH was 6.5.
In the first experiment, Sedimentation agent was used
to analyze maximum rate of removal and rate ofremoval by time. For the experiment, 0.1g ofSedimentation agent was put into soil including Cs
that has been stirred for 24 hours, stirred for 5
minutes at 450rpm to extract supernatant, and filteredusing 0.2μm(Cellulose Nitrate Membrance Filter) in
consideration of Cs particle size. Finally, Csremaining in experiment solution was analyzed using
ICP-OES (Parkin Elaer, US/Optima 2100).
Also, to study Cs removal performance ofSedimentation agent by time, supernatant of theexperiment solution was extracted five times, by 1
minute each time, and filtered using 0.2μfilter. Then,Cs remaining in experiment solution was analyzed
using ICP-OES. The graph is shown in Fig. 1.
With difference in Cs concentrations at 0.1, 1, 2, 5,

Fig 1. Sediment removal performance for each timeFig 2. Sediment removal performance for each concentration

10 mmole, 0.1g of Sedimentation agent was injected
to test Cs removal performance as shown in Fig. 2.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan4. Results and discussion
When using 0.1g of J-AF Sedimentation agent in theexperiment, maximum Cs removal performance wasapproximately 88% at Cs concentration of0.1mmolee, approximately 85.8% at concentration of
1mmolee, approximately 85% at concentration of2mmolee, approximately 71% at concentration of
5mmolee, and approximately 67% at concentration of
10 mmole.
To review maximum Cs removal performance thatwas resulted from the experiment using ICP-OES,
Visual MINTEQ Code, which is a chemical
equilibrium code, was to derive the binding rate of Cs
and soil, and turbidity was multiplied on the binding
rate to compare the values. Turbidity is measured tostudy soil removal rate of Sedimentation agent.
Visual MINTEQ code is a chemical equilibrium
model that was developed to calculate equilibrium,sorption, adsorption, etc. in an aqueous solution. It isa code that uses Visual Basic Interface based on
MINTEQA2 software of USEPA (KTH, Jon Petter
Gustafsson)[5].
To apply soil and Cs concentration on the Input valueof Visual MINTEQ Code, replaceable cation andanion concentrations in soil were applied byconverting them into units of ppm [6]. Binding of Cs
and soil using Visual MINTEQ Code is shown inTable 2. The amount of replaceable cation and anion
is shown in Table 3 [7]-[8].

Table 2. Combining soil with Cs through Visual MINTEQ CodeCsCsCl

0.1
8.433
47.877

Cs concentration (mmole)
12
5
8.605
8.801
9.431
47.946 48.014 48.172

10
10.63348.271

CsSO

15.41715.23015.02814.45513.595CsNO

28.27228.21928.15727.94327.502

Table 3.Concentrations of cations and anions in soil
K
1
Cl
4

Soluble cation and anion (cmolc/kg)
CaMg
5.3
1.7
Concentration of Anion(cmolc/kg)
N0
7.1

PO
4.8

SO
7.7

Also, turbidity (LAMotte 2020, Turbidity Meter) was
measured to study soil removal rate in the experiment
solution. Turbidity was conducted in the same
conditions with those of the experiment using
Sedimentation agent. Initial turbidity of muddy water
was 47.2NTU. After injecting 0.1g of Sedimentation
agent, the solution was stirred for 5 minutes, and thensupernatant was collected and filtered using 0.2μm
filter to measure turbidity. Turbidity after using
Sedimentation agent was measured to be 4.39NTU,
showing that Sedimentation agent removes soil withCs by approximately 90%.
Fig 4 shows a comparison of the values from using
ICP-OES with the values multiplying the soil
removal rate of the sedimentation agent obtained
from measuring turbidity (NTU) before and after
adding the sedimentation agent by the binding rate
between Cs and the soil obtained from the code.

Fig 3. Comparison of ICP-OES and Visual MINTEQ Code

The Cs removal performance of the sedimentation
agent using ICP-OES and the product of the codevalue and turbidity indicated conservative trends atlower concentrations, but it was shown that values
differed in the approximately 2 mmole or higher
concentration levels. Based on this, it is expected that
the Code and ICP values will exhibit sufficiently
similar trends at concentrations of 2 mmole andhigher as well if sufficient stirring time of 24 hours ormore is allowed for the Cs and soil.
5. Conclusions
Methods for removing radioactive nuclide that is
exposed to soil when decommissioning or repairing
power plant have been applied in domestic andforeign cases. Soil washing process, which has arelatively short decontamination period, is mostappropriate for use. Experiment result of Cs removalusing Sedimentation agent at an environment thatassumes to use soil washing process that uses water
as the cleansing agent showed that maximum of
approximately 90% of Cs was removed at Cs
concentration of 0.1 mmole. This indicates thatcyclical recycling of cleansing water is possible. This
result shows that soil washing process can beoperated in a very efficient and economical manner
within a short period of time. Also, the value of Cs
removal performance of Sedimentation agent using
ICP-OES and the value of multiplying the binding
rate of soil and Cs by soil removal rate ofSedimentation agent using Visual MINTEQ Codeshowed a similar trend. If the actual data obtained
from analyzing the soil component around the actual

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

NPPs and estimating the Cs and the amount ofradioactive materials, which will be exposed to thesoil, can be applied to the code, it is possible toobtain more accurate values in the future. And it isanticipated that the main output from the code as themain data will be used to predict the rate of soil
remediation and to select a decontamination method
satisfying the site release criteria.
6. Reference[1] J. S. Song, S. S. Shin, and S. I. Kim, A Study on
The Assessment of Treatment Technologies forEfficient
RemediationofRadioactively-ContaminatedSoil,KoreanRadioactive Waste Society, Vol. 14, No. 3, pp.
245-251, 2016.
[2] M. J. Kim, Soil Remediation Technology andCasebook, Pergamon Press, pp. 3-99, 2002.
[3] H. J. Won, G. N. Kim, W. G. Choi, C. H. Jung,and W. J. Oh, Decontamination of Soil from theResearch Reactor Site, Korea Nuclear Society, Vol. 1,2002.
[4] United States Environmental Protection Agency,
Technology Reference Guide for Radioactively
Contaminated Media, EPA 402-R-07-004, 2007.
[5] J. P. Gustafsson, Visual MINTEQ 3.1 user guide,KTH, Sweden, 2010.
[6] R. N. Carrow, and R. R. Duncan, Salt-Affected
Turfgrass Sites, John Wiley &Sons, pp. 49-70, 1998.
[7] G. J. Lee, B. G. Kang, K. S. Kim, I. H. Kim, and J.
U. Han, Investigation of Chemical Properties of theJujube Orchard Soils at Boeun Region in Chungbuk,Korean Journal of Environmental Agriculture, Vol.
33, pp. 24-29, 2014.
[8] B. Y. Chung, K. S. Lee, M. K. Kim, Y. H. Choi,M. K. Kim, and J. Y. Cho, Physico-Chemical
Properties of Rainfall Interception Culture and OpenField Culture Soils of Rubus sp. in Gochang-gun,Jeollabuk-do, Korean J. Soil Sci. Fert., Vol. 41, No.5,
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6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan