Remediation of Contaminated Soil with Radium-226 and 228 by Various Methods

Abstract


Introduction
Oil and gas extraction produces naturally occurring radioactive material (NORM), and contains 226Ra (1620 years from the uranium-238 decay chain) and 228Ra (5.8 years from the thorium-232 decay chain) radionuclides (Abdelbary et al., 2019;Ahmed et al., 2022;Jassam and Awadh, 2021;Khalid A. et al., 2022).These radionuclides can be concentrated on the surface of equipment and pipes in the form of sludge and scale due to chemical and physical processes that come from the produced brine water associated with crude oil.These radionuclides and their progeny can contaminate production equipment and systems ( IAEA, 2014;Ali, et al., 2017;Ali et al., 2019;Attallah et al., 2020;Ibrahim and Kamal, 2023;Afifi et al., 2023).The produced water may be considered the greatest source of radioactive waste production by the oil and gas industry, which is the source of soil contamination and eventually requires remedial action following radiation protection principles ( Mohsen et al, 2020;Garner and Read, 2020;Desouky et al, 2021;Lim et al., 2021).As an example, there is a huge amount of NORM-contaminated soil in the Iraqi oilfields.Therefore, remediation projects to remove and treat contaminated soil must be initiated to reduce the risks to workers and the public.Since the radionuclides 226Ra is belong to 238U and 228Ra to 232Th decay chain, as mentioned before, these radium isotopes are leached and transferred with extracted oil and produced water because its relatively high soluble in water than uranium and thorium in high depth by a physical condition (increasing in pressure and temperature) which will be in the liquid phase, whereas uranium and thorium elements stay in the reservoir rocks and they did not transfer ( IAEA, 2011;IAOGP, 2008).
Radium is very significant in radiological protection due to its relative presence in nature, long halflife, radiotoxic, relatively high physical and biological mobility, furthermore, radium is the radon ( 222 Rn) parent, which is radioactive gaseous (Ali et al. 2023;Abd Ali et al. 2018;Al-Khafaji et al., 2019).The biological behavior of Ra is similar to that of other alkaline earth metals, where it is the heaviest (group IIA in the periodic table), and it has the same chemical behavior as Ba, Sr, and Ca which belong to the same group of the periodical table, i.e. because of the chemical similarity between radium and calcium, it may be accumulated by plants and animals and transferred to humans through the food chain ( Attallah et al., 2019;Awwad et al., 2015;De-Paula-Costa et al, 2018;Kirby, 1964).
Treatment of NORM wastes from many industries still needs more efforts, whereas the traditional methods are subsurface disposal, volume reduction using inhibitors, recycling, and chemical leaching.According to International Atomic Energy Agency (IAEA) publication of GSR Part 3, the recommended exemption levels for NORM wastes are 1 Bq.g -1 for 238 U-series and 232 Th-series including radium, whereas 10 Bq.g-1 for 40 K (IAEA, 2023;Adedapo, 2022).
Radium element exhibits only one oxidation state (Ra ++ ), where the most its compounds are simple ionic that they were either insoluble salts in water such as sulfate, carbonate, and chromate salts, or soluble salts such as chloride, bromide, nitrate, and hydroxide (Kirby, 1964;IAEA, 2014;Awwad et al., 2015).Radium sulfate is the most insoluble radium compound known yet, it is converted to radium carbonate by fusion with sodium carbonate resulting in radium carbonates which is soluble in any dilute mineral acid (Ruediger and peter, 2012;El-Didamony et al., 2013;Attallah et al 2019).
The chemical leaching technique involves extracting a component from a solid that has come into contact with a liquid, it is most frequently employed to remove materials from ore and used for the treatment of contaminated soil with heavy elements to reduce their concentration to the optimum limits.There are two approaches to carrying out the chemical leaching methods; a single (direct) extraction process that involves introducing the target solvent directly to contaminated soil and a sequential extraction process that involves pretreatment in many steps before introducing the target solvent, the last technique has been frequently utilized to examine how metals are distributed within various phases of soil.Leaching the contaminated soil with highly concentrated acid (single extraction) can produce better removal for the different radionuclides, yet the use of strong acid with high molarity concentration is not recommended, whereas the sequential chemical treatment of soil despite of time conception is recommended, due to allowing minimal contamination with low molarity concentration of solvents that are used (El Afifi et al., 2009;Al Abdullah et al., 2016;You et al., 2022).
The mechanical separation of contaminated soil with NORM may reduce the cost of final disposal by reducing the volume of contaminated soil within limits without chemicals or any complicated methods.The mechanical method is used also to screen the contaminated soil and evaluate the feasibility of particle size separation (Abdellah and Al-Masri, 2014;Zayir et al., 2016).
The current study objective is the remediation of NORM-contaminated soil at a laboratory scale.In this study, actual two NORM soil samples from Al-Rumaila southern oilfields in Al-Basra governorate, Iraq, were utilized, the experiments were carried out in two different methods, where the patch chemical sequential leaching using low chemical concentrated solvents to extract radium radionuclides from soil samples and the mechanical separation process to reduce the amount of contaminated soil.

Samples Collecting, Preparation, and Radiological Measurement
Two different types of soil samples were collected from an elected location in Al-Rumaila oilfield in southern Iraq for mechanical separation and chemical treatment with the aid of portable radiological survey devices.A part of each soil sample (500mL volume) was taken for radiological measurement and identified as S-1 to represent the first type of soil sample and S-2 to the second one.The samples were sealed and stored for 3-4 weeks before the measurement to establish an equilibrium of the decay daughters' radionuclides with their parents and measured by gamma spectrometer to determine the activity concentrations (AC) of the NORM soil samples ( IAEA, 2011;Ahmed et al., 2020;Rejah et al., 2021).
A gamma spectrometry system (ORTEC Company) was used to radiological measurement and radionuclides analyses of gamma-ray spectra of soil samples, this system has a coaxial high-purity germanium detector (HPGe) with 65% relative efficiency and resolution 1.95keV based on measurements of 1.332MeV gamma-ray photo peak of 60Co was used in this study for the measurements and analysis of gamma-ray spectra of soil samples.Standard multi-gamma radioactive sources of 32mL and 100mL were used for efficiency calibration type CBSS 2/ certification C. No. 1035-SE-40296-19 and CBSS 2/ C. No. 1035-SE-40297-19 respectively, from Czech Metrology Institute with reference date 1/5/2019 for both, which contain 11 radioisotopes with different gamma-ray energies to cover all radionuclides of NORM samples, and CBSS 2 C. No. 9031-OL-506/13 with 500mL volume (Marinelli beaker) with reference date 23/9/2013, which contain 10 radioisotopes.Two-point sources (60Co and 137Cs) were used for energy calibration for the gamma spectrometry system.Gamma Vision software performs report that includes information such as dead time, isotope gamma-energies, minimum detection activity (MDA), and compound relative uncertainty for each radionuclide in each sample.Quality control procedures were applied using certified reference material SAEC-448 (radium-226 in soil from oilfield) which, was provided by the Atomic Energy Commission of Syria.
Table 1 presents the activity concentration of the radionuclides for S-1 and S-2 (500mL-volume) soil samples.The gamma spectrometry system was used to determine the activity concentrations of the NORM soil samples, The measurements can be conducted by two methods; direct and indirect, indirect measurement is done using progeny radionuclides which is a commonly applied for determining the activity concentration of parent 226Ra and 228Ra isotopes.The determination of 226Ra in environmental samples has long been based on the detection of emissions of the radon gas progeny (222Rn) nuclides, i.e. 214Pb and 214Bi (solid elements) after an ingrowth period of at least 20 days (Shafik et al. 2019;Ali. et al. 2023).The direct measurement method of 226Ra can be used at 186.2 keV energy photo-peak, while 235U activity can determine at 185.72 keV, which overlaps with the 186.2 of 226Ra keV energy line.235U is usually present at a much lower concentration than 226Ra in environmental samples due to its abundance ratio in nature especially in oil and gas extraction fields (Ali et al. 2017;IAOGP 2008;Sooyeon et al. 2021).The indirect measurements was used to determine the activity concentration of 226Ra from their progeny (214Pb and 214Bi ) for S-1 and S-2 soil samples, while 228Ra determine at 911.2 keV energy photo-peak that belong to 228Ac radionuclide which its the first daughter (IAEA, 2011;El-Taher et al. 2022), as presented in Table 1.

Sample preparation for mechanical separation
The first soil sample (9.6 kg weight) dried at 80 C for 5 hours (BINDER oven) and separated directly for seven particle sizes {(+900), (-900+600), (-600+250), (-250+125), (-125+63), (-63+37), (-37)} µm using the electric sieve shaker 8411 with a maximum rotation speed of 1400 rpm.The material held on each of the sieves and the fraction of each particle size was separated, collected, weighed, and analyzed for each weight fraction.All seven fractions samples of the S-1 soil sample were dried and then moved to a spatial standard container (100 mL-volume).

Samples preparation for chemical leaching of radium
The second soil sample (S-2) of about 4 kg was dried at 80 C for 5 hours, sieved by 30-mish sieve shaker (600μm pore size), homogenized, and moved to special standard plastic containers (32 mLvolume) for radiological measurement as a reference representative sample for comparison with followed steps of treated soil with chemical leaching method (IAEA, 2011;Zaidoon and Asia, 2024).

Soil Sample Characterization
The soil texture of grain size analysis (clay, silt, and sand contents) of the S-2 soil sample was determined by the Pipette analysis method, and organic carbon content (C-org) was determined using Carver, )1971("Procedures in Sedimentary Petrology".The oil content was carried out by extracting method, where measured by HORIBA oil content device model: OCMA-350-E.by EPA test method 418.1 " total recoverable petroleum hydrocarbons", see Table 2.The pH of the sample was performed using the potentiometric method by a commercial glass electrode HQ411d pH/mV HACH company Benchtop meter.The soil salinity is measured by passing an electric current between the two electrodes of a salinity meter in a sample of soil or water.The salinity (Sal) measures of the grams number of salts per kilogram or parts per thousand ppt.The electrical conductivity or EC of a soil sample is influenced by the concentration and composition of dissolved salts.The salinity of soil sample, total dissolved solid TDS and electrical conductivity EC were determined according to extracting methods, where the extraction solution was measured directly by into Lab meter Cond 7110 devices, the results of pH, TDS, EC, and the salty for S-2 present in the Table 2.The X-ray fluorescent (XRF) technology was used to determine the concentrations of chemical elements in the S-2 NORM soil sample, which was manufactured by Spectro Xepos Company, with a detector silicone-lithium.Table 3 presents the concentration of the major elements of the S-2 soil sample before and after chemical treatment.

Chemical Leaching of Radium Procedure
The treatment methods in this study were carried out by sequential extraction method (SE) that involves pretreatment in three successive steps before introducing the target solvent (purification, pH moderation, anion exchanging, and leaching with the final solvent), SE has been frequently utilized to examine how metals are distributed within various phases of the soil.The batch tests were utilized in this study, with different molarity concentrations of the extraction solution agents, where the used solution were inorganic strong acids, such as HNO3, HCl, and H2SO4, organic weak acids such as C2H4O2 and C₆H₈O₇, deionized water H2O, salty solutions such as Na2CO3, CaCl2 and NaNO3, basic solution such as NaOH and natural and synthetic chelating agents such as (C₆H₈O₇ and EDTA Na2) (Chao et al., 1998).The chelating agents are used for capturing heavy metals such as radium, where the citric acid (C₆H₈O₇) is a weak organic acid and is used as a natural chelator.It is commonly found in citrus fruits like lemons and oranges; therefore, it is an environmentally friendly chelating agent.The ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA Na 2 ) with molecular formula C10H18N2Na2O10 which has a high molecular weight (372.24g/mol) is widely used as an artificial chelating agent for soil remediation, where it uses to extract the heavy metals such as the divalent and trivalent metals (an atom, ion, or element with a valence of two and three) and forming soluble stable complexes that are readily excreted, Fig. 1. shows the molecular structure of the natural and synthetic chelators (Alzubadi and Radhi, 2017;Chao et al., 1998;Shuang et al., 2021).Each of all used solutions (250 mL) was added to the soil sample (50g) in glass beakers (500 mL) under study, the contents were shaken for 2 h at a constant temperature of 40-50°C with a relative error (±10%) for acids and deionized water and 75-85 °C for salty solutions in a hot plate magnetic stirrer (model L-81, and VWR model 984VW7CHSEUA) and mechanical stirrer (heavy-dusty, ISOLAB company) which was used for the amount of soil that the magnetic stirrer cannot mix, the mixing ratio was 5:1 (liquid to solid ratio) and 400 rpm stirrer.After shaking, the solution was separated from the solid by filtration using medium filter speed Whatman-40 filter papers, the solid residue was dried at 80 C for 4 h and transferred to a 32mL volume container to be measured by gamma-ray spectrometer then to determine the remaining activity (C) (El-Didamony et al., 2012;Abdellah and Al-Masri, 2014).The activity removal percentage (R %) of radium in the chemical leaching is calculated using the relation below ( Alzubadi and Radhi, 2017;El-Didamony et al., 2012;Abdellah and Al-Masri, 2014).
The sequential extraction procedure was carried out in four processes to improve the radium extraction with final solvents as a pretreatment, the first was washing the soil samples with deionized water twice to remove not concerned salt and elements that can dissolve in water, (40-50°C, 3h, L: S=5, and 200rpm).The second process was converting the reaction conditions from neutral to basic media by washing soil samples with dilute sodium hydroxide solution and 0.07M NaOH (25-30°C, 1h, L:S=3, and 200 rpm), then the third process was washing the soil with sodium carbonate solution (2M Na2CO3) to convert the sulfate structure of radium into carbonate structure (70-80°C, 4h, L: S=4, and 200rpm), which easily chemically interacts and dissolve in dilute acids (weak and strong), the mixture then cooled to room temperature and filtered, then washed with different acids and chelating agents under the optimum conditions.

The Mechanical Separation
The results of particle size weight percent and radioactivity distribution were obtained for seven fractions with different mesh sizes of the first soil sample (S-1) as presented in Table 4 and illustrated in Fig. 2. The fractions obtained varied between ≤37μm (400 mesh) to >900μm (20 mesh).The figure shows the greatest weight percent in the second fraction (900μm ≤Particle Diameter>600μm), where 42.30% of total weight appears in this fraction, whereas the reverse in seven fraction (D≤37μm), while it can be seen that the greatest value of the radium isotopes activity concentration is concentrated in ≤ 37.5μm particle size diameter.There is a small fluctuation in the first four fractions of the activity concentrations of radium isotopes ( 226 Ra, 228 Ra), whereas there is an observation increasing with smaller particle size than higher.

The Chemical Leaching of Radium
The single (direct) chemical leaching method using different solvents was carried out on the S-2 soil sample, and it is found there is very low efficiency removable (R%) of 226Ra and 228Ra, as presented in Table 4.This type of soil has many characteristics such as a high presence of oil content (hydrocarbons) and organic materials, as presented in Table 1 that makes the chemical reaction of diluted acid with the target element (Radium) with low probability.Table 3 presents the concentration of major elements of the S-2 soil sample before and after treatment by XRF-system, the results in the second and third column in this table refer to positive R% extracting of some elements (Ca, Mn, Fe, Cu, and Pb) and the reverse in the other elements.While the same table in other columns by washing with many acids and one chelator using the sequential leaching method, there is stability in the R% of the most dissolved elements with the used solvents under the same optimal conditions, which the most of them have similar physicochemical characteristics to radium (group-2 in the periodical table), especially barium (Ba2+) ion which represents the radium where radium element does not included in the standard source of chemical systems such as XRF-system due to all radium isotopes are radioactive.
The weight loss as seen in Tables 5, and 6 after washing with the solvents, makes R% decrease because the soil loses some of the common elements during the chemical leaching with solvents where these elements compete and contribute with Ra in chemical reactions, which agrees with previous studies (Lan Zhang, et al. 2015;Punam Thakur, 2022;Savva Savvaki, 2016).Another reason for the poor R% of Ra in the direct leaching method (Table 5) is the particle size of the soil, the results of the mechanical separation show radium concentrates within smaller particle sizes than larger, which it dissolves and transfers to the aqueous phase only with strong and concentrated acids such as nitric acid.In this study, the experiments were carried out with particle size below 600 µm with low molarity concentration acids.During the chemical washing with acids, the soil particle size decreased, which will increase radium concentration in case washing soil with the strongest acids which refers to a partial chemical digestion was happen which reflects to decrease in R% of radium.The poor performance of all used solutions to remove radium from the soil in this study indicates that requires chemical preparation before leaching with acids using some selective extraction solutions to know the nature of the chemical forms of radium associated with soil particles.The efficiency removable (R%) of sequential leaching method results of 226 Ra and 228 Ra from the NORM soil are given in Table 6 and shown in Fig. 3, where pretreatment was carried out in the first and second step by washing the soil sample with deionized water two times and with diluted sodium hydroxide (0.07M NaOH).The third step of the sequential leaching procedure was washing the sample with three salty solutions separately (2M CaCl2, 2M Na2CO3, and 2M NaNO3), and finally, the dried soil from the third step was washed with different acids.(Abdellah et al., 2014) used many salty solutions as a pretreatment of the contaminated soil with NORM, (Awwad et al., 2015) used two approaches of TENORM treatment by four steps using many alkali, salty, and acidic solution for that, they were gotten a good result of removing radium (Abdellah and Al-Masri, 2014;Awwad et al., 2015).There are very poor results of efficiency percent of radium removal (R%) when CaCl2 and NaNO3 solutions were used and their followed acids in the last step of the sequential leaching procedure, while sodium carbonate (Na2CO3) shows the highest efficiency removable of the used salty solutions (25.6% and 24.4%, for 226 Ra and 228 Ra respectively), which agrees with previous studies and the scientific theories about radium behavior (Matyskin, 2016;O'Neil et al., 2013), which indicates radium in contaminated soil may be in the form of an insoluble salt, such as sulfate (RaSO4), that must convert to radium carbonate by fusion with sodium carbonate which is soluble in any dilute mineral acid while using strong acids is not recommended.Whereas using CaCl2 and 2M NaNO3 in the third step of sequential leaching did not affecting on the radium removal from the soil, which means there is no conversion of sulfite to chlorite and nitrate.The last step of treatment by chemical sequential leaching method which follows the washing with Na2CO3 appears a good result of R% by washing with different diluted organic and inorganic acids, and chelator.Therefore, it can be repeated as a second washing phase to improve the R% of radium, where the treated S-2 soil sample was washed in the second stage by the same solvent in the same conditions as the first washing, the soil was responded in this stage and gave a high removal efficiency, where 85.2%, 86.1% of 226 Ra and 226 Ra respectively, were removed and converted to aqueous phase using acetic acid.See Table 6.
Five parameters were investigated in this study to determine the best solvent and conditions for the sequential leaching process, where the first experiment of soil treatment is the selecting of the best solvent for the final step of the chemical leaching method, where six solvents were used, the results are presented in Table 6 and illustrated in Fig. 3, they show that the acetic acid (Ac) ensures a high-R% of 226 Ra and 226 Ra, where 78.4% and 80.6% respectively in the first phase-washing were removed from initial activity.Therefore, sodium carbonate as a pretreatment solution in the third step and followed by acetic acid in the final step of the sequential leaching process were chosen as the best solvents in this study.Table 5 also presented the soil loss and acidity when it was washed in the final step of chemical leaching with different solutions.Table 7 and Fig. 4 present three parameters to determine the best conditions for the leaching process; molarity concentration of the solvent, temperature of medium (30, 40, 60, and 80) ˚C, and contact time in washing the soil with Ac-acid.The results show that the three-molarity concentration (3M) at 80˚C and four hours of mixing time ensure a high-efficiency removable percentage (R%) of radium.The results in the same table explain there is no high difference in R% of radium at the studied first parameter (molarity concentration), therefore, 1M of acetic acid was depended on the second test.The second parameter was the changing of R% with the contact time of acid with soil, it was found that two hours is the optimum condition for the next test.The third parameter was the changing of R% with changing of the medium temperature, it was found there is a slight difference in R% of radium by changing the temperature (30-80) ˚C.Therefore, 1M of acetic acid at two hours of contact time with soil at 40˚C are the optimum conditions for the sequential chemical leaching method.In the first stage of treatment, as presented in Table 7, there are low variance in efficiency removable (R%) of 226 Ra and 228 Ra from S-2 for all experiments (molarity concentration of the solvent, temperature of medium and contact time) by washing the soil with Ac-acid.The experiment of contact time of solution with soil, the washed soil collected together, dried, weighted and measured to be ready to the next experiment.In the second stage of treatment, as presented in Table 8 and Fig. 5, the initial activity

Discussion
The mechanical separation of NORM-contaminated soil by various mesh sizes (20-400), shows that Ra-element concentrates within small particle size (≤37µm) than larger particle size (≥600), therefore, fine particles show the most absorptive properties of the materials, which indicates that only small portions of radium are present on the surface of soil particles, while most radium located and trapped within the soil particles, that agrees with the previous studies (Abdellah and Al-Masri, 2014;El Afifi et al., 2010;Zayir et al., 2016).
The chemical treatment techniques mainly include a chemical conversion of the target element into a water-soluble form.The treatment of contaminated soil with radium depends on its chemical behavior, soil characteristics, the content of organic matter, oil content, and other components in the soil.The single leaching experiments with different dilute solvents showed a low extraction rate, indicating that Ra-isotopes in contaminated soil may be in the form of insoluble sulfate, this indicates that the NORM soil sample under this study requires chemical preparation before leaching with dilute acids by using some selective extraction solutions to know the nature of the chemical forms of radium associated with soil particles, that agreed with previous studies (Abdellah and Al-Masri, 2014;Awwad et al., 2015).Therefore washing the soil with sodium carbonate before leaching with dilute acids or chelating agents converts the radium sulfate salts to the carbonate and facilitates the final leaching of radium (the sequential extraction method), which agrees with previous studies that radium may be in insoluble salts form (Ruediger and Peter, 2012;El-Didamony et al., 2013;Awwad et al., 2015;Kozempel et al., 2015;Attallah et al., 2019).

Conclusions
The study scope is an extracting or reducing radium element from the contaminated soil with NORM of the oilfields by physical and chemical methods.The mechanical separation method does not fully solve the contamination problem but it reduces the waste volume and it was found to be easy and effective, taking into account safety procedures to be followed during the implementation.
Due to the response of contaminated soil to direct washing with different diluted solvents, the sequential extraction method can be a useful tool and better than single extraction for evaluating the chemical fractionating and mobility of radium with low molarity concentration of acids (strong and weak) that finally allows minimal contamination of soil which agree with national and international limits of the clearance levels of solid materials to release them into the environment.
The removal efficiency (R%) of stage-2 of 226Ra and 228Ra by repeating the washing of soil in the last step in the sequential extraction process with different solvents explained that the washing with 0.1M Ethylenediaminetetraacetic disodium (EDTA Na2) after washing with 1M acetic acid to be the most effective solvent which gave the higher R%.Despite EDTA giving a higher R% and being widely used for soil remediation, it has limitations due to its toxicity to plants and micro-organisms, low biodegradability, high cost, and tendency to cause secondary contamination in soil and groundwater (Chao et al., 1998).Consequently, replacing the EDTA Na2 solution with low molecular weight organic acids which are easy to degrade, where the degradation products are harmless.As a result, acetic acid at low concentration is an effective solvent for soil treatment because of its ability to react with radium salts, medium acidity, optimum used molarity concentration, cost, and availability, as well as the last containing as a liquid radioactive waste, where acetic acid is an organic weak acid.The pH of soil after treatment with acetic-acid was 7.2 (neutral acidity), and the generated eluent liquid was 5.6 (a low acidity), therefore, the dilute acetic-acid can be chosen as the best medium of chemical treatment for radium extraction from NORM-contaminated soil.
a. EDTA Na 2 b.C₆H₈O₇ Fig.1.a & b the molecular structure of two chelators

Fig. 2 .
Fig. 2. Particle size distribution with activity concentrations for 226 Ra

Fig. 3 .
Fig. 3.The removal efficiency %, of 226 Ra and 228 Ra, soil loss, and soil acidity for S-2 soil sample by leaching method with Ac-acid at the final step ) of the washed soil sample from first stage from

Fig. 5 .
Fig. 5.The removal efficiency % of stage-2 of 226 Ra and 228 Ra for S-2 soil sample with different solvent

Table 1 .
The concentration of radionuclides of S-1 and S-2 NORM soil samples Bq.kg -1

Table 2 .
The S-2 soil sample characterization

Table 3 .
The concentration % of the major elements of the second soil sample before and after treatment by the XRF-system * Increasing of element concentration, and bold number decreasing of element concentration

Table 4 .
Particle size distribution with Activity Concentrations (AC) for 226 Ra and 228 Ra Bq.kg -1

Table 5 .
The removal efficiency % of 226 Ra 228 Ra for S-2 soil sample after treatment with different solvents by direct extraction leaching

Table 6 .
The removal efficiency % of 226 Ra and 228 Ra for the S-2 soil sample of step three and four after treatment with different solvents by sequential extraction method

Table 7 .
The removal efficiency % of 226 Ra and 228 Ra for S-2 soil sample with different parameters Table 7 was 9970.1±398.8 and 1106.8±55.3Bq.kg - of 226 Ra and228Ra respectively, it found that washing the contaminated soil with 0.1M Ethylenediaminetetraacetic disodium (Na2EDTA) after washing with 1M acetic acid to be the most effective solvent at the optimum mention conditions, where 94.33, 93.44% of 226 Ra, 228 Ra, were removed to the aqueous phase respectively.

Table 8 .
The removal efficiency (R%) of 226 Ra and 228 Ra for S-2 soil sample stage-2 with different solvents