Sorption Of Radium Research Articles

Construction and validation of parametric models to predict radium sorption in soils

Elucidating the factors affecting the transfer of naturally occurring radionuclides (NOR) between environmental compartments is a key part of the assessment of ecosystem's exposure to naturally occurring radionuclide materials (NORM). For that, the sorption and desorption solid-liquid distribution coefficients (Kd) of radium (Ra) were quantified in a collection of 31 soil samples with contrasting edaphic properties under controlled conditions in laboratory batch experiments. Ra sorption was demonstrated to be moderate to high, with Kd (Ra) values ranging from 102 to 103 L kg−1. Ra sorbed was mostly irreversible, as evidenced by desorption percentages lower than 2 %. An exploratory analysis with partial least squares (PLS) regression identified the soil properties that correlated with Kd (Ra) and discarded those that were not relevant for describing Kd variability. A dataset of the sorption Kd (Ra) values and associated soil properties was built from our own data and from the literature after performing an in-depth review of similar Ra sorption studies. For the first time, Kd (Ra) parametric prediction models were constructed using univariate linear regression (ULR) and multivariate linear regression (MLR). Ra sorption in soils was mostly explained by the soil properties directly or indirectly related to the available exchange sites, such as the levels of water-soluble and exchangeable Ca and Mg as well as the pH of the contact solution. The most promising models explained around 80 % of the Kd (Ra) data variance, only needing Kd (Ca + Mg) or additional soil descriptors such as pH, Mn content, and the specific surface area. The validation of the proposed models confirmed that Kd (Ra) can be predicted with only a few soil properties that can be characterised in routine analysis. Thus, the proposed models could be used to estimate the interaction of Ra in soils in risk assessment.

Radium sorption on crystalline rock; spatial distribution and sorption modeling study

Spent nuclear fuel from the Finnish and Swedish nuclear power plants will be permanently disposed of in deep geological disposal facilities located on the coast of the Baltic Sea. As a part of the disposal's safety case, the migration properties of the safety-relevant spent nuclear fuel-borne radionuclides, such as the radionuclide progeny of the waste component 238U, 226Ra, need to be assessed in the lithosphere surround the facility. To this end, the sorption of Ra on disposal-relevant rock and groundwater types was studied in batch sorption experiments in a wide Ra and Ba concentration isotherm (2.6 × 10−9 M to 1 × 10−3 M). The experimental results of the batch sorption experiments were further interpreted using a PHREEQC geochemical model with ion exchange and surface complexation reactions considered. Additionally, the sorption of Ra was studied with thin section sorption studies where autoradiography analysis was combined with mineralogical data obtained in SEM/EDX to establish spatial distribution and mineral specific sorption of Ra on the studied rocks. In the study, it was observed that Ra sorbs well on all tested rock types and water conditions of low ionic competition, regardless of the rock type's projected sorption affinity based on its highly sorbing mica mineral content. In conditions of high ionic competition, Ra tends to stay in the sorption solution, facilitating migration in the disposal context. The obtained experimental and modeled Ra sorption data will be used in the safety case calculations and modeling of the Finnish and Swedish spent nuclear fuel disposal.

Study of Radium Behavior in Contact With Calcium-Silicate-Hydrates

Abstract Radium-226 is an important radionuclide with respect to the long-term safety of repositories for low and intermediate-level radioactive wastes, as well as deep geological repositories for high-level radioactive waste and spent nuclear fuel. To evaluate its mobility in the engineered barrier system of a repository, the sorption of radium on calcium-silicate-hydrates (CSH), which form the major hydration phases in cementitious materials, was studied. Radium sorption to CSH was found to be very fast, leading to steady-state between solid and liquid phase after less than four days. The dependency of the equilibrium distribution ratios on radium concentration, the calcium to silicon ratio in CSH, liquid to solid ratio, and temperature was investigated, and estimates of apparent activation energy, reaction enthalpy, entropy, and Gibbs energy of the sorption process were derived. Radium sorption on CSH can be described by linear isotherms with Rd values mostly in the order of 104 L/kg. Radium sorption was found to be an exothermic and spontaneous reaction probably governed by chemical reaction rather than diffusion. As expected, the presence of ethylene diamine tetraacetic acid (EDTA) at low concentrations led only to a small decrease in radium sorption, due to the strong competition of dissolved calcium for EDTA complexation. A comparison of the sorption behavior of various alkaline earth elements used as chemical analogs for radium confirmed the significant difference in the Rd values with sorption on CSH decreasing in the order Ra > Ba > Sr.

Radium sorption on biotite; surface complexation modeling study

The sorption of Ra on Olkiluoto biotite in the context of deep geological disposal of spent nuclear fuel was studied with isotherm batch sorption experiments. Ba was used as an analog for Ra in the experiments and modeling studies. A wide concentration range of Ra/Ba was used in the isotherm studies (2.6 × 10−9 M to 1 × 10−3 M) in addition to four different Olkiluoto reference groundwaters with salinity types ranging from fresh to saline. Experimental results show that both in the fresh and saline reference groundwaters, the distribution coefficients of Ra tend to decrease in the higher isotherm concentrations of Ba. With one reference groundwater, the distribution coefficients increased with the concentration of Ba due to significant coprecipitation of Ra. With the fresh reference groundwaters, the distribution coefficients of Ra were consistently approximately one order of magnitude lower than in the saline reference groundwater. A PHREEQC multi-site complexation model coupled with an optimization tool in Python was used to interpret the experimental Ra sorption results. Molecular modeling with CASTEP code implemented into Materials Studio was used to update the PHREEQC model with more realistic biotite sorption site density data. It was observed that while the multi-site model predicts the sorption of Ra well in lower isotherm concentrations, auxiliary reactions of Ra disrupt the model in high Ba isotherm concentrations. The experimental and modeled distribution coefficient data of Ra on biotite can be used in the safety case calculations of the deep geological disposal of spent nuclear fuel in Finland and Sweden.

Diffusion and Sorption of Radium and Strontium in a Layer of Porous Sorbent Based on Hydroxyapatite

A cell for studying the diffusion of therapeutic medical radionuclides into the macrolayer of the carrier sorbent was fabricated using 3D printing. The diffusion of ultramicroquantities of radium and strontium within a layer of watered hydroxyapatite was investigated. The value of the effective diffusion coefficient obtained using a one-dimensional nonstationary model was (1.0 ± 0.4) × 10–8 cm2/s for Ra and (3.0 ± 0.3) × 10–8 cm2/s for Sr.

Comparative study of radium and strontium behaviour in contact with cementitious materials

A comparative study of the sorption behaviour of radium and strontium was performed on various cementitious materials including crushed hardened cement pastes (HCP) and concretes as well as a synthesised calcium silicate hydrate (CSH) phase.Rd values obtained for the Ra and Sr uptake on commercial cement materials were in the range of 50–380 L kg−1 and 10–30 L kg−1, respectively. No significant difference between the distribution ratios of the isotopes 226Ra and 223Ra was observed in the studied liquid to solid (L/S) ratio range, although different isotherms were determined. The Rd values for Ra were found to increase with increasing L/S ratio. The cause of this effect is obviously the non-linearity of the sorption isotherm, here of the convex type. In contrast, Sr uptake seemed to be largely unaffected by variation of L/S ratios; this indicates an isotherm of almost linear type. Sorption experiments with the CSH phase confirmed the distinctive differences in the sorption behaviour between Ra and Sr as expected, with Rd values significantly higher for Ra. Similarly, the difference between real cementitious materials and the pure CSH phase was confirmed, indicating that the sorption of alkaline earth elements is mainly due to uptake by CSH.The kinetics of Ra and Sr uptake on cementitious materials were evaluated by a set of models describing the sorption in heterogeneous systems based on different rate-controlling processes. The FD (film diffusion) model in the case of Ra, and the ID (diffusion in inert layer) model in the case of Sr provided the best fits.The influence of temperature on the kinetics of radium sorption was studied, suggesting change in the shape of isotherm with increasing temperature. Evaluation of sorption kinetic data yielded values of the apparent activation energy of the uptake process.Complementary through diffusion experiments using compacted crushed HCP confirmed and extended the findings obtained by evaluation of the batch sorption experiments performed with Ra and Sr.

Determination, Modeling and Evaluation of Kinetics of 223Ra Sorption on Hydroxyapatite and Titanium Dioxide Nanoparticles.

Sorption kinetics of radium on hydroxyapatite and titanium dioxide nanomaterials were studied. The main aim of the current study was to determine the rate-controlling process and the corresponding kinetic model, due to the application of studied nanomaterials as α-emitters’ carriers, and to assess the sorption properties of both materials from the radiopharmaceutical point of view by time regulated sorption experiments on the nanoparticles. Radium-223 was investigated as radionuclide used in targeted alpha particle therapy as an in vivo generator. It was found that the controlling process of the 223Ra sorption kinetics was the diffusion in a reacted layer. Therefore, parameters like particle size, their specific surface area, contact time and temperature played important role. Moreover, the composition of liquid phase, such as pH, the concentration of 223Ra, ionic strength, the presence of complexation ligands, etc., had to be considered. Experiments were conducted under free air conditions and at pH 8 for hydroxyapatite and pH 6 for titanium dioxide in Britton–Robinson buffer. Initial 223Ra concentration was in the range from 10−11 to 10−12 mol/L. It was found that sorption kinetics was very fast (more than 90% in the first hour) in the case of both nanomaterials, so they can be directly used for efficient radium sorption.

Sorption of Radium from Tap Water with Inorganic Sorbents

Radium-224 isolated from a generator having the form of a solution of thorium and Trilon B with pH 6.5–7.0 (molar ratio 4 : 1) was used to examine the sorption of radium from tap water by inorganic sorbents of T-3A, T5(400), and T5 (MnO2) brands under dynamic and static conditions.

Selective Sorption of Radium with Inorganic Sorbents from Solutions of Thorium with Trilon B

A generator of radium-224 based on a neutral solution of thorium with Trilon B with EDTA : thorium molar ratio of 4 : 1 was suggested. The properties of the generator were examined and its efficiency for obtaining radium-224 as a radioactive tracer was demonstrated.

The radionuclide distribution onto different mineral phases of the rocks of the exocontact zone of Nizhnekansky granitoid massif

The sorption experiments with the five rock samples drilled in the deep-well in the exocontact zone of Nizhnekansky granitoid massif (EZNGM) in the range of depth 166–476m were carried out. The distribution of radium was studied. The radiograms of radionuclide sorption were obtained by digital autoradiography. Heterogeneous sorption of radium was demonstrated by digital radiography and phases with higher sorption ability were revealed. The technique for the treatment of radiograms with the help of ImageJ program for obtaining quantitative parameters of radionuclides distribution in the granite-gneiss rock samples was developed. Relative sorption efficiency of different mineral phases of the rock samples of Eniseysky area (EZNGM) toward radium is presented in the paper.

Removal of Radium from Uranium Effluent by Manganese Oxide Coated Modified Bentonite (Mn-NaB)

The results of radiometric analysis show the presence of high level concentration of 226Ra (50 to 125 Bq/L) in the uranium effluent solutions waste of Gattar uranium pilot plant Eastern Desert of Egypt. These levels are higher than the maximum permissible level of 226Ra (1.1Bq/L) which needs treatment. Normally treatment consists of lime addition to increase the pH to 8 which precipitates most contaminants except 226Ra. Adsorption process provides an alternative treatment in comparison with other removal techniques. The sorption of radium (226Ra) on different adsorbent, modified bentonite (Na-B) and a mixture of modified bentonite coated by Manganese oxide (Mn-NaB) was studied. The present study focuses at the option to improve the sorption properties of bentonite via its modification and presents the possibility to remove radium cations from the uranium effluent solutions by the usage of non-homogenous bentonite coated by manganese oxides. Experimental conditions (pH, clay materials quantity to manganese oxide, contact time and associated elements) were changed in order to determine the optimal state for adsorption of 226Ra. Column sorption of radium from uranium effluent solutions from Gattar pilot plant using (Mn-NaB) were conducted. The results showed that good adsorption capacity for radium removal in uranium influent. The capacity at breakthrough point 1.1 Bq/1 is 94.28Bq/g (Mn-NaB).

Chemical reactivity of natural peat towards U and Ra

Peat is a complex material with several organic constituents that contribute to its high capacity to retain metals. In the context of uranium mining, peat can accumulate high concentrations of uranium and its decay products such as radium. Hence, interaction with peat appears to be a key factor in the understanding of the geochemical mechanisms controlling the fate of these products. This study aims to determine the sorption properties of two trace elements, U(VI) and 226Ra, on natural organic matter from peat. The presented method was applied to both natural peat samples originating from a mining context, with various contents of organic matter (from 40 to 70%) and detrital loads, and wetland peat with a more than 98% composition of organic matter. In the present study, considering peat material as a sorbent, its reactivity towards metals and other contaminants can be described as that of an ion-exchanger. A relatively simple model of ion-exchange based on the sorption properties of carboxylic sites has been applied with success to describe the sorption of uranium and radium. In the general overview of the different mechanisms able to control the mobility of these radionuclides in a uranium mining context, organic matter is likely one of the main contributors to radionuclide scavenging even under oxic conditions.

Radium Sorption to Iron (Hydr)oxides, Pyrite, and Montmorillonite: Implications for Mobility.

Radium (Ra) is a radioactive element commonly found within soils, sediments, and natural waters. Elevated Ra activities arising through natural and anthropogenic processes pose a threat to groundwater resources and human health, and Ra isotope ratios are used to decipher groundwater movement, estimate submarine discharge flux, and fingerprint contamination associated with hydraulic fracturing operations. Although adsorption to metal (hydr)oxides and certain clay minerals is well established as a dominant mechanism controlling Ra transport and retention, the extent of Ra sorption to other minerals and under variable environmental conditions (e.g., pH and salinity) is limited. Accordingly, we present results of sorption studies and surface complexation modeling (SCM) of Ra to ferrihydrite, goethite, montmorillonite, and pyrite, for a range of pH values and common background cations. Ra sorption to all substrates is observed under geochemical conditions considered, but varies according to mineral, solution pH and specific competing cations. Literature derived SCMs for Ra sorption were fitted to match either sorption impacts due to pH or different background cations, but were not able to predict the impacts of different geochemical conditions. Despite this, the use of SCMs provided a more mechanistic understanding of Ra sorption as compared to commonly used distribution coefficients.

Sorption of radium onto early cretaceous clays (Gault and Plicatules Fm). Implications for a repository of low-level, long-lived radioactive waste

The repository of low-level and long-lived radioactive waste from REE purification and treatment is presently under investigation by the French National Radioactive Waste Management Agency (Andra). This waste consists of Ra-bearing solids, mainly Ra-barite (Ba,Ra)(SO4), along with other salts such as NH4NO3 and monazite. The current repository concept under study is based on a shallow (∼30 m deep) geological disposal in a clay formation. This work deals with the experimental study of the sorption of Ra onto two clay rocks from Lower Cretaceous geological formations in the Department of Aube, in France, the Gault (tégulines) Formation and Plicatules Formation.Clay samples were extracted from different boreholes from the both geological clay formations, and consisted mainly of illite, illite-smectite mixed layers (35–65% and 25–70%). Sorption experiments were carried out on raw materials as well as on samples exchanged with different cations (homoionic forms of Na, NH4, Ba and Ca, respectively). The results indicate that Ra sorption in raw materials is linear within the range of concentration investigated (10−8 - 10−11 M). In most of the samples, Kd values from 170 to 300 g·mL−1 were measured for Ra and from 30 to 70 g·mL−1 for Ba. The sorption experiments (from 1 h to 92 days) of Ra showed small kinetic effects as Kd values tend to increase with time from approximately logKd = 2.15 to 2.65. In all exchanged samples, a dependence of sorption on the ionic strength was observed -the higher the ionic strength, the lower Kd values-; except for Na, this dependence is consistent with an ionic exchange process and selectivity coefficients (Ra-Ca; Ra-Ba and Ba-Ca) have been determined. A non-negligible effect of pH on sorption was also observed that could be explained considering surface complexation on the amphoteric groups present at the solid surface. In these materials, the selectivity of Ra was higher than that of Ba (half an order of magnitude).The experimental results indicate that sorption of Ra in the studied clay formations is high enough to limit the radium migration in the near field of a low-level, long lived disposal site.

A Study on Sorption of (226)Ra on Different Clay Matrices.

The sorption of radium 226 ((226)Ra) on different clay materials (bentonite, illite and a mixture of bentonite-illite) was studied. Clay materials are used in the construction of disposal pits for technically enhanced naturally occurring radioactive materials (TENORM) wastes (i.e., contaminated soil and sludge) generated by the oil and gas industry operations. Experimental conditions (pH, clay materials quantity, and activity concentrations of (226)Ra) were changed in order to determine the optimal state for adsorption of (226)Ra. The results showed that the concentration of adsorbed (226)Ra on clay materials increased with time to reach an equilibrium state after approximately 5h. More than 95% of the radium was adsorbed. The mixture of bentonite-illite (1/9) exhibited the greatest adsorption of radium under all experimental conditions.

Study of uranium(VI) and radium(II) sorption at trace level on kaolinite using a multisite ion exchange model

Uranium and the long-lived decay product radium-226 are abundantly present in mine wastes produced during uranium extraction activities. In the case of release to the surrounding environment, these radionuclides are at trace level compared to groundwater solutes, and the presence, content and properties of clay minerals in the host environment influence the extent of radionuclide sorption and, in turn, migration. Since clays are known to have the distinctive property of retaining ions, the aim of this work was to study the sorption of trace U(VI) and Ra(II) on a common phyllosilicate mineral, kaolinite, in the presence of excess K, a common groundwater cation, in order to obtain a thermodynamic database that describes the ion exchange equilibria occurring at the mineral–solution interface. Following a detailed experimental protocol using chemical and radiochemical analytical techniques, batch experiments over a wide pH range (from 2 to 11) and fixed concentration (ca. 10−9 M), and additional adsorption isotherms at two different solution pH (6.2 and 10.4) over a concentration range (10−10 to 10−4 M) were carried out to measure the distribution coefficient (Kd) of U(VI) and Ra(II) sorption on kaolinite. The experimental sorption data was processed according to a general multisite sorbent/multispecies sorbate ion exchange model, which allowed deducing the charge of adsorbed species and the stoichiometry of the associated adsorption equilibria on kaolinite's surface sites. Aqueous speciation calculations predicted Ra(II) as Ra2+ over the working pH range, and its adsorption curves and isotherms were explained using three sorption sites. Adsorption of U(VI) occurred on four sorption sites and was governed by its solution speciation, with positively charged hydroxylated (UO22+ and UO2(OH)+) and silicate (UO2(H3SiO4)+) species being adsorbed between pH 2 and 6, whereas its negatively charged forms (UO2(OH)3- and UO2(OH)42-) dominated U(VI) sorption at pH > 7. Nonlinear fitting of the experimental data using the ion exchange model provided the associated equilibrium constants as corrected selectivity coefficients.

Radium and Thorium Sorption by Monosodium Titanate (MST) and Modified MST (mMST)

To confirm performance assessment inputs for the Saltstone Facility at the Savannah River Site (SRS), a series of experiments were performed to examine the removal of Ra and Th by monosodium titanate (MST) and modified MST (mMST). The solubility of Th in the simulated high-level waste solutions was found to be extremely low; therefore, its removal by MST could not be measured. Radium was rapidly removed from the high-level waste simulant by both MST and mMST.

Adsorption of radium and barium on goethite and ferrihydrite: A kinetic and surface complexation modelling study

Radium and barium uptake onto ferrihydrite and goethite have been studied in the concentration range 1nM to 5mM and from pH 4 to 10, to develop a model to predict radium behaviour in legacy uranium mining wastes. For ferrihydrite, uptake of Ra2+ at nM concentrations was strong at pH >7. At higher concentrations, Ba2+ sorption to ferrihydrite was slightly weaker than that of Ra2+. Experiments with goethite showed weaker binding for both metal ions in all systems. The interactions of radium with both ferrihydrite and goethite are fully reversible. The behaviour of radium during transformation of ferrihydrite to goethite has been studied, and no evidence for irreversible incorporation within the goethite lattice was found; radium uptake to goethite was the same, whether or not it was present during its formation. Calcium competed with radium for ferrihydrite sorption only at high calcium concentrations (>10mM). Barium is a more effective competitor, and a concentration of 1mM reduced radium sorption. Sediment samples from a legacy uranium mining site have been analysed, and the in situ Rd values are consistent with radium uptake by surface coatings of ferrihydrite or goethite like phases. Surface complexation models have been developed for radium sorption to ferrihydrite and goethite which simulate the experimental data successfully. In both cases, approaches based on a single surface functional group and tetradentate binding sites simulated the data successfully. These data could be used in underpinning the safety case for legacy mining sites.

Sorption of 226Ra from waste effluents using Syrian bentonite

In view of environmental concern, sorption of radium on natural bentonite mineral (Aleppo, Syria) was investigated using a batch‐type method. Data were expressed in terms of distribution coefficients. An attempt to increase the selectivity of bentonite for radium was made by preparing M‐derivatives. Loss of mineral crystallinity in acidic media and the formation of a new phase, such as BaCO3, in Ba‐derivative were evidenced by XRD characterizations. Of the cationic forms, Na‐bentonite showed the highest affinity. Mechanisms of radium uptake were studied using M‐derivatives and simulated radium solutions. The obtained results indicated that surface sorption/surface ion exchange were the predominant processes. The distinct sorption behaviour observed with the Ba‐form was, possibly, a reflection of radium coprecipitation with barium carbonate. The competing order of macro components, likely present in waste streams, was investigated by studying different concentrations of the corresponding salt media. Sodium was found to be the weakest inhibitor. The performance of natural bentonite and the most selective forms, i.e. Ba‐ and Na‐derivatives, to sorb radium from actual oil co‐produced waters, collected form Der Ezzor Petroleum Company (DEZPC), was studied. This showed the influential effect of pH compared with other parameters.

Sorption of uranium, radium, and thorium by analcym-containing rock and sorbents based on plant tissue

Capacity of analcym-containing rock, hydrolytic wood lignin, and sorbents based on oat straw to absorb uranium, radium, and thorium from acid and weakly acid solutions of their salts was studied. Possible sorption mechanisms of radionuclides are considered on the basis of data furnished by IR spectroscopy and method of successive extractions.