Adsorption characteristics of traces of radium on membrane filters,glass and polyethylene

Adsorption of radium was studied on glass and polyethylene from aqueous solutions containing 8–40 pg·dm^{–3 224}Ra and on membrane filters, glass and polyethylene bottles from waste and river waters containing 2–170 pg·dm^{–3 226}Ra. The adsorption from aqueous solutions was determined as a function of pH and composition of the solutions and interpreted as due to ion exchange of Ra²⁺ ions for counter ions in the electric double layer on glass and polyethylene or due to chemisorption of RaSO₄ (RaCO₃) ion pairs on glass. Borosilicate glass adsorbed radium substantially more than polyethylene. The adsorption of dissolved forms of radium from the waste and river waters during storage and membrane filtration of the waters was negligible, but a significant loss of particulate forms of radium was sometimes observed during the storage. It has been recommended to separate dissolved and particulate forms of radium soon after the sampling and to prefer polyethylene to glass as container material for storage of dissolved forms of radium.     

Interaction of radium with freshwater sediments and their mineral components

A radiotracer method was used for investigation of the adsorption and desorption of radium on stream sediments under conditions similar to those prevailing in waste and surface waters. The effects of pH, ionic strength and Ca²⁺ or SO ₄ ^2– ions were studied. The results were compared with analogous data characterizing radium interaction with model solids representing components of the sediments. It has been found that the adsorption affinity of the sediments for radium cannot be easily derived from their composition or other properties. No simple correlation with specific surface area, organic matter, oxidic coatings or other components of the sediments was observed. However, an exceptional role of barite (barium sulfate) in the sediments was noted. In the presence of sulfate ions (60 mg/l) this component was responsible for the uptake of predominant or at least significant part of radium, depending on the barite content of sediments. In the absence of added sulfate ions, the adsorption of radium at ph 5–9 on sediments containing barite was lower than on similar sediments without this component, indicating that other components may be more efficient in radium adsorption.     

Natural radioactivity and hazard-level assessment of Portland cements in Turkey

The natural radioactivity levels and some radiological parameters of Turkish Portland cements (PC) originated in various regions were determined in this study. The activity concentration of cement samples for ²²⁶Ra, ²³²Th, and ⁴⁰K were measured using a gamma-ray spectrometer with high purity germanium radiation detector. The PC samples had activity concentrations of 33.0, 16.7, and 239.5 Bq kg⁻¹ for ²²⁶Ra, ²³²Th, and ⁴⁰K, respectively. The mean value of radium equivalent value (Ra_eq) was found to be 75.4 Bq kg⁻¹. The radium equivalent values in the cement samples were lower than the acceptable level of 370 Bq kg⁻¹. The calculated radiological parameters were found to be below the acceptance levels.

     

Interaction of radium with freshwater sediments and their mineral components. I.

The radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on ferric hydroxide and quartz under conditions similar to those prevailing in waste and surface waters. The effects of pH, liquid to solid ratio, ionic strength and presence of Ca²⁺ or SO ₄ ^2- ions have been studied. It has been concluded that at pH less than 7 and at concentration of suspended sediments (of common composition) less than 100 mg·1^–1 ferric hydroxide and quartz have negligible effect on the state and migration of radium in surface waters. Radium adsorbed on quartz can be easily desorbed with dilute solutions of hydrochloric acid or sodium chloride.     

The use of thermal analysis in the approximate determination of the cement content in concrete

Thermal analysis was first used to investigate the pattern of dissociation of hydrated ordinary Portland cement. Portlandite (Ca(OH)₂) decomposes at about 500°C. This was confirmed by kinetic calculations. Thermal analysis was then performed to establish the effect of varying the cement content on the percent mass loss associated with the decomposition of Ca(OH)₂ in cement mortar cured for 28 days. An increasing relation was obtained. Standard concrete cubes were then prepared with cement contents ranging from 200 to 450 kg m^-3. The loss in mass on heating, up to 750°C, of concrete samples cured for 28 days was then related to the cement content in concrete. The relation obtained was tested for concrete cubes of known cement content and found to be in better agreement than the results obtained by conventional chemical analysis. This method can be used for an approximate determination of the cement content in concrete. This revised version was published online in July 2006 with corrections to the Cover Date.     

Leaching behavior of137Cs in cement

To assess the safety of disposal of a radioactive waste-cement composite, the leaching of¹³⁷Cs from a waste composite into a surrounding fluid has been studied. Leaching tests were carried out in accordance with a method recommended by IAEA.¹ The leachability was measured as a function of bentonite clay to cement ratio. The fraction of¹³⁷-Cs leached from a specimen of Portland cement is 0.03–0.13 at a leaching time of 400 d. Results presented in this paper are examples of data obtained in a 10 y mortar and concrete testing project, which will influence the design of the engineered trench system for a future Yugoslav radioactive waste storage center.^2,3     

Determination of the leaching rate of radionuclide 134Cs from the solidified radioactive wastes in Syrian Portland cement and cement–microsilica matrixes

The suitability of Syrian Portland cement for disposal of solidified low-level radioactive waste was assessed by measuring the leaching rate of ¹³⁴Cs. In ordinary cement concrete, a leaching rate of 1.309 × 10^?3 g/cm² per day was measured. Mixing this concrete with microsilica reduced significantly the leaching rate to 3.106 × 10^?4 g/cm² per day for 1% mixing, and to 9.645 × 10^?5 g/cm² per day for 3% mixing. It was also found that the application of a latex paint reduced these leaching rates by about 10%. These results, along with mechanical strength tests (under radiation exposure, high temperature, long water immersion and freeze–thaw cycling) indicate that Syrian Portland cement is suited for the disposal of low-level radioactive waste.     

Influence of Doping of NaNO3 on the Solid Phase Thermal Decomposition of Bitumen and Cement

The thermal stability of solidified NaNO₃ salts in bitumen and cement has been investigated for safety considerations in the field of solidification of radioactive waste. The thermal decomposition of bitumen and cement in presence of NaNO₃ in a temperature range 22–650°C has been studied. The fraction decomposed of the pure samples and mixtures showed slow linear reactions followed by acceleratory and decay stages. Data are analyzed according to both Freeman-Carroll and Coats-Redfern kinetics to evaluate the activation energy and the order of reactions of all mixtures. It is found that the activation energies of bitumen and cement were 594 and 203 kJ mol^-1, respectively. The order of reactions of bitumen and cement was 2 and 4, respectively. The addition of NaNO₃ shortens the duration of the induction period in all mixtures. It was concluded that solidification of radioactive waste containing NaNO3 in bitumen and cement should be applied in the temperature range 22–300°C. At temperature higher than300°C solidification should be in cement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Leaching kinetics of <Superscript>54</Superscript>Mn and <Superscript>89</Superscript>Sr radionuclides fixed in cement­vermiculite composition

Summary Leach characteristics of ⁵⁴Mn and ⁸⁵Sr radionuclides from ordinary Portland cement have been studied using International Atomic Energy’s (IAEA) standard leach method. The retardation factors, K_F, and coefficients of distribution, k_d, have been determined using a simplified mathematical model for analyzing the migration of radionuclides. The lowest leaching values after 60 days were achieved in samples with 5% of vermiculite. Results presented in this paper are the examples of results obtained in a 10 year mortar and concrete testing project, which will influence the design of the engineered trench system for a future central Serbian radioactive waste storage center.     

Releases of radium from an abandoned uranium mine site: Žirovski Vrh uranium mine, Slovenia

Since the beginning of explorative uranium mining at the Žirovski Vrh uranium ore deposit area in 1968, a radioactivity monitoring programme has been carried out. The extent of the programme has varied according to the pre-operational, operational, and, finally, post-operational conditions. In this paper, our ten year results on the dissolved radium concentrations in surface waters, which have been contaminated and potentially affected by the uranium mining and milling activities, are reported. With the exception of waters drained from the hydrometallurgic waste site with radium content ranging from 2 to 9 kBqm⁻³, radium content is far below the drinking water limit of 1000 Bqm⁻³; in the Brebovŝčica stream, which collects all the waters affected by the mine, the present radium concentration does not exceed 10 Bqm⁻³.     

Treatment of an aqueous radioactive waste solution with elevated levels of226Ra and228Ra

Treatment of an aqueous radioactive waste solution to remove radium prior to discharge was conducted at a laboratory scale. The actual solution is mainly composed of combined radium (²²⁶Ra and²²⁸Ra) with high concentrations of manganese, iron and calcium, which are present as chlorides in dilute hydrochloric acid. Direct precipitation by sulfate anions was selected to be the more viable treatment technique. Sulfate anion concentration, free acidity, temperature and aging of the sulfate precipitate in the supernate prior to filtration are factors that were investigated for their effect on the separation efficiency. The data obtained are discussed in detail.     

Methodological advances for measuring low-level radium isotopes in seawater

A new approach for quantifying radium isotopes in seawater was developed in advance of the international GEOTRACES program, which has the goal of identifying processes and quantifying fluxes that control the distribution of trace elements and isotopes (TEIs) in the ocean. High-resolution water column samples were collected via a commercially available in situ pump modified to accept multiple filter media including a manganese-oxide (MnO₂) impregnated acrylic cartridge for extracting dissolved radionuclides from seawater. The modifications mitigated prefilter clogging and allowed for up to 1,800 L filtrations in 4 h of pumping. Different MnO₂ cartridge preparation methods were investigated to achieve maximum radium (Ra) extraction efficiency under high sample flow rates. Full-ocean depth profiles were measured for short-lived radium isotopes (²²³Ra and ²²⁴Ra) in shipboard laboratories using a delayed coincidence alpha scintillation counter (RaDeCC). Samples were reanalyzed 4 weeks and 2 months after collection for ²²⁸Th and ²²⁷Ac to correct for supported ²²⁴Ra and ²²³Ra, respectively. Finally, the cartridges were measured on a gamma-ray spectrometer for the long-lived radium isotopes (²²⁶Ra and ²²⁸Ra). Parallel 20 L samples at each pumping depth were collected from Niskin bottles and analyzed via alpha scintillation for ²²⁶Ra to determine radium extraction efficiencies for the cartridges. These modified methods will allow for increased sample throughput, and hence higher spatial resolution for radium isotopes in the ocean. Such resolution will greatly improve the determination of oceanic vertical and horizontal mixing rates over small and large scales, which in turn can be used to calculate fluxes of TEIs into the ocean.     

On the chemical durability of a metal-metalloid glass from the alloy (Fe,Cr)80(P,C,Si)20 in hardened Portland cement investigated by FT-IRRS, ESCA, and SEM/EDX

Composites of metal-metalloid glass fibres FIB-RAFLEX^TM (Fe,Cr)₈₀(P,C,Si)₂₀ with ordinary Portland cement (OPC) were prepared and used for an accelerated ageing procedure to study the cement paste-fibre interfaces which affect the mechanical behaviour of concrete composites. The role of the interface on the global behaviour of the concrete composite as a basis for the development of high-performance cementitious materials was studied on pulled out fibres by EDX, ESCA and by FTIR/RAMAN microspectroscopy. A Ca(OH)₂ rich layer is predominant for the surface of the reinforced cementitious material and represents the interface between aggregate and matrix. The interaction between aggregate and matrix is the reason for the strength of composites with this fibre in the highly alkaline environment of hydrating cements.     

On the chemical durability of a metal-metalloid glass from the alloy (Fe,Cr)80(P,C,Si)20 in hardened Portland cement investigated by FT-IRRS,ESCA, and SEM/EDX

Composites of metal-metalloid glass fibres FIB-RAFLEX^TM (Fe,Cr)₈₀(P,C,Si)₂₀ with ordinary Portland cement (OPC) were prepared and used for an accelerated ageing procedure to study the cement paste-fibre interfaces which affect the mechanical behaviour of concrete composites. The role of the interface on the global behaviour of the concrete composite as a basis for the development of high-performance cementitious materials was studied on pulled out fibres by EDX, ESCA and by FTIR/RAMAN microspectroscopy. A Ca(OH)₂ rich layer is predominant for the surface of the reinforced cementitious material and represents the interface between aggregate and matrix. The interaction between aggregate and matrix is the reason for the strength of composites with this fibre in the highly alkaline environment of hydrating cements.     

Determination of radium isotopes in mineral and environmental water samples by alpha-spectrometry

Summary A method for the determination of low-level radium isotopes in mineral and environmental water samples by alpha-spectrometry has been developed. Radium-225, which is in equilibrium with its mother ²²⁹Th, was used as a yield tracer. Radium were preconcentrated from water samples by coprecipitation with BaSO₄and iron (III) hydroxide at pH 8-9 using ammonia solution, then isolated from uranium, thorium and iron using a Microthene-TOPO chromatography column at 8M HCl, separated from barium in a cation-exchange resin column using 0.05M 1,2-cyclohexylenedinitrilotetraacetic acid monohydrate at pH 8.5 as an eluant, and finally electrodeposited on a stainless steel disc in a medium of 0.17M (NH₄)₂C₂O₄at pH 2.6 and current density of 400 mA^. cm^-2, and counted bya-spectrometry. Optimum experimental conditions for radium separation, purification and electrodeposition have been studied and discussed in the paper. The lower limits of detection of the method are 0.11 mBq^. l^-1for ²²⁶Ra, ²²⁸Ra and ²²⁴Ra, respectively, if 2 l of water are analyzed. The method has been checked with a certified reference material IAEA-Soil-6 supplied by the International Atomic Energy Agency and reliable results were obtained. Eighteen water samples collected in Italy have been analyzed with the method, the mean radiochemical yields for radium were 86.2±6.5%. The obtained radium concentrations were in the range of 0.50-60.8 mBq^. l^-1for ²²⁶Ra, of 0.10-25.7 mBq^. l^-1for ²²⁸Ra, and of￡LLD-7.97 mBq^. l^-1for ²²⁴Ra. The ²²⁸Ra/²²⁶Ra and ²²⁴Ra/²²⁶Ra ratios were in the range of 0.189-4.45 and￡LLD-0.941, respectively.     

Interaction of radium with freshwater sediments and their mineral components

Radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on muscovite and feldspar (albite) under conditions similar to those prevailing in waste and surface waters. The effects of pH, liquid to solid ratio, time, ionic strength (Na⁺) and presence of Ca²⁺ or SO ₄ ^2? ions have been studied. It has been concluded that both minerals can significantly affect the fate and migration of radium in surface waters if present as major components of bottom sediments or as suspended solids in concentrations of several milligrams per liter or higher. Muscovite can absorb radium even from moderately acidic waters. Radium adsorbed on muscovite and albite cannot be easily released upon an increase of the salinity of ambient water. However, almost complete desorption can be achieved with 1M HCl. Mechanisms of radium adsorption on both minerals and character of the adsorption sites are discussed.     

Interaction of radium with freshwater sediments and their mineral components

Radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on kaolinite and montmorillonite under conditions similar to those prevailing in waste and surface waters. It has been found that adsorption depends on the pH and ionic strength of the solution, and the character of these dependences is different for kaolinite and montmorillonite. Sulfates at concentration 60 mg·l^–1 have negligible effect on the adsorption. Montmorillonite represents better adsorbent for radium than kaolinite, but both minerals may significantly affect the form and migration of radium in surface waters, if present as (major) components of freshwater sediments. Radium can be quantitatively desorbed by 1M HCl from kaolinite but not from montmorillonite. The desorption by 0.1M NaCl is generally lower and depends on the pH during the preliminary adsorption. Mechanisms of radium adsorption on both minerals and the character of the adsorption sites are discussed.     

A rapid method for the separation of radium from Tuwa spring waters for determining the activity ratio of223Ra/226Ra

A rapid method for the separation of radium in spring waters of Tuwa, Panchamahal district, Gujarat State, India, containing large amounts of calcium (0.5 g/l) has been developed. It consists of concentrating polyvalent cations from 21 samples using 10 g of carboxylate exchanger, Zeokarb 226 (NH ₄ ⁺ ) and then precipitating radium as sulfate in the presence of 400 μg of barium.     

Determination of radium isotopes by BaSO4 coprecipitation for the preparation of alpha-spectrometric sources

A coprecipitation procedure for the preparation of -spectrometric sources for radium, using BaSO₄ as carrier, has been applied to the determination of alpha radium isotopes in water samples. The use of¹³³Ba as a suitable tracer for radium determination and possible losses of radon isotopes from the sources are studied and discussed.     

Method for determination of radium in seawater using MnO<Subscript>2</Subscript> co-precipitation technique

Radium is considered to be a useful tracer for studying various physical processes of seawater. There are several methods for analysis of radium; however, analysis of radium in seawater by those analytical techniques is a tedious job. Thus a new methodology was optimized for analysis of radium in sea water using MnO₂ co-precipitation followed by gamma spectrometry. The method produced good yield which ranged from 85–98%. The method is simple and requires less amounts of chemicals and no use of acids. Seawater from different western Indian coastal environments viz. Tarapur, Mumbai and Goa were collected and analysed for ²²⁶Ra and ²²⁸Ra using this method.