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.     

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.     

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

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.     

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.     

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.     

Rapid radiochemical separation of radium from environmental samples using ion-exchanger Zeokarb-225

A rapid radiochemical method has been developed for the separation of radium in the presence of excess calcium from environmental samples such as spring waters and marine sediments. Radium is preconcentrated by co-precipitation as carbonates along with other alkaline earths. Subsequently, most of the alkaline earths are complexed with EDTA at pH 7.5 and the solution is passed through a column of Zeokarb-225 (NH ₄ ⁺ ). Radium, along with traces of calcium, is sorbed on the exchanger. Radium is desorbed with 2N HNO₃ and finally coprecipitated with 400 μg of barium as isulfate. The alphas of²²⁶Ra are counted in a silicon surface barrier detector and²²⁸Ra betas are counted in an end-window GM Counter.     

Mapping short-lived radium isotopes in estuarine residential canals (Gold Coast,Australia)

Distributions of short-lived radium isotopes (²²⁴Ra and ²²³Ra) were investigated on the Gold Coast waterways, one of the largest residential estuarine canal systems on Earth, in an attempt to estimate radium-derived residence times and obtain insights into sources of radium isotopes. Surface and bottom canal waters were sampled in 61 locations over ~300 km of waterways. Radium isotope activities were 12-fold higher in groundwater than estuarine waters. Surprisingly, radium activities were usually higher in surface waters than bottom waters implying a radium source associated with tidal pumping in artificial beach sediments. Estimated radium ages were usually younger within artificial canal surface waters than in the natural estuarine waterways. This study shows that the tidally driven groundwater radium source can be enhanced by the extended canal shoreline.     

Evidence for the Formation of Trioctahedral Clay upon Sorption of Co on Quartz

The sorption mechanism of Co on quartz at room temperature has been investigated by an in-depth analysis of published extended X-ray absorption fine structure (EXAFS) spectroscopy and solution chemistry data. In particular, the 3.5–5 Å mid-range atomic environment of Co has been determined with unprecedented precision by combining ad initio FEFF7.02 calculations and results obtained by polarized EXAFS on the mid-distance structure of sheet silicate minerals. The local atomic environment around sorbed Co atoms is identical to that of Co in trioctahedral clays and substantially different from that in the cobalt hydroxide Co(OH)_2(s). Neoformation of a trioctahedral clay is consistent with calculated thermodynamic solubilities, which indicate that 2:1 and 1:1 Co-rich hydrous silicates, similar to kerolite and chrysotile, are less soluble than Co(OH)_2(s). Consequently, precipitation of Co-rich clay is favored over that of Co(OH)_2(s) at pH values below 9 and for a dissolved Si concentration equal to quartz solubility. New experimental data show that dissolved Si concentrations can approach, and even exceed, that of quartz solubility during the short times of sorption experiments. Based on the available data, it is not possible to conclude unequivocally if the Co layer silicate grew epitaxially on the quartz surface, topotactically in a surface amorphous layer, or independently of the quartz framework structure. The structural and chemical interpretation is supported by recent published studies in which sorption of a hydrolyzable cation leads to the neoformation of a mixed layer phase formed from the sorbate species and the sorbent metal. This surface-induced precipitation mechanism is a general phenomenon that may account for the formation of secondary clays as coatings on silicates.     

Mechanism of hydrolyzable metal ions effect on the zeta potential of fine quartz particles

The effects of ion species, cation valence, ionic strength, and hydrated ionic radius on the zeta potential of quartz have been systematically studied through the measurement of zeta potential, sedimentation rate, and aggregation observation. The results show that the interaction between hydrolysis components and quartz particles results in three critical points – CR₁, CR₂, and CR₃. The results of sedimentation and aggregation observation are in good agreement with the changes of the zeta potential in 0.1?M MgCl₂, the maximum sedimentation rate being 99.26% at pH 10.85. When the pH is around 6.25 or 10.00, the sedimentation rate is relatively lower and the size of aggregation smaller. The adsorption of hydrolyzable multivalent metal ions on the quartz surface is a combination of three adsorption forms, namely electrostatic adsorption, hydroxyl complex adsorption, and hydroxide precipitation adsorption. Then the hydrolysis properties of metal ions and the surrounding environment determine the action of the hydrolysis components and the main form of adsorption.     

Sorption of nickel on marl

Batch sorption experiments using nickel have been carried out on marl, a sedimentary, carbonaceous rock. All experiments were performed with a synthetic water of pH 7.3 and in an atmosphere of N₂/1% CO₂. Over the equilibrium nickel concentration range of 10^–11–10^–5M, sorption was linear and reversible with R_d of 819 ml g^–1. Owing to the linear sorption behavior, R_d was independent of rock/water ratio (r/w=1/5–1/100). The data suggested that at [Ni] lower than 10^–7M an isotope exchange mechanism operated, whereas at higher [Ni], sorption involved ion exchange. Sorption experiments on some of the components of marl indicated that nickel adsorbs mainly on the clay minerals and on the trace of iron hydroxide present; sorption on calcite and quartz was low.     

Synergistic extraction of radium using 2-thenoyltrifluoroacetone and tributyl phosphate or trioctylphosphine oxide

The extraction of radium into a mixture of 2-thenoyltrifluoroacetone (HTTA) and tributyl phosphate (TBP) or trioctylphosphine oxide (TOPO) in n-hexane or cyclohexane has been investigated with regard to the dependence on pH, and TBP and TOPO concentrations. It has been found that the formation of mixed complexes of the type Ra(TTA)₂ (TBP)₂ and Ra(TTA)₂(TOPO)₂ occurs and the overall extraction constants of both complexes were calculated. With the systems described, very high distribution ratios of radium have been attained; these may advantageously be used for the separation and concentration of traces of radium.     

Zur Kenntnis der künstlichen Alterung aluminiumhaltiger Eisen(III)-hydroxide

Study of the ageing process of amorphous ferric hydroxide has shown that the presence of traces of Al³⁺ can drastically change the course of the reaction under certain conditions. Al³⁺ traces delay crystallization, an effect which is dependant on the pH of the solution in which the originally amorphous gel is boiled. With increasing pH they favour the formation of the α-F₂O₃-phase, whereby the α-FeOOH modification, the formation of which should otherwise be favoured by the dehydrative conditions employed, is not formed at all. Inhibition of the formation of the α-FeOOH phase is already crystallographically detectable at a molar ratio of Al₂O₃/Fe₂O₃=0.001. The complete disappearance of this phase at pH=10 of the ageing medium is found at the molar ratio Al₂O₃/Fe₂O₃=0.03. At higher Al³⁺ concentrations the amorphous gel is converted into α-Fe₂O₃. In the range 10–20 mol% Al₂O₃, crystallization is strongly inhibited. Further increase in the Al³⁺ content favours the formation of Bayerite-phase, which then at 50 mol% Al predominantes, alongside poorly crystalline α-Fe₂O₃. For Al₂O₃/Fe₂O₃=0.55, three phases are present, hydrohematite, bayerite and boehmite. With still greater amounts of Al³⁺ only the boehmite modification is found. By stepwise crystallographic study of the progressive dehydration the duration of reaction has been established for ferric hydroxide both in the pure state and when doped with Al³⁺.     

Europium speciation by time-resolved laser-induced fluorescence

Time-resolved laser-induced fluorescence has been used to investigate Eu complexes formed with a few main ligands encountered in natural waters: hydroxide, carbonate and humic substances. By varying pH and concentrations of ligands at fixed europium concentration and ionic strength, it was possible, together with free europium Eu³⁺, to identify spectrally and temporally carbonate complexes, namely Eu(CO₃)⁺, Eu(CO₃)₂⁻ and Eu(CO₃)₃³⁻ and humate complexes EuHA. For hydroxide complexes, no differences were found in terms of fluorescence spectra and lifetimes. A spectral interpretation is described by using deconvolution for all systems.     

The influence of the solutions pH on the microstructure of hydrogels of yttrium and europium oxohydrates prepared via the sol-gel method

Evolution of the mother liquor pH in the course of the sol-gel precipitation of hydrogels of yttrium and europium oxohydroxides has been studied at different acidity of the system and the precipitant (NaOH) concentration. The optimal pH and components concentrations have been determined; the specific surface area of 210 m²/g (yttrium hydroxide) and of 100 m²/g (europium hydroxide) has been attained under these conditions.     

Radium removal from aqueous solutions by adsorption on non-treated and chemically modified biomass by-product

The adsorption efficiency of a biomass by-product (olive cake) regarding the removal of radium (²²⁶Ra) from aqueous solutions has been investigated prior and after its chemical treatment. The chemical treatment of the biomass by-product included phosphorylation and MnO₂-coating. The separation/removal efficiency has been studied as a function of pH, salinity (NaCl) and calcium ion concentration (Ca²⁺) in solution. Evaluation of the experimental data shows clearly that the phosphorylated biomass by-product presents the highest adsorption capacity and efficiency followed by the MnO₂-coated material and the non-treated biomass by-product. However, regarding the effect of salinity and the presence of competitive cations (e.g. Ca²⁺) on the adsorption/removal efficiency, the MnO₂-coated material shows the lowest decline in efficiency (only 2 % of the relative adsorption efficiency) followed by the non-treated and the phosphorylated biomass by-product. The results of the present study indicate that depending on the physicochemical characteristics of the radium-contaminated water, all three types of the biomass by-product could be effectively used for the treatment of radium-contaminated waters. Nevertheless, the MnO₂-coated material is expected to be the most effective adsorbent and an alternative to MnO₂ resins for the treatment of environmentally relevant waters.     

Study of the surface properties of titanium hydroxide using a radioactive tracer technique

The surface properties of titanium hydroxide precipitates, formed under different conditions were studied in the presence of carrier-free radioactive⁸⁹Sr. It was found that titanium with concentrations equivalent to 24 mg TiO₂/litre, was enough to remove by adsorption more than 95% of the carrier-free strontium activity from an alkaline solution (pH≈13) in less than 6 hrs, regardless of whether the precipitate was freshly prepared or aged for a few days. If the precipitate was formed in situ, at the above pH value, the percentage removal of the strontium activity from the solution was even greater, and this was attributed to an internal adsorption process. At a lower pH value (∼2.5), however, the adsorption of strontium activity by titanium hydroxide was very low (<5%), whether the precipitate was preformed or formed in situ. The increase in the adsorption ability of titanium hydroxide precipitate on going from low pH (2. 5) to higher values was attributed to the inversion of the charge of titanium hydroxide sols from cationic particles at pH 2. 5 to negatively-charged particles at pH>3. 5, these latter particles adsorbing any positive strontium ions in solution.     

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.     

Kinetics of polymerization of N-tert-butylacrylamide. Part II

The effect of ferric chloride on the kinetics of the radical polymerization of N-tert-butylacrylamide has been investigated in methanol solution at 25°C, with the use of 4,4′-dicyano-4,4′-azodipentanoic acid as initiator. A shrinkage factor of 0.193 mmole polymerized for 1 mm contraction in a capillary of 1 mm diameter has been obtained from density measurements. In the absence of ferric chloride, rates of polymerization were found to be proportional to the concentration of monomer and to the square root of the initiator concentration. With ferric chloride present, the rate of polymerization becomes directly proportional to the initiator concentration and inversely proportional to the concentration of ferric salt. From measurements of the rates of production of ferrous iron, the specific rate constant of the initiation reaction has been found to be (1.8 ± 0.4) × 10^?6sec^?1 at 25°C, compared with a value of 7.63 × 10^?8 sec^?1 calculated from the kinetic data obtained with no ferric salt present. The value of the ratio k_p/k₄. where k_p is the propagation coefficient and k₄ is the velocity coefficient for termination by ferric chloride, has been calculated to be 6.0 × 10^?4 at 25°C, which is considerably smaller than the value found for the ferric chloride-terminated polymerization of acrylamide in water. This markedly lower value of k_p/k₄ has been attributed principally to the steric effect of the tert-butyl group on the magnitude of k_p.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

An attempt to obtain aluminium hydroxide that could give aluminium oxides of increased thermal stability was made. Aluminium hydroxide was precipitated during a hydrolysis of aluminium chloride in ammonia medium. The influence of preparative conditions, such as a dosing rate of aluminium precursor, pH, duration of the precipitate refluxing and temperature of calcination, on the properties of obtained hydroxides and oxides was investigated. The materials were studied with the following methods: thermal analysis, IR spectroscopy, low-temperature nitrogen adsorption and adsorption–desorption of benzene vapours. Precipitated boehmites had high values of S _BET determined from nitrogen adsorption (220–300 m²g^–1), good sorption capacity for benzene vapours, developed mesoporous structure and hydrophilic character. It has been proved that a high pH value during the precipitation of aluminium hydroxide favoured better crystallisation of boehmite structure, higher temperature of its dehydroxylation into γ-Al₂O₃, and delayed transformation of γ phase into α-Al₂O₃. Aluminium oxides derived from the hydroxides precipitated at a high pH were the most stable at high temperatures, and were characterised with the best surface properties. The online version of the original article can be found at