Effect of gamma-irradiation on adsorption properties of Slovak bentonites

One of the basic prerequisites for the use of bentonite as engineering barrier in deep geological repositories for radioactive waste and spent nuclear fuel is their stability against ionizing radiation stemming from radionuclides present in radioactive waste and spent nuclear fuel. The aim of this study was to compare the changes in the adsorption properties of selected Slovak bentonites in relation to uranium fission products (¹³⁷Cs and ⁹⁰Sr), prior to and after irradiation of bentonites with a ⁶⁰Co γ-source and specifying the changes in the structure of Slovak bentonites induced by γ-radiation. The changes in irradiated natural forms of Slovak bentonites and the changes in their natrified analogues and fractions with different grain sizes were studied from five Slovak deposits: Jelšovy potok, Kopernica, Lastovce, Lieskovec and Dolná Ves. The EPR spectra of bentonites from deposits Jelšovy potok and Lieskovec with absorbed doses of 10⁴ and 10⁵ Gy γ-rays showed no changes in the structure of the studied Slovak bentonites. The changes, which in terms of structure destabilization can be considered insignificant, occurred only in bentonites with absorbed doses of γ-radiation as much as 1 MGy. The absorbed dose of 1 MGy γ-radiation did not have an effect on the adsorption of cesium on every studied bentonite. Changes that can also be regarded as insignificant occurred only during strontium adsorption, especially on Fe–bentonite from deposit Lieskovec and Ca–Mg–bentonite from deposit Jelšovy potok, when an increase in the adsorption capacity occurred. Attention should be paid in further research of this topic which would require carrying out experiments on bentonite samples with absorbed doses higher by several orders of magnitude.     

Cesium sorption on bentonites and montmorillonite K10

The physical and chemical properties of illitic clay minerals from Slovak deposit suitable for application in engineering barriers for high level radioactive waste repositories and spent nuclear fuels were studied. The isolation of spent nuclear fuels and high level radioactive wastes from the outer environment in a deep repository is gained by means of a system of multiple engineering and natural sealing barriers. Vital segments in a multiple barrier system are clay rocks, of which bentonites represent the most suitable clay material. Cs-adsorption on fine fractions of adsorbents (bentonites from three Slovak deposits: Jelšovy potok J15, Kopernica K15, Lieskovec L15 and montmorillonite K10) has been studied with using batch of radiometric techniques. Adsorption parameters have been determined for adsorbent-cesium solution system as a function of contact time and adsorbate concentration. The influences of pH change, the effect of competitive cations, complex-forming organic chelating agents on the adsorption of Cs have also been studied.     

Feasibility study of k0-INAA at the ITU TRIGA Mark II research reactor,Turkey

In this study, the effect of contact time, pH, competitive cations and equilibrium study of adsorption on Slovak illite/smectite Dolná Ves was investigated. The sorption processes was studied using batch techniques under aerobic conditions with radioisotope indication using ⁶³Ni as a radiotracer. Studied material has proved to be as promising candidate for practically used as a barrier against the spread of undesirable substances in the environment landfill as insulating material of toxic and hazardous waste.     

Comparative study of cesium adsorption on dioctahedral and trioctahedral smectites

Bentonites which are characterized by good rheological, mineralogical and chemical stability is considered used as sealing barriers in multibarrier Slovak system of deep geological repository for high-level radioactive waste and spent nuclear fuel. In Slovak Republic there are several significant deposits of bentonite, which are characterized by appropriate adsorption properties and meet the geotechnical requirements for this type of barriers. Study of adsorption properties of bentonites and other smectites is an essential step for developing the migration model long-lived corrosion and activation products, and fission products of uranium. Nuclear wastes contain the most important nuclear fission products, radioisotopes ¹³⁴Cs and ¹³⁷Cs. The present paper investigates and compares the cesium adsorption properties of Slovak and North America bentonites composed mainly of dioctahedral smectite montmorillonite (J, L, SAz-1 and STx-1) and trioctahedral smectites saponite (SapCa-2) and hectorite (SHCa-1).     

Utilization of Slovak bentonites in deposition of high-level radioactive waste and spent nuclear fuel

The basic strategic aims in the field of managing high-level radioactive waste and liquidation of nuclear power plants are all contained in the Energy policy of the Slovak Republic. Its aim is to resolve the concept of the backside of the nuclear energetics fuel cycle??long-term deposition of high-level radioactive waste and spent nuclear fuel (SNF). The most important form of high-level radioactive waste and SNF long-term deposition is their deposition in deep geological formations created by natural as well as engineering barriers used to isolate the long-lived radionuclides from the biosphere. The basic components of these barriers are clays, of which bentonite is generally referred to as the most suitable clay material. There are a few significant bentonite deposits in the Slovak Republic: Jel?ový potok, Kopernica, Lastovce, Lieskovec, Dolná Ves. The review article summarizes the information on geotechnical properties of Slovak bentonites published up-to-date, which is inevitable to know for the intention of their use. It highlights the advantages and shows drawbacks of five Slovak deposits. It suggests further research direction, to draw a thorough hydraulical, microbial and radiation profile of Slovak bentonites.     

Influence of organic surfactants on structural stability of mechanochemically treated bentonite

The aim of this work was to compare the influence of organocations with different length of alkylammonium chain on the structural stability of clays towards mechanochemical treatment. An industrial product JP A030 (Envigeo, Inc., Slovakia) based on Jelšovy Potok bentonite (Slovakia) and three organoclays prepared from this material via ion exchange with tetramethylammonium, octyltrimethylammonium and octadecyltrimethylammonium cations (TMA-JP A030, OTMA-JP A030 and ODTMA-JP A030, respectively) were ground for 1–20 min in a high-energy planetary mill. The products were investigated by X-ray diffraction analysis, thermal analysis, scanning electron microscopy and energy dispersive X-ray analysis. The long-chain organic cations apparently enhance the structural stability of bentonite during high-energy grinding.     

First shrinkage parameters of Slovak bentonites considered for engineered barriers in the deep geological repository of high-level radioactive waste and spent nuclear fuel

The high potential of bentonites to volume changes depending on the water content is considered as their advantage for the engineered barriers in the deep geological repository of high-level radioactive waste and spent nuclear fuel because of swelling and self-healing of cracks in contact with water. On the other hand, drying may lead to opening of cracks and spaces between the bentonite blocks. This would increase the permeability and contamination risk around the hot container with high-level radioactive waste and spent nuclear fuel, especially if the host rock mass is dry. First shrinkage tests on four Slovak bentonites studied for engineered barriers were carried out. The water content at the shrinkage limit and the relative linear shrinkage are the first available shrinkage parameters received for the bentonite paste. The shrinkage hazard is higher in the best bentonites with high swelling potential—from Kopernica and Jel?ový potok. The results indicated the necessity of further shrinkage tests to determine the relative linear and volume shrinkage of bentonite elements pressed of the loose bentonite powder of low water content.     

Sorption of strontium on Slovak bentonites

Sorption of Sr on five Slovak bentonites of deposits has been studied with the use of batch technique. In the experiments there have been used natural, chemically modified and irradiated samples, in three different kinds of grain size. The pH influence on sorption of strontium on bentonites, pH change after sorption and influence of competitive ions have been studied. Distribution ratios have been determined for bentonite–strontium solution system as a function of contact time, pH and sorbate concentration. The data have been interpreted in term of Langmuir isotherm. The uptake of Sr has been rapid and the sorption of strontium has increased by increasing pH. The percentage sorption has decreased with increasing metal concentrations. The pH value after sorption for the natrificated forms of bentonite starts already in the alkaline area and moves to the higher values. For the natural bentonites the values occur in the neutral or in the acidic area. Sorption of Sr has been suppressed by presence of competitive cations as follows: Ba²⁺ > Ca²⁺ > Mg²⁺ > NH₄ ⁺ > K⁺ > Na⁺. By sorption on natrificated samples colloidal particles and pH value increase have been formed. The bentonite exposure as a result of interaction of γ-rays has led to expansion of the specific surface, increasing of the sorption capacity and to the change in the solubility of the clay materials.     

Comparative study of strontium adsorption on dioctahedral and trioctahedral smectites

Slovak bentonites characterized by good rheological, mineralogical and chemical stability are considered as suitable sealing barriers for construction of Slovak deep geological repository for high-level radioactive waste and spent nuclear fuel. There is several Slovak bentonite deposits, bentonites of which have appropriate adsorption properties meeting the geotechnical requirements for this type of barriers. Study of adsorption properties of bentonites (mainly smectites) is an essential step for developing the migration model long-lived corrosion and activation products, and fission products of uranium. Nuclear wastes contain the most important nuclear fission products, β-emitter ⁹⁰Sr with long half-life, biological half-life and high mobility. The present paper investigates and compares the strontium adsorption properties of bentonites of different mineral composition consisted mainly of dioctahedral and trioctahedral smectites.     

Thallium fractionation in polluted environmental samples using a modified BCR three-step sequential extraction procedure and its determination by electrothermal atomic absorption spectrometry

Determination of thallium in polluted environmental samples and their extracts obtained by a modified BCR three-step sequential extraction procedure was used to study thallium distribution and mobility in the monitored polluted area affected by acidification (Šobov, Central Slovakia). The results of fractionation applied to 5 soil certified reference materials and 14 environmental samples show that the vast majority of thallium occurred in the residual fraction. This means that highly toxic thallium is strongly entrapped in the parent rock materials remains immobile and its environmental toxicity is therefore reduced. The limit of detection for thallium in the studied fractions was lower than 0.050 mg kg⁻¹, the precision (RSD) of the ultratrace determination of thallium in the studied fractions was better than 17 % and the accuracy of the used method was verified by analyzing certified reference materials. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Acidity of montmorillonite pillared by alumina, zirconia and chromia

Acidic properties of Al-, Zr- and Cr- pillared montmorillonites prepared from Jelšovy Potok bentonite (Central Slovakia) have been investigated using temperature-programmed desorption of ammonia. The number of acid sites varied with different interlayer cations from 0.06 to 0.23 mmol g⁻¹. The character of acid sites was similar in the case of Al- and Zr- forms. It is obvious that the chromium analogue contains fewer acid sites, nevertheless, they seem to be stronger compared to Al- and Zr- pillared montmorillonites.     

Adsorption of cesium and strontium on natrified bentonites

The influence of chemical activation–natrification of bentonites on adsorption of Cs and Sr was studied with regards to utilization of bentonites for depositing high-level radioactive waste and spent nuclear fuel. Bentonite samples from three Slovak deposits in three different grain-size (15, 45 and 250 μm), natural and natrified forms (Na-bentonites); under various experimental conditions, such as contact time, adsorbent and adsorbate concentration have been studied. When comparing the Na-bentonites and their natural analogues, the highest adsorbed Cs and Sr amounts were reached on the natrified samples. After the Sr adsorption a drop in the pH equilibrium value was observed together with the increase of the initial Sr concentration. A disadvantage of the natrified bentonite forms is formation of colloid particles. After 2 h of phase mixing a gentle turbidity was observed as well as formation of a gel-like form. The above findings were confirmed by observing the particle distribution in dry and wet dispersion and centrifugation at two different speeds. Natrification as a technological process of bentonite quality improvement cannot be applied when constructing a long-term repository for high-level radioactive waste and spent nuclear fuel. The main problem of natrification is a technological process which leads to a significant pH increase. Alkaline environment in combination with the K presence and increased temperature in the vicinity of radio-active waste can lead to a rapid illitization of smectite and loss of the original adsorption qualities. Moreover, sodium additions are a significant point of uncertainty since it is not possible to state what amount of Na enters the interlayer space and what amount stays in the inter-partition space.     

Mobility of important toxic analytes in urban dust and simulated air filters determined by sequential extraction and GFAAS/ICP-OES methods

The modified BCR three-step sequential extraction procedure has been applied to homogenized urban dust samples and to simulated air filters loaded with the prepared urban dust via the wet deposition procedure. This work has been focused on comparative study of the distribution of trace elements in both samples and evaluation of the factors influencing the reliability of results with respect to the proposed extraction procedure. Extracted chemical fractions were analyzed by ICP-OES and GFAAS depending on the concentration levels of investigated trace elements As, Cd, Cr, Mn, Ni, and Pb, selected according to their adverse effect on the human health. Statistically evaluated results indicate significant differences between the extracted portions of analytes in urban dust and simulated air filters, where the mobility of some analytes in simulated air filters was higher than that in urban dust samples. The impact of surfactant Triton X-100 (0.05 vol. %) on the extraction procedure was also investigated. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Effect of gamma irradiation on trichromatic values of spices

The effect of γ-irradiation on trichromatic color values L*, a*, and b* was determined in black pepper, oregano, and allspice samples irradiated at average doses from 5 kGy to 30 kGy. Trichromatic values a* measured in methanol extracts of treated spices immediately after the irradiation process were significantly changed, but the subsequent storage of allspice and oregano caused much more distinctive alteration of these color values than the irradiation itself. Additionally, the differences in redness between the reference (non-irradiated) allspice and oregano samples and samples treated by γ-radiation gradually disappeared during the storage period. On the contrary, the post-irradiation storage of black pepper samples did not reveal any changes of a* values. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Long-term operation of a domestic wastewater treatment plant with membrane filtration

Possibilities of membrane technology and the use of membrane processes in wastewater treatment were investigated. The main focus was the monitoring of the starting phase of a domestic wastewater treatment plant. Experimental part of the study was realized at the municipal wastewater treatment plant (WWTP) Devínska Nová Ves — Bratislava during the period from February 2005 to September 2006. The system was stable without any external chemical treatment of the membrane modules and the permeate quality was very high. Observed decrease of COD and BOD₅ values ranged between 91 % and 98 %. The process of nitrification was very successful considering its high efficiency (> 95 %). Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Adenosine,adenosine monophosphate,and adenosine triphosphate adsorption from aqueous solutions on the surface of multiwall carbon nanotubes

Adenosine, adenosine monophosphate, and adenosine triphosphate adsorption from aqueous solutions on the surface of carbon nanotubes is studied. Adsorption isotherms are plotted and adsorption free energies, as well as areas per molecules of the adsorbates, are calculated at their concentrations in solutions of 0–10⁻³ mol/dm³. It is shown that the monomolecular adsorption is characterized by rather loose packing of adsorbate molecules on the nanotube surface, with the packing density increasing in the presence and upon a rise in the concentration of phosphate groups in adsorbate molecules. In the range of the polymolecular adsorption, at high adsorbate concentrations in solutions (C > (5–6) × 10⁻⁴ mol/dm³), the adsorption decreases in a series adenosine > adenosine monophosphate > adenosine triphosphate, i.e., with an increase in the solubility of the examined compounds in water.     

A new method of evaluation of element pollutant mobility in sediments

The application of a strong chelating agent for the screening test of element mobility in sedimentary systems was investigated. Single-step and sequential extraction procedures were applied to four sediment samples collected from an industrially polluted region of Eastern Slovakia. A sequential extraction procedure (SEP), recommended by the Institute for Reference Materials and Measurements (IRMM), was applied and used as a reference extraction method. A single-step extraction with 0.05 mol dm⁻³ ethylenediaminetetraacetic acid (EDTA) was adapted for sediments when extraction conditions were optimised. The extraction efficiency of the single-step procedure was compared with that of SEP. The contents of elements extracted by Na2EDTA were in good agreement with the sum of the first three steps of the SEP for Fe, Mn, and Co. Na₂EDTA can therefore be considered capable to extract the majority of elements associated with the reducible sedimentary phase — bound to Fe and Mn oxides in the regional geological conditions of the monitored region. Thus, Na₂EDTA extraction of Fe and Mn can serve as an economical, time-saving supplementary test for the IRMM procedure. This paper is dedicated to the memory of Erika Krakovská Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Effect of addition of ameliorative materials on the distribution of As,Cd, Pb,and Zn in extractable soil fractions

The effects of lime, limestone, and zeolite addition on the availability of As, Cd, Pb, and Zn in three contaminated soils were investigated in a pot experiment after four vegetation periods of spring wheat, spring barley, and oat. The results showed different responses of extractable element portions to soil amendment when 0.01 mol dm⁻³ aqueous CaCl₂ was applied as a soil extraction agent. Substantial differences were evident among the investigated elements as well as among the individual soil treatments. Except natural zeolite, the ability of ameliorative materials to redistribute cadmium and zinc from a soil solution into less mobile but labile soil fractions was observed. The lead availability was less affected and the extractability of arsenic even increased in some of the treated pots. Moreover, the availability of arsenic was more affected by different characteristics of experimental soils than by individual soil treatments. It was found that these treatments can be applied neither for multicontaminated nor for all the soil types. The soil treatments had a lower effect on the less mobile soil fractions. Presented at the XVIIIth Slovak Spectroscopic Conference, Spišská Nová Ves, 15–18 October 2006.     

Modification and characterization of montmorillonite fillers used in composites with vulcanized natural rubber

Parent Ca-montmorillonite (Jelšovy Potok, Slovakia, Ca-JP) and Na-montmorillonite Kunipia-F (Japan, Na-KU) were ion-exchanged with octadecyltrimethylammonium (ODTMA) cations. Characteristics of the samples were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (IR) and thermogravimetry (TG). Surface areas were measured by sorption of N₂ and ethyleneglycol monoethyl ether. Scanning electron microscopy photographs (SEM) were used to characterize the texture of samples. The XRD patterns show that, upon intercalation, the basal spacing of montmorillonite is expanded and corresponds to the pseudotrimolecular arrangement of organic cations in the interlayers. The IR spectra of organically modified montmorillonite show C-H stretching and bending bands of both CH₃ and CH₂ groups in the 3000–2800 cm⁻¹ and 1500–1400 cm⁻¹ region, respectively. Modification of montmorillonite by organic cations decreased the hydrophilicity of their mineral surface and adsorbed water evaporated at lower temperatures. The SEM photographs reveal a tendency towards lump formation and agglomeration of the ODTMA-montmorillonite particles. The modification introducing organic moiety lead to a substantial decrease in the surface area of both montmorillonites; however, it remained remarkably high, being at the level typical for silica. Completely characterized fillers were used to prepare rubber compositions with enhanced physical properties, as described in Hrachová et al. (2008).     

Adsorption equilibrium and kinetic studies of strontium on Mg-bentonite, Fe-bentonite and illite/smectite

Radionuclide adsorption on clay rocks has in recent years been studied mainly in connection with their use as sealing barriers in nuclear waste and spent nuclear fuel repositories. In Slovakia we find deposits of bentonites which should be used for the above mentioned purpose. The usability of adsorbents in practical applications depends on the speed of the adsorption process of the adsorbate on the adsorbent surface and distribution ratio. The work objective was the study of the kinetics of Sr adsorption on clay adsorbents with different geological origin. The geological origin of bentonite significantly influences its mineralogical and chemical composition and therein its adsorption properties. The adsorption process of strontium was fast. Adsorption equilibrium was reached for all three samples studied within 1 min from the beginning of the contact between solid and liquid phases. After the adsorption equilibrium was reached there were no more changes in the values of distribution coefficients and the adsorption percentage, and comparable values were reached in the contact-phase time span studied within 10 days. The values of adsorbed strontium were decreasing in the following order: J250 > L250 > DV45. The pseudo second-order kinetic models was used to describe model the kinetic data and provided excellent kinetic data fitting (R ² > 0.999).