Sorption of anthropogenic radionuclides on natural and synthetic inorganic sorbents

Agricultural Solid Wastes Based Adsorbent Materials in the Remediation of Heavy Metal Ions from Water and Wastewater by Adsorption: A Review

Adsorption has become the most popular and effective separation technique that is used across the water and wastewater treatment industries. However, the present research direction is focused on the development of various solid waste-based adsorbents as an alternative to costly commercial activated carbon adsorbents, which make the adsorptive separation process more effective, and on popularising the sustainable options for the remediation of pollutants. Therefore, there are a large number of reported results available on the application of raw or treated agricultural biomass-based alternatives as effective adsorbents for aqueous-phase heavy metal ion removal in batch adsorption studies. The goal of this review article was to provide a comprehensive compilation of scattered literature information and an up-to-date overview of the development of the current state of knowledge, based on various batch adsorption research papers that utilised a wide range of raw, modified, and treated agricultural solid waste biomass-based adsorbents for the adsorptive removal of aqueous-phase heavy metal ions. Metal ion pollution and its source, toxicity effects, and treatment technologies, mainly via adsorption, have been reviewed here in detail. Emphasis has been placed on the removal of heavy metal ions using a wide range of agricultural by-product-based adsorbents under various physicochemical process conditions. Information available in the literature on various important influential physicochemical process parameters, such as the metal concentration, agricultural solid waste adsorbent dose, solution pH, and solution temperature, and importantly, the adsorbent characteristics of metal ion removal, have been reviewed and critically analysed here. Finally, from the literature reviewed, future perspectives and conclusions were presented, and a few future research directions have been proposed.

Sorption study of long-lived 94Nb on laterite: Effects of physicochemical parameters on sorption

Zr-Nb alloy is used as the pressure tube in pressurized heavy water reactors (PHWR). Prolonged neutron irradiation of the pressure tubes leads to the formation of a long-lived radioisotope ⁹⁴Nb. Thus, the discharged pressure tubes possess huge ⁹⁴Nb activity which persists for a prolonged period.If these discharged pressure tubes come in contact with ground water, ⁹⁴Nb isotope may leach and migrate and this can lead to a long-term radiological impact in the environment.In the present study, we have explored the capability of laterite as a filler material for the containment and retarding the migration of ⁹⁴Nb. In this regard, detailed characterization of the laterite soil was carried out using energy dispersive X-ray fluorescence (EDXRF), X-ray diffraction (XRD), fourier transform infra-red spectrometry (FTIR), total cation exchange capacity determination, zeta potential measurement and thermogravimetric analysis (TGA). The sorption study of ⁹⁴Nb on laterite was carried and the effects of different physico-chemical parameters like pH, ionic strength, temperature and equilibration time were evaluated. Ionic strength, temperature and time dependent sorption studies assist to explore the probable sorption mechanism of ⁹⁴Nb on laterite, which helps in understanding the migration behaviour of ⁹⁴Nb in natural aquatic environment. This study suggests that laterite is a promising material in containment of ⁹⁴Nb isotope owing to its good cation exchange behaviour in the acidic medium and ability to form surface complex in the neutral medium.

Sorption and transport characteristics of europium on sandy soils

Radioactive europium can be released as a fission product during nuclear incidents and pose a threat to the human and surrounding environment because of its biological activity and long decay half-lives. For safe design issues and human health protection demands in construction of the planned nuclear power plants (NPPs) at Al-Dabaa site, it is necessary to study the sorption and transport of different radionuclides as europium within the selected area for predicting their fate at any crisis. Many soil samples were collected from different locations at the area selected along the northwestern coast of Egypt. The samples were transported to the laboratory, preserved, and characterized using X-Ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT-IR), and X-Ray diffraction (XRD). Experiments were performed to study the sorption and transport kinetics of Eu(III) ions on two sandy soil samples from the collected ones. The effect of different parameters (e.g. contact time, pH, initial europium concentration, and temperature) on the sorption behavior europium was explored in a static condition. The maximum sorption capacity was determined and found to be 3.4 and 7.0 mg g^-1 for sorption of Eu(III) ions onto soil-1 and soil-2, respectively. Different models were applied to assess the sorption of europium onto the surface of the investigated soils. Data confirmed that Eu retention was attained through a chemisorption process. Further, the thermodynamic parameters were determined and their values confirmed the endothermic nature of the sorption process. The transport of europium radionuclides, with groundwater, through homogeneous porous media with uniform one-dimensional flow in the geosphere was processed and the relative migration velocity was determined in presence of both distilled and seawater media. The transport of Eu(III) radionuclides was higher in presence of seawater than that in presence of distilled water by about two order of magnitude. This obviously clarified the effect of seawater in accelerating the transport of radionuclides with groundwater in the geosphere of studied area. The role of different competing ions have various valances on the relative migration velocity was explored. Further, the time required for studied radionuclides to reach Mediterranean Sea was determined.

Molecular Sieve, Halloysite, Sepiolite and Expanded Clay as a Tool in Reducing the Content of Trace Elements in Helianthus annuus L. on Copper-Contaminated Soil

The aim of this study was to determine the effect of copper soil contamination on the trace element content of sunflower aerial parts and in roots. Another aim was to assess whether the introduction of selected neutralizing substances (molecular sieve, halloysite, sepiolite and expanded clay) into the soil could reduce the impact of copper on the chemical composition of sunflower plants. Copper soil contamination with 150 mg Cu²⁺ kg^-1 of soil and 10 g of each adsorbent per kg of soil were used. Soil contamination with copper caused a significant increase in the content of this element in the aerial parts (by 37%) and roots (by 144%) of sunflower. Enriching the soil with the mineral substances reduced the amount of copper in the aerial parts of sunflower. Halloysite had the greatest effect (35%), while expanded clay had the smallest effect (10%). An opposite relationship was found in the roots of this plant. In copper-contaminated objects, a decrease in the content of cadmium and iron and an increase in the concentrations of nickel, lead and cobalt in the aerial parts and roots of sunflower were observed. The applied materials reduced the content of the remaining trace elements more strongly in the aerial organs than in the roots of sunflower. Molecular sieve had the greatest reducing effect on the content of trace elements in sunflower aerial organs, followed by sepiolite, while expanded clay had the least impact. The molecular sieve also reduced the content of iron, nickel, cadmium, chromium, zinc and, especially, manganese, whereas sepiolite reduced the content of zinc, iron, cobalt, manganese and chromium in sunflower aerial parts. Molecular sieve contributed to a slight increase in the content of cobalt, while sepiolite had the same effect on the content of nickel, lead and cadmium in the aerial parts of sunflower. All materials decreased the content of chromium in sunflower roots, molecular sieve-zinc, halloysite-manganese, and sepiolite-manganese and nickel. The materials used in the experiment, especially the molecular sieve and to a lesser extent sepiolite, can be used effectively to reduce the content of copper and some other trace elements, particularly in the aerial parts of sunflower.

Adsorption behavior of molybdenum onto K-doped γ-Al2O3 and iron clay nanocomposite

Adsorption of molybdenum was carried out on two materials; potassium doped γ-Al2O3 (KA) and bentonite iron oxide composite (BIOC) with purpose of using in production of chromatographic 99mTc generators, for KA absorbent, different ranges of potassium loadings have been considered, for BIOC solid the used weight ratio was (Bentonite/Fe = 2/1). Samples were characterized by XRD and WDXRF. Adsorption of MoxOy z− species was carried out at pH 2.5 and 25 °C, effects of contact time and pH were studied. The Mo adsorption data onto used materials were well fitted using Freundlich and Langmuir models. Doped alumina samples showed higher adsorption capacities (∼90 mg g−1) than the usual alumina used in generator technology (∼60 mg g−1), whereas adsorption capacities of BIOC solid were in the range of (∼75 mg g−1).

Separation of anthropogenic radionuclides from aqueous environment using raw and modified biosorbents

In this study, two types of biosorbents were used to remove ¹³⁷Cs and plutonium isotopes from aqueous solutions - moss (Ptilium crista - castrensis) and oak sawdust (Quercus robur), both in the form of natural and modified state. Sorbent modification significantly increases the sorbent surface area (for moss sorbents - from 4.0 to 47.2 m²/g, and for sawdust sorbents - from 1.1 to 26.3 m²/g), pore volume (from 10^-3 to 10^-2), concentration and amount of basic cations and anions, as well as active functional groups on the sorbent surface. The main functional groups on the surface of natural sorbents modified with iron hydroxide interacting with analytes are carboxyl and hydroxyl groups. For carbonized sawdust and its subsequent activation with concentrated HCl, in addition to carboxyl and hydroxyl groups, acetyl groups also become active. Carbonated sawdust treated with HCl showed the highest average removal efficiency and sorption capacity for radiocesium and plutonium isotopes in laboratory column experiments - for ¹³⁷Cs ∼78.6% and ∼196.6 Bq/g and for ^239+240Pu ∼83% and ∼41.5 Bq/g, respectively. The moss and moss modified with iron hydroxide also showed good properties of adsorbing plutonium isotopes in field (in-situ) experiments. The best results on the sorption of ¹³⁷Cs in field experiments were shown by carbonated sawdust activated with HCl, and for isotopes of plutonium - the raw moss and moss modified with iron hydroxide. The results of the study showed that sorbents can be used not only for purification of water from plutonium isotopes but allow the operational sampling and more accurate measurement of radiocesium and plutonium isotopes in the fresh water reservoirs by the dynamic flow method.

A new way to ensure selective zirconium ion adsorption

This work studies the adsorption of zirconium ions by mesoporous titanium dioxide with surface arsenate groups. Experimental maximal adsorption values of zirconium ions were found to be 109.6 mg/g in neutral medium. This process depends on the interaction time, the equilibrium concentration of zirconium ions, and the acidity of the solution. Adsorption kinetics fit well into the kinetic model based on the pseudo-second-order equation (R 2 = 0.9984). Equilibrium adsorption of zirconium ions is well described by Langmuir’s adsorption theory (R 2 = 0.9856 and χ 2 = 1.307). Although zirconium ions are less actively adsorbed from a neutral medium than strontium or yttrium ions, in the 2% nitric acid only zirconium is adsorbed out of the mixture of zirconium, strontium, and yttrium. The results obtained by inductively coupled plasma mass spectrometry have shown that the investigated adsorbent selectively adsorbs zirconium ions from their mixture with strontium and yttrium in the range of solution acidity pH = 0–1. The average percentage of maximum extraction of zirconium ions is 94.3 ± 2.4%, and the highest percent of zirconium ions taken up from the mixture with strontium and yttrium is ∼98.4%. Investigated titanium dioxide selectively separate 90Zr from 90Sr with the presence of 1000-fold excess of stable 88Sr in radioactive liquid β − source. This fact is extremely valuable for the age dating of 90Sr-containing device in nuclear forensics or the determination of 90Sr in low activity background samples.

Influence of the Nanotube Morphology and Intercalated Species on the Sorption Properties of Hybrid Layered Vanadium Oxides: Application for Cesium Removal from Aqueous Streams

The present paper examines the impact that the nanotube morphology and organic or inorganic intercalated species may have on the cesium sorption by layered vanadium oxides prepared with the use of hexadecylamine as a structure-directing agent. The hybrid material represented by a chemical formula of (V₂O₅)(VO₂)_1.03(C₁₆H₃₆N)_1.46(H₂O)_x was achieved through accelerated microwave-assisted synthesis carefully optimized to ensure the best compromise between the scroll-like morphology and the hydrophobic character. To enhance its dispersibility in water, this sample was subsequently modified by progressive replacement of the C₁₆H₃₆N⁺ units by NH₄⁺ cations. The final materials represented a stacking of lamellar sheets with a worse scroll-like morphology. Both the optimization procedure and the template removal were monitored on the basis of scanning and transmission electronic microscopy, X-ray diffraction, infra-red spectroscopy, inductively coupled plasma-optical emission spectrometry, X-ray photoelectron spectroscopy, and elemental analysis, supplemented by adequate simulations methods providing the reference IR spectra and XRD patterns for comparison or the textural parameters of the samples. The comparison of the cesium sorption from either a 4:1 ethanol–water mixture or aqueous solutions pointed toward the solubility of intercalated cations in the bulk solution as the main factor limiting their displacement from the interlayer space by the oncoming cesium ones. The sample obtained after 70% exchange with NH₄⁺ exhibited a maximum sorption capacity of 1.4 mmol g⁻¹ from CsNO₃ aqueous solutions and its retention efficiency remained significant from low-concentration Cs solutions in river or sea water.

Ion-Imprinted Polymers: Synthesis, Characterization, and Adsorption of Radionuclides

Growing concern over the hazardous effect of radionuclides on the environment is driving research on mitigation and deposition strategies for radioactive waste management. Currently, there are many techniques used for radionuclides separation from the environment such as ion exchange, solvent extraction, chemical precipitation and adsorption. Adsorbents are the leading area of research and many useful materials are being discovered in this category of radionuclide ion separation. The adsorption technologies lack the ability of selective removal of metal ions from solution. This drawback is eliminated by the use of ion-imprinted polymers, these materials having targeted binding sites for specific ions in the media. In this review article, we present recently published literature about the use of ion-imprinted polymers for the adsorption of 10 important hazardous radionuclides-U, Th, Cs, Sr, Ce, Tc, La, Cr, Ni, Co-found in the nuclear fuel cycle.

Silver-hydroxyapatite nanocomposites prepared by three sequential reaction steps in one pot and their bioactivities in vitro

Hydroxyapatite (HA) combined with antimicrobial agents for biomedical application can effectively avoid the bacteria infection, while HA have the good performance. In this study, we prepared silver-hydroxyapatite (Ag-HA) nanocomposites using a one-pot method consisting of three sequential steps of wet chemical precipitation, ion exchange, and a silver mirror reaction. The HA nanoparticles used as the precursor for Ag ion doping were first synthesised by wet chemical precipitation. Next, Ag⁺ absorbed on HA surface through ion exchange reaction. Glucose was then added to initiate the silver mirror reaction, which made the Ag⁺ ions reduce to Ag⁰ and Ag nanoparticles in situ formed on HA nanoparticles. Subsequently, Ag-HA nanocomposites with different Ag content were prepared. X-ray diffraction, SEM, EDX mapping and TEM imaging confirmed that spherical Ag nanoparticles ~20-40 nm in diameter were adhered to the surface of HA nano-rods (0.4-0.8 μm in length and 15-40 nm in diameter). The Ag content (1.9-15.2 wt%) in the Ag-HA nanocomposites was adjusted by varying the feeding Ag/Ca molar ratio (2.0-20%). The cell viability evaluation in vitro proved that Ag-HA nanocomposites had low cytotoxicity to L929 normal cells. Meanwhile, the antibacterial examinations in vitro demonstrated that Ag-HA nanocomposites had obvious antibacterial effects on Gram-positive bacteria, Gram-negative bacteria, and fungus. The antibacterial results were dose-dependent on the accumulation of silver content. The Ag-HA nanocomposites loaded PMMA resins also demonstrated a potential antibacterial activity against S. mutans. This paper presents a convenient and bio-friendly approach for preparing Ag-HA nanocomposites with adjustable Ag content, which are a promising material for biomedical applications.

Rare Earths (La, Y, and Nd) Adsorption Behaviour towards Mineral Clays and Organoclays: Monoionic and Trionic Solutions

Metals from electric and electronic waste equipment (WEEE) can be recovered by dissolution with acids followed by liquid–liquid extraction. A possible alternative to liquid–liquid extraction is liquid–solid adsorption, where sorbents efficiency is the key factor for process efficiency. In this respect, aim of this paper is the study of the behaviour of two solid sorbents for the recovery of Rare Earths (REs)—in particular, La, Nd, and Y—from scraps of end-of-Life (EOL) electronic equipment. Two solid matrices were considered: a pristine montmorillonite clay and a modified-montmorillonite clay intercalated with a commercial pentaethylen-hexamine. The capture ability of the solids was tested towards single-ion La, Nd, and Y solutions and a multi-element solution containing the three ions. Before and after the uptake step, samples of both the solid and liquid phases were analysed. For both sorbents, at lower metal initial concentrations, the ions were captured in similar amount. At higher concentrations, pure clay showed a high total uptake towards La ions, likely due to surface interactions with clay sites. The organoclay preferentially interacts with Nd and Y. Considering the presence of the polyamine, this behaviour was related to ion coordination with the amino groups. The capture behaviour of the two sorbents was related to the different physicochemical properties of the ions, as well as to the ionic radius.

Possibilities of Uranium Deposit Kuriskova Mining and Its Influence on the Energy Potential of Slovakia from Own Resources

Uranium is one of the strategic minerals used mainly in energetics. The main purpose of uranium mining is to achieve maximum production to meet the rapidly growing demand for energies. It needs to become aware that technological progress in mining processes could significantly reduce the negative impacts associated with environmental, economic, and social risks. Uranium mining is one of the most controversial topics. It is dealt with by many experts and scientists around the world. Various methods and technologies of uranium mining are encountered in professional journals, as well as political or socio-economic decisions based on the impact and importance of the energy potential of uranium deposits, or the environmental impacts of uranium mining. The deposit of Kuriskova is one of the most perspective deposits not only in Slovakia but also in the world. The deposit is located near the town of Kosice (with near 240,000 inhabitants) and near the recreational area of Jahodna in the east of the Slovak Republic. The analysis and determination of the energy potential of the deposit of Kuriskova shows that uranium reserves from this deposit would be able to fully cover the needs for nuclear power plants for the production of nuclear fuel, in the Slovak Republic, even in the longer term. With the above-mentioned energy potential of the deposit of Kuriskova at the level of 600 TWh, nuclear power plants in the Slovak Republic are able to be supplied with raw materials from the deposit of Kuriskova for about 40 years with the current amount of electricity produced (approx. 15 TWh). Therefore, for the purposes of this research, a proposal for the extraction of uranium reserves at the deposit of Kuriskova was made. Based on it, it is possible to determine the amount of recoverable uranium reserves from the deposit. A methodology has been determined with mining this proposal, which takes into account the basic criteria of uranium deposit mining, which was used for the selection of a suitable mining technology for the uranium deposit of Kuriskova.

A novel sorbent based on Ti-Ca-Mg phosphates: synthesis, characterization, and sorption properties

This work focuses on the synthesis procedure of a new sorbent based on a TiCaMg phosphate. The synthesis strategy includes stepwise interaction between solid precursors and phosphorus-containing agents. The solid precursors were ammonium titanyl sulfate and calcined dolomite, which were used as titanium, calcium, and magnesium sources. The effect of the nature and concentration of phosphoric agent on the sorbent composition and properties has been investigated using elemental analysis, TG, XRD, IR spectroscopy, BET, and SEM techniques. The novel sorbent has been demonstrated to be a composite material consisting of the following components: TiO(OH)H₂PO₄·H₂O, Ti(HPO₄)₂·H₂O, CaHPO₄·2H₂O, MgНPO₄·3H₂O, and NH₄MgPO₄·6H₂O. The ratio between these phases in the composite depends on synthesis conditions. The optimal conditions, ensuring full conversion of Ti, Ca, and Mg containing in the initial precursors into the final product, have been found. The sorption properties of the obtained composite sorbent towards Co²⁺, Cs⁺, and Sr²⁺ cations and their radionuclide analogues have been studied. The obtained data has indicated that the purification effect was based on both precipitation and ion exchange mechanism. The combined action of the individual components of the composite sorbent ensures its high sorption capacity towards different cations in a wide pH range. The new sorbent shows high sorption ability towards radionuclides in multicomponent liquid radioactive waste (LRW) systems, and the distribution coefficient of the studied radionuclides was found to be 10⁵ mL g^-1. The presence of different types of functional groups in the composite sorbent allows realizing the one-step purification process of LRW that, in turn, simplifies the sorption system design.

Effect of Nano-Montmorillonite on Osteoblast Differentiation, Mineral Density, and Osteoclast Differentiation in Bone Formation

Calcium-type montmorillonite, a phyllosilicate mineral, has diverse health benefits when introduced into the gastrointestinal tract or applied to the skin. However, the predominant use of this layered material has thus far been in traditional industries, despite its potential application in the pharmaceutical industry. We investigated the effects and mechanism of nano-montmorillonite (NM) on osteoblast and osteoclast differentiation in vivo and in vitro. We examined the osteogenic effects of NM with high calcium content (3.66 wt%) on alkaline phosphatase (ALP) activity, mineralization, bone microarchitecture, and expression level of osteoblast and osteoclast related genes in Ca-deficient ovariectomized (OVX) rats. Micro-computed tomography of OVX rats revealed that NM attenuated the low-Ca-associated changes in trabecular and cortical bone mineral density. It improved ALP activity and mineralization, as well as the expression of osteoblast and osteoclast differentiation associated genes. NM also activated the expression of runt-related transcription factor 2, osteocalcin, bone morphogenetic protein 2, and type 1 collagen via phosphorylated small mothers against decapentaplegic homolog 1/5/8 signaling. Further, NM repressed the expression of receptor activator for cathepsin K, nuclear factor kappa-B ligand and tartrate-resistant acid phosphatase. Therefore, NM inhibits osteoclastogenesis, stimulates osteoblastogenesis, and alleviates osteoporosis.

Use of a Zeolite and Molecular Sieve to Restore Homeostasis of Soil Contaminated with Cobalt

Since contamination of soil with cobalt disturbs the soil’s biological balance, various types of compounds are being sought that could be used to restore the homeostasis of contaminated soil. The aim of the study was to determine the use of a Bio.Zeo.S.01 zeolite and molecular sieve in restoring the microbiological and biochemical balance of soil contaminated with cobalt. Soil samples were contaminated with cobalt (CoCl2·6H2O) at 0, 20, 80 mg·kg−1, and a Bio.Zeo.S.01 zeolite and molecular sieve were introduced at 0 and 15 g·kg−1. The soils on which the experiment was conducted were loamy sand and sandy clay loam. The experiment was carried out in two series on soil with and without a crop sown in it. The multiplication of microorganisms and the soil enzymes’ activity were determined on days 25 and 50 (harvest) of the experiment, and the yield of the underground and above-ground parts of maize and chemical and physical properties of soil were determined on the day of harvest. It was found that the microorganisms’ multiplication, enzyme activity, and maize yield were significantly disturbed by the excess of cobalt in the soil regardless of the soil type. The zeolite Bio.Zeo.S.01 used in the study had a smaller impact on microorganisms and soil enzyme activity than the molecular sieve. Cobalt accumulated more in the roots than in the above-ground parts of maize. An addition of sorbents decreased the accumulation of cobalt in maize grown only on sandy clay loam.

Reactive Mesoporous pH-Sensitive Amino-Functionalized Silica Nanoparticles for Efficient Removal of Coomassie Blue Dye

In this work, new smart mesoporous amine-functionalized silica nanoparticles were prepared from hydrolyzing microgels based on N-isopropyl acrylamide-co-vinyltrimethoxysilane microgels with tetraethoxysilicate and 3-aminopropyltriethoxysilane by sol-gel method. The thermal stability and Fourier transform infrared were used to determine the amine contents of the silica nanoparticles. The pH sensitivity of the synthesized silica nanoparticles in their aqueous solutions was evaluated by using dynamic light scattering (DLS) and zeta potential measurements. The porosity of the amine-functionalized silica nanoparticles was evaluated from a transmittance electron microscope and Brunauer-Emmett-Teller (BET) plot. The results have positively recommended the pH-sensitive amine-functionalized silica nanoparticles as one of the effective nano-adsorbent to remove 313 mg·g⁻¹ of CB-R250 water pollutant.

Structural and Thermal Properties of Montmorillonite/Ionic Liquid Composites

Composites of montmorillonite K10 (MMT K10) and ionic liquid (IL) containing a 1-butyl-3-methyl-imidazolium cation ([BMIm]⁺) and various anions, such as bis (trifluoromethylsulfonyl) imide ([NTf₂]⁻), trifluoromethanesulfonate ([OTf]⁻), and dicyanamide ([DCA]⁻) have been obtained in this work. A number of methods, such as dynamic light scattering (DLS), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal gravimetry (TG), differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and nitrogen adsorption–desorption have been used to characterize clay, and to study the structure and thermal behaviour of the composites. It has been found that the MMT K10 powder has a narrow particle size distribution with a peak at 246 nm and a mesoporous structure (S_BET=195 m²/g). According to the FTIR spectra, MMT K10/IL interaction depends on the IL type. It has been identified that confined ionic liquid interacts with both clay and adsorbed water in accordance with the hydrophilicity and size of the anion, in the following order: [DCA]⁻ > [OTf]⁻ > [NTf₂]⁻. Characteristic temperatures of glass transition, crystallization, and melting have been determined for the ionic liquids under study and their MMT K10 composites. It has been revealed that when IL is adsorbed on the surface of clay, the phase transitions in IL change. The greatest changes are observed in the case of BMImNTf₂. By applying the method of thermogravimetric analysis, it is shown that composite formation is accompanied by a decrease in the IL thermal stability. Apparently, the highly developed surface of montmorillonite K10, obtained by acid treatment, plays a major role in the decrease in the IL’s thermal stability. The influence of the IL anion on the thermal and spectral characteristics of an MMT K10/IL composite was studied for the first time.

Inorganic and Hybrid (Organic⁻Inorganic) Lamellar Materials for Heavy metals and Radionuclides Capture in Energy Wastes Management-A Review

The energy industry (nuclear, battery, mining industries, etc.) produces a large quantity of hazardous effluents that may contain radionuclides (¹³⁷Cs and ⁹⁰Sr in particular) and heavy metals. One of the hardest tasks of environmental safety and sustainable development is the purification of wastewater holding these pollutants. Adsorption is one of the most powerful methods for extracting toxic compounds from wastewater. This study reviews the usefulness of clay minerals as adsorbent for removing these hazardous elements to clean up energy production processes. Phyllosilicates are able to extract several heavy metals from effluent, as widely examined. A particular focus is given to synthetic phyllosilicates and their abilities to entrap heavy metals with a special attention paid to those synthesized by sol-gel route. Indeed, this method is attractive since it allows the development of organic–inorganic hybrids from organosilanes presenting various functions (amino, thiol, etc.) that can interact with pollutants. Regarding these pollutants, a part of this review focuses on the interaction of lamellar materials (natural and synthetic phyllosilicates as well as layered double hydroxide) with heavy metals and another part deals with the adsorption of specific radionuclides, cesium and strontium.

Microwave-assisted hydrothermal synthesis of manganate nanoflowers for selective retention of strontium

An alternative microwave-assisted hydrothermal route for the preparation of manganate nanoflowers under basic conditions has been proposed in view of potential uses in selective retention of strontium from multicomponent aqueous streams. Based on the combination of such characterization techniques as Scanning and Transmission Electronic Microscopy, X-ray photoelectron spectroscopy, and X-ray Diffraction, as well as taking advantage of the computer-aided structure simulation, homogeneous nanoflower morphology possessing a layered structure and K⁺ compensating cations was evidenced as corresponding to the KMn₄O₈ chemical formula. The nanoflower sample was subsequently tested for the selective adsorption of strontium and cesium by measuring the individual adsorption isotherms from single-solute and multicomponent aqueous solutions. The material appeared selective towards strontium against cesium even in multicomponent solutions provided that the concentration of calcium remained low. This difference in the retention selectivity was rationalized based on the Density Functional Theory (DFT) calculations of the energy of adsorption and direct calorimetry measurements of the enthalpy of displacement for the individual cations.

Retention behavior of anionic radionuclides using metal hydroxide sludge

With the speedy growth of nuclear power production, the removal and disposal of radioactive nuclides such as 129I, 99Tc, 79Se, 36Cl, 93Mo, and 137Cs become major environmental security issues. Retention of these radionuclides, especially anionic species such as 129I (t1/2 1.7 × 107 years), 93Mo (t1/2 4 × 103 years) and 79Se (t1/2 3.27 × 105 years) has been challenging. 129I, 93Mo and 79Se bind very weakly to most sorbents and deposits. This study has examined the sorption potential of Metal hydroxide sludge (MHS) for 125I (t1/2 60.2 days), 99Mo (t1/2 2.75 days) and 75Se (t1/2 120 days) as a surrogate for 129I, 93Mo and 79Se, respectively. MHS has been characterized by different techniques and the factors affecting the sorption processes were investigated. The experimental data were analyzed using kinetic models and thermodynamic parameters. The results showed that the kinetics of sorption of 125I and 99Mo on MHS proceeds according to the pseudo-first-order, on the contrary of 75Se sorption follows pseudo second-order kinetic model. The maximum sorption capacity of MHS was found to be 51.2 mg/g, 46.5 mg/g and 40.2 mg/g for 125I, 99Mo and 75Se, respectively. It can be concluded that, in the case of release of anionic radionuclide species to the surroundings the MHS could act as a succeeded and economical sorbent material for retention of different anionic radionuclides such as 133, 129I, 79Se, 36Cl, 93, 99Mo, and 99Tc. To avoid the release of such anionic species from the stored nuclear wastes to the environment.

Introducing Bentonite into the Environment in the Construction Stage of Linear Underground Investment Using the HDD Method

The study discusses the issue of introducing drilling fluid (bentonite) into the environment during the construction of linear underground investments, considering the example of the construction of the high-pressure gas pipeline, Czeszów—Kiełczów DN1000, which involved the use of the Horizontal Directional Drilling (HDD) method. The analyses concern the drilling stage as a low-waste technology, indicating the use and management of bentonite drilling fluid in a closed circulation cycle in the area of Pęciszów, poviat Trzebnica (Poland). The loss of drilling fluid in valuable natural areas during the construction stage of the gas pipeline has been analyzed. Drilling fluid is an element of the horizontal directional drilling technology (HDD). The analyzed area included a section of the route of the strategic gas pipeline, realized in June–July 2017 in an area of lowland ash and alder forest 91E0-3, a probable breeding site of the Bluethroat for a detailed description and common frog. The loss of the drilling fluid used in the drilling phase has been determined, depending on the type of soil and the related fraction as well as the possibility of treating the drilling fluid used to construct the drilling.

Impacts of nitrate and electron donor on perchlorate reduction and microbial community composition in a biologically activated carbon reactor

The sensitivity of perchlorate reduction and microbial composition to varied nitrate and acetate loadings was studied in a biologically activated carbon reactor with perchlorate loading and empty bed contact time fixed at 5 mg/L and 226 min, respectively. In stage 1, the sole electron acceptor ClO₄^- realized complete removal with ≥21.95 mg C/L of acetate supply. As nitrate loading gradually increased to 5 mg/L (stage 2), perchlorate reduction was slightly promoted and both ClO₄^- and NO₃^- were completely removed at an acetate loading of 29.7 mg C/L. When nitrate loading continued increasing to 10-60 mg/L (stage 3), perchlorate reduction converted to be inhibited, along with nondetectable NO₃^- and approximately exhausted DOC in effluent. When acetate loading increased to 43.9 mg C/L in stage 4, both ClO₄^- and NO₃^- were again removed, though lags still existed in perchlorate reduction. β-Proteobacteria accounted for about 60%, 55%, 58%, 61% and 12% in samples from the base and top of the filter in stage 1 and those from the base, middle and top in stage 4, respectively. These findings implied that ratio of NO₃^- to ClO₄^- loadings and acetate loading were two key factors impacting ClO₄^- reduction and microbial structure along the filter.

Sorption behavior of cesium, cobalt and europium radionuclides onto hydroxyl magnesium silicate

The radioactive wastes from different activities have to be safely disposed of and isolated from the human environment. The retardation of radioactive materials by designed barriers is originally controlled by the sorption ability of the mineral compositions. In this work, a naturally available mineral composite, a hydroxyl magnesium silicate (HMS) was investigated as potential natural inorganic sorbent for the retention of long-lived radionuclides (134Cs, 60Co and 152+154Eu) from aqueous solutions. The factors affecting the sorption process, such as contact time and pH were evaluated. Furthermore X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal and thermogravimetry analyses (DTA/TGA) measurements were examined in order to assess the physicochemical properties of the magnesium silicate mineral. Langmuir and Freundlich isotherms fitted the result s substantially better than the Flory–Huggins isotherm and the sorption was found to follow pseudo-first order kinetic model. The proposed mineral has been successfully applied for the sorption of 134Cs, 60Co and 152+154Eu radionuclides from real radioactive waste. The results indicated that about 97.4–99% of 134Cs, 60Co and 152+154Eu radionuclides were efficiently retained onto the HMS mineral. Based on the results obtained, it can be concluded that the HMS mineral is an economic and efficient retaining material for environmental hazardous migration and/or leakage of some radionuclides such as 134Cs, 60Co and 152+154Eu and trivalent actinide (241Am, 242mAm and 243Am) ions. Therefore, this study could be used as a starting point to establish and consider that mineral as an engineered barrier around the disposal facilities at the nuclear activity centres.

Radioactive Barium Ion Trap Based on Metal-Organic Framework for Efficient and Irreversible Removal of Barium from Nuclear Wastewater

Highly efficient and irreversible capture of radioactive barium from aqueous media remains a serious task for nuclear waste disposal and environmental protection. To address this task, here we propose a concept of barium ion trap based on metal-organic framework (MOF) with a strong barium-chelating group (sulfate and sulfonic acid group) in the pore structures of MOFs. The functionalized MOF-based ion traps can remove >90% of the barium within the first 5 min, and the removal efficiency reaches 99% after equilibrium. Remarkably, the sulfate-group-functionalized ion trap demonstrates a high barium uptake capacity of 131.1 mg g(-1), which surpasses most of the reported sorbents and can selectively capture barium from nuclear wastewater, whereas the sulfonic-acid-group-functionalized ion trap exhibits ultrafast kinetics with a kinetic rate constant k2 of 27.77 g mg(-1) min(-1), which is 1-3 orders of magnitude higher than existing sorbents. Both of the two MOF-based ion traps can capture barium irreversibly. Our work proposes a new strategy to design barium adsorbent materials and provides a new perspective for removing radioactive barium and other radionuclides from nuclear wastewater for environment remediation. Besides, the concrete mechanisms of barium-sorbent interactions are also demonstrated in this contribution.

Artificial environmental radionuclides in Europe and methods of lowering their foodstuff contamination – a review

This review discusses the consequences of the food chain contamination with radionuclides, especially focusing on the radiocaesium impact after the Chernobyl nuclear accident. In particular, the137Cs isotope still represents a risk. Until present it is still detectable in the meat of game animals, especially in wild boar, but also in elk and reindeer. Although the occurrence of highly contaminated foods in most of Europe is currently limited, along the German-Czech border (the Šumava Region) the activity concentration of the137Cs isotope in the meat of wild boar exceeds the acceptable limit several times. Additionally, the article describes simple processing technologies (cooking, pickling etc.) that lead to reduction of radionuclides in contaminated food.

Immobilization of Metal Hexacyanoferrate Ion-Exchangers for the Synthesis of Metal Ion Sorbents--A Mini-Review

Metal hexacyanoferrates are very efficient sorbents for the recovery of alkali and base metal ions (including radionuclides such as Cs). Generally produced by the direct reaction of metal salts with potassium hexacyanoferrate (the precursors), they are characterized by ion-exchange and structural properties that make then particularly selective for Cs(I), Rb(I) and Tl(I) recovery (based on their hydrated ionic radius consistent with the size of the ion-exchanger cage), though they can bind also base metals. The major drawback of these materials is associated to their nanometer or micrometer size that makes them difficult to recover in large-size continuous systems. For this reason many techniques have been designed for immobilizing these ion-exchangers in suitable matrices that can be organic (mainly polymers and biopolymers) or inorganic (mineral supports), carbon-based matrices. This immobilization may proceed by in situ synthesis or by entrapment/encapsulation. This mini-review reports some examples of hybrid materials synthesized for the immobilization of metal hexacyanoferrate, the different conditionings of these composite materials and, briefly, the parameters to take into account for their optimal design and facilitated use.