Decontamination Of Liquid Radioactive Waste Research Articles

Development and testing of four stage chemical reactor (FSCR) for decontamination of liquid radioactive waste

Development and testing of four stage chemical reactor (FSCR) for decontamination of liquid radioactive waste

Дезактивація рідких радіоактивних відходів Чорнобильської зони відчуження: шляхи вирішення

The purpose of the study: on the basis of information analysis of modern approaches and experimental studies, to develop effective methods of decontamination of radioactively contaminated waters of the Chernobyl Exclusion Zone. Research materials and methods. The object of our research was liquid radioactive waste stored in the sumps of one of the decontamination points for equipment and vehicles (PuSO) - the "Dibrova" facility. Modern research methods are applied - scanning electron microscopy, X-ray diffractometry, laser sedimentography. The mass fraction of cesium, strontium, cobalt, and manganese was determined by the atomic absorption method using an AA-8500 atomic absorption spectrophotometer (Nippon Jarrell Ash Co Ltd, Japan). The results. The effectiveness of the proposed sorbents based on nickel-potassium ferrocyanide-modified iron oxide micro- and nanotubes and iron (III) hydroxide nanoparticles, the size of which is mainly 1-100 μm, is shown. The choice of decontamination algorithm depends on the composition of liquid radioactive waste to be cleaned. To increase the degree of strontium extraction while maintaining the high efficiency of cesium and transition metal extraction, it is advisable to apply preliminary plasma chemical treatment followed by the use of sorbents based on iron oxides/hydroxides modified by ferrocyanides. Conclusions. The possibility and expediency of using the proposed method for the decontamination of liquid radioactive waste accumulated in the Chernobyl exclusion zone and for the current control of the condition of the storage sites of accumulated radioactive waste and radiation monitoring are shown.

Effective removal of 137Cs ions from radioactive wastewater by Melamine-Styrene based Polymer (MSP)

Cesium (Cs) is a major product of uranium fission, which is one of the most existed radionuclides in radioactive wastes. Removal of Cs-137 has a critical role in the decontamination of liquid radioactive waste due to its half-life of 30.17 years. Concordantly, melamine styrene based conjugated polymer (MSP) was designed, synthesized, and characterized with FTIR, TGA, SEM and BET measurements. The novelty of the study is that the MSP adsorbent is designed as a highly conjugated structure to have better interaction with Cs over the Cs-π bond of the benzene groups of the adsorbent. In this work, the adsorption behavior and rate of MSP were investigated as parameters of adsorbent amount, pH, contact time, particle size, initial Cs+ concentration, and temperature. Besides, the adsorption efficiency of Cs-137 was examined by Gamma Spectroscopy. Adsorption results were fitted to three different isotherms which were Freundlich, Langmuir and Dubinin-Radushkevich (D-R). The maximum adsorption capacity of polymer for Cs+ ion was found from Langmuir isotherm as 78 mg g−1. As a part of kinetic parameters, pseudo first and second orders were investigated and in terms of the correlation coefficient pseudo second order was much more appropriate for adsorption of Cs-137 onto MSP.

Phytoremediation of 137Cs, 60Co, 241Am, and 239Pu from aquatic solutions using Chlamydomonas reinhardtii, Scenedesmus obliquus, and Chlorella vulgaris

This work is focused on the phytoremediation of radionuclides using eukaryotic green microalgae Chlamydomonas reinhardtii, Scenedesmus obliquus, and Chlorella vulgaris. This study highlights the potential use of microalgae in the process of phytoremediation in polluted aquatic solutions due to the unique cellular mechanism of uptake of different radionuclides. The kinetics of radionuclide removal from the samples was described according to the first-order kinetics and expressed by the rate constant k and calculated for each microalga at the most suitable pH. The activity of 137Cs and 60Co was measured in the presence of S. obliquus or C. reinhardtii and the activity of 241Am and 239Pu was measured in the presence of C. vulgaris. A significant decrease of activity of 137Cs was observed using C. reinhardtii with a rate constant of 2.4 Bq min−1 and S. obliquus after 3 h of incubation at pH 7 with rate constant of 2.5 Bq min−1. Chlorella vulgaris was able after 3 h of incubation to remove 241Am and 239Pu up to 90 and 70% in aquatic solutions at pH 1.7 and pH 1.5, with rate constants of 4.4 mBq min−1 and 2.8 × 10−2 mBq min−1, respectively. Novelty statement Ecologically suitable methods for the decontamination of liquid radioactive waste or radioactively contaminated areas are becoming more and more important due to the pollution of the planet. We believe that phytoremediation of radionuclides using microalgae is one of the optimal ecological methods to decontamination of radioactive waste. Microalgae as unicellular organisms have a number of advantages over the other organisms used in bioremediation—high level of tolerance to the environment, fast growth rates, high tolerance to various pH levels, etc. In this study, we used 3 different strains of microalgae for phytoremediation of various radionuclides (137Cs, 60Co, 241Am, and 239Pu). This research was focused on ex situ phytoremediation of radionuclides using microalgae at various pH levels of radioactively contaminated solutions. Due to the ability of microalgae to adapt to sometimes even extreme pH values, this research may be interesting for many institutions and researchers dealing with more environmentally friendly methods of decontamination of radioactive waste.

Effect of the surface hydration of clay minerals on the adsorption of cesium and strontium from dilute solutions

The use of clay minerals for the decontamination of liquid radioactive waste generated during the work of nuclear energy enterprises remains currently relevant. The effect of the surface hydration of a montmorillonite nanocrystal on the adsorption of cesium and strontium ions from dilute solutions was studied. As opposed to the generally accepted mechanism of the adsorption of cesium and strontium ions on active sites of clay mineral crystals, we considered the adsorption of radiocesium and radiostrontium by montmorillonite taking into account its colloidal chemical properties. When montmorillonite nanocrystals interact with water, a double electric layer with a mobile diffuse ionic atmosphere forms on the surface of the solid phase. The adsorption of cesium and strontium ions from dilute aqueous solutions confines itself to ion-exchange reactions of cesium and strontium ions of a dispersion medium with exchange cations of the diffuse ionic atmosphere of montmorillonite. Enhanced adsorption of cesium ions compared with strontium ions was explained by low charge density on the outer shell of cesium ions and the ability of cesium ions to overcome the diffuse ionic atmosphere easily and to be fixed firmly on the outer surface of the montmorillonite nanocrystal.

Sorbents Based on the Phosphates and Complex Oxides of Titanium(IV) for Decontamination of Liquid Radioactive Waste

The prospects of using of sorbents based on oxohydroxophosphate titanium(IV) to extract 134 Cs,137Cs and 90Sr from solutions close in composition to sea water have shown. The optimal conditions for the use of sorbents providing effective joint extraction of 134,137Cs and 90Sr in the presence of background macro components were determined. Modification of sorbents improves their sorption properties. It was established that the titanate ion exchangers are of interest for selective extraction of 90Sr. Optimum conditions of their application was defined. Heat treatment of waste sorbents provides reliable immobilization of radioactive sorbate. The titanium ortophosphate sorbents was tested for decontamination of liquid radioactive waste. The efficiency of their use is shown.

Deactivation of Spent Ion-exchange Resins Contaminated by Cesium and Cobalt Radionuclides

Simulation of iron oxide (magnetite and maghemite) and aluminosilicate (sillimanite and cyanite) deposits formed on the surface of spent ionexchange resins in the process of decontamination of liquid radioactive waste contaminated by cesium and cobalt radionuclides has been performed. A method of deep deactivation of spent ion-exchange resins contaminated by aluminosilicate and iron oxide deposits using alkaline and acidic solutions containing Zn-EDTA complexes has been suggested. The method of two-stage concentrating of cesium radionuclides using selective sorption materials (resorcinol-formaldehyde resin and Thermoxid-35 ferrocyanide sorbent) has been improved. The method advantage consists in using a solution containing EDTA complexes for elution of cesium radionuclides from the resorcinol-formaldehyde resin with their transition onto Thermoxid-35. High stability of the resorcinol-formaldehyde resin and Thermoxid-35 in the course of concentrating has been demonstrated. A scheme of deactivation of spent ion-exchange resins, which enables one to decrease the volume of secondary wastes due to utilization of a circulating water supply, has been suggested.

Novel procedure for removal of the radioactive metals from aqueous wastes by the magnetic calcium alginate

Upon incorporation of iron oxide particles into calcium alginate gels, composite magnetic materials called ferrogels can be obtained. It has already been found that the alginic ferrogel sorbent can be applied for purification of aqueous solutions containing ions of various heavy metals. In present paper, batch sorption experiments were carried out to remove radionuclides of caesium(I), strontium(II), europium(III) and americium(III) from aqueous solutions. The recovery of the radioactive metals was achieved by direct dosing of sodium alginate/iron carbonyl, followed by stirring the system for 2 h. The process was investigated as a function of the following parameters: pH, initial concentration of calcium ions and the amount of the dispersed iron in the 2% (w/w) aqueous solution of sodium alginate. The optimum conditions were: 15 g/L of iron carbonyl suspended in 1 L of aqueous solution of sodium alginate and about 20 g CaCl2 added to 1 L of the solution containing the radiometals. The results revealed that trivalent Am-241 was totally eliminated. Also trivalent Eu-152/154, divalent Sr-85 and monovalent caesium-137 were removed with the efficiency of about 80, 50 and 30%, respectively. It was found that exchange of calcium chloride with other metal salts does not influence significantly the removal efficiency. Laboratory-scale pilot experiments have shown that with aim to purify water, excess of the gelling agent can be removed with the method of nanofiltration. A one-step procedure for decontamination of liquid radioactive waste has been proposed. Calcium alginate with the inner magnetic core formed from iron carbonyl was found to be effective for aqueous solutions containing Am(III), Eu(III) and Sr(II) radionuclides, while only 30% of Cs(I) was removed in this process. It was demonstrated that there is no need to prepare the sorbent beads prior to the batch sorption.

Role of simple anionic ligands in deep decontamination of liquid radioactive waste

The influence of the NO9-, SO42–, HCO3–, and Ac– anions on the efficiency of the sorption of bivalent metals by sulfonic cation exchangers was studied. The main method was elution of the Mg2+, Ca2+, and Co2+ cations with individual solutions of the corresponding sodium salts and their mixed solutions with sodium nitrate from the Dowex-50 ion-exchange resin at fixed temperatures. The exchange efficiency is influenced both by neutral complexes of the metal cations mainly with inorganic acid ligands and by the single-charged species. The latter species affect the efficiency of the ion-exchange waste reprocessing considerably more strongly. An increase in the temperature of the solution being treated leads to a significant shift of the peak position toward larger retention volumes, which indicates that it is appropriate to perform the water treatment on sulfonic cation exchangers at elevated temperatures. The first formation constant of the single-charged cobalt dihydrogen phosphate complex species at an ionic strength of 0 M was obtained: logK1(CoH2PO4+) = 1.36.

PLASMA ARC WATER TREATMENT

In the article we consider the plasma-chemical method for cleaning water of radionuclides and organic compounds after hydroseparation. We analyze the main fields of use of electric-discharge technology for cleaning and decontamination of water. We define the main factors of plasma originating from electric discharge in bubble medium, and analyze their impact on the process of cleaning and decontamination of water. Therein we provide the description of plasma arc water treatment facility. We consider hydroseparation method for restoration of soils contaminated with radionuclides. We set forward the idea of combined methods, the main of which is plasma synthesis of finely-divided selective sorbent with simultaneous sorption and codeposition of radionuclides. Whereby the chemical composition and morphology of nanoparticles (sorbents) are modified by electrode material. We present information on basic oxidizers synthesized in plasma, and analyze conditions of oxidation reactions taking place in the course of water treatment. In this work, for the purpose of decontamination of liquid radioactive waste of caesium radionuclides, we used finely-divided ferrocyanide compositional sorbents produced via precipitation of ferrocyanide of the corresponding metal in the presence of finely-divided calcium carbonate and strontium synthesized in the zone of plasma treatment. We conducted tests on plasma codeposition of the radionuclides Cs-137 and Sr-90, as well as on purifying waters of organic compounds after hydroseparation of soils. The results proved high work efficiency of plasma-chemical treatment facility.

Effect of cobalt and manganese on radionuclides adsorption by modified clay sorbents

The process of decontamination of liquid radioactive wastes, containing Cs-137 and Sr-90, by the sorption method using clay sor­bents, modified by copper and copper-potassium ferrocyanides, and also antimony hydroxide was studied in the paper. The adsorption capacity of samples of the modified clay in the presence of equipment corrosion products, ions of cobalt and manganese, was studied. It was found that the modified clay sorbents are effective in the process of decontamination of liquid radioactive wastes since Cs-137 is re­moved by 99-100 % and Sr-90 - by 70-97 %. Ions of cobalt and man­ganese do not inhibit the adsorption of Cs-137 while the adsorption of strontium is reduced by 5-10 %. Based on the analysis of results of adsorption of Cs-137 in the presence of cobalt, the hypothesis on a significant adsorption capacity of modified clay samples on cobalt was stated.

Approaches to rehabilitation of radioactive contaminated territories

AbstractBACKGROUNDAccidents at nuclear fuel cycle plants may lead to contamination of areas of land and water. Cheap and available sorbents including natural aluminosilicates can be used for rehabilitation and decontamination of large volumes of radioactively contaminated water, including drinking water, prevention of migration of radionuclides into ground and surface waters through the soil and returning contaminated soil to farming.RESULTS AND DISCUSSIONA comparative study of sorption properties of various natural and surface‐modified aluminosilicates with respect to caesium is made. It is shown that sorption features of surface‐modified aluminosilicates for Cs were improved by 100–1000 times compared with respective natural aluminosilicates. It is shown that surface modification of glauconite by a mixed nickel–potassium ferrocyanide phase allows it to considerably increase its specificity (caesium distribution coefficients (2.9 ± 0.8)×103 mL g‐1 for natural and (4.5 ± 0.5)×105 mL g‐1 for modified glauconite) as well as making it selective to caesium in the presence of other alkaline ions and also provides irreversible caesium sorption.CONCLUSIONSDue to improved features, modified aluminosilicates can be more successful than natural ones when used for rehabilitation of radioactive contaminated territories (including agriculture) and water areas, as well as for decontamination of liquid radioactive wastes and for creation of geochemical barriers in solid radioactive waste storage. © 2013 Society of Chemical Industry

Development and trials of an improved process for decontamination of liquid radioactive wastes from Radon Moscow Research and Production Association

Speciation of radionuclides in low-salinity liquid radioactive wastes (LRW) formed in the course of reprocessing and storage of radioactive wastes at the Radon Moscow Research and Production Association was studied. 137Cs is present in LRW mainly in the ionic form; α-emitting radionuclides, in the colloidal form; and 90Sr, in both colloidal and ionic forms. Coagulation methods with FeCl3 and methods of peroxide and permanganate oxidation were tested for removing organic substances from LRW. A two-step reverse-osmosis apparatus was tested for removing the major fraction of radionuclides and salts from the LRW. Laboratory experiments on sorption refinement of the permeate from the first step of reverse osmosis were performed with ionexchange resins and an NZhS type ferrocyanide sorbent. A new flowsheet for a water-treatment installation (WTI), allowing considerable reduction of the volume of secondary radioactive wastes, was suggested. The WTI was put into operation in 2010.

Decontamination of liquid radioactive waste from transuranium elements and uranium by complexation with functionalized oligoethers, combined with ultrafiltration

Decontamination of liquid radioactive waste (LW) from transuranium elements (TUEs) and uranium by complexation with phosphorus-containing and guanidine phosphate oligoethers and by ultrafiltration was studied. The rejection coefficient of TUEs and U on these oligomers reaches 99.0–99.6% of the initial concentration.

Use of local soil for the decontamination of liquid radioactive wastes at PINSTECH

The use of locally available mineral clay for the removal of radionuclides from the low and intermediate level liquid waste has been studied. Adsorption behavior of this naturally available inorganic adsorbent is reported. The factors such as contact time, nature of the waste, pH and adsorption capacity have been considered. These optional physico-chemical conditions suggest an effective use of this locally available adsorbent for the decontamination of the liquid radioactive waste at Pakistan Institute of Nuclear Science and Technology (PINSTECH), Islamabad.

Evaluation of decontamination using an apparatus for decontamination of liquid radioactive waste in in vitro tests

Evaluation of decontamination using an apparatus for decontamination of liquid radioactive waste in in vitro tests

A Laboratory Based Study On The Movement Of Radiocaesium In Some Soil Columns By Gamma Spectrometer

The fate and movement of 137Cs in different types of soil profiles of Chittagong City and Ishwardi Upazila of Bangladesh were investigated with laboratory based column method by γ-spectrometer. The diffusion coefficient, distribution coefficient and retardation factors of 137Cs were measured. The physio-chemical characteristics and radioactive concentration of natural radionuclides of the soil samples were also measured. The maximum diffusion coefficient was found 2.06 X 10-5 cm2/s in the investigated soils. The vertical movement of 137Cs in those soil samples found to be slow. Maximum of clay content corresponded with the maximum of retardation factor and with the minimum of diffusion coefficient. This experimental findings demonstrated that caesium is strongly absorbed in soil particles and therefore, do not pose any threat to ground water contamination by the approximated future accidental release of 137Cs in the study area. Moreover, the locally available clay can be used as an adsorbent for the decontamination of liquid radioactive waste generated at nuclear facilities without any pretreatment. Key words: Radioisotopes; Physio-chemical; Transport parameters; Soil column DOI: http://dx.doi.org/10.3329/jbas.v35i2.9417 JBAS 2011; 35(2): 141-151