Sorption recovery of radionuclides from alkaline solutions using fibrous “filled” sorbents

The possibility of using POLIORGS 33-n and 34-n fibrous “filled” sorbents with amidoxime groups for recovering U(VI), Am(III), and Pu(IV) from alkaline solutions of various compositions was studied. These sorbents exhibit high performance and excellent kinetic properties in recovery of uranium and transuranium elements from alkaline solutions. The distribution coefficients in their sorption from alkaline solutions at various (even high) values of pH and salt content were determined. Original Russian Text N.P. Molochnikova, I.G. Tananaev, G.V. Myasoedova, B.F. Myasoedov, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 1, pp. 58–60.     

Concentration and Separation of Actinides in Nitric Acid Media with Fibrous “Filled” Sorbents

The behavior of actinides in sorption from nitric acid solutions with fibrous filled sorbents was studied. It was found that the sorbents with methylpyrazole groups POLIORGS 4-n and 17-n and anion exchanger AV-17-n sorb completely only Pu(IV) from strongly acidic solutions. The other actinides studied [Am(III), U(VI), Pa(V), Np(V)], and also Eu(III), Tc(VII), and Cs(I) are not appreciably sorbed under these conditions. The sorbents are characterized by good kinetic properties and chemical stability in HNO₃ solutions. The possibility of using fibrous "filled" sorbents for concentrating plutonium from nitric acid solutions and separating plutonium from other radionuclides was demonstrated. Pu can be desorbed with 0.5-1 M HNO₃.     

Sorption Recovery of Np(V) from Aqueous Solutions with POLIORGS Complexing Sorbents

Sorption of neptunium with fibrous complexing sorbents containing amidoxime and hydrazidine groups was studied. The influence of solution pH and the nature and concentration of salts on sorption of neptunium was examined; the sorption kinetics and the exchange capacity of the sorbents were evaluated. The sorbents are suitable for recovery and concentration of neptunium from aqueous solutions to solve production and environmental problems at the Mayak Production Association.     

Modification of rice hull and sawdust sorptive characteristics for remove heavy metals from synthetic solutions and wastewater

In this work two modified agricultural residues, rice hull and sawdust were examined as sorbents to remove heavy metals Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) from synthetic solutions or wastewater samples. To modify their sorptive characteristics, samples were treated with HCl, NaOH and heat. The sorption of the heavy metals from the synthetic solutions was increased with pH and initial concentration. In pH 5, Pb(II) and Cd(II) showed the highest sorption and Cu(II), Zn(II) and Ni(II) showed the following orders, respectively. Sorption capacity of rice hull was higher than sawdust. The modifications changed the sorption capacity of the natural sorbents in the following order base>heat>natural>acid. The sorption isotherms of sorbents were best described by the Freundlich and Langmuir models. The basic treated rice hull and sawdust followed by the heat treated rice hull sorbed the maximum of heavy metals from the industrial wastewater samples. In the column experiment, the synthetic solutions and the wastewater samples gave almost the same results as the suspensions. The recovery of the columns using water and HCl showed positive results. Commercial sorbents removed Pb(II), Zn(II) and Ni(II) a little more than rice hull.     

Membrane-based hybrid processes for high water recovery and selective inorganic pollutant separation

The removal of heavy metals (e.g. Pb(II), Cd(II), Cu(II), etc.) and oxyanions (e.g. nitrate, As(III, V), Cr(VI), etc.) is of immense interest for treatment of groundwater and other dilute aqueous systems. However, the presence of non-toxic components, such as hardness (Ca, Mg) and sulfate, can interfere with the separation of toxic species. For example, pressure-driven membrane processes, such as reverse osmosis (RO), have been limited for water treatment due to problems that these extraneous components cause with water recovery and ionic strength (osmotic pressure) of the retentate. In addition, nitrate rejection by RO is considerably lower than NaCl rejection, resulting in permeate concentrations that may be too high for groundwater recharging. Other separation systems that rely solely on sorption of toxic species (e.g. ion exchange resins) may not have sufficient selectivity for efficient use in the presence of competing ions. Hence, implementation of pressure-driven membrane separations and high capacity sorbents in hybrid processes shows much promise for remedying these difficulties. For example, selective separation of nitrate may be achieved by combining nanofiltration (NF) for sulfate removal, followed by RO or ion exchange for nitrate removal (see example 1). When small concentrations of toxic metals are present, the large retentate volumes of RO processes may be reduced by selective removal of toxic species with a high capacity sorbent, thus permitting disposal of a lower volume, non-toxic stream (see example 2). The use of microfiltration membrane-based sorbents containing multiple polymeric functional groups is a novel technique to achieve high metal sorption capacity under convective flow conditions. These sorbents are formed by the attachment of various polyamino acids (MW: 2500-10,000), such as polyaspartic acid (cation sorption), polyarginine (oxyanion sorption), and polycysteine (chelation exchange), directly on the membrane pore surfaces. Since these sorbents have also been found to have high selectivity over non-toxic metals, such as calcium, they are ideal candidates for hybrid processing with RO/NF.     

Treatment of hazardous sorbents generated from the adsorption of heavy metals during incineration

The emission of heavy metals during waste incineration can be effectively reduced through the practice of employing non-toxic sorbents. These sorbents can react with toxic metals at high temperatures and create metal binding between them by various physical and chemical mechanisms. After the adsorption process, the used sorbents, which contain heavy metals, need to be desorbed to reduce their potential environmental hazards or provide reusable sorbents for economical aspect. The sorbent's adsorption efficiency is affected by different operating conditions and waste elemental compositions during incineration, which, in turn, affect their desorption characteristics. However, the effects of operating condition and waste elemental composition on the stability of heavy metals in the sorbents and the desorption efficiencies have been little studied. This study investigates the desorption characteristics of heavy metals (Cr, Pb, Cu, and Cd) from the hazardous sorbents with different extracting reagents (H(2)O, HCl, EDTA, and Na(2)S(2)O(5)). The hazardous sorbents were generated under different adsorption time and various input waste elemental compositions during incineration process.     

Speciation, selective extraction and preconcentration of chromium ions via alumina-functionalized-isatin-thiosemicarbazone

A method is presented and described for speciation, extraction and preconcentration of Cr(III) and Cr(VI) based on dynamic and static solid phase extraction techniques. Three newly designed alumina phases-physically adsorbed-isatin-thiosemicarbazone (I-III) were synthesized, characterized, tested for stability and applied as inorganic ion exchangers and chelating solid sorbents for various metal ions. The selectivity characteristics incorporated into these alumina phases were studied and evaluated via determination of the distribution coefficients and separation factors of chromium species versus other interacting metal ions. Quantitative recovery of Cr(VI) was accomplished by alumina phases (I-III) in pH 1.0 giving percentage extraction values of approximately 99.9-100.0%, while Cr(III) was found to be quantitatively recovered by these sorbents in pH 7.0 leading to percentage extraction values approximately 100.0% with minimal or no interference between these two species under the studied buffering conditions. Selective solid phase speciation and preconcentration of Cr(III) and Cr(VI) in various real water samples were successfully performed and accomplished by newly designed alumina phases (I-III) via a preconcentration micro-column.     

Heavy metal vaporization and abatement during thermal treatment of modified wastes

This study examines the vaporization percentage and partitioning of heavy metals Cd, Pb and Zn during thermal treatment of wastes with added PVC, heavy metals or phosphate, and the efficiency of sorbents for removal of these metallic compounds in flue gas of an industrial solid waste incinerator. Firstly, vaporization experiments were carried out to determine the behavior of heavy metals during combustion under various conditions (type of waste, temperature, presence of chloride or phosphate ...). The experimental results show relatively high vaporization percentage of metallic compounds within fly ash and limestone matrix while heavy metals within sediments treated with phosphoric acid are less volatile. Vaporization of metals increases with increasing temperature and with chloride addition. The thermal behavior of the selected heavy metals and their removal by sorbents (sodium bicarbonate, activated carbon) was also studied in an industrial solid waste incinerator. These pilot scale experiments confirm that heavy metals are concentrated in fly ashes and cyclone residues, thus effectively controlling their release to the atmosphere.     

Colloid stable sorbents for cesium removal: preparation and application of latex particles functionalized with transition metals ferrocyanides

In this paper we suggest a principally new approach to preparation of colloid stable selective sorbents for cesium uptake using immobilization of transition metals (cobalt, nickel, and copper) ferrocyanides in nanosized carboxylic latex emulsions. The effects of ferrocyanide composition, pH, and media salinity on the sorption properties of the colloid stable sorbents toward cesium ions were studied in solutions containing up to 200 g/L of sodium nitrate or potassium chloride. The sorption capacities of the colloid sorbents based on mixed potassium/transition metals ferrocyanides were in the range 1.3-1.5 mol Cs/mol ferrocyanide with the highest value found for the copper ferrocyanide. It was shown that the obtained colloid-stable sorbents were capable to penetrate through bulk materials without filtration that made them applicable for decontamination of solids, e.g. soils, zeolites, spent ion-exchange resins contaminated with cesium radionuclides. After decontamination of liquid or solid radioactive wastes the colloid-stable sorbents can be easily separated from solutions by precipitation with cationic flocculants providing localization of radionuclides in a small volume of the precipitates formed.     

Preconcentration of rare earth elements(III) by sorption from nitric acid solutions using carbamoylmethylphosphine oxide and an ionic liquid

Sorption of microamounts of rare earth elements(III) from HNO₃ solutions with complexing sorbents prepared by noncovalent immobilization of diphenyl(dibutylcarbamoylmethyl)phosphine oxide and an ionic liquid, 1-methyl-3-butylimidazolium bis[(trifluoromethyl)sulfonyl]imide, on the surface of carbon nanotubes was studied in relation to the component ratio in the sorbent and to the HNO₃ concentration in the aqueous phase. The efficiency of the recovery of rare earth elements considerably increases when the sorbent phase contains the ionic liquid.     

A comparative study of the removal of trivalent chromium from aqueous solutions by bentonite and expanded perlite

Local bentonite and expanded perlite (Morocco) have been characterised and used for the removal of trivalent chromium from aqueous solutions. The kinetic study had showed that the uptake of Cr(III) by bentonite is very rapid compared to expanded perlite. To calculate the sorption capacities of the two sorbents, at different pH, the experimental data points have been fitted to the Freundlich and Langmuir models, respectively, for bentonite and expanded perlite. For both sorbents the sorption capacity increases with increasing the pH of the suspensions. The removal efficiency has been calculated for both sorbents resulting that bentonite (96% of Cr(III) was removed) is more effective in removing trivalent chromium from aqueous solution than expanded perlite (40% of Cr(III) was removed). In the absence of Cr(III) ions, both bentonite and expanded perlite samples yield negative zeta potential in the pH range of 2-11. The changes of expanded perlite charge, from negative to positive, observed after contact with trivalent chromium(III) solutions was related to Cr(III) sorption on the surface of the solid. Thus, it was concluded that surface complexation plays an important role in the sorption of Cr(III) species on expanded perlite. In the case of bentonite, cation-exchange is the predominate mechanism for sorption of trivalent chromium ions, wherefore no net changes of zeta potential was observed after Cr(III) sorption. X-ray photoelectron spectroscopy measurements, at different pH values, were also made to corroborate the zeta potential results.     

Effect of EDTA on divalent metal adsorption onto grape stalk and exhausted coffee wastes

In the present work, two industrial vegetable wastes, grape stalk, coming from a wine producer, and exhausted coffee, coming from a soluble coffee manufacturer, have been investigated for the removal of Cu(II) and Ni(II) from aqueous solutions in presence and in absence of the strongly complexing agent EDTA. Effects of pH and metal-EDTA molar ratio, kinetics as a function of sorbent concentration, and sorption equilibrium for both metals onto both sorbents were evaluated in batch experiments. Metal uptake was dependent of pH, reaching a maximum from pH around 5.5. EDTA was found to dramatically reduce metal adsorption, reaching total uptake inhibition for both metals onto both sorbents at equimolar metal:ligand concentrations. Kinetic results were successfully modelled by means of the pseudo second order model. Langmuir and Freundlich models were used to describe the sorption equilibrium data. Grape stalk showed the best performance for Cu(II) and Ni(II) removal in presence and in absence of EDTA, despite exhausted coffee appears as less sensitive to the presence of complexing agent. The performance of Cu(II) and Ni(II) sorption onto grape stalk in a continuous flow process was evaluated. In solutions containing EDTA, an initial metal concentration in the outlet flow corresponding to the complexed metal fraction was observed from the beginning of the process. A high metal recovery yield (>97%) was achieved by feeding the metal-loaded column with 0.05 M HCl.     

Arsenic sorption onto natural hematite, magnetite, and goethite

In this work the sorption of As(III) and As(V) on different natural iron oxides (hematite, magnetite, and goethite) has been studied as a function of different parameters. The sorption kinetics for the three iron oxides shows that equilibrium is reached in less than 2 days and the kinetics of sorption seems to be faster for goethite and magnetite than for hematite. The variation of the arsenic sorbed on the three different sorbents as a function of the equilibrium arsenic concentration in solution has been fitted with a non-competitive Langmuir isotherm. The main trend observed in the variation of the arsenic sorbed with pH is the decrease of the sorption on the three sorbents at alkaline pH values, which agrees with results found in the literature. Highest As(III) sorption was observed on hematite surface in all the pH range compared to goethite and magnetite. Natural minerals studied in this work had similar sorption capacities for arsenic than synthetic sorbents.     

Adsorptive and structural characteristics of carbon sorbents

This paper describes the adsorptive, structural, and textural characteristics of carbon sorbents of various origins: OU-A activated charcoal powder (unmodified and modified with a cellulose polyelectrolyte), AUT-MI fibrous activated carbon, and expanded graphite intercalated with sulfuric acid. In accordance with their pore structure parameters and specific surface area, the highest adsorption capacity for water-soluble markers (iodine and methylene blue) and anionic surfactants is offered by the activated charcoal and fibrous carbon. Surface modification with an anionic polymer increases the adsorption of positively charged methylene blue molecules.     

Concentration of Tc(VII) from Aqueous Solutions with Filled Fibrous Sorbents

Sorption of Tc(VII) on fibrous sorbents filled with finely dispersed anion exchangers (AV-17-n and AN-31-n) and on a chelating sorbent bearing 1,3(5)-dimethylpyrazole groups (POLYORGS-17-n) is studied. The Tc(VII) distribution coefficients (K_d, cm³ g^?1) are determined in sorption from simulated nitric acid, alkaline, and saline solutions. The highest distribution coefficients (K_d ～10³ ? 10⁵ cm₃ g^?1) were obtained in sorption of Tc from weakly acidic (≤0.1 M HNO₃) and alkaline (0.1–1.0 M NaOH) solutions. In sorption of Tc from alkaline and nitric acid solutions containing NaNO₃, POLYORGS-17-n demonstrated the highest efficiency. Tc is totally recovered with the sorbents studied in 10 min. Then it can be eluted with 1 M HNO₃. The sorbents AV-17 and POLYORGS-17-n can be used for Tc(VII) recovery from saline solutions like groundwater (pH ～8).     

Sorption of CH3 131I from a water vapor-air flow onto inorganic sorbents containing Ag and nonferrous metals (Cu,Ni, Zn)

Sorption of CH₃ ¹³¹I from a water vapor-air medium onto Fizkhimin inorganic sorbents containing Ag and nonferrous metals (Cu, Ni, Zn) was studied. Ag-free Fizkhimin inorganic sorbents exhibit poor ability to take up CH₃ ¹³¹I. No more than 51% of the initial 10-mg portion of CH₃ ¹³¹I is taken up by the sorbents heated to 350°C. The sorbents containing 1.4–2 wt % Ag and 5.6–8 wt % nonferrous metal (Cu, Ni, Zn) show high ability to take up CH₃ ¹³¹I (>99.8% uptake), with the performance of the Ni-containing sorbents remaining very high (>99.9%) with variation of various parameters of both the sorbents and the medium. The Cu- and Zn-containing analogs do not exhibit such properties.     

Phosphoryl-Containing Chelating Sorbents for Concentrating Actinides

New chelating sorbents with phosphinate, carbamoylmethylphosphinate, and methylenediphosphine dioxide functionalities are synthesized by chemical and noncovalent binding of the ligands to polymer matrices, chloromethylated styrene copolymer and XAD-7 acrylate polymer. The sorption and kinetic characteristics of the sorbents with respect to U(VI), Th(IV), Pu(IV), and Am(III) are studied in nitric acid solutions. The sorbents obtained by noncovalent binding of the ligands to XAD-7 demonstrate better kinetic properties. The sorbents can be used for concentrating actinides from 3–5 M HNO₃ and for their partitioning.     

Studies on the sorption of praseodymium (III), holmium (III) and cobalt (II) from nitrate medium using TVEX-PHOR resin

The use of TVEX-PHOR resin for the sorption of praseodymium (III), holmium (III) and cobalt (II) from nitrate medium was carried out using batch and column techniques. Various parameters affecting the uptake of these metal ions such as v/m ratio, pH and the metal ion concentration were separately studied. Effect of temperature on the equilibrium distribution values has been studied to evaluate the changes in standard thermodynamic quantities. Experimental results of the investigated metal ions were found to fit to Freundlich isotherm model over the entire studied concentration range. Selectivity sequence of the resin for these metals is Ho>Pr>Co. The recovery of the investigated metals from the loaded resin is preformed with 0.1M sulphuric acid.     

Modified Sorbents Based on BAU-A Activated Carbon and Coarsely Porous Silica Gel for Removing Radionuclides and Nonferrous Metals from Aqueous Solutions

Radiochemistry - Sorption of radionuclides (90Sr, 90Y, 137Cs, 152Eu) and nonferrous metals (Cu, Ni, Zn, Pb) from aqueous solutions onto granulated sorbents based on coarsely porous silica gel of...     

Sorption Recovery of Strontium from Seawater

Sorption recovery of strontium from seawater and prospects of using selective sorbents for treatment of seawater or mixtures of liquid radioactive wastes (LRW) with seawater to remove ⁹⁰Sr are examined. A comparative analysis is made of characteristics of various sorbents. The most of the sorbents studied demonstrate low distribution coefficients and selectivity with respect to strontium, being unable to provide efficient removal of ⁹⁰Sr from seawater. The exceptions are new sorption reagents developed by the authors, which show promise for treatment of LRW to remove strontium. The possible mechanism of strontium sorption with these sorbents is suggested.