Effects of phosphate and Cr3+ on the sorption and transport of uranium(VI) on a silica column

Six column experiments were performed and seven breakthrough curves (BTCs) and seven displacement (desorption) curves (DPCs) of phosphate and U(VI) were obtained, which demonstrated the effects of phosphate and Cr³⁺ on the sorption and transport of U(VI) on a silica column at pH 3 and uranium concentration 10⁻⁵–10⁻⁶ mol/L of the influent. It was found that in the presence of phosphate sorbed preliminarily on the silica column, the amount of U(VI) sorbed on this column is significantly increased owing to the interaction of U(VI) with phosphate sorbed as compared with that in the absence of phosphate, and the breakthrough and the mean residence time of U(VI) on this column are similar to those in the absence of phosphate. While the effect of simultaneous injection of Cr³⁺ on the retardation of U(VI) on the silica column, the maximum concentration of BTC and the amount of U(VI) sorbed was found to be insignificant. Transport and sorption studies of U(VI) are important, since all uranium isotopes are radioactive, there is a need to understand the potential for migration away from radioactive waste storage and mill tailing sites.     

Effects of phosphate and fulvic acid on the sorption and transport of uranium(VI) on silica column

Column experiments were performed, breakthrough curves (BTCs) and displacement curves (DPCs) were obtained of uranium(VI) in the absence and presence of phosphate or fulvic acid individually and simultaneously which demonstrated the effects of phosphate and fulvic acid on the sorption and transport of U(VI) in a silica column at pH 3.7 and U(VI) concentration of 5·10⁻⁶ mol/L. It was found that in the presence of phosphate or fulvic acid sorbed preliminarily on the silica column, the amount of U(VI) sorbed increased significantly and the transport of U(VI) delayed significantly relative to that in the absence of phosphate or fulvic acid. Moreover, in the presence of phosphate and fulvic acids sorbed preliminarily and simultaneously on the silica column, the amount of U(VI) sorbed on the silica column is significantly increased again relative to that in the presence of phosphate or fulvic acid individually. Transport studies of U(VI) are important, since all uranium isotopes are radioactive, and uranium contamination of soils and groundwaters occurs at mining and mill sites. A fundamental understanding of the transport behavior of U(VI) in the water-mineral systems is necessary for accurate risk assessments.     

Sorption of Th(IV) ions onto TiO2: Effects of contact time, ionic strength, thorium concentration and phosphate

Summary The sorption of Th(IV) onto TiO₂ was studied by the batch technique as a function of pH and ionic strength at moderate concentration (10^-4-10^-5 mol/l) and in the presence and absence of phosphate. It was found that the sorption rate of Th(IV) was relatively slow, the sorption percent was abruptly increased from pH 2 to 4, and the sorption was decreased with increasing ionic strength as a whole. In the concentration range of Th(IV) from trace concentration to 1.4 ^. 10^-4 mol/l and in the absence of phosphate, the sorption isotherms were roughly fitted the Freundlich equation at different ionic strengths and approximately constant pH. These sorption characteristics of Th(IV) onto TiO₂ were compared with those of uranyl on the same sorbent. In addition, the positive effect of phosphate on the sorption of Th(IV) onto TiO₂ was demonstrated obviously and can be attributed to strong surface binding of phosphate, and the subsequent formation of ternary surface complexes of Th(IV). The difference between the sorption characteristics of Th(IV) ions and uranyl ions onto TiO₂ is discussed.     

Comparative study on Th(IV) sorption on alumina and silica from aqueous solutions

The effects of pH, ionic strength and concentration on the sorption of Th(IV) on alumina and silica were investigated and the sorption isotherms of Th(IV) on alumina and silica at different pH values were determined. It was found for both sorbents that the absorbability of silica is less than that of alumina. The relative sorption rate of silica is similar to that of alumina. The sorption edges are similar to each other, that the insensitivity of sorption to ionic strength is about the same. These similarities between the sorbents suggest that the speciation of Th(IV) in aqueous solutions plays a significant, but subtle role, in controlling the sorption process, because the charges of both sorbents are distinctly different. The mechanism of Th(IV) sorption on alumina is distinctly different from that of the sorptions of Cs⁺, Eu³⁺ and Yb³⁺ on alumina, and similar to that of the sorption of Co(II) on alumina.     

Potential use of tungstocerate matrices on the separation of <Superscript>113m</Superscript>In from <Superscript>110m</Superscript>Ag relevant to the separation of the cyclotron-produced <Superscript>111</Superscript>In from its silver target

A procedure for separation of no-carrier-added ^113mIn(III) radioisotope from a bulk of ^110mAg has been developed. The sorption behavior of ^113mIn(III) and ^110mAg(I) ions in HNO₃ acid solutions on different tungstocerate matrices showed high affinity of ^110mAg(I) ions towards tungstocerate(IV) gel matrices compared with ^113mIn(III) ions. No-carrier-added ^113mIn radionuclide was separated from ^110mAg on 12-tungstocerate(IV) column matrix. 11 mL 0.3M HNO₃ acid solution was enough for eluting the ^113mIn from the column bed. ^110mAg was recovered from the column by eluting the column bed with 12 mL 2M HNO₃ acid solution.     

Migration and sorption of <Superscript>137</Superscript>Cs and <Superscript>152,154</Superscript>Eu in crushed crystalline rocks under dynamic conditions

In migration experiments, sorption of ¹³⁷Cs and ^152,154Eu in the columns of crushed crystalline rocks of 0.25–0.8 mm grain size under dynamic flow conditions from the synthetic groundwater (SGW) has been studied. Five samples of crystalline rocks from Cavernous Gas Reservoir near Příbram were taken. Plastic syringes of 8.8 cm length and 2.1 cm in diameter were used as columns. The water phase was pumped downward through the columns, using a multi-head peristaltic pump, with a seepage velocity of about 0.2 cm/min. The radioactive nuclides, containing chemical carriers, were added into the water stream individually in the form of a short pulse. Desorption experiments were carried out with 2:1 (v/v) mixture of H₂SO₄ and HNO₃. In the columns the longitudinal distribution of the residual ¹³⁷Cs and ^152,154Eu activities was also determined. By the evaluation of respective breakthrough and displacement curves, the experimental and theoretical retardation factors, distribution coefficients and hydrodynamic dispersion coefficients were determined using the integrated analytical form of a simple advection-dispersion equation (ADE). Dynamic sorption experiments were also compared with the results of static sorption experiments. The paper was presented in part as a poster No. PB1-1 at the 11th International Conference Migration’ 07, held in Munich, Germany, August 26–31, 2007, Abstracts, p. 212.     

Effect of pH,fulvic acid and temperature on sorption of Th(IV) on zirconium oxophosphate

Sorption of Th(IV) on Zr₂O(PO₄)₂ as a function of contact time, reaction temperature, pH, ionic strength and solid-to-liquid ratio (m/V) is studied under ambient condition by using batch technique. Effects of fulvic acid (FA), phosphate, sulfate and citrate on Th(IV) sorption are investigated in detail. A pseudo-second-order rate equation is used to simulate the kinetic sorption. The removal of Th(IV) increases with increasing pH and hardly depends on ionic strength. Sorption of Th(IV) increases with increasing m/V and reaction temperature. The presence of FA and phosphate enhances the sorption of Th(IV) on Zr₂O(PO₄)₂ while sulfate and citrate decrease the sorption. The Langmuir and Freundlich models are used to simulate the sorption isotherm of Th(IV) on Zr₂O(PO₄)₂ at different temperatures. The thermodynamic data (i.e., ∆H ⁰, ∆S ⁰, ∆G ⁰) are calculated from temperature dependent sorption isotherms. The results suggest that the sorption process of Th(IV) on Zr₂O(PO₄)₂ is spontaneous and endothermic.     

Effect of humic acid on the sorption of technetium on hematite colloids using <Superscript>95m</Superscript>Tc and <Superscript>96</Superscript>Tc as tracers

Sorption of technetium on hematite colloids, at varying pH (3–10), has been studied in absence and presence of humic acid using ^95mTc-⁹⁶Tc radiotracers. Technetium was found to be weakly sorbed on hematite at lower pH (<5) values, while no sorption was observed at higher pH values. Humic acid was found to have no effect on the sorption of technetium on hematite under aerobic conditions, while at lower pH values small reduction was observed which was attributed to the reduced zeta potential of the hematite colloids owing to the strong sorption of humic acid.     

Sorption of Mo(VI), W(VI), Cr(VI), and V(V) anions on a silica gel modified with immobilized polyionene

The sorption of polyionene 1,4-MePh on the silica gel surface was studied. The silica gel modified with polyionene sorbed was used for sorption preconcentration of MoO ₄ ^2? , WO ₄ ^2? , Cr₂O ₇ ^2? , and VO ₃ ^? anions from aqueous solutions. The sorption isotherms of these anions on the initial and modified silica gels were obtained and analyzed.     

Studies on sorption of plutonium on inorganic ion exchangers from sodium carbonate medium

Sorption of Pu(IV) from sodium carbonate medium has been investigated by using three inorganic ion exchangers, viz. alumina, silica gel and hydrous titanium oxide (HTO). Distribution ratios (D) of Pu(IV) for its sorption on these ion exchangers have been determined. The values are 700, 10³ and 10⁴ for alumina, silica gel and hydrous titanium oxide, respectively, from 0.1M sodium carbonate medium. The high distribution ratios indicate their suitability for the removal of Pu(IV) from sodium carbonate waste streams. Pu(IV) breakthrough capacities have been determined with 5 ml bed at a flow rate of 30 ml per hour. The 10% Pu(IV) breakthough capacities for alumina and silica gel are 3 g l^–1 and 14 g l^–1, respectively. The capacity of HTO is 60 g of Pu(IV) per liter of exchanger at 4% Pu(IV) breakthrough.     

Correlations between data of <Superscript>29</Superscript>Si NMR and thermogravimetry for silica/monetite nanocomposites

Silica/monetite nanocomposites were synthesized through controlled hydrolysis of tetraethoxysilane at concentrations of 5, 10, 15, and 20% mol/mol of calcium phosphate forming the solids named CaPSil1, CaPSil2, CaPSil3, and CaPSil4, respectively. XRD patterns showed formation of nanocomposites with a decrease in crystallinity. The NMR ²⁹Si spectra suggested an increase in the content of incorporated silica with reduction of Q³ (–SiOH) signal, which contributes for mass loss, in agreement with thermogravimetry. The incorporation of silica increased the chemical stability of the precursor phosphate in an acidic medium.     

Determination of <Superscript>137</Superscript>Cs and <Superscript>85</Superscript>Sr transport parameters in fucoidic sand columns and groundwater system

The determination is based on the evaluation of experimentally obtained breakthrough curves using the erfc-function. The first method is founded on the assumption of a reversible linear sorption/desorption isotherm of radionuclides on solid phase with constant distribution and retardation coefficients, whereas the second one is based on the assumption of a reversible non-linear sorption/desorption isotherm described with the Freundlich equation, i.e., with non-constant distribution and retardation coefficients. Undisturbed cores of 5 cm in diameter and 10 cm long were embedded in the Eprosin-type cured epoxide resin column. In this study the so-called Cenomanian background groundwater was used as transport medium. The groundwater containing radionuclides was introduced at the bottom of the columns at about 4 mL h⁻¹ constant flow-rate. The results have shown that in the investigated fucoidic sands: (i) the sorption was in principle characterized by linear isotherms and the corresponding retardation coefficients of ¹³⁷Cs and ⁸⁵Sr, depending on the type of sample, were approximately 13 or 44 and 5 or 15, respectively; (ii) the desorption was characterized by non-linear isotherms, and the retardation coefficients of the same radionuclides ranged between 23–50 and 5–25, respectively. The values of the hydrodynamic dispersion coefficients of these radionuclides varied between 0.43–1.2 cm² h⁻¹.      

Effect of pH, ionic strength and temperature on sorption characteristics of Th(IV) on oxidized multiwalled carbon nanotubes

Oxidized multiwalled carbon nanotubes (MWCNTs) were characterized by SEM and FTIR. The sorption of Th(IV) on MWCNTs was studied as a function of contact time, pH, ionic strength, Th(IV) concentration and temperature. The results indicate that the sorption of Th(IV) on MWCNTs is strongly dependent on pH and weakly dependent on ionic strength. The sorption thermodynamics of Th(IV) on MWCNTs was carried out at 293.15, 313.15 and 333.15 K, respectively, and the thermodynamic parameters (standard free energy changes (??G ⁰), standard enthalpy change (??H ⁰) and standard entropy change (??S ⁰)) were calculated from the temperature dependent sorption isotherms. The sorption of Th(IV) on MWCNTs is a spontaneous and endothermic process. The oxidized MWCNTs may be a promising candidate for the preconcentration and solidification of Th(IV), or its analogue actinides from large volumes of aqueous solutions.     

Determination of sorption capacity of fucoidic sands for Cs+ and Sr2+ under dynamic column conditions

In this paper, the sorption behavior of Cs⁺ and Sr²⁺ on column of fucoidic sands under dynamic flow conditions was investigated, and their sorption capacities (SC) towards these two cations were studied. The determination of SC is based on the construction of respective breakthrough curves using ¹³⁷Cs and ⁸⁵Sr radionuclides as isotopic indicators in laboratory experiments. The samples were taken from several parts of the borehole in the area of interest. Undisturbed cores of 5 cm in diameter and 10 cm long were put in the glass columns and the cores were perfectly tightened using acrylate resin. In this time-dependence study, the so-called cenoman background groundwater was used. A concentration of 10^?6 mol/dm³ of Cs⁺ and Sr²⁺ in liquid phase individually was established using neutral salts of CsNO₃ and Sr(NO₃)₂, respectively. The groundwater was introduced at the bottom of the columns by a multi-head peristaltic pump, at a constant flow-rate of about 4 cm³/h. The results show that the sorption capacity of the investigated fucoidic sands for ¹³⁷Cs and ⁸⁵Sr is 0.1–1.5 and 0.05–0.5 μmol/100 g, respectively, in dependence on the evaluation of corresponding breakthrough curves. Some differences in the behavior of the cores during the experiments have also been observed and explained.     

Ion exchange studies of U(VI) from aqueous Arsenazo-III solutions using AG-2X8, Dowex-50WX8 and Chelex-100 resins

The distribution of U(VI) between the anion exchanger AG-2X8, the cation exchanger Dowex-50WX8 and the chelating resin Chelex-100 and aqueous solutions of Arsenazo-III at different pH values was studied. The concentration of Arsenazo-III was in the range of 1.53·10^–4–1.23·10^–3M. Equilibrium pH was varied from 1.0 to 8.78 while U(VI) original concentration was held constant at 3.39·10^–4M. The effect of Arsenazo-III concentration and the variation of hydrogen ion concentration on U(VI) species formed in solution as well as the sorbed species was discussed. Use was made of IR spectroscopy to investigate the sorption behavior. The sorption of some interfering ions such as Th(IV), Zr(IV) and Ce(III) on the resins used at optimum conditions for the sorption of U(VI) was also investigated.     

Production of low and high specific activity <Superscript>64</Superscript>Cu in a reactor

Production of radioactive scandium by irradiating natural titanium metal in Pakistan Research Reactor-1 was evaluated. The production rate of ⁴⁷Sc and other radioactive scandium was estimated. High specific activity ⁴⁷Sc can be produced by irradiating enriched ⁴⁷Ti in sufficient quantities needed for therapeutic applications. A new separation technique based on column chromatography was developed. Neutron irradiated titanium was dissolved in hydrofluoric acid, which was evaporated and taken in distilled water. The resulting solution was loaded on silica gel column. The radioactive scandium comes out first and the inactive titanium is removed with 2 M HCl. More than 95% radioactive scandium was recovered, while chemical impurity of titanium determined by optical emission spectroscopy was less than 0.01 μg/mL in final product.     

Transport and sorption of <Superscript>85</Superscript>Sr and <Superscript>125</Superscript>I in crushed crystalline rocks under dynamic flow conditions

Transport and sorption of water-soluble ⁸⁵Sr²⁺ and ¹²⁵I⁻ in the columns with beds of crushed crystalline rocks from synthetic groundwater has been studied under dynamic flow conditions. Samples of crystalline rocks: diorite-I, diorite-II, gabbro, granite and tonalite, having the grain size between 0.25 and 0.80 mm, were used. Plastic syringes of 8.8 cm length and 2.1 cm in diameter were applied as columns. The synthetic groundwater was pumped downward through the columns with a seepage velocity of about 0.2 cm/min and the given radioactive nuclide was added into the water stream individually in a form of a short pulse. In case of ⁸⁵Sr, desorption from diorite-I was also studied using an artificial acid rainfall and then, the longitudinal distribution of the residual ⁸⁵Sr activity along the bed was measured. Retardation, distribution and hydrodynamic dispersion coefficients were determined by the evaluation of respective breakthrough curves. A corrected integral form of a simple advection–dispersion equation was derived and used for fitting the experimental data. The K _d-parameters resulting from dynamic experiments were also compared with the results of static sorption experiments.     

Extraction chromatography for the separation of <Superscript>239</Superscript>Np from <Superscript>243</Superscript>Am

Summary An extraction chromatography method was developed for the separation of 239Np from ²⁴³Am in nitric acid solution. A sorbent based on aliphatic quaternary amine Aliquat-336 and hydrophobized silica gel was prepared. ²³⁹Np reduced to the oxidation state(IV) with ferrous sulfamate in 2M or 6M HNO₃ sorbs on the prepared silica gel column. After washing with 0.1M ferrous sulfamate in 2.5M HNO₃, ²³⁹Np is eluted with 0.1M HNO₃ containing 0.02M HF. The separation of ²⁴³Am from ²³⁹Np is very effective. The purity of ²³⁹Np was found to be better than 99.5%. The proposed ²³⁹Np milking procedure is suitable for the preparation of ²³⁹Np tracer that can be used for the determination of ²³⁷Np radiochemical yield.     

Continuous sorption of synthetic dyes on dried biomass of microalga Chlorella pyrenoidosa

The sorption of thioflavine T (TT) and malachite green (MG) cationic synthetic dyes on dried biomass of green microalga (Chlorella pyrenoidosa) immobilised in polyurethane foam under continuous column systems conditions using spectrophotometric methods of detection was investigated. Data characterising the sorption of TT and MG on microalgal biomass immobilised in polyurethane foam in a column system from single (C ₀ = 25 μmol dm^?3) or binary equimolar (C ₀ = 25 μmol dm^?3) dye solutions in the form of breakthrough curves were well described by the Thomas (R ² = 0.994–0.912), Yoon-Nelson (R ² = 0.994–0.911), and Clark (R ² = 0.993–0.911) models. Useful parameters characterising the sorption column system were obtained from these mathematical models. The Thomas model, in particular, provided the Q _max (maximal sorption capacity in μmol g^?1) parameter for characterisation of biosorbent and also for evaluation of competitive effects in the TT and MG dyes sorption. For the purposes of biomass regeneration, a one-step desorption of the dyes studied from the microalgal biomass in batch and continuous column systems was performed. Efficiency of TT desorption from microalgal biomass increased in the order: deionised H₂O (50.7 %), 99.5 vol. % 1,4-dioxane (67 %), 20 mmol dm^?3 NiCl₂ (83 %), 96 vol. % ethanol (85 %), 0.1 mol dm^?3 HCl (89 %), 1 mol dm^?3 acetic acid (89 %). In the case of MG, the desorption efficiency increased in the order: deionised H₂O (13 %), 20 mmol dm^?3 NiCl₂ (50 %), 0.1 mol dm^?3 HCl (91 %), 99.5 vol. % 1,4-dioxane (94 %), 1 mol dm^?3 acetic acid (99 %), 96 vol. % ethanol (> 99 %). The presence of carboxyl, phosphoryl, amino, and hydroxyl groups, the important functional groups for sorption of cationic xenobiotics, was also confirmed on the algae biomass surface by potentiometric titration and ProtoFit modelling software. The data obtained showed that the dried immobilised algae biomass could be used as a sorbent for removing toxic xenobiotics from liquid wastewaters or contaminated waters and also presenting the possibilities of mathematical modelling of sorption processes in continuous column systems in order to obtain important parameters for use in practice.     

Kinetics of radioeuropium sorption on Gorleben sand from aqueous solutions and ground water

Kinetics of Eu sorption on sandy sediment from Gorleben, Germany, containing humic substances, was studied by radiotracer method in batch experiments at very low europium concentration (3.4^.10^-8 mol/l), with the aim to find kinetic parameters suitable for modeling Eu migration in bed of the sediment and to elucidate the mechanism of the sorption. Experiments were evaluated using a new simplified method taking into account simultaneous sorption/desorption of Eu on the walls of sorption vessel. Five kinetic functions were tested, of which that describing diffusion in inert surface layer of sorbent proved most suitable. The effects of pH (3.0-8.8) by addition of Aldrich humic acid (10 mg/l), addition of hydrogencarbonates (5^.10^-3 mol/l) and preequilibration of the sediment with solution or of Eu with solution were examined. From the results it has been concluded that the kinetics and mechanism of the sorption strongly depend on pH. At pH 4.8 Eu is sorbed mainly as humate complex from the solution of humic acid. The addition of humic acid accelerates the sorption. Carbonate complexes of Eu are the probable forms sorbed at pH 8.8. The presence of humic substances in the slightly alkaline solutions suppresses the rate of the sorption due to slow dissociation of Eu-humate complexes.