Carbonate hydroxylapatite (CHAP), prepared from eggshell waste, was used to remove 60Co(II) from aqueous solutions. The sorption of 60Co(II) on CHAP as a function of contact time, pH, ionic strength and foreign ions in the absence and presence of humic acid
and fulvic acid under ambient conditions was studied. The sorption of 60Co(II) on CHAP was strongly dependent on pH and ionic strength. The thermodynamic parameters (ΔH0, ΔS0, ΔG0) of 60Co(II) sorption on CHAP were calculated from the temperature-dependent sorption isotherms, and the results indicated that
the sorption process of 60Co(II) on CHAP was endothermic and spontaneous. At low pH, the sorption of 60Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on CHAP surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. Experimental results
also indicated that CHAP was a suitable low-cost adsorbent for pre-concentration and solidification of 60Co(II) from large volumes of aqueous solutions.
The aim of this study is to compare different resins regarding their separation and pre-concentration efficiency for uranium
from aqueous solutions and its subsequent radiometric determination by liquid scintillation counting (LSC). The different
types of the investigated resins include: (a) a pure cation-exchange resin (Dowex Marathon C), (b) a complex forming resin
(Chelex 100) and (c) an impregnated resin (5% diethylene glycol succinate on Chromosorb W-H). The radiometric measurements
were performed after mixing of the pre-concentrated aqueous phase with the liquid scintillation cocktail. The effect of experimental
conditions such as pH, salinity (e.g. [NaCl]) and the presence of other chemical species (e.g. Ca2+ and Fe3+ ions or humic acid and silica colloids) on the separation recovery have been investigated at constant uranium/radioactivity
concentration. According to the experimental results the maximum chemical recovery differs significantly from one resin to
another as a function of either, pH or the other chemical parameters. The optimum pH is found to be 8, 4 and 8 for Marathon
C, Chelex-100 and diethylene glycol succinate, respectively. On the other hand, generally Ca2+ and Fe3+ ions as well as the presence of colloidal species in solution (even at low concentrations) result in a significant decrease
of the chemical recovery of uranium, particularly for Marathon C and the diethylene glycol succinate impregnated resins. Generally,
among the studied resins Chelex 100 was superior regarding chemical recovery, selectivity, regeneration and reuse.
The sorption of Co(II) on Na-montmorillonite was conducted under various conditions, i.e., contact time, adsorbent dosage,
pH, ionic strength, foreign ions, fulvic acid (FA), humic acid (HA) and temperature. Results of sorption data analysis indicated
the sorption of cobalt on Na-montmorillonite was strongly dependent on pH and ionic strength. At low pH, the sorption of Co(II)
was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Na-montmorillonite, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence
of different cations influenced Co(II) sorption, while the presence of different anions had no differentiable influences on
Co(II) sorption. The presence of HA and FA decreased the sorption of Co(II) on montmorillonite. The sorption isotherms are
simulated well with the Langmuir model. The thermodynamic parameters (ΔH°, ΔS° and ΔG°) calculated from the temperature dependent isotherms indicated that the sorption reaction of Co(II) on montmorillonite was
an endothermic and spontaneous process. The sorption test revealed that the low cost material was a suitable material in the
preconcentration of Co(II) from large volumes of aqueous solutions.
The aim of this study is the separation and pre-concentration of thorium from aqueous solutions by cloud point extraction
(CPE) and its the radiometric determination by liquid scintillation counting (LSC). For CPE, tributyl phosphate (TBP) was
used as the complexing agent and (1,1,3,3-Tetramethylbutyl)phenyl-polyethylene glycol (Triton X-114) as the surfactant. The
radiometric measurements were performed after phase separation by mixing of the surfactant phase with the liquid scintillation
cocktail. The effect of experimental conditions such as pH, ionic strength (e.g. [NaCl]) and the presence of other chemical
species (e.g. Ca2+ and Fe3+ ions, and humic acid colloids) on the CPE separation recovery have been investigated at constant reactant ratio (m(TBP)/m(Triton) = 0.1). According to the experimental results the maximum chemical recovery is (60 ± 5)% at pH 3. Regarding the other
parameters, generally Ca2+ and Fe3+ ions as well as the presence of colloidal species in solution (even at low concentrations) results in significant decrease
of the chemical recovery of uranium. On the other hand increasing NaCl concentration leads to enhancement of chemical recovery.
Generally, the method could be applied successfully for the radiometric determination of thorium in water solutions with relatively
increased thorium content.
Authors:Hui Zhang, Xianjin Yu, Lei Chen, and Jiaqiang Geng
The sorption of 63Ni(II) from aqueous solution using ZSM-5 zeolite was investigated by batch technique under ambient conditions. ZSM-5 zeolite
was characterized by point of zero net proton charge (PZNPC) titration. The sorption was investigated as a function of shaking
time, pH, ionic strength, foreign ions, humic acid (HA), fulvic acid (FA) and temperature. The results indicate that the sorption
of 63Ni(II) on ZSM-5 zeolite is strongly dependent on pH. The sorption is dependent on ionic strength at low pH, but independent
of ionic strength at high pH values. The presence of HA/FA enhances 63Ni(II) sorption at low pH values, whereas reduces 63Ni(II) sorption at high pH values. The sorption isotherms are simulated by Langmuir model very well. The thermodynamic parameters
(i.e., ∆H0, ∆S0 and ∆G0) for the sorption of 63Ni(II) are determined from the temperature dependent sorption isotherms at 293.15, 313.15 and 333.15 K, respectively, and
the results indicate that the sorption process of 63Ni(II) on ZSM-5 zeolite is spontaneous and endothermic.
With increasing global nuclear activities, there is a growing interest in understanding the migration behavior of transuranic elements in the terrestrial environment. The laboratory investigations on the adsorption behavior of AM(III) (10–7M) in aqueous solutions showed that there was not adsorption of Am(III) on glass or polyethylene vials from aqueous solutions at pH<3. The rate of adsorption was found to be inversely related to the (H+) in the pH range 4–7. It was also found to be strongly influenced by stirring/shaking as well as by the presence of particulate matter in the aqueous phase. The presence of particulate matter (>0.6 m) in the aqueous solutions significantly inhibits the adsorption rate. Attempts to fit the kinetic data (collected on filtered [particle size >0.6 m] or unfiltered distilled water at pH 6) to the reversible or irreversible first order rate equation did not successfully indicate the complexity of the adsorption process. The presence of 20mg/liter of humic acid at pH 6.3 completely inhibits the adsorption of Am on glass surfaces.
The sorption behavior of the pertechnetate anion in various solid-solution systems under aerobic conditions and pH 1.3–12.5 has been investigated. Batch techniques were employed. On most of natural minerals only surface adsorption occurs. Rs-values were no larger than 2.0 ml · g–1. Adsorption on various natural minerals and rocks such as sandstone, basalt, granite, pyrite, peat and others are comparaed with the analogous processes on artificial inorganic sorbents: titanium oxides (thermoxide-34, thermoxide-3), crystaline cadmium sulfide, zirconium phosphate, and complex inorganic sorbents: antimony oxide — silicon oxide — phosphorus pentoxide, antimony oxide — silicon oxide — aluminium oxide, lithium oxide — manganese oxide — aluminium oxide — water, lithium oxide — titanium oxide —chromium oxide — water. For comparison the sorption of Tc on some organic sorbents was included. The solubility of Tc2S7 in water was measured to be 0.257 g/l. It has been shown that preliminary irradiation of sorbents such as sandstone, peat and humic acid by -rays with doses not less than 107 rad results in the decrease of Tc(VII) sorption.
The migration of radionuclides with groundwater into the environment of a radioactive waste repository is an important aspect in evaluating the safety assessment of such repositories. The potential transport and fate of these radioactive species are dependent upon their speciation and the geochemical behavior of the predominant ones. The speciation of different valence states of neptunium [Np(IV, V and VI)] and their migration behavior are investigated. The data revealed that the uptake is highly dependent upon pH and the distribution coefficient (Kd) is depressed by the presence of organic ligands. The relative migration velocities (Vn) of the valence states relative to that of groundwater, in the concerned area, clarified that Np(V) is the most mobile species and their transport rates are highly accelerated by the presence of humic acid. Also, a radionuclide dispersion model was applied to elucidate the migration behavior of these radioactive species in the selected site and to quantitatively predict their concentrations at different distances in both x and z directions over long time scales.
Authors:P. Beneš, K. Štamberg, L. Široký, and J. Mizera
The sorption of trace europium, as a trivalent actinide homologue, was studied in the system Gorleben sand - aqueous solution with the aim to elucidate its mechanism. Radiotracer method (152/154Eu) and batch experiments were used. Simultaneously, the distribution of humic substances present in, or added to the system was measured. The evaluation of the sorption was complicated by the adsorption of Eu on the walls of polyethylene vials used for the experiments, which was rather high and had to be taken into consideration. It has been found that Eu sorption on Gorleben sand increases from pH 2 to pH 5-7 and then it decreases. The decrease is due to the complexation of Eu with humic substances leached from Gorleben sand at pH >7. The position of the sorption maximum depends on the composition of the solution and on the liquid-to-solid ratio. It is shifted to lower pH values in the presence of added humic acid (HA), which enhances Eu sorption at low pH values and suppresses it at pH values higher than 5. The regions of the enhancing/suppressing effects coincide with the high/low adsorption of HA on Gorleben sand, respectively. The increasing ionic strength (from 0.01 to 0.1) and europium concentration (3.4.10-8 to 9.3.10-7 mol/l) suppress the relative sorption (expressed in %) at low pH values and enhance it at pH>6-8. Addition of carbonates (5.10-3 mol/l) supports Eu sorption at pH>7.5 so that no decrease with pH is observed till pH 9. Alkaline leaching of the sand significantly changes most of the effects found. These results were qualitatively interpreted and conclusions were drawn on the mechanism of the sorption.
Authors:Qifeng Liu, Jiali Liao, Ning Liu, Dong Zhang, Houjun Kang, Yuanyou Yang, Bing Li, Haijun Zhu, and Jiannan Jin
As an important radioisotope in nuclear industry and other fields, 241 Am is one of the most serious contamination concerns due to its high toxicity and long half-life. In order to supply useful
reference for disposal of 241Am waste with low-medium radioactivity, the adsorption and migration behavior of 241Am on aerated zone soil were investigated by the static experimental method and column experiments. The results showed that
more than 98% of the total 241Am could be adsorbed from 241Am solution of 0.32·10−7−1.1·10−7 mol/l by the soil at pH 4–9. The adsorption of 241Am on the soil was a pH-dependent process at pH<4, but for pH>4, the adsorption rate of 241Am on the soil changed minutely. The adsorption equilibrium was achieved within 24 hours and no significant effect on adsorption
of 241Am was observed at liquid-solid ratios of 50:1–500:1. The relationship between concentration of 241Am and adsorption capacities of 241Am can be described by the Freundlich adsorption equation. Adsorption of 241Am on the soil can be inhibited by humic acid, ferric hydroxide colloid, or some anions, such as citric acid anion, saturated
EDTA solution, C2O42− and CO32−. It was also noted that the adsorption rate of 241Am drops in solutions containing Eu3+ or Nd3+, even 0.5 times above the 241Am concentration. A migration distance of 8 mm for 241Am(III) is observed only in the aerated zone soil containing ferric colloid, while a migration distance of less than 2 mm
is noted in other soil samples after more than 250 days. All these results indicate that the aerated zone soil is an efficient
sorbent for 241Am and can inhibit the migration of 241Am.