The complexation of technetium with humic acid is usually done by a reduction of pertechnetate by Sn2+ ions. A Tc-HA complex can be scavenged in a Sn-HA complex, if tin is present as reductant. The main aim of the study was a preparation of the Tc-HA complex without impurities of Sn ions or other metal reductant, which was performed by a ligand exchange with hexakis(thiourea-S)technetium(III) under nitrogen atmosphere at pH 5.5. The [Tc(tu)6]3+ complex was prepared from TcO4- in acidic solution with thiourea as a reductant. Presence of the Tc-HA complex and other technetium species was determined by gel chromatography, paper chromatography and dialysis. Yield of Tc-HA complex was about 80% and reaction mixture contains about 20% of technetium dioxide, which is a side product of ligand-exchange.
The thermal behaviour of humic acids and their sodium salts in oxygen has been studied. The sodium humates were prepared by neutralization of humic acids or by dialysis of their pseudosolutions in sodium hydroxide. Infrared and X-ray diffraction spectra of samples taken between the dissociation steps obtained from the DTA-TG-DTG curves suggest a double mechanism. Below 500°, sodium carbonate and carbon are formed. At 600°, the dissociation of carbonate starts. The residual carbon burns at once at 770°. The extent of reaction changes with the amount of sodium initially present.
A landfill leachate sample was radiolyzed with γ-rays at 12.5, 25, 50, 100, 200 and 400 kGy. The radiolyzed solutions were
studied by UV–VIS–NIR spectroscopy to measure the color change, by chemical oxygen demand (COD) analysis to check the degree
of mineralization of the soluble organic matter present in the leachate and by FT–IR spectroscopy of the humic substance of
the leachate. The results have shown that the humic substance present in the landfill leachate is extremely refractory to
radiolysis: even at 400 kGy it was detected and recovered only with minor changes. It is shown that the radiolysis followed
by ozonolysis is able to cause important improvements of the leachate color and important reduction on the COD. However, the
results in terms of bleaching and COD abatement after radiolysis and ozonolysis of the leachate can be achieved directly by
a simple exhaustive ozonolysis of the leachate. The structural changes occurring in the humic substances and in the humic
acids present in the leachate after radiolysis and ozonolysis were analyzed by FT–IR spectroscopy.
The sorption of radiocadmium on Ca-montmorillonite as a function of contact time, pH, ionic strength, foreign ions, humic
acid (HA) and fulvic acid (FA) was studied using batch technique. The results demonstrated that the sorption of Cd(II) was
dependent on ionic strength at pH < 9, and was independent of ionic strength at pH > 9. Outer-sphere surface complexation
and/or ion exchange were the main mechanism of Cd(II) sorption on Ca-montmorillonite at low pH, whereas the sorption at high
pH was mainly dominated via inner-sphere surface complexation. The sorption of Cd(II) on Ca-montmorillonite was dependent
on foreign ions at low pH values, but was independent of foreign ions at high pH values. A positive effect of HA/FA on Cd(II)
sorption was found at low pH values, whereas a negative effect was observed at high pH values. The thermodynamic parameters
(i.e., ΔH0, ΔS0, ΔG0) were calculated from the temperature dependent sorption isotherms, and the results indicated that the sorption process of
Cd(II) on Ca-montmorillonite was spontaneous and endothermic.
Authors:Wang Mingming, Xie Hongqin, Tan Liqiang, Qiu Jun, Tao Xingquan, and Wu Cuiping
Herein, the sorption properties of Eu(III) on Na-attapulgite were performed by using batch sorption experiments under different
experimental conditions, such as contact time, pH, ionic strength, humic acid and temperatures. The results indicated that
the sorption of Eu(III) on Na-attapulgite was strongly dependent on pH and temperature. At low pH values, the sorption of
Eu(III) was influenced by ionic strength, whereas the sorption was not affected by ionic strength at high pH values. The sorption
of Eu(III) was mainly dominated by ion exchange or outer-sphere surface complexation at low pH values, and by inner-sphere
surface complexation or surface precipitation at high pH values. The sorption of Eu(III) onto Na-attapulgite increased with
increasing temperature. The Langmuir and Freundlich models were applied to simulate the sorption isotherms, and the results
indicated that the Langmuir model simulated the sorption isotherms better than the Freundlich model. The thermodynamic parameters
(∆Go, ∆So, ∆Ho) were calculated from the temperature dependent sorption isotherms at 293, 313 and 333 K, respectively, and the results indicated
that the uptake of Eu(III) on Na-attapulgite was an endothermic and spontaneous process. The results of high Eu(III) sorption
capacity on Na-attapulgite suggest that the attapulgite is a suitable material for the preconcentration and immobilization
of Eu(III) ions from large volumes of aqueous solutions.
The ammonium citrate tribasic was successfully modified to attapulgite clay and the effect of modifying was characterized
by FTIR and XRD techniques. Experimental results showed that the ammonium citrate tribasic modified attapulgite clay had a
strong sorption ability to remove Th(IV) from aqueous solutions. The sorption of Th(IV) from aqueous solutions has been systematically
investigated as a function of several variables including contact time, solid content, pH, ionic strength, Fulvic acid (FA)/humic
acid (HA) and temperature under ambient conditions. The results indicate that the sorption of Th(IV) onto ammonium citrate
tribasic modified attapulgite clay is strongly dependent on pH, Th(IV) initial concentration, ionic strength, temperature
and HA/FA. Surface complexation and ionic exchange are the main sorption mechanisms. Sorption of Th(IV) onto ammonium citrate
tribasic modified attapulgite is quick and can be fitted by a pseudo-second-order rate model very well. Sorption of Th(IV)
onto ammonium citrate tribasic modified attapulgite is promoted at higher temperature and the sorption reaction is an endothermic
process. Langmuir isotherm model fits the experimental data better than Freundlich and D-R isotherm models. The results suggest
that the ammonium citrate tribasic modified attapulgite sample is a suitable material in the preconcentration and solidification
of radionuclide Th(IV) from large volumes of aqueous solutions.
Authors:Juan Mou, Guoju Wang, Wenxian Shi, and Shouwei Zhang
A novel hierarchically structured γ-MnO2 has been synthesized using a simple chemical reaction between MnSO4 and KMnO4 in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. As an example
of potential applications, hierarchically structured γ-MnO2 was used as adsorbent in radionuclide 63Ni(II) treatment, and showed an excellent ability. The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic
acid (FA) on the sorption of radionuclide 63Ni(II) to hierarchically structured γ-MnO2 have been investigated by using batch techniques. The results indicated that the sorption of 63Ni(II) on γ-MnO2 is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption
of 63Ni(II) on γ-MnO2 at low pH values, whereas reduces 63Ni(II) sorption at high pH values. The sorption of 63Ni(II) on γ-MnO2 is attributed to inner-sphere surface complexation rather than outer-sphere surface complexation or ion exchange. The thermodynamic
parameters (ΔH0, ΔS0, ΔG0) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of 63Ni(II) on γ-MnO2 is a spontaneous and endothermic process.
Authors:H. Basu, R. Singhal, M. Pimple, V. Manisha, M. Bassan, A. Reddy, and T. Mukherjee
During this work highly particle reactive nature of thorium was exploited for the separation of Th from aquatic stream containing
U/Th. The Kd value of Th(IV) ions is 106 which is two order of magnitude higher than uranium (IV & VI). Laboratory simulated experiments were conducted to study the
preferential removal of thorium by using siliceous material having particle size of about 2,000 μm. Siliceous material was
prepared by decomposing the organic layer on soil particles by giving treatment with HNO3 and H2O2. Experimental solutions were generated by spiking the surface water with Th (NO3)4 and UO2(NO3)2. Experimental results shows preferential uptake of Th compared to U by siliceous material. This association is further improved
by coating the siliceous material with high and low molecular weight organic materials i.e. humic and fulvic acid, respectively.
Characterization of the organic material was done by ATR–FTIR whereas determination of Th was done by ICP-OES and alpha spectrometry.
Experimental results clearly showed that Th and U sorption capacity is 1 and 0.3 μg mg−1 (w/w), respectively, in case of siliceous material. Thorium sorption is increased five and eight times in the case of coating
with fulvic acid and humic acid, respectively. Whereas the same does not shows any pronounced impact on sorption of uranium.
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.
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.