In order to assess radionuclide diffusion and transport properties in compacted bentonite, the “in-diffusion” method based
on bentonite filled capillaries is used. The effect of 99TcO4- concentration and pH value of the solution, the contact time and the dry density of compacted bentonite on the apparent diffusion
coefficient (Da) and on the distribution coefficient (Kd) values obtained from the capillary test was studied. The Da and Kd values decrease with increasing of the bulk dry density of compacted bentonite. Ion exclusion influences the diffusion of
99TcO4- in the same substance. As compared to literature data, the Kd values obtained from capillary tests are in most cases lower than those from batch tests, the difference between the two
Kd values is a strong function of dry density of the compacted bentonite.
The sorption of cesium onto g-Al2O3 was studied by using batch technique and ultra-filtration method at room temperature, at pH 4.0, 6.0 and 8.0 and ionic strength ranged from 0.001M to 0.1M NaClO4. The pore size of the filter 1000K was used to separate the liquid from the solid phase. UV vis spectrophotometer was used to determine the concentration of humic acid in the solution at wavelength of 254 nm. The sorption of humic acid and Cs on the g-Al2O3 was studied in the pH range from 2 to 12. The sorption of humic acid on the g-Al2O3 was strong (»98% HA was sorbed on the surface of g-Al2O3 below pH 9) and strongly depended on the pH values (above pHzpc the sorption of HA decreased markedly with the increasing of pH), humic acid has a little negative effect on the sorption of cesium. This may be attributed to the formation of HA-Cs complexation in the solution. The sorption of Cs onto g-Al2O3 was weak depending on the pH and independent on the ionic strength. The sorption of Cs onto g-Al2O3 may be contributed to cation exchange and surface complexation mechanism.
The effect of pH and fulvic acid on the sorption of Sr on bentonite was investigated by using batch experiments. The sorption
and desorption isotherms of Sr on bentonite were determined at room temperature, at pH 6.0±0.2 and in presence of 0.1M NaCl.
It was found that the sorption of Sr is independent at pH<8, and then increases slightly with increasing pH. Fulvic acid increases
the sorption of Sr significantly on bentonite at low pH, but decreases the sorption of Sr at pH>8. The sorption of Sr on bentonite
can be described by a reversible sorption process and the sorption mechanism consists mainly of ion exchange.
Authors:Dong Wenming, Wang Xiangke, Du Jinzhou, Wang Dongqi, and Tao Zuyi
The effect of organic matter and iron oxides as solid components of the red earth on the retention of SeO3 has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO3 on the untreated red earth and the three treated soils were determined at 20°C, pH 6.8 or 7.2 and in the presence of 0.01M
CaCl2. It was found that the sorption-desorption hysteresis for untreated an treated soils is obvious and the clays play an important
role in the sorption-desorption hysteresis, and that the retention of SeO3 on red earth is attributed to the iron oxides to a great extent.
Authors:Wang Xiangke, Dong Wenming, Gong Yingchun, Wang Changhui, and Tao Zuyi
The factors affecting the sorption of radioeuropium(III) by bentonite and kaolinite were studied with the aim to assess the important factors which should be included in modeling of radioeuropium(III) migration in soils and sediments. Europium(III) is an analogue of trivalent actinides. The distribution coefficients of radioeuropium for sorption on bentonite and kaolinite from aqueous solutions were determined by using the batch method, and it was found that they were sensitive to the loading, the pH, the humic substance and the sorption direction. Thus, these sorption characteristics of radioeuropium on bentonite and kaolinite were found to be different from those of radiocobalt1, and the mathematical modeling of trivalent lanthanides and actinides migration will be more complicated than that of radiocobalt. It is improbable that the migration modeling with a constant distribution coefficient will be successful in the case of trivalent lanthanides and actinides.
Authors:Wang Xiangke, Dong Wenming, Yao Jie, and Tao Zuyi
This paper is an extension of previous papers1–3. The breakthrough curves and the displacement curves of125I− and75SeO3 on the calcareous soil, the treated soil to remove CaCO3 and the treated soil to remove organic matter were determined at pH 7.8, at 20°C and in the presence of 1·10−3 or 1·10−4 mol/l CaCl2. These results from column experiments and from batch experiments in the previous papers1,2 were mutually complementary. It can be definitely concluded that iodide is retained to a very small degree and tetravalent-selenium
is retained to a small degree by calcareous soil and that organic matter in calcareous soil acts as a significant trap of
iodide and CaCO3 acts as a trap of tetravalent selenium. Iodide and tetravalent-selenium would be expected to have relatively high dissemination
in calcareous soil.
Authors:Wang Xiangke, Dong Wenming, Du Jinzhou, and Tao Zuyi
The sorption and desorption of radiocesium on a calcareous soil from Jiuqian County of Gansu Province (China) were studied
by using batch and column experiments. The sorption-desorption isotherms and the breakthrough curves, displacement curves
on the whole soil and two treated soils were determined. Based on these results, it was found that the sorption and retention
of cesium are mainly determined by the clay minerals, that the sorption-desorption hysteresis of cesium on the calcareous
soil is obvious and that the organic matter has a little positive contribution and the calcium carbonate has a little negative
contribution to the sorption of cesium on the whole soil. The results from batch experiments were consistent with the results
from column experiments.
Authors:Xiangke Wang, Jinzhou Du, Zuyi Tao, and Zhongxiu Fan
The migration of radionuclides 85+89Sr2+, 134Cs+, 125I- and 75SeO32- in calcareous soil from Yuzhong county of Gansu Province (China) at pH 7.8±0.2 and 152+154Eu(III) in red earth from Yingtan county of Jiangxi Province (China) at pH 4.6±0.2, in presence of CaCl2 was studied using column experiments. Results indicate that the negative anions, iodide and selenide are mobile nuclides while the migration of positive cations is related to the sorption capacity for the element. Iodide can be assumed to be non-reactive in calcareous soil. The breakthrough curves (BTCs) were fitted to the analytical solution or numerical solution of one-dimensional convection-dispersion transport models. Good agreements were obtained between the measured and predicted concentration profiles.
Authors:Changlun Chen, Di Xu, Xiaoli Tan, and Xiangke Wang
The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions.
The extent of sorption of divalent metal cations is controlled by a number of factors including cosorbing or complexing. In
this work, the effects of pH, humic acid HA/Co(II) addition orders, ionic strength, concentration of HA, and foreign cations
on the Co(II) sorption on γ-Al2O3 in the presence of HA were investigated. The sorption isotherms of Co(II) on γ-Al2O3 in the absence and presence HA were also studied and described by using S-type sorption model. The experimental results showed
that the Co(II) sorption is strongly dependent on the pH values, concentration of HA, but independent of HA/Co(II) addition
orders, ionic strength, and foreign cations in the presence of HA under our experimental conditions. The results also indicated
that HA enhanced the Co(II) sorption at low pH, but reduced the Co(II) sorption at high pH. It was hypothesized that the significantly
positive influence of HA at low pH on the Co(II) sorption on γ-Al2O3 was attributed to strong surface binding of HA on γ-Al2O3 and subsequently the formation of ternary surface complexes such as ≡S-OOC-R-(COO−)xCo2−x. Chemi-complexation may be the main mechanism of the Co(II) sorption on γ-Al2O3 in the presence of HA.
Authors:Dong Wenming, Wang Xiangke, Qin Zhi, Zhou Chongyang, and Tao Zuyi
Th(NO3)4 was irradiated with 25 MeV/nucleon 40Ar ion beam. The target material irradiated was dissolved in 12 mol/l HCl and the Th in the HCl solution was extracted with 20% (V/V) TBP solution in CCl4 successively, then the TBP solution remaining in the aqueous phase after 4 successive extractions was stripped with benzene. A carrier-free and salt-free multitracer solution containing 38 elements from Be to Bi and 67 radionuclides was prepared. The convenient extraction method was developed for the separation between the target material Th(NO3)4 and the large number of fission products.