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Humic acid is ubiquitous in soils and water. It affects the migration of radionuclides by complexation or redox reactions. The effect of humic acid on the diffusion of ReO in GMZ bentonite was investigated at dry density from 1,300 to 1,800 kg/m. The effective diffusion coefficient D and rock capacity factor α were measured by through-diffusion method. The D decreased from 5.5 to 0.59 × 10 m/s and α decreased from 0.2 to 0.12 with the dry density increasing from 1,300 to 1,800 kg/m. The retardation factor R in GMZ bentonite at three dry densities was obtained, which were less than one. Archie's law was used to describe the relationship between accessible porosity ε and D. An empirical parameter n ( n = 2.2 ± 0.2) was obtained for Re diffusion in GMZ bentonite in the presence of humic acid. [ABSTRACT FROM AUTHOR]

In this study, the removal of radionuclide Co(II) from wastewater by Ca-rectorite was studied as a function of various environmental parameters such as contact time, pH, ionic strength, coexisting electrolyte ions, humic substances (HS) and temperature under ambient conditions. The results indicated that the sorption of Co(II) on Ca-rectorite was strongly dependent on pH and ionic strength. The Langmuir and Freundlich models were used to simulate the sorption isotherms of Co(II) at three different temperatures of 298.15, 318.15 and 338.15 K. The thermodynamic parameters ( $$ \Updelta H^{0} ,\,\Updelta S^{0} $$ and $$ \Updelta G^{0} $$) calculated from the temperature-dependent sorption isotherms indicated that the sorption process of Co(II) on Ca-rectorite was spontaneous and endothermic. At low pH, the sorption of Co(II) was dominated by outer-sphere surface complexation and ion exchange with Ca/H on Ca-rectorite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that Ca-rectorite has good potentialities for cost-effective disposal of radiocobalt bearing wastewaters. [ABSTRACT FROM AUTHOR]

Abstract: 129I concentration in the seawater samples near a nuclear power plant was determined in the Xi''an Accelerator Mass Spectrometer (AMS) Center. Isotope dilution method was used via addition of excessive amount of stable iodine (127I) in the sample before separation, and iodine in the seawater was separated by solvent extraction, and the back extracted iodine in iodide form was precipitated as AgI, which was used as AMS target for 129I measurement. 125I tracer was added to monitor the recovery of iodine in the whole separation process. 129I/127I ratios in the prepared target were determined by AMS. The concentration of 127I in seawater samples was determined by inductively coupled plasma mass spectrometry. The results show that the 129I/127I atomic ratios in the seawater range from 8.29×10−11 to 9.45×10−10, approximately one order of magnitude higher than that in seaweed collected in the pre-nuclear era, but fall in the environmental level of global fallout. [Copyright &y& Elsevier]

Abstract: The newly established 3MV Accelerator Mass Spectrometry (AMS) facility in Xi’an, with an instrument background of 2×10−14 for 129 I/127I ratio, provides efficient analytical capability to carry out 129 I environmental tracing studies. Chemical separation methods of iodine from different types of samples have been established at the Xi’an AMS Center, including solvent extraction and combustion followed by extraction or coprecipitation depending on sample types. A carrier free method for iodine separation and AMS measurement of ultra low level 129 I in samples with low total iodine concentration has been established, which can be used for analysis of geological samples for 129 I dating. Some environmental samples collected in China have been analyzed using the developed methods. The analytical results show 129 I/127I ratios of (0.9–1.1)×10−10 for seawater collected adjacent to a nuclear power plant, and (3.02–5.43)×10−10 for soil samples collected in a less than 10km area surrounding the NPP. These values are not significantly different from those measured in remote areas, reflecting a safe nuclear environment in terms of 129 I level. [Copyright &y& Elsevier]