Effect of ionizing radiation on the extraction of Am(III) with p-tert-butylthiacalix[4]arene from alkaline carbonate solutions

© 2017, Pleiades Publishing, Inc. The effect of γ-irradiation of tert-butylthiacalix[4]arene (TCA) solutions in m-nitrobenzotrifluoride (NBTF) and tetrachloroethylene (TCE) on the extraction of 241 Am from alkaline carbonate solutions was studied. TCA itself remains stable upon γ-irradiation of its solutions in NBTF to a dose of 200 kGy, but the diluent undergoes strong degradation. The radiation resistance of TCA in TCE is considerably lower: A dose of 70 kGy causes complete degradat ion of TCA. In the TCA–TCE–aqueous phase system, sulfate ions appear upon γ-irradiation as the final product of the extractant radiolysis. A large number of γ-radiolysis products of TCE and TCA were detected by HPLC and GCMS. The products of radiolysis of TCA in TCE, compared to the initial extractant, have lower molecular mass and higher polarity. The results show that chlorinated diluents are not promising diluents for thiacalixarene in extraction processing of alkaline high-level waste

Microbial and Geochemical Evidence of Permafrost Formation at Mamontova Gora and Syrdakh, Central Yakutia

Biotracers marking the geologic history and permafrost evolution in Central Yakutia, including Yedoma Ice Complex (IC) deposits, were identified in a multiproxy analysis of water chemistry, isotopic signatures, and microbial datasets. The key study sections were the Mamontova Gora and Syrdakh exposures, well covered in the literature. In the Mamontova Gora section, two distinct IC strata with massive ice wedges were described and sampled, the upper and lower IC strata, while previously published studies focused only on the lower IC horizon. Our results suggest that these two IC horizons differ in water origin of wedge ice and in their cryogenic evolution, evidenced by the differences in their chemistry, water isotopic signatures and the microbial community compositions. Microbial community similarity between ground ice and host deposits is shown to be a proxy for syngenetic deposition and freezing. High community similarity indicates syngenetic formation of ice wedges and host deposits of the lower IC horizon at the Mamontova Gora exposure. The upper IC horizon in this exposure has much lower similarity metrics between ice wedge and host sediments, and we suggest epigenetic ice wedge development in this stratum. We found a certain correspondence between the water origin and the degree of evaporative transformation in ice wedges and the microbial community composition, notably, the presence of Chloroflexia bacteria, represented by Gitt-GS-136 and KD4-96 classes. These bacteria are absent at the ice wedges of lower IC stratum at Mamontova Gora originating from snowmelt, but are abundant in the Syrdakh ice wedges, where the meltwater underwent evaporative isotopical fractionation. Minor evaporative transformation of water in the upper IC horizon of Mamontova Gora, whose ice wedges formed by meltwater that was additionally fractionated corresponds with moderate abundance of these classes in its bacterial community. © Copyright © 2021 Cherbunina, Karaevskaya, Vasil’chuk, Tananaev, Shmelev, Budantseva, Merkel, Rakitin, Mardanov, Brouchkov and Bulat.We thank Samsonova Vera, Karzhavin Vladimir, Pankov Alexander, Andreevskaya Maya and Alexander Osipov for their for their invaluable assistance in field work

Fitting sediment rating curves using regression analysis: a case study of Russian Arctic rivers

Published suspended sediment data for Arctic rivers is scarce. Suspended sediment rating curves for three medium to large rivers of the Russian Arctic were obtained using various curve-fitting techniques. Due to the biased sampling strategy, the raw datasets do not exhibit log-normal distribution, which restricts the applicability of a log-transformed linear fit. Non-linear (power) model coefficients were estimated using the Levenberg-Marquardt, Nelder-Mead and Hooke-Jeeves algorithms, all of which generally showed close agreement. A non-linear power model employing the Levenberg-Marquardt parameter evaluation algorithm was identified as an optimal statistical solution of the problem. Long-term annual suspended sediment loads estimated using the non-linear power model are, in general, consistent with previously published results

Revising contemporary heat flux estimates for the Lena River, Northern Eurasia

The Lena River (Lena R.) heat flux affects the Laptev Sea hydrology. Published long-term estimates range from 14.0 to 15.7 EJ·a−1, based on data from Kyusyur, at the river outlet. A novel daily stream temperature (Tw) dataset was used to evaluate contemporary Lena R. heat flux, which is 16.4 ± 2.7 EJ·a−1 (2002–2011), confirming upward trends in both Tw and water runoff. Our field data from Kyusyur, however, reveal a significant negative bias, −0.8 °C in our observations, in observed Tw values from Kyusyur compared to the cross-section average Tw. Minor Lena R. tributaries discharge colder water during July–September, forming a cold jet affecting Kyusyur Tw data. Major Tw negative peaks mostly coincide with flood peaks on the Yeremeyka River, one of these tributaries. This negative bias was accounted for in our reassessment. Revised contemporary Lena R. heat flux is 17.6 ± 2.8 EJ·a−1 (2002–2011) and is constrained from above at 26.9 EJ·a−1 using data from Zhigansk, approximately 500 km upstream Kyusyur. Heat flux is controlled by stream temperature in June, during the freshet period, while from late July to mid-September, water runoff is a dominant factor

Seasonality of DOC Export From a Russian Subarctic Catchment Underlain by Discontinuous Permafrost, Highlighted by High‐Frequency Monitoring

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Investigation of the behavior of plutonium(V) in alkaline media

The stability of the plutonium(V) oxidation state in alkaline media was studied with respect to the neighboring Pu(IV) and Pu(VI) oxidation states. Tests were conducted in 1 M or higher NaOH solutions in the presence and absence of other components of Hanford Site high-level tank waste. Spectrophotometric techniques were found to be effective in studying the behavior of plutonium(V) in alkaline solution at plutonium concentrations above 10{sup -3} M. To this end, plutonium(V) and plutonium(VI) in NaOH were prepared and their spectra characterized. In alkaline solutions with NaOH concentration below 8 M, plutonium(V) was found to be unstable to disproportionation occurring according to the reaction 2 Pu(V)(aq) {yields} Pu(VI)(aq) + Pu(IV)(s). The disproportionation of Pu(V) is complicated by at least two simultaneous processes: (1) the sorption of a significant fraction of the Pu(V) onto the forming Pu(IV) hydrous oxide precipitate, and (2) partial reduction of Pu(VI) by water {alpha}-radiolysis products