タグ「colloids」
Author: Novikov A.P., Kalmykov O.V., Myasoedov B.F., Ivanov I.A., Rovny S.I.
Reference: Gazette “ВОПРОСЫ РАДИАЦИОННОЙ БЕЗОПАСНОСТИ“ (Issues on radiation safety), 2009
ISSN: 1816-9643
DOI:
Keywords: radionuclides, groundwater, colloids, migration
Abstract: Outcomes of the study are presented that concern bond strength of radionuclides with colloid particles of different sizes obtained from underground waters of the Karachai contamination plume. Using the method of photon-correlation spectroscopy, it was found out that the total content of colloid in deeper horizons is an order of magnitude higher than that in near-surface horizons. At that, an average particle radius also increases with depth. The main portion of Pu, Am, and Cm is bound with colloids (40-90 %). Portions of U and Np in the composition of colloid particles are smaller (2-20 %), and this fact determines their higher migration mobility in underground waters. An insignificant number of actinides is bond with large colloids with a size from 450 nm tо 200 nm. A significant part of actinides in water occurring at a depth of 40 m and deeper is in the fraction of colloid particles with a size from 200 nm tо 50 nm. In water of these horizons not more than 30 % of Pu and Am is bound with smaller size colloids (from 10 kDa tо 50 nm). As it gets closer to the surface, a number of actinides in the fraction of nano-particles (50 nm – 10 kDa) grows up to 50 %. Using the method of selective leaching, the bond strength of actinides with the colloid of underground waters from the Karachai contamination plume was investigated. Using the alpha-track analysis, it was shown that microdistribution of alpha-emitting radionuclides in the colloid is uniform. It was demonstrated that radionuclides, which are found in the colloid of underground waters sampled from three wells with various chemical composition, are in the forms that differ in the degree of their solubility. U and Np in colloid are bound only with highly soluble and mobile groups of compounds; these radionuclides were not identified in the sparingly soluble residue. While Pu and Am are, on the contrary, found in the colloid primarily in sparingly soluble forms. Am, to a greater extent, is bound with surface organo-metallic complexes. Pu was mainly found in the fraction of amorphous oxides.
URL: http://elibrary.ru/item.asp?id=11991986
Author: A. Yu. Romanchuk, S. N. Kalmykov, A. P. Novikov, E. V. Zakharova
Reference: Russian Journal of General Chemistry, 2011
ISSN: 1608-3350
DOI: 10.1134/S1070363211090490
Keywords: sorption, plutonium
Abstract: It is shown that an alternative to K d in describing sorption at low degrees of surface saturation of colloid particles is pH50 which takes into account both the properties of the sorbent and sorbate. The correlations of pH50 with cation charge density for the An(III)-An(IV)-An(V)-An(VI) series and with hydrolysis constants are presented. The redox reactions with plutonium that accompany its sorption onto Fe(III) oxides are discussed.
URL: http://link.springer.com/article/10.1134/S1070363211090490#
Title: Association of dissolved radionuclides released by the Chernobyl accident with colloidal materials in surface water
Author: Matsunaga, Takeshi / Nagao, Seiya / Ueno, Takashi / Takeda, Seiji / Amano, Hikaru / Tkachenko, Yu.
Reference: Applied Geochemistry, 19 (10), p.1581-1599, Oct 2004
doi:10.1016/j.apgeochem.2004.02.002
Keywords: radionuclides, 137Cs, 90Sr, Plutonium, colloids
Abstract: The association of dissolved 90Sr, 239,240Pu and 241Am with natural colloids was investigated in surface waters in the Chernobyl nuclear accident area. A 4-step ultrafiltration (UF) study (239,240Pu and 76% of 241Am are distributed in colloids of the two size fractions larger than 10 kDa (nominal molecular weight limit of the filter, NMWL), while 90Sr was found exclusively (85–88%) in the lowest molecular size fraction below 1 kDa (NMWL) for the Sahan River water at the highly contaminated area close to the Chernobyl Nuclear Power Plant (ChNPP). Consistent results were obtained by 2-step fractionation (larger than and smaller than 10 kDa (NMWL)) for river and lake waters including other locations within about 30 km away from ChNPP. It is likely that Pu and Am isotopes were preferentially associated with dissolved organic matter of high molecular size, as suggested by the fact that (i) only a few inorganic elements (Mg, Ca, Sr, Si, Mn, Al) were found in the colloidal size ranges, and (ii) the positive correlation between dissolved organic C (DOC) concentrations and UV absorbance at 280 nm, a broad absorption peak characteristic of humic substances (HS) was found. A model calculation on the complexation of Pu and Am with HS as an organic ligand suggests that the complexed form could be dominant at a low DOC concentration of 1 mgC L−1, that is commonly encountered as a lower limit in fresh surface water. The present results suggest the general importance of natural organic colloids in dictating the chemical form of actinides in the surface aquatic environment.
URL: http://www.experts.scival.com/kanazawa/pubDetail.asp?id=2942700456&o_id=36
