Authors:Y. Takahashi, Y. Minai, T. Ozaki, S. Ambe, M. Iwamoto, H. Maeda, F. Ambe, and T. Tominaga
The multitracer technique was applied to elucidate of influence of humate formation on adsorption behavior of ultratrace elements. Dissolved fractions of Co, As, Rb, Sr, Y, Zr, Ba, Ce, Eu, Gd, Tb, Yb, Lu, Hf, Re and Pt in contact with kaolinite or silica gel were determined simultaneously either in the presence or absence of humic acid, which was partly adsorbed on the solid. Percentage of dissolved fraction of rare earth elements was identical to that of humic acid, indicating high stability of the rare earth-humate complex. Hydrolysis was the most important factor controlling the behavior of Zr and Hf. Both hydrolysis and humate complexation influenced the adsorption of Co, Sr, Ba and Pt, whereas neither affected the distribution of As, Rb and Re.
Authors:Aleksandr Novikov, Dmitry Malikov, Sergey Vinokurov, Irina Kazinskaya, Tatyana Goryachenkova, and Boris Myasoedov
Neptunium(V) sorption from simulated and natural ground waters, containing ammonium carbonates, acetates, oxalates and citrates,
on multi-walled carbon nanotubes (MWCNT) «Taunit»® was studied. It has been discovered that ammonium acetate and carbonate are not adsorbed on MWCNT «Taunit», but humic acid,
oxalates and citrates are adsorbed quite efficiently. Neptunium is extracted from the ammonium carbonate solution by MWCNT «Taunit» with
low sorption degrees. While conducting the sorption process from the ammonium carbonate solution with addition of organic
substances, it has been revealed that the neptunium extraction degree is not dependent on addition of humic acid and acetate.
At the same time, the extraction degree is substantially increased at addition of ammonium oxalate and citrate. It enables
modifying MWCNT «Taunit» by means of related organic ligands and using them for the purpose of extraction and concentration
of neptunium from contaminated natural waters.
Authors:Y. Takahashi, Y. Minai, Y. Meguro, S. Toyoda, and T. Tominaga
Binding constants of Eu(III)- and Am(III)-complexes with soil-derived humic acid were determined by solvent extraction at various pH and ionic strength. Based on the dependence of binding constants on pH and ionic strength, stabilities of the humate complexes in land water and seawater were estimated. Speciation calculation based on the binding constants indicated that Am(III) could combine with humic substances in natural water system.
Humic acid has been shown to play a significant role in the environmental behavior of many metal cations as it can function as both a complexant and a redox agent. A number of models have been proposed to explain their complexing role, but most use quite different chemical descriptions of the metal-humate interactions. Two of these models which have been applied to humic acid interaction with actinide cations are briefly discussed. In one model in which humics are treated as anionic polyelectrolytes, cations can bind to specific anionic donor sites (site binding) as well as be attracted by the net anionic charge of the macromolecules (the Polyelectrolyte Model). In the second model (the Charge Neutralization Model), the binding for each cation is assumed to be associated with a number of carboxylate groups equal to the cationic charge. It is concluded that the Charge Neutralization Model is more useful in geochemical calculation codes, whereas the Polyelectrolyte Model can provide more insight into the chemical behavior of the humic acids.
Authors:P. Beneš, K. Štamberg, D. Vopálka, L. Široký, and Š. Procházková
Kinetics of Eu sorption on sandy sediment from Gorleben, Germany, containing humic substances, was studied by radiotracer method in batch experiments at very low europium concentration (3.4.10-8 mol/l), with the aim to find kinetic parameters suitable for modeling Eu migration in bed of the sediment and to elucidate the mechanism of the sorption. Experiments were evaluated using a new simplified method taking into account simultaneous sorption/desorption of Eu on the walls of sorption vessel. Five kinetic functions were tested, of which that describing diffusion in inert surface layer of sorbent proved most suitable. The effects of pH (3.0-8.8) by addition of Aldrich humic acid (10 mg/l), addition of hydrogencarbonates (5.10-3 mol/l) and preequilibration of the sediment with solution or of Eu with solution were examined. From the results it has been concluded that the kinetics and mechanism of the sorption strongly depend on pH. At pH 4.8 Eu is sorbed mainly as humate complex from the solution of humic acid. The addition of humic acid accelerates the sorption. Carbonate complexes of Eu are the probable forms sorbed at pH 8.8. The presence of humic substances in the slightly alkaline solutions suppresses the rate of the sorption due to slow dissociation of Eu-humate complexes.
Authors:T. Prochácková, R. Góra, J. Kandráč, and M. Hutta
Sequential multistep procedure, usually used for the fractionation and characterization of soil organic matter was tested
for Hg content in the individual steps and fractions. Under general laboratory conditions serious problems have arosen during
the attempt in the Hg mass balance calculation. Several sources of Hg contamination were recognized. The most serious was
the background concentration of Hg even in research grade chemicals (what is in general not declared) and laboratory air.
The work on operational Hg speciation as non-humic bound, humic acid, fulvic acid bound proceeds from the established status-quo
on distribution of mercury of soil organic matter.
Differential Scanning Calorimetry combined with Fourier transform infrared spectroscopy, was applied to the study of a number of fulvic and humic acids extracted from soils, peat, river and seawater. The thermal patterns obtained were related to the nature and origin of samples. The low-temperature endotherms were attributed to dehydration and loss of peripheral polysaccharide chains. The endotherm at 250°C observed for soil FA was ascribed to partial decarboxylation of more labile surface COOH groups, whereas the high-temperature exotherms at about 500°C were related to the degree of polycondensation of the aromatic network of the humic molecules.
Two fractions of both fulvic acids (FA) and humic acid (HA) were prepared by fractionation method of Pierce and Felbeck5 involving acid hydrolysis of soil rests. This step increases recovery of both FA and HA considerably what suggest us need for slight modification of IHSS method in some cases. The weight loss, change in organic carbon content and visible spectra are figures of merit discussed. After detailed characterization these humic substances (HS) will serve as the working standards for study of interactions between organomercurials and organic part of soil.
Authors:S. Steinberg, G. Schmett, G. Kimble, D. Emerson, M. Turner, and M. Rudin
Iodine-129 is a fission product and highly mobile in the environment. Along with other stable isotopes of iodine, 129I is released during reprocessing of nuclear fuel and must be trapped to prevent the release of radioactivity to the environment.
Past studies have provided evidence that iodine can become associated with natural organic matter (NOM). This research explores
the use of NOM (sphagnum peat and humic acid) to sequester iodine from the vapor and aqueous phases. NOM-associated iodine
may be stable for geological storage. NOM-sequestered iodine can be recovered by pyrolysis to prepare target materials for
transmutation. The nature of the NOM-iodine association has been explored.