Authors:Y. Takahashi, Y. Minai, T. Kimura, and T. Tominaga
Distribution of trace amount of Eu(III), or Am(III), in the aqueous/solid system containing humic acid and kaolinite, or montmorillonite,
was studied by batch experiments. Humic acid was also adsorbed on the clay minerals and its adsorption isotherm can be regarded
as a Langmuir type. It is shown that Eu(III), or Am(III), exists as humate complex either in the aqueous or on solid phase
in the system including kaolinite, or montmorillonite. These results suggest that the organic-inorganic complex like clay
minerals coated with humic substances is important as metal reservoir in the environment.
Authors:Michal Ilčin, Oľga Holá, Barbora Bakajová, and Jiří Kučerík
Samples of pure polyvinyl alcohol (PVA) and PVA doped with humic acids were exposed to gamma radiation. Gamma rays induced
the degradation of the pure polymer. Degradation changes were observed using ATR FT-IR equipment. Dehydration, double bond
creation, and their subsequent oxidation (surrounding atmosphere was air) were found out. Also, other degradation reactions
(e.g. chain scission, cyclization) occur simultaneously. Formation of C=C and C=O bonds is apparent from FT-IR spectra. In
contrast the presence of humic acids in the PVA sample showed stabilizing effect on PVA structure within the concentration
Complex formation of humic acids (HA)n with La3+ and Eu3+ was studied. Commercial (HA)n was purified and characterized. The stability constants were determined at several pH values and 0.2 M NaClO4 ionic strength by the Shubert’s method of radiochemical ionic exchange. The slopes of the lines
was determined as well for higher values of the j parameter and these values were: 12.2 ± 0.1 (j = 2, pH 7.7 ± 0.2), 15.6 ± 0.2
(j = 3, pH 4.9 ± 0.4) and 16.05 ± 0.07 (j = 3, pH 5.9 ± 0.1), for lanthanum and 13.18 ± 0.03 (j = 2, pH 5.9 ± 0.1) for europium.
A discussion is presented about the complex formation regarding pH and [(HA)n].
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 stability constants of Eu3+ and Am3+ with the site specific humic acid (YKHA) have been determined. The humic acid has been extracted from the soil of Yongkwang
area belonging geologically to the Okchon Basin of the Korean Peninsula, where the nuclear power plant is located. The total
carboxylate capacity, the acidity constant (pKa), and the binding constants with Eu3+ and Am3+ have been determined for humic acid.
The effect of Aldrich humic acid (HA) on the mobility of137Cs,85Sr,152Eu and239Pu radionuclides was studied in Ca-montmorillonite suspensions. Verified 2-sites-2-species (2s2s) models correspond to an
intensive interaction of all elements with humificated surface, what is in a remarkable contrast with the weak complexation
of cesium and even strontium in solutions — the neutral ligand interaction constants β (l/mol) are log β<−9.9 and 7.56±0.21
for Cs and Sr, respectively. The result for europium complexation in solution, log β=12.49±0.18 is in a good agreement with
literature data. For plutonium(IV) not only a high proton competitive constant in solution was obtained, log β β=(−0.67±0.32)+3pH,
but also a strong chemisorption, which at high concentrations of humic acid (above 0.05 g/l) indicates the formation of bridge
humate complexes of plutonium on the humificated surface. Logarithms of heterogeneous interaction constants (
24, l/g) for Pu(IV) −3.80±0.72. Distribution coefficients of humic acid and metal humates between 0.01 g HA/l solution and montmorillonite
were derived as logKd(AH)=−1.04±0.11, logKd(EuA)=1.56±0.11 and logKd(PuA)=2.25±0.04, while the values for Cs and Sr were obtained with very high uncertainty. Speciation of the elements on montmorillonite
surface is illustrated as a function of equilibrium concentration of humic acid in solution and of pH.
Authors:M. Nakayama, R. Fujiyoshi, and S. Sawamura
The uptake of manganese(II) and zinc(II) by humic acids (HA) was investigated using a radiotracer technique in order to elucidate their ability of scavenging heavy metals released into the soil environment. Metal uptake by HA was affected by aqueous pH, in which the amounts of Mn(II) and Zn(II) associated with HA showed a similar pattern against pH. These facts indicate that interactions of Mn(II) and Zn(II) with HA would be ionic in character, and affected by properties of the carboxyl groups in HA.
We investigated the influence of ionic strength on migration behaviors of Sr and Eu in the presence of humic acid (HA). The
breakthrough curve of Sr through a quartz sand column in the presence of HA was identical to that in the absence of HA. Europium
migration in quartz sand was enhanced by the presence of HA at low ionic strength. At high ionic strength, Eu migration in
the presence of HA was hindered compared to that in the absence of HA. Adsorption of europium on quartz sand in the absence
of HA decreases with increased ionic strength.
Sorption of NpO2+ on silicate (10.00 g/l) particles dispersed in sodium perchlorate media was studied as a function of pcH and ionic strength
at 298 K. The sorption increased with increased pcH in the range of ∼6.5 to 9.2, above which saturation was observed. An increase
in ionic strength from 0.20M to 1.00M (NaClO4), increased the NpO2+ sorption, which then decreased at 1.50M (NaClO4) for 7<pcH<8.5. The effects of different types of ligands on the sorption of NpO2+ to suspended silicate were investigated. The types of ligands included: (i) inorganic anions (fluoride, carbonate, phosphate
(ii) N-donors (ethylenediamine, 1,10 phenanthroline (iii) carboxylic acids (oxalic acid, citric acid, iminodiacetic acid,
ethylenediaminetetraacetic acid) and (iv) humic acid. A synergistic enhancement in sorption to the suspended silicate was
observed for phosphate, oxalate, ethylenediaminetetraacetic acid, ethylenediamine, 1,10 phenanthroline (5<pcH<8) and humic
acid (6.5<pcH<8.8). This behavior was attributed to the formation of ternary NpO2+/silicate/ligand complexes. The effects of Ca(II) (1.00·10−3M) and Eu(III) (1.00·10−4 and 1.00·10−3M) ions on NpO2+ sorption to suspended silicate were also investigated.
Authors:Barbora Bakajová, Michal Ilčin, Oľga Holá, and Jiří Kučerík
The dried blends containing sodium and ammonium salts of lignite humic acids (humates, 0.5–10% w/w) in polyvinyl alcohol (PVA)
were exposed to high dosage of γ-irradiation in the range of doses 127–806 kGy. Resulted products were then tested for their
stability using thermogravimetrical analysis. As a reference the non-treated blends were used since the pure PVA exposed to
γ-irradiation very quickly lost its stability and resulting consistence did not allow the stability tests. Stabilities showed
a strong concentration and counterion dependency. While sodium counterion caused mostly destabilization with increasing dose,
the ammonium counterion acted in an opposite way. The tests carried out in a moisturizing container revealed the changes in
water absorbing capacity of irradiated samples and allowed partial explanation of humate stabilizing effect. Generally, at
lower concentration of a humate the increase was observed with an increase in the γ-irradiation dose and vice versa. The results
confirmed the antioxidant and stabilizing effect of humic acids added to some synthetic polymers and their applicability in
materials exposed to γ-irradiation.