Authors:E. Polyakov, I. Volkov, V. Surikov, and L. Perelyaeva
Using physicochemical methods we showed that continuous (15 days) exposure of monazite powder in humic acid (HA) solutions
with different acidity gives rise to one to two orders of magnitude growth in the concentration of the monazite’ p-, d- and
f-elements of Periodic Table (Mg, Al, Si, P, Pb, Ti, Bi, Sc, Ti-Zn, REE, Th, U). The growth in the elements concentration
in the humic solutions contacting monazite is shown to depend on the initial concentration of HA in the solutions, pH. It
is concluded that these factors should be taken into consideration when inorganic phosphates and alike phases are used as
a matrix for the radionuclide wastes solidification.
This work investigates the sorption of americium [Am(III)] onto kaolinite and the influence of humic acid (HA) as a function
of pH (3–11). It has been studied by batch experiments (V/m = 250:1 mL/g, CAm(III) = 1 × 10−5 mol/L, CHA = 50 mg/L). Results showed that the Am(III) sorption onto the kaolinite in the absence of HA was typical, showing increases
with pH and a distinct adsorption edge at pH 3–5. However in the presence of HA, Am sorption to kaolinite was significantly
affected. HA was shown to enhance Am sorption in the acidic pH range (pH 3–4) due to the formation of additional binding sites
for Am coming from HA adsorbed onto kaolinite surface, but reduce Am sorption in the intermediate and high pH above 6 due
to the formation of aqueous Am-humate complexes. The results on the ternary interaction of kaolinite–Am–HA are compared with
those on the binary system of kaolinite–HA and kaolinite–Am and adsorption mechanism with pH are discussed. Effect of different
molecular weight of HA, with three HA fractions separated by ultrafiltration techniques, on the Am sorption to kaolinite were
also studied. The results showed that the enhancement of the sorption of Am onto kaolinite at the acidic pH conditions (pH
3–4) was higher with HA fractions of higher molecular weight. Also, the Am sorption over a pH range from 6 to 10 decreased
with decreasing molecular weight of HA.
Authors:C. Li, C. Wang, X. Liu, Z. Zheng, L. Wang, Q. Zhu, M. Kang, T. Chen, and C. Liu
In terms of pre-safety assessment of a potential site for high-level radioactive wastes disposal in China, the geochemical
behavior of key radionuclides which tend to be released from the repository must be thoroughly investigated. 99Tc is a long-lived fission product with appreciable productivity in nuclear fuel, and Tc (+7) has unlimited solubility in
near-field geochemical environments. In this study, the effects of ionic strength and humic acid on 99TcO4− sorption and diffusion in Beishan granite were investigated with through-diffusion and batch sorption experiments. Results
indicated that the effective diffusion coefficients (De) of 99TcO4− in Beishan granite varied from 1.07 × 10−12 to 1.28 × 10−12 m2/s without change with ionic strength, while the distribution coefficients (Kd) negatively correlated with ionic strength of the rock/water system. This study also indicates that there is no evident influence
of humic acid concentration on the diffusion behavior of 99TcO4− in Beishan granite, due to the limited interaction between humic acid and 99TcO4−.
To study the sorption behavior of Co(II) on soil and soil components such as birnessite, humic acid (HA) and their mixture,
a series of experiment were conducted using the batch equilibrium technique on parameters such as equilibrium time, ionic
strength, solution pH, and temperature. The soil samples collected from location near radioactive waste repository in Korea
were used and birnessite was synthesized using a method by McKenzie for experiment. The experimental results indicate that
Co sorption on soil, birnessite and soil with birnessite are strongly affected by the pH of solution. Typical for metal sorption
to soils, the fraction of Co adsorbed increased as a function of pH at the experimental conditions. For sorption isotherm,
the Freundlich equation provides a good fit for sorption on soil and soil with birnessite. Adsorption of HA on birnessite
decreased with increase of pH, with a sharp decrease at pH 5–6. From Co sorption experiment in a ternary system of Co, birnessite,
and HA, the presence of HA enhanced Co adsorption at pH below 6.5 and reduced the Co sorption at the intermediate and high
Authors:Liu Xia, Chen Yuantao, Chi Yaling, Guo Zhijun, and Cai Linsen
In this article, a series of batch experiments were carried out to investigate the effect of various environmental factors
such as contact time, solid content, pH, ionic strength, foreign ions, temperature and coexisting humic acid on the sorption
behavior radionuclide 60Co(II) on illite. The results indicated that the sorption of Co(II) was strongly dependent on pH, ionic strength and temperature.
At low pH, the sorption was dominated by outer-sphere surface complexation and ion exchange on illite surfaces, whereas inner-sphere
surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models
were used to simulate the sorption isotherms at three different temperatures of 303.15, 323.15 and 343.15 K. The thermodynamic
data (∆G0, ∆S0, ∆H0) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of
Co(II) on illite was an endothermic and spontaneous process. The sorption test revealed that the illite can be as a cost-effective
adsorbent suitable for pre-concentration of Co(II) from large volumes of aqueous solutions.
Fluoride (F–) binding to humic acid has been measured as a function of pH (5–6.6). The pH dependent binding is attributed to the anion being trapped within the large structure (territorial bound) but is not bound to a particular functional group (site bound). Studying fluoride binding provides insight to cation, anion and neutral species interactions with humic acid.
Authors:Caicai Zhang, Zhengjie Liu, Lei Chen, and Yunhui Dong
The sorption of 60Co(II) on γ-Al2O3 was conducted under various conditions, i.e., contact time, adsorbent content, pH, ionic strength, foreign ions, humic acid
(HA), and temperature. Results of sorption data analysis indicated that the sorption of 60Co(II) on γ-Al2O3 was strongly dependent on pH and ionic strength. At low pH the sorption was dominated by outer-sphere surface complexation
or ion exchange, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of different
cation ions influenced 60Co(II) sorption, while the presence of different anion ions had no obvious influences on 60Co(II) sorption. The presence of HA decreased the sorption of 60Co(II) on γ-Al2O3. The sorption isotherms were simulated well with the Langmuir model. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) calculated from the temperature-dependent sorption isotherms indicated that the sorption of 60Co(II) on γ-Al2O3 was an endothermic and spontaneous process. Experimental results indicated that the low cost material was a suitable material
in the preconcentration of 60Co(II) from large volumes of aqueous solutions.
The stability constants of the complex of Pu/III/ with a humic acid at pH 2.9 and 5.0 were measured using solvent-extraction technique. The organic extractant was dinonyl naphthalene sulphonic acid in sodium form /NaD/ in benzene while the humate aqueous phase had a constant ionic strength of 0.5M /NaClO4/. The total carboxylate capacity of the humic acid was determined by direct potentiometric titration to be 6.201 Meq g–1. The apparent pKa increased as the degree of ionization // increased. The 1g
1 values of the complex of Pu/III/ with humic acid have been determined to be 2.8 and 3.11 at pH 2.9 and 5.0, respectively.