Authors:D. H. Mu, J. Z. Du, D. J. Li, H. Q. Song, S. P. Yan, and Y. J. Gu
The comprehension of the behavior of radioactive nuclides in aquifer requires the study of the sorption processes of nuclides
in various geochemical conditions. The sorption/desorption of 65Zn(II) on surface sediments (0-2 cm) was investigated by batch method in sea water (pH 8.20, 35‰ salinity, filtered by 0.45mm)
at ambient temperature. The surface sediments were obtained from four stations around the Daya Bay of Guangdong Province (China),
where the first nuclear power station of China has been running from 1994. The sorption process is fast initially and around
39% average of sorption percentage (SP%) can be quickly obtained in 15 minutes for all the surface sediments. Then, the sorption
percentage becomes constant. In 30 days of contact time 79.6% sorption percentage and Kd=3.9. 103ml/g distribution coefficient was obtained. The value of Kdbecame constant, 4.0. 103ml/g, in contact time more than 120 hours. The distribution coefficient Kddecreases with increasing sediment concentration from 4.0 to 250 mg/l from 1.31. 104to 1.68. 103ml/g, respectively. Then the value of Kdgoes up to 5.38. 103ml/g with sediment concentration of 3000 mg/l. The desorption experiments suggest that the sorption of Zn(II) is irreversible
with a hyteresis coefficient of 66%.
The reactive mechanism of cesium in crushed granite was demonstrated in this study through a numerical analysis or a model
of the results of sorption/desorption kinetic tests. To employ such numerical analysis, this study applied batch kinetic tests
with different solid to liquid ratios (1: 20 and 1: 30) for the characterization of sorption/desorption reaction of Cs and
the calibration/validation of hypothesized reactive models. Based on the least square errors (LSE) between numerical analysis
and results of batch tests, the two-site sorption models, which are corresponding to two decay constants (λ1 and λ2), might be more adequate than one-site sorption models in characterizing Cs sorption/desorption. Moreover, a two-site Langmuir
kinetic model has been found to be capable of appropriately describing Cs sorption/desorption under test conditions.
The behavior of cadmium labeled with 109Cd in different depth horizons of arable and forest soils were studied under static (batch) conditions in three interconnected
processes, which consist of sorption, desorption and extraction. In the sorption, Cd2+ was applied in the aqueous calcium nitrate solution. Both untreated soils and peroxide treated soils were used in order to
remove organic matter from some of the soil samples used in parallel. The influence of the V/m ratio on the sorption coefficients was investigated in preliminary experiments with untreated soils. Contrary to the usually
short-term sorption, a long-term sorption of cadmium was investigated in untreated and treated soil horizons, which lasted
more than fortnight. Kinetic studies of sorption were carried out and cadmium concentration dependence in aqueous phase of
the second order kinetic constants was observed. For evaluation of sorption and desorption processes Freundlich isotherms
were used. It was found that the Freundlich adsorption intensity coefficient is more time dependent than the absorption capacity
coefficient, and the sorption itself consists of rapid and slow processes according to the soil constituents. Desorption and
extraction processes revealed the possibility of cadmium recovery from various soil horizons. Based on the obtained results
two- or three-stage theory of cadmium retention in soils was proposed. Some new insight into the role of organic matter in
the sorption/desorption process of cadmium is also presented.
Authors:J. Du, H. Song, D. Mu, D. Li, S. Yan, and Y. Gu
The sorption/desorption of radioruthenium was investigated by the batch method in sea water system at ambient temperature
on the surface sediments obtained around the Daya Bay of Guangdong Province, where the first nuclear power station of China
has been running from 1994. It was found that the sorption percentage was obtained to be around 40% for all the surface sediments
in 60 minutes. Then, the sorption percentage goes up slowly. The sorption percentage of radioruthenium reached around 80%
in 113 days (2713 hours). The distribution coefficients decreased from 3.16·104 to 1.35·103 ml/g with the increasing of sediment concentration in the range of 4–10000 mg/l. The results of the desorption experiments
suggest that the sorption of radioruthenium is irreversible with 81.5% relative hysteresis coefficient.
In this work, Na-montmorillonite was used as a novel adsorbent for the sorption of Ni(II) from aqueous solutions. The sorption
and desorption of Ni(II) on Na-montmorillonite was investigated as the function of pH, ionic strength, Ni(II) concentrations
and temperature. The results indicated that the sorption of Ni(II) on Na-montmorillonite was strongly dependent on pH, ionic
strength and temperature. The sorption of Ni(II) increases slowly from 22.1 to 51.4% at pH range 2–6.5, abruptly at pH 6.5–9,
and at last maintains high level with increasing pH at pH > 9 in 0.1 mol/L NaNO3 solutions. The Ni(II) kinetic sorption on Na-montmorillonite was fitted by the pseudo-second-order model better than by the
pseudo-first-order model and the experimental data implies that Ni(II) sorption on montmorillonite were mainly controlled
by the film diffusion mechanism. The Langmuir, Freundlich and D–R models were used to simulate the sorption data at three
different temperatures (298.15, 318.15 and 338.15 K) and the results indicated that Langmuir model simulates the experimental
data better than Freundlich and D–R models. The sorption–desorption isotherm of Ni(II) on montmorillonite suggested that the
sorption is irreversible. The irreversible sorption of Ni(II) on montmorillonite indicates that montmorillonite can be used
to pre-concentration and solidification of Ni(II) from large volumes of solution and to storage Ni(II) ions stably.
Authors:K. Ioannides, T. Mertzimekis, D. Karamanis, K. Stamoulis, and I. Kirikopoulos
The kinetics of radiocesium sorption and desorption by cation solutions and the corresponding radiocesium distribution profiles in sediment cores were investigated. The results have shown that a significant percentage of radiocesium is adsorbed in the sediments during the first 3 d. Radiocesium reaches rapidly (< than 5 d) at a depth which does not exceed 3.5 cm. The desorption of radiocesium was found to depend on cation concentrations. Empirical laws are derived both for cesium adsorption and desorption.
Authors:G. Pacheco, G. Nava-Galve, P. Bosch, and S. Bulbulian
The ability of some antural Mexican clays to sorb radioactive Co from aqueous solution and then desorb it has been measured. The clay cations seem to be exchanged with cations present in the solution. It was observed that the amount of sorbed Co2+ depends nearly linearly on the Na++K+ content in the montmorillonites. It was found that the crystallinity was not altered after Co2+ sorption. Crystallinity of clays, before and after cobalt exchange, was determined by X-ray diffraction.
The sorption and desorption properties of cesium on three sulfate-resistant Portland cements, and one Type III Portland cement, with water-to-cement ratios of 0.33, 0.43, and 0.53 were evaluated. Experimental sorption Kd values obtained at 1 day ranged from 0.60-37.1 l . kg-1 with the smallest values observed for the sulfate-resistant Portland cements, and the greatest amount of cesium sorption occurring in the Type III Portland cement. Results indicated that cesium sorption showed significant hysteresis and was only partially reversible on the time scale of these experiments.
In general, the amount of radiocesium sorbed by the five sorbents with 0.01 mol·dm–3 NaCl was in order zeolite > NiFeCN–SiO2 > montmorillonite > aerogel > silica gel. Addition of humic acid solution to the sorbents depressed the sorption of cesium by all sorbents, except for NiFeCN–SiO2 was not seen, with the greatest effect showing to the aerogel. The presence of humic acid resulted in an enhanced desorption of cesium from zeolite, NiFeCN–SiO2 and to a lesser extent from montmorillonite and silica gel. The order of cesium retention following desorption for both sorbent and sorbent/humic-acid mixtures was zeolit > NiFeCN–SiO2 > montmorillonite > silica gel. The presence of humic acid resulted in decreasing of distribution coefficient values for both sorption and desorption processes.
The properties of the solid-state of drug substances are critical factors that determine the choice of an appropriate salt
form for the development of the pharmaceutical formulation. The most relevant properties may affect the therapeutic efficacy,
toxicity, bioavailability, pharmaceutical processing and stability. The salt form must fulfil the needs of the targeted formulation,
be suitable for full-scale production and its solid-state properties maintained batchwise as well as over time. Comparison
of the solid-state properties of different salt candidates may be quite complicated if each salt candidate exist as different
solid phases: polymorphs, solvates or amorphous forms. Thermal analysis, microcalorimetry and combined techniques, X-ray diffraction,
solubility, intrinsic dissolution, sorption-desorption and stability studies are basic techniques for the characterisation
of the salt candidates. Some examples show the role of the salt form as well as the polymorphic form in the characteristics
of the solid-state. Thermal analysis and combined techniques are efficient for the detection of unexpected phase transitions
and for the comparison of the suitability of the salt candidates prepared for salt selection.