Jäntti introduced a method to calculate the adsorption equilibrium by the measurement of the actual adsorbed amount at three times after a change of the gas pressure. He applied that method for gas/solid systems in which simple adsorption processes occur and for an infinite number of adsorption sites. In the present paper we discuss the case that the number of sites is decreasing with increasing coverage.
Authors:António Brázio, Ana Cavaco, and Rui Guerra
A simple model of light diffuse reflectance in thin skin fruits is presented. The model is based in a semi-infinite two-layer geometry (skin and flesh) and introduces simplifications due to the fact that the first layer is very thin. The flesh is described in terms of the usual reduced scattering and absorption coefficients µs′ and µa but the skin is modeled by simple reflection (R), absorption (A) and transmission (T) coefficients. The problem of diffuse reflectance is thus reduced to the problem of determining the four constants µs′, µa, R and T. It is shown that the problem can be solved by using absolute reflectance and spatially resolved reflectance measurements simultaneously. The coefficients µs′ and µa are determined by the usual fit of the diffuse reflectance profile (photons re-emitted from the flesh far from the incidence point) to the diffusion approximation. The coefficients R and T are determined by a second fit involving the total reflectance profile (photons reemitted both from skin and flesh), the incident beam profile and the diffuse reflectance profile calculated according to the previously determined values of µs′ and µa. The anisotropy of the light re-emitted by the fruit can also be roughly compared with the Lambertian expected behavior. In order to test the model we have followed a population of 22 ‘Rocha’ pears along a period of two weeks. We have then performed the population averages along the time and checked the plausibility of the values obtained for µs′, µa, R and T according to the expected fruit physiological changes along ripening. The results show that all parameters are physically acceptable and evolve in time according to the expected fruit ripening physiology.
Authors:A. Kitamura, T. Yamamoto, S. Nishikawa, and H. Moriyama
Sorption behavior of Am(III) onto granite was investigated. The distribution coefficient (Kd) of Am(III) onto granite was determined in the solution of which pH was ranged from 2.9 to 11.4 and ionic strength was set
at 10−2 and 10−1. TheKd values were found to increase with increasing pH and with decreasing ionic strength. The obtained data were successfully
analyzed by applying an electrical double layer model. The optimum parameter values of the double layer electrostatics and
adsorption reactions were obtained, and the selective adsorption behavior of Am(III) onto the granite was discussed.
Authors:K. Štamberg, J. Škrkal, P. Beneš, K. Chalupská, and D. Vopálka
A surface complexation model, the so-called diffuse double layer model (DLM), was used in the description of the multicomponent
system consisting of Czech sodium bentonite SABENYL and synthetic granitic water spiked with233U(VI). The experimental data were evaluated and the characteristic parameters, e.g., the equilibrium constants of all the
reactions considered, were obtained and used for the numerical simulation of sorption selectivity of the uranium in relation
to the total carbonate concentration. The values of separation factors indicate that the selectivity of uranium sorption in
such multicomponent systems can depend not only on the pH and composition of both phases, but also on the phase ratio and
starting concentrations of participating components.
Authors:K.A. Venkatesan, P.R. Vasudeva Rao, and K. Štamberg
The amphoteric acid-base behavior of hydrous zirconium oxide (HZO) was investigated by titrating HZO with 0.05M HNO3 and NaOH at constant ionic strength. The sorption of strontium from 0.05M NaNO3 solution was measured as a function of pH. Abrupt increase in sorption was observed at the equilibrium pH of 9. The experimental titration and strontium sorption data on HZO were evaluated using the constant capacitance model (CCM) and diffuse double layer model (DLM). Various model parameters of Surface Complexation Models (SCM) were estimated, numerically, by non-linear regression. Modeling the sorption and speciation of Sr2+ on HZO indicated that the hydrolysis of Sr2+ to lower charged SrOH+ is the pre-requisite for the abrupt sorption behavior at pH 9.
The stability behaviour of a thin-film superconductor under a localized release of thermal disturbance is investigated. Two-dimensional conjugate film/substrate conduction equation with anisotropic thermal conductivity of the film, and Joule heat are employed to investigate effects of substrate and thermal properties on the intrinsic stability and quenching recovery. To consider the thermal boundary resistance between film and substrate, an interfacial-layer model (ILM) with very low diffusivity and an acoustic mismatch model (AMM) are employed. Results show that the thermal boundary resistance influences strongly the intrinsic stability. Thermal boundary resistance increases intrinsic stability if the thermal conductivity of the substrate or the disturbance energy is large. Higher Biot numbers and thermal conductivity ratios of film to substrate in longitudinal direction influence stability favorably. We demonstrate also that operation of a film/substrate system, such as YBCO/MgO, is either intrinsically stable or irrecoverably unstable.
The scavenging of UO22+ using 4-sulfonic calixarene in the presence of a strong adsorbent was studied as a function of pH. The adsorbent selected
was goethite because of its strong affinity for UO22+ and its abundance in natural soils. In order to understand the underlying chemistry of the scavenging process, the adsorption
of UO22+ and 4-sulfonic calixarene onto goethite, respectively, and the extraction of adsorbed UO22+ from goethite surface were modeled using the triple-layer model. The model well explained the pH dependence of the adsorption
and extraction processes. This work showed that maximum extraction was obtained around pH 10.5 in the presence of 12g/l goethite
in the case of a 1:3TU(VI):Tcalixareneratio.
Authors:J. Jung, S. Hyun, J. Lee, Y. Cho, and P. Hahn
The prediction of the adsorption behavior of natural composite materials was studied by a single mineral approach. The adsorption
of U(VI) on single minerals such as goethite, hematite, kaolinite and quartz was fully modeled using the diffuse-layer model
in various experimental conditions. A quasi-thermodynamic database of surface complexation constants for single minerals was
established in a consistent manner. In a preliminary work, the adsorption of a synthetic mixture of goethite and kaolinite
was simulated using the model established for a single mineral system. The competitive adsorption of U(VI) between goethite
and kaolinite can be well explained by the model. The adsorption behavior of natural composite materials taken from the Koongarra
uranium deposit (Australia) was predicted in a similar manner. In comparison with the synthetic mixture, the prediction was
less successful in the acidic pH range. However, the model predicted well the adsorption behavior in the neutral to alkaline
pH range. Furthermore, the model reasonably explained the role of iron oxide minerals in the adsorption of U(VI) on natural
U(VI) sorption on kaolinite was studied as functions of contact time, pH, U(VI) concentration, solid-to-liquid ratio (m/V) by using a batch experimental method. The effects of sulfate and phosphate on U(VI) sorption were also investigated. It
was found that the sorption kinetics of U(VI) can be described by a pseudo-second-order model. Potentiometric titrations at
variable ionic strengths indicated that the titration curves of kaolinite were not sensitive to ionic strength, and that the
pH of the zero net proton charge (pHPZNPC) was at 6.9. The sorption of U(VI) on kaolinite increased with pH up to 6.5 and reached a plateau at pH >6.5. The presence
of phosphate strongly increased U(VI) sorption especially at pH <5.5, which may be due to formation of ternary surface complexes
involving phosphate. In contrast, the presence of sulfate did not cause any apparent effect on U(VI) sorption. A double layer
model was used to interpret both results of potentiometric titrations and U(VI) sorption on kaolinite.
Authors:Songsheng Lu, Zhiqiang Guo, Caicai Zhang, and Shouwei Zhang
MX-80 bentonite was characterized by XRD and FTIR in detail. The sorption of Th(IV) on MX-80 bentonite was studied as a function
of pH and ionic strength in the presence and absence of humic acid/fulvic acid. The results indicate that the sorption of
Th(IV) on MX-80 bentonite increases from 0 to 95% at pH range of 0–4, and then maintains high level with increasing pH values.
The sorption of Th(IV) on bentonite decreases with increasing ionic strength. The diffusion layer model (DLM) is applied to
simulate the sorption of Th(IV) with the aid of FITEQL 3.1 mode. The species of Th(IV) adsorbed on bare MX-80 bentonite are
consisted of “strong” species
at pH > 4. Similar species of Th(IV) adsorbed on FA bound MX-80 bentonite are observed as on FA bound MX-80 bentonite. The
sorption isotherm is simulated by Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models, respectively. The sorption mechanism
of Th(IV) on MX-80 bentonite is discussed in detail.