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The effects of ionic strength on the adsorption behaviors of the monovalent cation NpO2+, the divalent cations UO22+, Zn2+, Sr2+, the trivalent cations Yb3+, AM(3+) onto Al2O3, SiO2 and Fe2O3 from aqueous solutions were investigated. It was found that depending on the adsorption system and solution condition, the ionic strength effects are promotive, reductive and insensitive to increasing ionic strength. Based on the comparison among the various effects of ionic strength on the various adsorption systems and the theoretical considerations, it may be concluded that the factors of ionic strength effect on cation adsorption are very complicated, that there are various effects on a certain adsorption system in the different pH ranges and different concentration ranges of background electrolyte, that the speciation of metals in aqueous solutions plays an important role in the cation adsorption, that the coulombic interaction and the chemical reaction could be directed towards the various ionic strength effects and that the satisfactory interpretation of various effects of ionic strength is very difficult to access and that ionic strength effect on cation adsorption is an open question and worthy of further study, because of the great practical importance and theoretical interest. (C) 2004 Elsevier B.V. All rights reserved.

The adsorption and desorption of radioiodine in a calcareous soil from Jiuquan County of Gansu Province (China) was studied using batch and column experiments. The adsorption and desorption isotherms and the breakthrough curves for the untreated soil and for soil treated to remove organic matter were determined at pH 8.1 and in the presence of CaCl 2 , respectively. It was found that radioiodine is a very mobile nuclide in calcereous soil, that the organic matter of the soil is the main component for the retention of radioiodine at very low concentration and that intra-organic diffusion of matter is the predominant rate-limiting step in the adsorption of the I − ion. It may be concluded that organic matter is a significant sink for radioiodine in calcareous soil.

The distribution coefficients, Kd of 47 elements from Na to Bi on a calcareous soil, a red earth and an alumina were, respectively, determined using a multitracer technique. The multitracer solution was prepared by irradiation of UO2(NO3)2 with 40Ar ion beam. It was found that there is a common general trend of variation in Kd for both soils and the alumina, i.e. all the shapes of plots of log Kd versus electron binding energy (Iz) are an 'inverted V', hence the important role of chemical interaction in the adsorption of trace inorganic cations, anions and neutral complexes on the soils and the oxides was demonstrated. For the alkali and alkaline earth elements, the common sequences of Kd values on the three adsorbents were Na+ < K+ < Rb+ < Cs+ (except for Rb+ on the alumina) and Mg2+ < Sr2+ < Ba2+ and accord with the sequences of effective ionic radii or single ion hydration enthalpies.

The sorption of Yb3+, UO22+, Zn2+, I- and SeO32- onto Al2O3, Fe2O and SiO2 were determined by a batch technique in the presence and absence of fulvic acids. The effects of fulvic acid on sorption were compared. The existing general consensus, that humic substances tend to enhance metal cation sorption at low pH, reduce metal cation sorption at high pH and reduce inorganic anion sorption between pH values 3 to 10, was generally shown to be true. However, in this work many exceptions to the general consensus were found. The study indicated that the effect of humic substances on sorption of inorganic cations or anions depends not only on pH, but also on the nature of the oxide, the nature of humic substance, fractionation of the humic substance by sorption, the relative strength of complexes of both soluble and sorbed humic substances, the extent of surface coverage by humic substance, the initial concentration of humic substance and the inorganic electrolyte composition. (C) 1999 Elsevier Science Ltd. All rights reserved.

The effects of pH, ionic strength and FA (fulvic acid) on the sorption and desorption of Eu(III) and Yb(III) on alumina were respectively investigated by using batch technique and radiotracers 152 + 154Eu and 169Yb. The distribution coefficients for sorption and desorption of Eu on alumina at pH 4.4, 4.6 and 5.7 in 1 mol/l NaCl solutions as a function of solid phase concentration were determined in the presence or absence of FA. The effects of pH, FA and ionic strength on the distribution coefficients for sorption and desorption of Yb on alumina were determined in 0.01-2.0 mol/l NaNO3. It was found that pH and FA influenced the sorption of Eu(III) and Yb(III) on alumina greatly. A surface hydrolysis model can satisfactorily and qualitatively explain the observations on bare alumina. The competition among the complexations of surface free hydroxyl groups, soluble and sorbed fulvic acids can satisfactorily and qualitatively explain the observations on the coated alumina.

The effect of organic matter and iron oxides as solid components of the red earth on the retention of SeO3 has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO3 on the untreated red earth and the three treated soils were determined at 20°C, pH 6.8 or 7.2 and in the presence of 0.01M CaCl2. It was found that the sorption-desorption hysteresis for untreated an treated soils is obvious and the clays play an important role in the sorption-desorption hysteresis, and that the retention of SeO3 on red earth is attributed to the iron oxides to a great extent.

The sorption and desorption of radiocesium on a calcareous soil from Jiuqian County of Gansu Province (China) were studied by using batch and column experiments. The sorption- desorption isotherms and the breakthrough curves, displacement curves on the whole soil and two treated soils were determined. Based on these results, it was found that the sorption and retention of cesium are mainly determined by the clay minerals, that the sorption-desorption hysteresis of cesium on the calcareous soil is obvious and that the organic matter has a little positive contribution and the calcium carbonate has a little negative contribution to the sorption of cesium on the whole soil. The results from batch experiments were consistent with the results from column experiments.

The distribution coefficients of 47 elements from Na to Bi on untreated calcareous soil, treated soil to remove CaCO3 and treated soil to remove both CaCO3 and organic matter, respectively, were determined by using a multitracer technique. The variation of the distribution coefficients of 47 elements was explained in terms of chemical bond formation and hydration. The effect of different solid components of the calcareous soil on the adsorption was investigated.

In this study, we added increments of acid and base to three calcareous soils from the eastern, middle and western parts of Gansu Province (China) and to three treated soils to remove calcium carbonate, organic matter and both carbonate and organic matter, respectively. the titration curves were measured and the magnitudes of buffer capacities as a function of pH were computed. It was found that the buffer capacity of calcareous soil is mainly attributed to calcium carbonate, as expected from the chemical composition of calcareous soil, while cation exchange system, silicate buffer system and organic matter play a minor role. the results clearly show that these soils of Gansu Province will not become a problem in the near future from the entrance of H+ into these soils.

The surface charge σ0 on aqueous suspensions of alumina was measured as a function of pH in various NaNO3 concentrations and at different temperatures. The values of the point of zero charge (p.z.c.), pK1(int), pK2(int), pKNa+(int) and pKNO3–(int) for alumina suspended in NaNO3 solutions were obtained in the temperature range 17–45°C from potentiometrie titration data. The values of ΔS0 and ΔH0 of the dissociation equilibria and complexation equilibria were calculated from these equilibrium constants. Standard Gibbs energies, enthalpies and entropies for proton adsorption on alumina were also obtained. The surface charge σ0 on aqueous suspensions of alumina was measured as a function of pH and concentration of Ca(NO3)2 or Na2SO4 solution.

The adsorption/desorption of H+ and OH− ions under static conditions on to alumina in aqueous NaNO3 solution was studied at 30°C by potentiometric titration and calculations undertaken using the triple layer model (TLM). Intrinsic dissociation constants and intrinsic complexation constants at 30°C were used to calculate surface charge density, surface potential and surface species as a function of pH and ionic strength (I). Related adsorption/desorption studies of H+ and OH− ions under dynamic conditions on to alumina in aqueous NaNO3 solution were studied by means of the concentration-jump technique. Mechanistic information regarding H+ and OH− ion adsorption/desorption on to alumina was discussed using the experimental data in conjunction with the TLM.

Uranyl nitrate, UO2(NO3)2, was irradiated with a 25 MeV/nucleon 40Ar ion beam, and the target material removed by means of solvent extraction. A radioactive multitracer solution containing 47 elements and 83 nuclides free from carriers was thereby prepared. The multitracer solution was used in an adsorption study of 47 elements on alumina and bentonite. The distribution coefficients (Kd) of the 47 elements were simultaneously determined and correlated with the electron binding energy (Iz), and explained by the thermodynamic model for adsorption of James and Healy (1972).

The adsorption and the desorption of radiocesium from aqueous solutions containing NaNO3 or CaCl2 on Al2O3 were studied over a wide range of background electrolyte concentration and solution pH by using batch techniques in polyethylene and glass test tubes. It was found that the wall of the glass test tubes has a great effect on the adsorption and desorption data, and the adsorption-desorption hysteresis on the same time scale is negligible by using the same aqueous solutions for both adsorption and desorption in the polyethylene test tubes. The dependences of the distribution coefficient on the pH and background electrolyte concentration and the adsorption mechanism were discussed.

The methods for the determinations of dissociation or protonation constant and ion exchange equilibrium constant for weakly dissociating ion exchange resin and hydrous oxide by means of potentiometric titration are presented in this paper. The weakly acidic cation exchange resin and basic anion exchange resin, the chelating exchange resin in which the iminodiacetic acid groups are covalently bound to the matrix, and the chromatographic grade finely divided alumina are concerned.

The stability constants of uranyl ion complexes with three soil fulvic acids were determined by using the modified Ardakani-Stevenson's method at pH = 6, ionic strength 0.1 mol/l and 25 degrees C. It was found that 1:1 and 1:2 type complexes, respectively, are formed at different concentration ratios of UO22+ to the fulvic acid.

65Zn was used as a radiotracer to study the sorption characteristics of zinc by two calcareous soils from Gansu Province (China). The sorption and desorption isotherms of Zn on two untreated calcareous soils and on two soils treated to remove CaCO3 were determined at 20 +/- 2 degrees C, pH 7.8 +/- 0.2 in the presence of 0.001 mol/l CaCl2. The contribution of CaCO3 to the Zn sorption by the two calcareous soils was approximately 70% of the total amount sorbed and the sorption-desorption hysteresis was definitely demonstrated, thus the CaCO3 in calcareous soil is undoubtedly the most significant sink for zinc at high pH range.