Zuyi Tao

Comparative study on sorption/desorption of radioeuropium on alumina, bentonite and red earth: effects of pH, ionic strength, fulvic acid, and iron oxides in red earth.

The sorption and desorption of Eu(III) as a representative of trivalent lanthanides and actinides on bentonite, alumina, red earth and red earth treated to remove free iron oxides were comparatively investigated by using batch technique and radiotracer 152 + 154Eu. The effects of pH, ionic strength, fulvic acid, iron oxides in red earth and the sorption mechanism were also discussed. As compared to alumina and red earth, Eu(III) presents a considerable distribution coefficient (Kd) onto bentonite. It was found that the pH and the presence of clay minerals are the main factors dominating the sorption/desorption characteristic of Eu3+ in the soil, and that a sorption-desorption hysteresis on bentonite and red earth actually occurs. Furthermore, the main sorption mechanism of lanthanides onto bentonite, alumina and red earth is the formation of bridged hydroxo complexes with the surface, and there are negative effects of fulvic acid and free iron oxides in red earth on the sorption of Eu(III). The results of this paper indicate that the additivity rule on the sorption characteristic of a soil from the individual components characteristics is not general.

Sorption and desorption of radioiodine on calcareous soil and its solid components

The effect of different solid components of calcareous soil on the retention of I was investigated by a batch technique and selective extraction method, and the effect of γ-irradiation was also investigated. The sorption and desorption isotherms of I on the one untreated, three treated soils and the calcareous soil irradiated with γ-rays were determined at 30 °C, pH 8.1±0.2 and in the presence of 1.0×10−4M or 0.67×10−5M CaCl2. It was found that the sorption-desorption hysteresis on the calcareous soil actually occurs on the same time scale, that iodine can be easily transported in the calcareous soil and that the exceptionally high contribution of organic matter to the iodine sorption is demonstrated.

Sorption and desorption of Co(II) on alumina: mechanisms and effect of humic substances

The effects of pH, ionic strength and humic substances on the sorption and desorption of Co(II) on alumina and silica were, respectively investigated by using radiotracer 60Co. The distribution coefficients, the breakthrough curves and the displacement curves were experimentally determined in the batch and the column experiments. The pH and the humic substances influenced the sorption of Co(II) on alumina greatly as compared with the sorption of Co(II) on silica. It was found that the sorption characteristics of Co(II) onto alumina and silica are distinctly different, that the strong chemical bonds are formed between the bare alumina surface and Co(II) and between the coated alumina surface and Co(II), and that a transition from the adsorption to the surface-induced precipitation of Co(II) on the bare alumina surface takes place.

A multitracer study on the adsorption of 36 elements on a silica: Effects of pH and fulvic acid

The distribution coefficients,Kd of 36 elements from Na to Bi on a silica were determined at pH 4, 7, 9 and in the absence and presence of fulvic acid (FA) using a multitracer technique. The multitracer solution was prepared by irradiation of Th(NO3)4 with 40Ar ion beam. The effects of pH and fulvic acid on the Kd values of 36 elements were studied. It was found that the sequences of the Kd values of alkali elements (Cs>Rb>K>Na) and of alkaline earth elements(Ba>Ca>Mg) in the absence of FA can be qualitatively explained in terms of chemical bond formation and hydration. Various effects of pH and the negative or positive effect of FA on the adsorption of 36 elements were observed and are probably related to the species of 36 elements in the aqueous solutions containing CO32−, OH−, Cl− and FA. For most of the elements studied here the Kd values are increased with increasing pH and are decreased with adding FA.

A multitracer study on the adsorption of 32 elements on a natural hematite (α-Fe2O3): effects of pH and fulvic acid

Abstract The distribution coefficients (K d ) of 32 elements from Na to Bi on a natural hematite (α-Fe 2 O 3 ) were determined at pH 4, 7, 9 and in the presence and absence of fulvic acid (FA) by using a multitracer technique and the batch method. The multitracer solution was prepared by irradiation of Th(NO 3 ) 4 with 40 Ar ion beam. The effects of pH and FA on the K d values of 32 elements on the natural hematite were studied. It was found that both the sequences of alkali elements and alkaline earth elements can be roughly explained in terms of chemical bond formation and ion hydration enthalpies. Though the various effects of pH and the positive and negative effects of FA on the K d values of 32 elements were found, the prevailing tendencies were the increase in K d value with increasing pH and the negative effect of FA on the adsorption of elements from Na to Bi at very low concentration and pH 7. The adsorption of lanthanides on the hematite against the atomic number exhibited approximately as a “W” figure, the peak was around the element Tb and the valley was around the elements Eu and Yb.

Sorption and desorption of radiocesium on red earth and its solid components: relative contribution and hysteresis.

Abstract The relative contributions of organic matter and iron oxides to the Cs+ sorption on red earth were investigated by using the batch technique and selective extraction methods. The sorption and desorption isotherms and the distribution coefficients of Cs+ on the untreated red earth and the three treated soils to remove organic matter, iron oxides and organic matter plus iron oxides were determined at 20°C, pH 6.3±0.2, in the presence of 0.01 mol/l CaCl2. It was found that all the isotherms are linear in the Cs+ concentration range used here, that the sorption–desorption hysteresis on the red earth actually occurs, and besides the clay minerals, the organic matter present in the red earth is a significant trap of Cs+ and is responsible for the hysteresis instead of the iron oxides.

Migration characteristics of radionuclides 85+89Sr2+, 134Cs+, 125I-, 75SeO32- and 152+154Eu(III) in Chinese soils

The migration of radionuclides 85+89Sr2+, 134Cs+, 125I- and 75SeO32- in calcareous soil from Yuzhong county of Gansu Province (China) at pH 7.8±0.2 and 152+154Eu(III) in red earth from Yingtan county of Jiangxi Province (China) at pH 4.6±0.2, in presence of CaCl2 was studied using column experiments. Results indicate that the negative anions, iodide and selenide are mobile nuclides while the migration of positive cations is related to the sorption capacity for the element. Iodide can be assumed to be non-reactive in calcareous soil. The breakthrough curves (BTCs) were fitted to the analytical solution or numerical solution of one-dimensional convection-dispersion transport models. Good agreements were obtained between the measured and predicted concentration profiles.

Use of ion exchange for the determination of stability constants of metal-humic substance complexes

Humic substances (HSs) occur throughout the ecosphere in soils, waters and underground systems. The strong complexation of HSs is of importance in the migration of radionuclies in geological media. Renewed interest in stability constants of complexes of radioelements and radionuclides with humic and fulvic acids has been generated by problems associated with the nuclide migration in the environment. Use of the ion exchange method for the determination of conditional stability constants of metal-HS complexes was examined and reviewed. The complexation of HS to metal ions cannot be described in rigorous mathematical terms because of the ill-defined nature of HSs in contrast with the complexation of single ligands. Furthermore, the advantages and disadvantages of Schuberts and, Ardakani-Stevensons, curve fitting methods were discussed. The great stabilities of HS complexes to rare earths (Yb(III), Tb(III), Eu(III), Gd(III)), americium(III), cobalt(II), uranyl(VI) and thorium(IV) were revealed.

Preparation of multitracer nuclides from UO2 (NO3)2 irradiated by40Ar ion beam

UO2 (NO3)2 was irradiated with a 25 MeV/nucleon40Ar ion beam. The target material irradiated was dissolved in ethyl ether, and the uranyl was removed from the back extractant 5M HNO3 saturated with NH4NO3 by means of solvent extraction with TBP in CCl4. A carrier-free multitracer solution containing 47 elements from Na to Bi and 83 radionuclides was prepared and has been applied to adsorption studies on alumina and soils.

USE OF THE CATION EXCHANGE EQUILIBRIUM METHOD FOR THE DETERMINATION OF STABILITY CONSTANTS OF CO(II) WITH SOIL HUMIC AND FULVIC ACIDS

The stability constants for tracer concentrations of Co(II) complexes with both the red earth humic and fulvic acids were determined at pH 5.9 and ionic strength 0.010 mol/l by using theArdakani-Stevenson cation exchange equilibrium method and the radiotracer60Co. It was found that the 1:1 complexes of Co(II) with the red earth humic and fulvic acids were formed and that the average values of logβ (stability constant) of humic and fulvic acid complexes were 5.76±0.19 and 4.42±0.03, respectively.