[en] 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

[en] 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 (K_d) 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 component's characteristics is not general

[en] There has been a lot of interest in generalizing orthodox quantum mechanics to include POV measures as observables, namely as unsharp observables. Such positive operator-valued (POV) measures are related to symmetric operators. The present paper examines how symmetric operators arise and how they can represent observables. (author)

[en] 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 radionuclides 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 Schubert's and, Ardakani-Stevenson's, 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. (author)

[en] The batch method and the column method were simultaneously employed to study the sorption and desorption of Eu(III) on red earth as a function of pH (4.6-6), the presence of a well-characterized fulvic acid (FA) and the iron oxides content of red earth. The results from both methods were consistent qualitatively. The Eu(III) sorption showed significant dependences on pH and FA, the sorption was increased with increasing pH and by addition of FA to the solutions, while the iron oxides content of the red earth had a negative contribution to the sorption of Eu(III). Additionally, the sorption-desorption hysteresis of Eu(III) on red earth occurred at a pH range of 4.6-6. Therefore, the humic substance and high pH have a great tendency to immobilize Eu(III) on red earth. (author)

[en] Five column experiments have been carried out to investigate the effect of flow rate on the breakthrough curves (BTCs) of phosphate, fulvic acid, and uranium(VI) onto a silica column. Both BTCs of phosphate and fulvic acid, and three BTCs of uranium(VI) in the presence and absence of phosphate or fulvic acid at high flow rate published in the previous paper were compared with corresponding initial parts of BTCs at low flow rate in this paper. Each BTC in this paper was expressed as both C/C_o-t and C/C_o-V/V_o plots, where C and C_o are the concentrations in the influent and the effluent respectively, t and V are the time and the effluent volume from the start of injection of pulse solution respectively, V_o is the pore volume of the SiO₂ column. Based on the experimental results and the relationship among V, t, and flow rate F, it was found that there are advantages to using C/C_o-V/V_o plot as BTC to study the effect of flow rate. Based on these comparisons of C/C_o-V/V_o plots at different flow rates and the theoretical analysis from the Bohart-Adams sorption model, it was found that the right shift (increase in V/V_o of breakthrough), the left shift (decrease in V/V_o of breakthrough), and the non-shift (non-change in V/V_o of breakthrough) of initial parts of BTCs with increasing flow rate are certain to occur instead of only left shift and that three different trends of shifts can be mainly attributed to different rate-controlling mechanisms of sorption process. (author)

[en] The distribution coefficients, K_d 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 K_d values of 36 elements were studied. It was found that the sequences of the K_d 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 CO₃^2-, OH^-, Cl^- and FA. For most of the elements studied here the K_d values are increased with increasing pH and are decreased with adding FA. (author)

[en] 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 the ARDAKANI-STEVENSON cation exchange equilibrium method and the radiotracer ⁶⁰Co. 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. (author)

[en] The stability constants for tracer concentrations of Co(II) complexes with the red earth fulvic acid were determined at pH 3.8-6.8 and ionic strength 0.0010-1.0 mol/l by using the cation exchange equilibrium method and the radiotracer ⁶⁰Co. The effects of ionic strength and pH on the stability constants of 1:1 Co(II) complexes were investigated, and it was found that the stability constants of complexes of humic substances do not vary with ionic strength and pH in a manner similar to that of simple complexes. (author)