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  • Author: Shizuko Ambe x
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Summary

A method combining radioactive ‘multitracer’ and dialysis techniques was developed to study the binding of multiple metal ions to humic acid (HA). Technical problems such as the leakage of small-molecule HA segment and the slow diffusion of metal ions through the dialysis membranes were examined. Under the condition of pH = 4.0, I = 0.100 M NaNO3, [MgII] = 0 M, or [MgII] = 0.500×10-3 M, the interactions between Inogashira humic acid and metal ions (BeII, ScIII, ZnII, CoII, MnII and SrII) were investigated by varying the metal concentrations in a wide range. It was found that as the concentrations of the trace metals are significantly smaller than that of HA, there are abundant binding sites available and there are no competition interactions between the trace metal ions of interest. Therefore, the stability constants for multiple metal ions binding onto humic substances can be obtained readily using the present method. The method is useful for quickly determining trace metal binding onto humic substances in environmental chemistry.

Summary

The simultaneous permeation of Sc, Y, Ce, Pm, Eu, Gd, Yb and Lu through a 2-ethylhexyl phosphonic acid-2-ethylhexyl ester (EHEHPA)-decalin membrane supported on a microporous polytetrafluoroethylene sheet was studied using a multitracer. The permeation rates of the elements from feed solutions of various acidity into receiving solutions of 2mol dm-3 HCl were determined. The feed solution at pH 1.5 gave the highest percentage of permeation for Ce, Pm, Eu, Gd and Yb, amounting to about 90 after -25h permeation. The percentage of permeation of Y and Lu was the highest at pH 1, amounting to about 90 after -25h permeation. The permeation of Sc from all the feed solutions was less than 4 due to its adsorption on the vessel. The permeation from the feed solution at pH 1.5 into the receiving solutions of 1, 2, 3, 4 and 5mol dm-3 HCl showed that the maximum percentage of transport for Y and Yb was obtained in 2mol dm-3 HCl receiving solution and that for Lu in 2-4mol dm-3 HCl receiving solutions. The other elements gave a percentage of transport more than 90 in 1-5mol dm-3 HCl receiving solutions, showing no obvious HCl concentration effect. The permeability coefficients of these elements were determined. Solvent extraction of the elements by EHEHPA-decalin was also carried out for comparison.

Using a multitracer technique, the effects of acid rain pH on the adsorption of 15 trace elements on soil were studied. Kaolin, forest soil (original and with partially removed oxides), black soil (original and without organic matter)and Kureha soil (original, with partially removed oxides, and without organic matter) were employed as the adsorbents. Instead of H2SO4 solution, HCl solution was selected as the model acid rain based on the results of adsorption experiments on kaolin. In general, the percentage adsorption of cationic elements on three original soils and kaolin increased with increasing pH. The adsorption of oxyanionic elements, As and Se, on three soils was high over the entire pH range studied, while that on kaolin was low and decreased with an increase in pH. The differences in the physical and chemical properties of soils were reflected on the adsorption. The organicmatter in soil had positive effects on the extent of adsorption of most elements studied, while the oxides apparently showed positive effects only for Fe and Se adsorption. The results indicate that acid rain decreases the retention of cations in soil and that it increases or does not change the adsorption of anions.

With the aim of preparing carrier-free 28Mg and 47Ca simultaneously, Ti, V and Fe targets were examined by irradiating with high-energy ions of 12C, 14N and 16O accelerated by the RIKEN Ring Cyclotron. Among the targets, V gave the highest cross section for the formation of both 28Mg and 47Ca irrespective of the kind of beams. The cross section for the formation of 28Mg by the reactions of Ti, V and Fe targets with ion beams increased in the order of 12C < 16O<14N. On the other hand, the three beams exhibited almost the same cross sections for the formation of 47Ca by the reaction of a given target. Titanium and V were selected as prospective targets and 14N as a suitable beam for the production of 28Mg and 47Ca. Chemical separation procedures of the radiotracers in carrier- and salt-free states have been established by using cation exchange resins. The recovery yields of 28Mg and 47Ca from Ti target were 70 and 90%, respectively, and the decontamination factor was less than 10-5. The recovery yields of 28Mg and 47Ca from V target were 80% and the decontamination factor was less than 10-7.

Summary

Irrespective of low bioavailability, some plant species accumulate Y and rare earth elements (REEs) to a great extent (accumulator species). The uptake mechanisms of Y and REEs were investigated for autumn fern, one of accumulator species. For comparison, plant species which accumulated poorly REEs (non-accumulator species) were also studied. In the present investigation, two noticeable phenomena were observed. (I) Autumn fern showed no ionic-radius dependence of Y-REE uptake by leaves, while non-accumulator species showed an extremely high uptake for Y compared with REEs. (II) Y-REE uptake by autumn fern was influenced by the addition of chelating reagents to the uptake solution, while no effect was observed for non-accumulator species.