Model study of acid rain effect on adsorption of trace elements on soils, 2

Abstract

The adsorption of trace elements on the kaolin and the soil affects the vegetation. The adsorption characteristics depend greatly on the chemical properties of soils and elements involved, and also are greatly influenced by acid rain. Using a multitracer technique, experiments have been performed to study the acid rain effect on element adsorption by the soils without organic matter or oxides. In the experiment, model acid rains were prepared by dissolving 16 elements in solutions with different HCl concentrations. Seven soils with or without oxides and organic matter were employed as the adsorbents. The pH effect (pH 1.9 - 5.6) of the model acid rains on the adsorption of some trace elements in Kureha soil was studied, and it was found that the adsorption of almost all the elements depended greatly on the pH value. The results indicated that the oxides in Kureha soil did not affect the adsorption of Be, As, Co, Zn, Zr, Tc and Re over the pH range studied. If oxide components were removed, the adsorption percentage of Rb, Sr and Sc increased in the whole pH range. The removal of organic matter did not change the adsorption percentage of Be, As, Se, Zr, Ru and Rh. However, the adsorption percentage of the other elements became much lower than that in the original soil. The removal of oxides from forest soil made the adsorption percentage of Mn and Fe higher. However, it made no difference with the other elements.

微量元素のカオリン及び土壌への吸着は植生に影響を与えるが、この吸収特性は土壌および元素の化学的特質に大きく依存し、酸性雨にも大きく影響される。マルチトレーサ法を用い、有機物又は酸化物を除去した土壌による元素吸着への酸性雨の効果を調べる実験を行った。実験では16種類の元素を濃度の異なる塩酸に溶解し、酸性雨のモデルとした。酸化物や有機物を含んだ土壌と除去した土壌を7種類用いた。いくつかの微量元素のクレハ土壌への吸着に対するモデル酸性雨のpH(1.9?5.6)効果を調べた。ほとんどすべての元素の吸着は、pH値に強く依存する。クレハ土壌の酸化物は、調べた全pH領域で、Be、As、Co、Zn、Zr、Tc、およびReの吸着に影響を与えない。酸化物を除去すると、全pH領域で、Rb、SrおよびScの吸着率は高くなった。有機物を除いても、Be、As、Se、Zr、RuおよびRhの吸着率は変わらなかった。しかし、他の元素の吸着率は、初めの土壌よりずっと低くなった。森林土から酸化物を除去すると、MnとFeの吸着率は高くなったが、他の元素では変わらなかった。