| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1994: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1993: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
Modeling was made of ion adsorption on metal oxides which are common in soils and sediments and affect the migration of ions in environments. 1. Ion exchange on metal oxide surfaces : with increasing pH the cation adsorption increases, while the anion adsorption decreases, showing a deviation from the mass-action law. The following two assumptions were made to develop an equilibrium model : (1) formation of surface complexes by exchanging hydrogen ions of surface hydroxyl groups with cations and hydroxide ions with anions, and (2) suppression of adsorption due to lateral interaction between adsorbed ions. With increasing electronegativity of the oxide lattice metal ions, the cation exchange (acid dissociation) increases while the anion exchange (base dissociation) decreases. This indicates that the electron density of surface hydroxyl groups is low with large electronegativity, favoring proton release while disfavoring proton uptake (hydroxide ion release). 2. Selective incorporation o
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f lithium ions into the lattice vacancy of spinel type manganese oxide : the incorporation velocity increases with the lithium ion concentration tending toward limiting values, while it increases exponentially with pH.A kinetic model was developed by considering two elementary reactions : (1) the lattice Mn(IV) ion oxidizes a hydroxide ion and excites a vacancy with a backward reaction, and (2) the excited vacancy takes up a lithium ion. 3. Incorporation of multivalent heavy metal ions into manganese dioxide particles : the amount of incorporation during the deposition of manganese dioxide by electrolytic oxidation of manganese (II) ions is proportional to the concentration of ions in solution and is higher for ions with higher adsorption affinities. This suggests a model in which manganese dioxide incorporates ions from the solution through adsorption on its new growing surface. All these models reproduce the observed results well and enable a prediction of the extent of ion adsorption and an evaluation of the ion adsorption properties of metal oxides. The models developed here can also be applied to ion adsorption on other components, clay minerals, humic substances, and so on. Less
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