Modeling of ion adsorption on soil constituents

金属氧化物在土壤和沉积物中普遍存在，影响环境中离子的迁移，对金属氧化物的离子吸附进行了模拟。1.金属氧化物表面的离子交换：随着pH值的升高，阳离子的吸附增加，而阴离子的吸附减少，偏离了质量作用定律。建立平衡模型的两个假设是：(1)表面羟基的氢离子与阳离子交换形成表面络合物，氢离子与阴离子交换形成表面络合物；(2)吸附离子之间的横向相互作用抑制吸附。随着氧化物晶格金属离子电负性的增加，阳离子交换(酸解离)增加，阴离子交换(碱解离)减少。这表明表面羟基的电子密度较低，电负性较大，有利于质子释放，但不利于质子吸收(氢氧化物离子释放)。2.选择性地合并…尖晶石型锰氧化物晶格空位中锂离子的掺入速率随锂离子浓度趋于极限值而增大，随pH呈指数增加。考虑了两个基本反应：(1)晶格锰(IV)离子氧化氢氧离子，激发空位后向反应；(2)激发空位占据锂离子。3.多价重金属离子在二氧化锰颗粒中的掺入：在电解氧化锰(II)离子沉积二氧化锰的过程中，掺入量与溶液中的离子浓度成正比，且吸附亲和力较高的离子的掺入量较高。这提出了一种模型，在该模型中，二氧化锰通过在其新生长的表面上吸附来结合溶液中的离子。所有这些模型都很好地再现了观察结果，并能够预测离子吸附的程度和评估金属氧化物的离子吸附性能。所建立的模型也适用于其他组分、粘土矿物、腐殖质等的离子吸附。较少

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 … More 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