土壤胶体中氧化物表面性质的初步研究

我们以蒙脱石为对照,测定了以水合氧化物型表面为主的试样四个方面的表面性质:电荷零点(ZPC)、滴定曲线、羟基释放量及不同pH条件下对NH₄⁺和Cl^-的吸附。结果表明,在pH 4—9范围内,氧化物型表面提供可变正电荷1—8 meq/100g,提供可变负电荷3—15meq/100g;三二氧化物使土壤的ZPC升高,而永久负电荷和有机质使土壤的ZPC降低。作为粘土酸,氧化物表面的酸性较弱,其表面质子逐步解离,使滴定曲线不出现突跃。氧化物表面的羟基和水合基密度很高,增加了土壤对离子的专性吸附能力。土壤中常见的氧化物型表面主要来自Fe,Al氧化物及非品质矿物,就它们的化学式而言,主要有Si—OH、Fe—OH及Al—OH,它们可存在于同一土壤中,在土壤常见的pH范围内,具有低ZPC的Si—OH亚表面提供可变负电荷,具有高ZPC的Fe—OH和Al—OH亚表面提供可变正电荷。

STUDY ON THE PROPERTIES OF OXIDE SURFACES IN SOIL COLLOIDS

This paper presents the properties of oxide surfaces in soil colloids, including zero point of charge (ZPC), titration curves,amount of hydroxyl(OH) released, and adsorption of NH₄⁺ and Cl^- under various pH.The results showed that as compared with the properties of siloxane surface in montmo-rillonite, the oxide surfaces supplid larger amount of variable charge, the sesquioxide in soils increased the ZPC, but the permanent negative charge and organic matter decreased the ZPC of sons. As clay acids, the proton on oxide surfaces dissociated gradually, so the titration curues showed no inflexions. The density of hydroxy and hydrous group on oxide surfaces which responded to specific adsorption of ion were higher.So far as the chemical formula is concerned, the oxide surfaces in soils are commonly Si-OH, Al-OH and Fe-OH. They can coexist to one kind of soil. The Si-OH suh-surfaces of oxide with low ZPC usually supply negative variable charge, the Al-OH and Fe-OH sub-surfaces with high ZPC supply positive variable charge.