电解质种类和浓度影响磷酸根解吸的机理研究

本文研究了吸附性阳离子、电解质浓度和组成影响几种矿物和土壤吸附态磷的解吸的机理。结果表明,吸附性阳离子影响磷酸根解吸与离子桥有关。桥接静电场愈强,被束缚磷的释放就愈困难。电解质阳离子对磷酸根解吸的影响则取决于其对表面负电荷的屏蔽效应。阳离子电价高,屏蔽作用大,磷解吸就少。电解质浓度影响吸附态磷的解吸主要与表面电位的变化有关。当pH>PZC值时,提高电解质浓度降低表面负电位,从而减少磷的吸附;当pH<PZC时,提高电解质浓度则降低表面正电位,促进磷的解吸。磷酸根解吸盐效应零点(P_PZSE)值一般都介于土壤或矿物样品吸附磷酸根前后测得的两个PZC值之间。不同浓度电解质溶液中磷解吸量之差与吸附层电位变化量(△ψ_x)呈正相关。

EFFECT OF IONIC STRENGTH AND CATION ON PHOSPHATE DESORPTION

Effects of ionic strength of electrolyte solution and narrue of canon on phosphate desorption in some variable-charge clay minerals and soils were studied. It was observed that Ca²⁺-saturated montmorillonite, kaolinite and clay colloid from red soil sorbed more Phosphate than Na⁺-saturated samples, but much less phosphate than Al³⁺-saturated samples. Such differenct was more significant for montmorillonite than kaolinite or soil clay, suggesting that cation bridge mechanism was in action. The bonding strength of formed surface complex depended on the ability of canon to neutralize the negative change on the solid surface and its chemical affinity for phosphate ion. With increasing valence of the canons from Na⁺ through Ca²⁺ to Al³⁺, decreasing phosphate was desorbed at the same adsorption saturation for all tested samples, especially for montmorillonite, due to stronger electrostatic attraction of the cation for both negatively charged surface and phosphate ion.