摘要
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。
Effects of ionic strength of electrolyte solution and natrue of cation on phosphate desorption in some variable-charge clay minerals and soils were studied, It was observed that Ca^(2+)-saturated montmorillonite, kaolinite and clay colloid from red soil sorbed more Phosphate that Na^+-saturated samples, but much less phosphate than Al^(3+)-saturated samples. Such difference 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 cation to neutralize the negative change on the solid surface and its chemical affinity for phosphate ion. With increasing valence of the cations from Na^+ through Ca^(2+) to Al^(3+), 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.Much more phosphate ws desorbed in 0.02molL^(-1)KCl than in 0.01 molL^(-1) CaCl_3 solution for all the tested samples. This can be attributed to the more effective shielding of Ca^(2+) than of K^+ on the sorbed phosphate.The effect of concentration of electrolyte in desorbing solution on phosphate desorption was related to the medium pH and the PZC value of solid phase. Increasing concentration of electrolyte reduced desorption of the sorbed phosphate at pH above PZC but reverse case was found at the pH value of solution below the PZC value. The pH value at which the concentration of electrolyte has no influence on phosphate desorption, defined as the point of zero salt effect on phosphate desorption (P_(PZSE)), was observed to be between the two PZC values (PZC_(?) and PZC_f, representing PZC value of the sample before and after phosphat adsorption, respectively) of the solid adsorbent for all the tested samples. The difference of phosphate amount desorbed in 0.02molL^(-1) and 1.00molL^(-1)KCl solutions was positively correlated ith the electrical potential difference on phosphate-adsorbing plane in the two solutions, with a correlation coefficient of 0.8368 on average.Therefore, it seems reasonable to suggest that the influence of electrolyte concentration on phosphate desorption is mainly through the change of surface potential
出处
《土壤学报》
CAS
CSCD
北大核心
1992年第1期26-33,共8页
Acta Pedologica Sinica
关键词
阳离子
电解质
土壤
磷酸盐
解吸
Cation, Electrolyte, Soil, Clay mineral, Phosphate, Desorption, Potential
