支持电解质浓度对磷酸根在可变电荷土壤表面吸附和解吸的影响

EFFECT OF BACKGROUND ELECTROLYTE CONCENTRATION ON ADSORPTION-DESORPTION OF PHOSPHATE IN VARIABLE CHARGE SOILS

研究了离子强度对2种可变电荷土壤中磷酸根吸附和解吸的影响。结果表明,当pH分别大于3.7和4.0时,红壤和砖红壤对磷酸根的吸附量随离子强度的增加而增加;当pH分别小于3.7和4.0时,红壤和砖红壤对磷酸根的吸附量随离子强度呈相反的变化趋势。电解质主要通过改变离子专性吸附面上的电位来影响磷酸根的吸附。Zeta电位的测定结果表明,当pH大于土壤胶体的等电点(IEP)时,吸附面上电位为负值,且随离子强度增加数值减小,对磷酸根的排斥力减小,土壤表面对磷酸根的吸附量增加;当pH小于IEP时,吸附面上的电位为正值,它随离子强度增加而减小,不利于磷酸根的吸附。解吸实验的结果表明,吸附于可变电荷土壤表面的磷酸根在去离子水中的解吸量高于0.1 mol L-1NaNO3体系中的解吸量。这同样由于电解质浓度对土壤表面吸附面上的电位的影响所致。

Effects of ionic strength on adsorption and desorption of phosphate in variable charge soils were investigated with batch method.Results indicate that when pH was higher than 3.7 or 4.0,the amount of phosphate adsorbed by red soil and latosol increased with increasing ionic strength,and when pH was lower a reverse trend was observed for both soils.Electrolyte affected the adsorption of phosphate by the soils through its effect on electrostatic potential of the ionic specific adsorption plane,which existed between Stern layer and diffuse layer.Zeta potential of soil colloids suggested that when pH was greater than the isoelectric point（IEP）,the potential in the adsorption plane was negative and became less negative with increasing ionic strength,thus allowing increase in phosphate adsorption by the soils;when pH was less than the IEP of soil colloids,the potential was positive and decreased with increasing ionic strength,thus decreasing phosphate adsorption by the soils.The results of desorption of pre-adsorbed phosphate indicated that the amount of phosphate desorbed by deionized water was greater than that by 0.1 mol L^-1 NaNO3.This was also ascribed to the effect of ionic strength on potential in the adsorption plane.