恒电荷土壤及可变电荷土壤与离子间相互作用的研究 Ⅱ.共存体系中Cl^-的吸附特性

STUDIES ON THE INTERACTION OF IONS WITH CONSTANT CHARGE SOILS AND VARIABLE CHARGE SOILS II. CHARACTERISTICS OF Cl^- ADSORPTION IN SYSTEM CO-EXISTING CATIONS AND ANIONS

对 3种可变电荷土壤和 4种恒电荷土壤在陪伴阳离子分别为Na+、K+、NH+4 、Mg2 +、Ba2 +、Al3+和共存SO2 -4下Cl- 的吸附量进行了测定。结果表明 ,供试土壤的Cl-吸附量顺序均为AlCl3>BaCl2 和MgCl2 >KCl和NH4 Cl>NaCl,其中可变电荷土壤的差异较大。不同电解质溶液中Cl- 吸附量的顺序与土壤所带正电荷量的顺序一致。Langmuir方程的K值较小 ,且在不同介质中的差异不大。随SO2 -4浓度的增大 ,可变电荷土壤对Cl- 的吸附量减少 ,平衡液的pH值增大 ,而恒电荷土壤则变化甚微 ,说明共存的SO2 -4使可变电荷土壤的表面负电荷增加 ,但对恒电荷土壤则影响不大。这些结果说明 ,Cl- 以电性吸附的机理不因介质而变。可变电荷土壤在一价阳离子存在时 ,除土壤本身所带的正电荷外 ,还有一价阳离子吸附后产生的正电荷以及由此引起的对Cl- 的协同吸附。在二、三价阳离子存在时 ,还有Cl- 的离子对吸附 ,而恒电荷土壤在所有介质中 ,似乎总是以与Cl-

The adsorption of chloride ions by three variable charge soils and four constant charge soils of China were determined in different concentrations of co-existing SO 2- 4 and accompanying Na +, K +, NH + 4, Mg 2+ , Ba 2+ and Al 3+ , respectively. The results indicated that the amount of Cl - adsorbed by soils in different electrolyte solutions decreased in the order AlCl 3>BaCl 2 and MgCl 2>KCl and NH 4Cl>NaCl. However, the difference of Cl - adsorption among electrolyte solutions was more significant in variable charge soils. In the same electrolyte solution, the amount of Cl - adsorbed by different soils decreased in the order latersol>red earth>red latersol>yellow brown earth>brown earth, dark brown earth and black soil, which agreed with the order of positive surface charge of these soils. For variable charge soils, within the range of 0.5 to 5 mmol L -1 of Cl - added, the adsorption can be described by the Langmuir equation satisfactorily, and the adsorption energy parameter ( K ) calculated from the equation was similar in magnitude when different cations co-existed. The pH of the equilibrium solution increased and the amount of Cl - adsorbed by variable charge soils decreased significantly with increasing concentration of SO 2- 4 co-existed. However, there was some difference in Cl - adsorption by constant charge soils in the presence of SO 2- 4 when compared with Cl - adsorption by variable charge soils in the same condition. It suggested that the negative surface charge of variable charge soils increased with increasing concentration of SO 2- 4 co-existed, but the SO 2- 4 co-existed did not influence the negative surface charges of constant charge soils remarkably. The results obtained in this work imply that for variable charge soils, co-adsorption (simultaneously adsorption) and ion-pair adsorption of Cl - with cations might be involved except electrostatic adsorption when accompanied by univalent cations and bivalent or trivalent cations respectively. For constant charge soils, only co-adsorption of Cl - with cations might occur except electrostatic adsorption.\;