Interactions And Energy Relationships Between Ions And Clay Fractions Of Variable Charge Soils

The interactions and energy relationships between soil clay particles and electrolyte ions have always been the subject which all of soil scientists want to finish.This work has been finished on basis of the Wien effect measurements in dilute suspensions which was established recently.The interactions of cations(Na⁺,K⁺,NH₄⁺,Ca²⁺,Zn²⁺,Cd²⁺ and La³⁺) and clay mineral(kaolinite),typical variable charge soils(red soil,lateritic red soil and latosol),the interactions of anions(Cl^-,NO₃^-,ClO₄^-,SO₄^2- and PO₄^3-) and red soil and latosol were investigated via the Wien effect measurements in dilute suspensions;the mean Gibbs free binding energy(ΔG_bi) and adsorption energy(ΔG_ad) of cations with red soil clay particles were calculated as well.The major results of the work are summarized as follows:In the tested pH values,the ratios of positive charge densities to the negative charge densities(Po./Ne.) of latosol particles were in the range of 0.4 to 0.8,the Po./Ne.of lateritic red soil particles were in the range of 0.08 to 0.22,whereas the Po./Ne.of red soil particles were only in the range of 0.016 to 0.064,therefore the positive charge in red soil can be negligible.The Wien effects of three variable charge soils(red soil,lateritic red soil and latosol) saturated with various chlorides in electric field were different.The relative electrical conductivities(ΔEC) of red soil saturated with various chlorides increased apparently with the increase in field strength,whereas that of latosol were almost equal to 1 in the test field strength(15 kV cm^-1 to 250 kV cm^-1),the increase ofΔEC in lateritic red soil were between that of red soil and latosol.The Wien effects of the test soils were affected obviously by the iron oxide component.In the tested pH values(5.6～7.1),theΔG_bi values of cations Na⁺,K⁺,NH₄⁺,Ca²⁺, Zn²⁺ and Cd²⁺ with red soil were 4.50,7.35,7.15,9.12,9.84 and 9.63 kJ mol^-1 respectively, which were similar to the results determined from the "activity method".Theζpotentials of the particles of red soil saturated by divalent cations closed to -44 mV,whereas theζpotentials of red soil saturated by monovalent cations were more negative(-56～-70 mV). TheΔG_ad values of various cations with red soil were very near in low field strength, while theΔG_ad values of divalent cations were equal to 2～3 times of that of monovatent cations at high strength(＞100 kV cm^-1).In the filed strength of 14 kV cm^-1 to 200 kV cm^-1,the increase of electrical conductivities(EC) of iron-removed red soil and iron-removed latosol were higher than that of red soil and latosol.TheΔG_bi andΔG_ad values of cations with variable charge soils were affected by the iron oxide component,and the influence caused by iron oxide in latosol was more obvious than that in red soil.The Wien effects in kaolinite saturated by various cations were similar with that in red soil.TheΔG_bi values of monovalent cations with kaolinite,which in the order Na⁺＜NH₄⁺＜K⁺,were less than that of divalent cations,in whichΔG_bi value of Pb²⁺ was the highest andΔG_bi value of Zn²⁺ was the lowest.TheΔG_ad values of various cations with kaolinite generally increased with the increase in field strength.The values of same of valence cations with kaolinite at the same field strengths were very near,and theΔG_ad values among different valence cations were in the order divalent cations＞monovalent cations. TheΔG_ad values of La³⁺ with kaolinite was the lowest among the tested cations.The EC values of red soil and latosol saturated by various sodium salts were different. The Wien effects of red soil saturated by various acids were affected by the anions' properties.The EC values at week fields(EC₀) of red soil saturated by hydrochloric acid, nitric acid and hypochiorous acid were similar,and EC values generally increased with the increase in field strengths,whereas the EC₀ values of red soil saturated by sulfuric acid and phosphoric acid were higher and EC values almost unchangeable in the test fields.In the red soil suspensions,the EC values in the field were dependent on the properties of the anions;whereas in the latosol suspensions,the EC values in the field were dependent on the properties of the cations.