Interactions And Energy Relationships Between Heavy Metal Ions And Clay Fractions Of Constant 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 equations which are used for calculating the mean Gibbs free binding energy (â–³G_bi) and adsorption energy (â–³G_ad) between cations and soil clay particles were introduced in this dissertation. The interactions of heavy metal ions (Zn²⁺, Cd²⁺, Cu²⁺, Pb²⁺, Cr³⁺) and other cations (Na⁺, K⁺, NH₄⁺, Ca²⁺) with two clay minerals (kaolinite and montmorillonite), and typical constant charge soils (yellow-brown soil, brown soil, and black soil) and their energy relationships were investigated via the Wien effect measurements in dilute suspensions. The major results of the work are summarized as follows:The mean Gibbs free binding energies of monovalent cations with kaolinite are less than that of divalent cations, but ones of monovalent and divalent cations with montmorillonite are nearer.â–³G_bi of Pb²⁺ with kaolinite and montmorillonite are the highest, and that of Cr³⁺ with the two clay minerals are all the lowest among the five heavy metal cations.â–³G_bi of the tested cations with kaolinite are in the range of 0.75 to 2.6 kJ mol^-1, and that with montmorillonite in the range from 7.9 to 9.9 kJ mol^-1, which is much more than that with kaolinite. The mean Gibbs free adsorption energies of tested cations with kaolinite and montmorillonite increased generally with the increase in field strength. Theâ–³G_ad values of same valence cations with the two clay minerals at the same field strengths are very near, and theâ–³G_ad values among different valence cations are in the order divalent cations＞monovalent cations. Theâ–³G_ad of Cr³⁺ with clay minerals is also the lowest among the tested cations. Theâ–³G_ad values of cations with montmorillonite at 100 kV cm^-1 are equal to 2-4 times that with kaolinite.Theâ–³G_bi values of various cations with the clay fractions of the soils are different. The mean free binding energies of monovalent cations with tested soils are in the range of 4.7 to 7.4 kJ mol^-1; and ones of divalent cations are in the range from 7.2 to 9.9 kJ mol^-1; ones of Cr³⁺ are a bit less than that of divalent heavy metal ions. The mean free binding energies of Pb²⁺ with four tested soils are always the biggest, being as high as 9.88 kJ mol^-1 for black soil. The mean free binding energies of monovalent cations with four tested soils are of the order yellow-brown soilⅠ＜brown soil＜yellow-brown soilⅡ＜black soil. The mean free adsorption energies of monovalent cations with four tested soils increased all with the increase in field strength. There is no distinct difference in theâ–³G_ad values of different cations with the soils at low field strength of 15-80 kV cm^-1, but theâ–³G_ad values of divalent cations are conspicuously larger than that of monovalent cations at the field strength more than 100 kV cm^-1, and the difference between the two kinds of cations increased with field strength, theâ–³G_ad of divalent cations is about 2-2.5 times that of monovalent cations. The adsorption energies of various heavy metal ions with the soils at respective field strengths are also in different orders. Theâ–³G_ad values of Zn²⁺ are in the order black soil＞yellow-brown soilⅠ＞yellow-brown soilⅡ＞brown soil, ones of Cd²⁺ and Pb²⁺ are in the order yellow-brown soilⅡ＞yellow-brown soilⅠ＞brown soil＞blacksoil, and ones of Ca²⁺ in the order yellow-brown soilⅠ＞black soil＞yellow-brown soilⅡ＞brown soil.As measuring the wien effects in the suspensions of soils saturated with divalent cations and Cr³⁺ at low field strengths, the electrical conductivities of the suspensions decreased with the increase in field strength. The negative Wien effect occurred in the range of field strength from 10 to 25 kV cm^-1 for divalent cations, and in the range of 10-60 kV cm^-1 for Cr³⁺, which is much more than that for divalent cations.