Electrochemical Effects Of Zn²⁺ Adsorption On Humus

Humus is an important kind of natural organic matter which is widespread in soil and environment. Humus plays an important role in improving soil fertility, controling erosion, fixing and decomposing toxic substance, and controling agricultural area source pollution,ect.In recent years, a large number of studies on the interaction between metal ions and humus have been done. However, most of these studies always apply the relevant theory of classical thermodynamics and dynamics directly, making the mutual mechanism between humus and ions indistinct and the equilibrium constants uncalculated so far. The fundamental reason is that people have ignored the influence induced by the electric field of humus colloidal on adsorption rate and adsorption equilibrium.In the field of colloidal chemistry, the stability and flocculation of colloidal dispersion system is an important research content, always using the DLVO theory to describe them. During the study of colloidal particles aggregation and the fractal structure, the two irreversible aggregation models were gradually formed:the one was diffusion limited cluster aggregation; the other was the reaction limited cluster aggregation. Light scattering techniques provide a favorable means for determining aggregation's dynamic change and structural features in laboratory.This project bases on the current research results, taking variable charge "humus colloid" as the research material. On the one hand, researching on the Zn2+/Ca2+ ions exchanged in different concentrations of background electrolyte and comparing the result of Mg2+/Ca2+ ions exchange experiment; we concluded that the surface electric field had an influence on the coefficient rates of adsorption and equilibrium adsorption capacities. On the other hand, as the ligand adsorption and electrostatic adsorption of Zn2+ on the humus surface, the surface field of humus would be greatly weakened. In this case, humus particles will aggregate rapidly and form the fractal polymer by the molecular force. The project studied the influence of Zn2+ adsorption on the kinetics aggregation and the structure of aggregation using the dynamic light scattering and static light scattering. The preliminary results indicated that:(1) According to the rigorous rate equation which is used to describe the ion diffusion /adsorption, the adsorption of Zn2+ to humus showed a first-order kinetics character.(2) By compared the the specific adsorption of Zn2+ and the non-specific adsorption of Mg2+, we found the electric field force had a significant effect on adsorption rate and the equilibrium adsorption capacity.(3) Studying on the aggregation kinetics of humus colloidal induced by Zn2+, we found that:â‘ stability of the light intensity in an aggregation process is a basis for judging whether the collision is dominated by Brown force or gravity;â‘¡in different concentration of Zn(NO3)2 systems, humus colloidal aggregation exhibited a diffusion-limited cluster aggregation (DLCA) character;â‘¢in different concentrations of electrolyte, the structure of humus aggregates had the smaller fractal dimension, then had bigger porosity and open approach space.