Humic Acid / Montmorillonite Colloid Aggregation Kinetics Hofmeister Effects: The Role Of Non-electrostatic Mechanism

Soil particle size <10³ nm of the order of the organic / inorganic particles play an important role in the formation of soil function. In nature, due to the alternating wet and dry, hot cyclical changes and interventions and other human activities, soil p H, temperature, type of electrolyte thermodynamic conditions are changing. Changes in the forces caused by soil colloids and colloidal particles interacting by the soil colloidal aggregation or dispersion alternating with frequent spontaneous. The occurrence of these processes, but also a profound impact on many of the microscopic processes in soil and macro phenomenon.Hofmeister effect known as ion-specific effects. About 120 years ago by Franz Hofmeister and his colleagues found the protein made by condensation experiments. The experiment found that when a solution containing different cations especially with different valence ions or anion, the combination of characteristics of the protein showed a huge difference, but recent studies have found that this difference is far more than by ion volume, volume and hydration different dispersion forces due to differences. In recent years, research on soil colloids aggregation found Hofmeister effects is very strong. However, the soil is a variety of nano micron sized organic matter humus and mineral complex system constituted. Therefore, it is necessary to adopt a single and a single mineral several macromolecule- aggregation kinetics of humus soil to reveal the nature of colloid aggregation of Hofmeister effects. This study used two materials are montmorillonite and humic acid research several cations and anions aggregation kinetics. Explore Hofmeister effects in a non-electrostatic adsorption of colloidal aggregation. Therefore, we used Cu²⁺ and Zn²⁺ two cations having different adsorptive ability to conduct research in the humus colloid aggregation. Because the montmorillonite negatively charged, so montmorillonite colloid aggregation choose not prone to electrostatic adsorption several anions were studied. Research on the use of dynamic light scattering, by measuring the rate of aggregation of colloidal aggregation, critical coagulation concentration, coagulation activation parameters and fractal dimension peers gather to reflect the dynamics of the process of cohesion and structural features of the body cohesion, in order to explore based on strength and mechanisms of action of non-electrostatic Hofmeister effects. It was found:1. Cu²⁺ and Zn²⁺ two cationic initiator Kinetics humic acid condensates are very different. Therefore there is a strong Hofmeister effects. In the Cu²⁺ induced aggregation, the aggregation rate far greater than the aggregate Zn²⁺ induced aggregation rate. For example, when the Cu²⁺ concentration of 0.8 mmol/L, humic acid condensation rate as high as 844.8 nm/min, while at the same concentration Zn²⁺ in the presence of humic acid condensation rate is 0 nm/min. When Zn²⁺ concentrations up to 5 mmol/L, humic acid coagulation speed to reach 831.4 nm/min, at the same time the concentration of Zn²⁺ is already Cu²⁺ concentration six times more.2. Cu²⁺ and Zn²⁺ two cationic initiator aggregation structure of the body after the formation of humic acid condensation has a very significant difference, still show significant Hofmeister effects. The fractal dimension of Zn²⁺ induced aggregation of the formed aggregates was significantly lower than the Cu²⁺ induced aggregation, indicate Zn²⁺ induced aggregation to form a more porous and more open structure.3. Cu²⁺ and Zn²⁺ ion hydration radius and radius are very close, so the humic acid condensation rate and significant differences in structure can not be derived from the difference hydrated ionic radius and radius of cohesion. As we all know, Cu²⁺ is more than Zn²⁺ likely to occur strongly adsorptive, and Zn²⁺ is more than Cu²⁺ the electrostatic adsorption occurs. Since the suction force adsorptive much larger than the electrostatic adsorption, so Cu²⁺ shielding around humic acid particles a negative electric field is stronger than the Zn²⁺. Eventually leading to Cu²⁺ in the presence of humic acid electrostatic repulsion between particles is weaker and more susceptible to aggregation and the formation of aggregates firmer exhibit greater fractal dimension.4. Montmorillonite colloidal aggregation rate of the three different monovalent anion H₂PO₄-, Cl-, NO₃- System aggregation rate significantly different, indicating the presence of a strong cohesion montmorillonite Hofmeister effects. For example, when the concentrations of these anions are the system of 20 mmol/L and coagulate when time is 10 min, H₂PO₄-, coagulation system in diameters of 480 nm, Cl- system is 1500 nm, and the system up NO₃- 2250 nm, Cl- and NO₃- system aggregate diameters are H₂PO₄- system 3.12 times and 4.68 times.5. Montmorillonite particles have distinct critical coagulation concentration in the coagulation process, also showed strong Hofmeister effects. For example, H₂PO₄-, Cland NO₃- concentrations of coagulation coagulation were 79.29,13.91,17.07mmol/L, H₂PO₄- critical aggregation concentration of Cl- six times.6. Montmorillonite cohesion during agglomeration activation energy characterizing ion-specific effects exhibited H₂PO₄- >> NO₃- > Cl- sequence, and with the electrolyte concentration decreases the activation energy difference between ions increases.