Measurment Of Point Of Zero Charge And Hofmeister Effects Of Colloid Aggregation By Light Scattering

Red and yellow soil are widely distributed in South China which contains a large number of variable charge colloid, hematite is an important variable charge colloid. Hematite is an integral part of soil mineral colloid, hydrated oxide surface of which constitutes an important source of soil variable charge. M-OH of colloid surface for hematite has active surface properties, which is closely related to soil heavy metal adsorption and desorption, soil degradation and water pollution decent. PZC (Point of Zero Charge) is important surface properties hematite colloids, hematite (variable charge) colloid surface are mainly hydrated oxide surface, M-OH, the change of pH may cause interaction between M-OH and H+, and emerge surface charge. Therefore, PZC affects the interaction force between particles, thus affect the aggregation between the particles of hematite colloid. Studies have shown that common methods were used to measure PZC of variable charge for potentiometric titration and potential method, the presence two methods for sensitivity and accuracy are lower. Therefore, the establishment of new high sensitivity and good stability theory and methods for determination PZC has important significance.Hematite colloid aggregation are not only influenced by surface electrochemical properties, but also by ion concentration and ionic species in colloid interface., and that showed Hofmeister effect in Colloid Aggregation. Hofmeister effects, known as ion-specific effects, found in protein aggregation experiments by Hofmeister in about 120 years ago. Over the past decade research has shown that the ion-specific effects plays an important role in the vicinity of the interface, and profoundly impact the microscopic and macroscopic effects process. Studies have shown that, with the same valence of cation specificity than anion.Under normal soil pH (pH<8) conditions, surface hematite colloids are with a net positive charge, and whose cohesion caused by the solution of the anion. Currently, research on soil colloids anionic cohesion rarely reported.This study selected as the material hematite, and propose a new method of measure ZPC of hematite colloid surface, based on this, take Cl-,Br- and SO42- to explore Hofmeister effects of the interaction between colloidal particles for hematite, and found that there indeed are a strong anion Hofmeister effects. Come to following conclusions:(1) In this study, eatablish a new theory and method for determination of PZC of variable charge colloidal. Dynamic light scattering measurement method established in this paper has the following advantages in theory:Firstly, the higher sensitivity and accuracy. When the pH close to PZC, the new method applied to the determination PZC depend on the total aggregation rate more sensitive to changes in pH. Compared with conventional potentiometric titration and potential method, which measures the situation of going further to PZC which is more sensitive PZC. Secondly, a simple measurement. The method depends on the total average aggregation rate with pH change in a linear relationship. Nevertheless, potentiometric titration and the potential method depends on the non-linear relationship of potential for the change in pH. For a linear relationship, that requires only a small number of experimental data which can be accurately determined PZC. But for non-linear relationship, the pH must be arranged more close to the point to accurately determine the PZC. However, for unknown material, PZC can not know in advance, so I can not do the most rational distribution of the experimental data points. Therefore, the new method is more convenient. Finally, this method can be easily used to determine point of zero net charge, while containing a mixing colloid surface of variable charge and constant charge. potential can only be measured point of zero net charge of shear plane, and if colloids constant charge amount is significantly greater than variable charge, potential can not be measured PZNC. Potentiometric titration system can not be used.(2) PZC of hematite colloids was measured successfully achieved by new method, the results show PZC= 7.60. At the same time, the potential was also determined PZC of the material, the results show the same as the new method. Therefore, the new method proposed measuring PZC are feasible in the principles and method, and results are reliable.(3) By dynamic light scattering techniques, the aggregation kinetics of hematite colloid do research at different concentrations of Cl-,Br- and SO42- conditions. three systems of Cl-, Br- and SO42- for growth rate of hematite particle aggregate as follows: v(Cl-)<v(Br-)<v(SO42-)。 critical coagulation concentration (CCC) for Cl-, Br- and SO42-were 99.2 mmol L-1,17.7 mmol L-1 and 0.1 mmol L-1. Therefore, that showed: CCC(Cl-)> CCC(Br-)> CCC(SO42-).(4) Obtaining the activation energy varies with the electrolyte concentration, when the electrolyte concentration is less than the CCC, there are significant differences in activation energy for the three systems, that show:△E(Cl-)>△E(Br-)>△E(SO42-). anion specific effects of growth rate,CCC and active energy for hematite colloid aggregation. anion specific effects order:Cl-<Br-<SO42-.