A study on the mechanism of calcium ion in promoting the sedimentation of illite particles

Abstract

Clay minerals are the main reason why coal slime water is difficult to settle. For the exploration of the influence of Ca2+ on the sedimentation effect of illite, the adsorption characteristics of illite were investigated under different Ca2+ concentrations. After adsorption equilibrium, the sedimentation test was carried out, and the changes in the surface properties of illite particles were analyzed by measuring Zeta potential and contact angle. The Theory of EDLVO was adopted to calculate the interaction energy between illite particles. The results showed that with the increase of Ca2+ concentration, the equilibrium adsorption capacity of illite increased, and the adsorption equilibrium was basically achieved at 60 min. The adsorption process was in accordance with the quasi-second-order kinetic model and Langmuir isothermal adsorption model. The sedimentation effect of illite was obviously improved after adsorption of Ca2+. When the concentration of Ca2+ was 10 mmol/L and pH = 8, the sedimentation rate was 92.5%. With the increase of Ca2+ concentration, the absolute value of the Zeta potential of illite after adsorption equilibrium decreased continuously, and the contact angle increased continuously. According to the Theory of EDLVO, the polar force is the dominant force affecting the interaction between particles. As the concentration of Ca2+ increases, the van der Waals attraction force between illite particles increases, the electrostatic and polar repulsive forces weaken, and the total interaction energy gradually decreases, indicating that Ca2+ can promote the agglomeration of illite particles, which is of benefit to the clarification of coal slime water.