Investigation of the Method for Measuring the Surface Property Parameters of Variable Charge Minerals Using Ion...

In this study, the surface property parameters of non-swelling variable charge minerals, kaolinite and goethite, were determined using the ion-selective electrode method. The effects of experimental conditions, such as pH, ion concentration ratio, and liquid addition method, on the measurement results were clarified to provide a reference for accurately assessing the surface properties of variable charge materials. The research employed ion adsorption equilibrium experiments under varying pH levels, ion concentration ratios, and liquid addition methods. A combined surface property analysis was conducted using K⁺ and Ca²⁺ as indicator ions to characterize surface parameters. The results were compared with the specific surface area obtained via the BET method to verify accuracy, thereby identifying optimal measurement conditions. The study led to the following five conclusions. (1) pH significantly affected the adsorption amount and ratio of indicator cations, thereby influencing the accuracy of surface property parameters. (2) The addition method and concentration ratio of electrolytes influenced the measurement accuracy by affecting the adsorption state and equilibrium time of the two indicator cations. (3) For kaolinite, the optimal initial pH ranged from 7.5 to 8.5 in the KOH + Ca(OH)₂ system and from 8.0 to 8.5 in the KOH + CaCl₂ system, while the equilibrium pH was 7.5 to 8.0 in both systems. The optimal ion concentration ratios were c_K:c_Ca = 2:1 and 9:1, respectively. (4) For goethite, the optimal initial and equilibrium pH values were 8.5 to 9.0 and 7.5 to 8.0, respectively, in both KOH + Ca(OH)₂ and KOH + CaCl₂ systems. The optimal ion concentration ratios were 4:1 and 20:1, respectively. (5) Through comparison, the optimal initial pH for measuring the two variable charge minerals was determined to be 8.5 ± 0.1, with the optimal equilibrium pH at 7.5 ± 0.1. However, the concentration ratios varied significantly, suggesting the need for systematic research by adjusting a series of ion concentration ratios based on the initial pH.