Surface Ionization and Complexation at the Sphalerite/Water Interface: I. Computation of Electrical Double-Layer Properties of Sphalerite in a Simple Electrolyte

Abstract

A triple-layer site-binding model was used to describe the electrical properties of the sphalerite/water interface. The assumptions (for example, that the capacitance of the outer layer varies according to the zeta potential) are considered more realistic than those in previous models, and the calculation procedure is easier. The zeta potential, surface charge density, and surface species distribution were calculated based on this model using MATLAB software and were in good agreement with the experimental data. The Broyden-Fletcher-Goldfarb-Shanno(BFGS) quasi-Newton method with a mixed quadratic and cubic line search procedure was shown to be an effective method for solving surface and solution equilibra including charge and mass balances. The surface ionization constants of sphalerite were determined by fitting zeta potential data. Using electrokinetic data and knowing surface ionization constants, surface potential and surface species as a function of pH of the solution were evaluated. The same approach was used on published data for the bochmite/water system and the ability to predict the surface charge-pH relationship successfully is illustrated.