SURFACE-IONIZATION AND COMPLEXATION AT THE SPHALERITE WATER INTERFACE.1. COMPUTATION OF ELECTRICAL DOUBLE-LAYER PROPERTIES OF SPHALERITE IN A SIMPLE ELECTROLYTE

A triple-layer site-binding model was used to describe the electrical properties of the sphalerite/water interface. The assumptions (for exa mple, that the capacitance of the outer layer varies according to the zeta potential) are considered more realistic than those in previous m odels, and the calculation procedure is easier. The zeta potential, su rface 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 pro cedure was shown to be an effective method for solving surface and sol ution equilibra including charge and mass balances. The surface ioniza tion constants of sphalerite were determined by fitting zeta potential data. Using electrokinetic data and knowing surface ionization consta nts, 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 boehmite/water system and the ability to predict the surface c harge-pH relationship successfully is illustrated. (C) 1995 Academic P ress, Inc.