Ion Adsorption into the Hydrothermal Regime: Experimental and Modeling Approaches

This chapter provides an overview of the experimental and modeling approaches that are used to study ion adsorption and zeta potential phenomena into the hydrothermal regime. There are many hydrothermal environments where the phenomena are important, including during the transport and deposition of ore-forming fluids, in the cooling circuits of fossil- and nuclear-powered steam generators, for the development and characterization of high temperature proton-exchange membrane fuel cells, and in the near-field environments of high-level nuclear waste repositories. The hydrogen electrode concentration cell (HECC) design and configuration are used in these studies. Multivalent cations and anions, and any other solution species that strongly adsorb at the mineral/water interface induce much larger release or uptake of H + than the relatively inert background electrolytes, MX, even at concentrations as low as 10 –4 to 10 –3 molal. Electrokinetic phenomena generally refer to the tangential motion of liquids with respect to charged solid surfaces, and the measurement of these phenomena provide important information on the structure of electrical double layers. Electrophoresis is the most suitable electrokinetic method to study particulate solids. A complete surface complexation model (SCM) consists of both mass-law expressions that describe ion binding to surface functional groups, and electrostatic correction terms for the mass law expressions derived from electrical double layer (EDL) theory, because the ion adsorption process results in charge development at the interface.