Treatment of temperature dependence of interfacial speciation by speciation codes and temperature congruence of oxide surface charge

摘要

In several published articles dealing with the temperature dependence of surface charging of and solute adsorption at mineral/water interfaces that involve surface complexation modelling via the purely diffuse layer model or the triple layer model, speciation codes were employed that do not allow specification of temperature in the input and therefore no explicit temperature variation. Omitting temperature variation should cause errors in the calculations. A priori it is expected that the temperature dependence of the dielectric constant of water, changes in volume (and thus molar concentration), and the appearance of absolute temperature in the electrostatic term of surface complexation models cannot be simply neglected. Calculations involving the models without temperature correction and with temperature correction, however, show that in the case of surface charging, no noticeable difference arises. In the present work we show that this arises from compensation of the respective temperature dependencies of the different variables. Our considerations and calculations explain why previous omission of temperature dependence has gone unnoticed. We also discuss temperature congruence of surface charging, i.e. master curves that do not depend on temperature, when the charge is normalized with respect to the point of zero charge at the respective temperatures. We conclude that temperature congruence is probably not a general phenomenon. Consequently, the validity of assuming temperature congruence has to be verified. We suggest a simple way to do so.