PROTONATION OF SOIL PARTICLE SURFACES: KINETICS

Abstract

A kinetic process was investigated by which H+ ions interact with soil surfaces giving rise to a positive electric charge distribution. A two-step process took place in the range of time examined. A first rapid step was always followed by a relatively slower step, and a first-order kinetic equation was applied to describe this second step of the process. The values of specific rate, calculated at different initial H+ ion activities and two different amounts of soil, indicated that a diffusion-controlled mechanism was governing the rate of the slower step and consequently the overall rate of the process. Protonation and deprotonation specific rates were also calculated in the presence of varying concentrations of supporting electrolytes. It was found that the specific rate was dependent on either the structure of the electric double layer formed on soil surfaces in the presence of electrolyte, or on the particular surface electric charge distribution of the examined soil. Key words: Protonation kinetics, specific rate, diffusion phenomena, permanent charge, pH-dependent charge, diffuse double layer