Proton transfer studies in the ferric oxyhydroxides. Part 1.—Hydrogen exchange between α-FeOOH and water

Abstract

The rates of hydrogen exchange between tritiated water and α-FeOOH have been measured in the temperature range 36–94°, using a Berthier ratio of 0.01 (which is the ratio of exchangeable atoms in the solid and liquid phases), and found to be independent of pH. The activation energy for self-diffusion and the pre-exponential factor D_o of the self-diffusion coefficient were calculated from the initial parabolic portions of the kinetic curves as 8.2±1.3 kcal mole^–1 and 6.5 × 10^–13 cm² respectively. A mechanism involving hydrogen-bond rupture and rotation of a defect water molecule within the solid is proposed. The anisotropic diffusion coefficients implied by such a mechanism are calculated.