Diffusion of Neptuiyl(V)- and Pertechnetate Ions in Marine Sediments

Abstract

The diffusion of the ²³⁵NpO₂⁺ and ^95m TCo₄⁻ -ions has been measured directly in sample cylinders of two different sediments from the floor of the deep sea. In smectiterich sediment not shielded from contact with atmospheric oxygen the following values were obtained for the effective diffusion coefficients of neptunyl- and pertechnetateions, respectively: D_eff(N_pO₂⁺) = 1.5 × 10⁻¹² m² s⁻¹ and D_eff(TcO₄⁻) = 3.2 × 10⁻¹⁰ m² s⁻¹. Under anoxic conditions in sediment with known reducing properties, the pertechnetate ion appears to undergo slow reduction and the effective diffusion coefficient of the reduced species of D_eff(Tc,red)= 1.1 × 10¹⁴ m² s⁻¹ reflects a substantial decrease of the mobility of the lower-valent technetium.