Fractionation of Zirconium-Hafnium in Ferromanganese Crusts

Abstract

We have attempted to clarify the accumulation/fractionation mechanisms of Zr and Hf in ferromanganese crusts (FMCs) by performing radio-Zr and radio-Hf adsorption experiments with XAFS for synthesised and natural samples obtained from seamounts. The observed Zr chemical states in natural FMCs resembled that for coprecipitations with ferrihydrite and δ-MnO₂. In the case of the adsorption experiments for Zr and Hf to ferrihydrite and δ-MnO₂, it was found that the Hf had larger K_D values for both minerals than Zr-DFO. In this case, the observed bond length of Hf-O was slightly shorter than that of Zr-O in the synthesized minerals.