Incorporation of Technetium into Spinel Ferrites

摘要

Technetium (~(99)Tc) is a problematic fission product for the long-term disposal of nuclear waste due to its long half-life, high fission yield, and to the environmental mobility of pertechnetate, the stable species in aerobic environments. One approach to preventing ~(99)Tc contamination is using sufficiently durable waste forms. We report the incorporation of technetium into a family of synthetic spinel ferrites that have environmentally durable natural analogs. A combination of X-ray diffraction, X-ray absorption fine structure spectroscopy, and chemical analysis reveals that Tc(Ⅳ) replaces Fe(Ⅲ) in octahedral sites and illustrates how the resulting charge mismatch is balanced. When a large excess of divalent metal ions is present, the charge is predominantly balanced by substitution of Fe(Ⅲ) by M(Ⅱ). When a large excess of divalent metal ions is absent, the charge is largely balanced by creation of vacancies among the Fe(Ⅲ) sites (maghemitization). In most samples, Tc is present in Tc-rich regions rather than being homogeneously distributed.