Activation and detoxification of UICC crocidolite: the effect of conversion of oxidation state of iron on the toxicity of the fibres

Detoxification of crocidolite, an asbestiform riebeckite with a coating of ferric salt, converted some of the ferrous ions into ferric ions and therefore decreased the activity of the fibres to catalyse the reduction of oxygen and peroxide. The H2-activation of crocidolite fibres on the other hand, changed some of the ferric ions into ferrous ions and therefore increased the capacity of the fibres to catalyse these two reactions. Moessbauer spectroscopy (MS) combined with wet chemical analysis, X-ray diffraction, X-ray fluorescence, and neutron activation analysis enabled us to determine the site occupancies of iron and magnesium in UICC (Union Internationale Contre le Cancer) crocidolite and the ratio of the recoil-free fractions f(Fe2+)/f(Fe3+)=0.86±0.07. These results and further MS studies with detoxified and activated fibres explained the effect of the two processes on the activity of iron in the fibres. (orig.)