Mössbauer investigation of the transformations of the iron minerals in oil shale during retorting

Abstract

Iron phases in raw and retorted shales have been studied from the TOSCO II, Paraho, and Lawrence Livermore Laboratory (LLL) 125 kg retorting processes by Mössbauer effect spectroscopy. Using the Mössbauer effect, changes in the iron mineralogy during retorting were monitored. Results show that the pyrite fraction in the TOSCO II, and LLL hydrogen run S-9 samples underwent changes during retorting whereas the iron-containing carbonates did not. As in other pyrolysis processes, FeS 2 breakdown is affected by the presence of organic matter. Hydrogen released by the indigenous kerogen acts to reduce pyrite to the magnetic sulphide pyrrhotite. In all of the retorts containing oxygen, carbonate breakdown was observed prior to pyrite oxidation. Free oxygen is introduced to several retorts. The iron minerals within these systems eventually become a mixture of the oxides hematite and magnetite. This study demonstrates that alteration of specific iron minerals during retorting may be controlled by varying the internal retorting conditions.