Role of Fe compounds in light aggregate formation from a reservoir sediment.

A one-step thermal process at 1050 degrees C and 1150 degrees C including bloating and sintering reactions produced lightweight aggregates (LWAs) with an apparent particle density of 2.08 and 1.18gcm(-3), respectively, from pellets made of the sediment of a local reservoir. The roles of Fe compounds occurred in the sediment in bloating mechanism were determined with X-ray absorption spectroscopy (XAS) technique. About 59at% of the total Fe is in forms of Fe(2+) in the raw sediment; whereas most Fe was oxidized to Fe(3+) in all LWAs, except in core part of the LWA produced at 1150 degrees C. The bloating reactions occurred in the core of the 1150 degrees C LWA is suggested to be mainly associated with the decomposition of FeSO(4) into FeO with a concomitant release of SO(2), SO(3), and O(2); the valence state of Fe was not changed. The generally accepted mechanism - the chemical reduction of Fe(2)O(3) component to FeO with a release of O(2) is responsible for the bloating phenomenon - is not observed in present study.