According to Ringwood (A.E. Ringwood, W. Sinclair, and G.M. McLaughlin, Nuclear Waste Immobilization, Lawrence Livermore Laboratory, Livermore, Rept. UCRL-15147 (1979)), the iron oxidation state is important in controlling, the spinel mineralogy and composition if the amount of titania (TiO/sub 2/) consumed in spinel formation is to be minimized in favor of the formation of the Synroc phases, zirconolite, perovskite, and nepheline. In our redox calcination studies we observed that the iron oxidation state of FeO/Fe/sub 2/O/sub 3/ can be controlled by the redoxcalcining atmosphere. In a CO atmosphere, the oxidation state was reduced to less than 7 wt % Fe/sub 2/O/sub 3/. With appropriate CO/sub 2//CO gas mixtures the resultant iron oxidation states were in the range of 45 to 59 wt % Fe/sub 2/O/sub 3/. Direct rotary redox calcination of spray dried powder at 600/sup 0/C, without prior air calcination, showed increased redox efficiency when compared to powder that had been previously air calcined at 650/sup 0/C. We believe this is caused by a reduction in particle size. Rotary calcination at 800/sup 0/C in argon has no measurable reduction affect on the iron oxidation state of Synroc D powder.