MINERALIZING ACTION OF IRON IN AMORPHOUS SILICA

The mineralizing action of iron in amorphous silica was investigated b y firing mixtures of silica gel and iron oxides at 1100 and 1150 degre es C. Silica gel did not crystallize in the absence of ferrous ion bel ow 1200 degrees C. When silica gel mixed with ferrous oxalate was heat ed at 1100 degrees C in a mildly reducing atmosphere(N-2, CO2, CO), qu artz, cristobalite and ferrous silicate (Fe2SiO4) were formed. Applica tion of the reducing atmosphere from room temperature promoted the cry stallization to quartz, while that from the soaking temperature after heating in N-2 accelerated the formation of cristobalite. Chemical ana lysis revealed that the N-2 atmosphere acted as a mildly oxidizing atm osphere to FeO possibly due to the coexistence of water vapor released from silica gel and impurity O-2. Furthermore, tentative crystallizat ion mechanism is proposed where mildly reduced and mildly oxidized Fe2 SiO4, produced nuclei for quartz and cristobalite, respectively.