Room temperature Mössbauer spectrum of fly ash-recycled glass (FARG), prepared with more than 86 mass% of fly ash and less
than 14 mass% of Fe2O3, comprises two types of doublets due to Fe(II) and Fe(III) of magnetite nanoparticles. Isothermal annealing of fly ash-recycled
glass at 1100 °C for 60 minutes results in a precipitation of ferrimagnetic magnetite phase having an internal magnetic field
of 46.4-48.2 T. When the Fe2O3 content is equal to or more than 14%, room temperature Mössbauer spectrum of FARG shows a magnetic hyperfine structure due
to a magnetite phase, in addition to two doublets due to Fe(II) and Fe(III). An increase in the electric conductivity is observed
from the order of 10-8 to 10-6 S . cm-1 after heat treatment at around the crystallization temperature. This can be ascribed to an improved step-by-step electron
hopping from Fe(II) to Fe(III) of distorted FeO4 tetrahedra in the three-dimensional glass network.