The Nature and Properties of Iron-Containing Nanoparticles Dispersed in an Aluminosilicate Matrix of Cenospheres

The forms of iron in the composition of cenospheres prepared from energy ashes are investigated using the electron paramagnetic resonance (EPR) method, Mössbauer spectroscopy, and thermodynamic analysis. Cenospheres of controlled composition are produced by sieve, gravimetric, and magnetic separation. It is established that iron in two states (Fe³⁺, Fe²⁺) enters into the cenosphere composition. At an Fe₂O₃ content of 3–4 wt %, iron(III) predominantly occurs in two forms: single ions in the glass and particles of the superparamagnetic phase with a spinel structure. These particles are 30–50 Å in size and are dispersed in aluminosilicate glass. The sublattices of the superparamagnetic spinel are diamagnetically diluted with Mg²⁺ and Al³⁺ ions. At an Fe₂O₃ content of higher than 7 wt %, cenospheres also contain a magnetic phase based on defect magnetite.