Mössbauer Studies of Adsorption and Thermal Treatment of Fe³⁺ Ions on Silica-Gel, Al₂O₃ and Natrolite

Abstract

Mössbauer studies of Fe³⁺ ions on Si-gel, Al₂O₃ and a natural zeolite mineral natrolite, treated with Fe(NO₃)₃ and FeCl₃ solutions and subsequently heated in steps upto 950°C, have been carried out to study the adsorption and change of chemical species caused by thermal treatment. It is inferred that iron ions exist as superparamagnetic particles of α-FeOOH on all the surfaces studied upto 200°C. Further heating to 400°C, transforms it partly into fine particles of α-Fe₂O₃, the conversion however, becoming complete by 600°C. At 800–950°C, Fe³⁺ enters the Al₂O₃ lattice substitutionally, while in the case of Si-gel, α-Fe₂O₃ particles register an increase in crystallite size only. In the case of natrolite, there results particles of α-Fe₂O₃ with size greater than 150 Å, when heated to 800–950°C.