UTJECAJ ADITIVA NA KRISTALIZACIJU HEMATITA IZ GUSTIH VODENIH SUSPENZIJA AKAGANEITA

THE INFLUENCE OF ADDITIVES ON THE

CRYSTALLIZATION OF THE HEMATITE FROM DENSE AKAGANAITE AQUEUS SUSPENSIONS

Mark ŽIC, Mira RISTIĆ, Svetozar MUSIĆ

Zavod za kemiju materijala, Institut “Ruđer Bošković”, P. p.180, 10000 Zagreb

Hematite (a-Fe2O3) is widespread mineral in nature (rocks, sediments, soils). It is also important material in many technological applications. Chemical and physical properties of a-Fe2O3 depend on the route of chemical synthesis. In the present work, the hydrothermal crystallization of a-Fe2O3 from dense b-FeOOH suspensions was investigated. a-Fe2O3 particles in the form of double spheres with the ring were formed at 160 oC for 24 h. The orientation effect of a-Fe2O3 subunits in double spheres with the ring was observed. a-Fe2O3 double spheres with the ring also showed two narrow particle size distributions. b-FeOOH transformed to a-Fe2O3 by the dissolution/repreciptation mechanism. The influence of inorganic anions on the phase composition, size and morphology of the particles during the transformation b-FeOOH to a-Fe2O3, was also investigated. With increased concentration of phosphate anion the crystallization of a-Fe2O3 was strongly suppressed. Tendency to the formation of ferrihydrite was noticed. The size and morphology of a-Fe2O3 particles were strongly influenced with added ammonium amidosulphonate (AAS). Up to 24 h of autoclaving the peanut-type a-Fe2O3 particles of good uniformity were obtained. They consisted of laterally arrayed primary aFe2O3 particles. Porosity of peanut-type a-Fe2O3 particles was visible. With prolonged autoclaving time up to 72 h and starting concentration 0.1 M AAS, a gradual formation of interconnected (with neck) double cupolas was observed. The cross-section of these cupolas showed that they consisted of linear chains of small interconnected a-Fe2O3 particles directed from the center towards the surface of cupola.

References:

[1] Mark Žic, Mira Ristič, Svetozar Musić, J. Alloys Comp. 464 (2008) 81-88.

[2] Mark Žic, Mira Ristič, Svetozar Musić, J. Alloys Comp. 466 (2008) 498–506.

[3] Mark Žic, Mira Ristič, Svetozar Musić, J. Mol. Struct. in press.