The Influence Of Additives On The Crystallization Of The Hematite From Dense Akaganaite Aqueus Suspensions

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 a-Fe2O3 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.