Kinetic Study of the Ferrocolumbite Dissolution in Medium Hydrofluoric Acid in an Autoclave

M. RODRIGUEZ; O QUIROGA; M. DEL C. RUIZ

Río de Janeiro (Brasil)

Congreso; 2nd Mercosur Congress on Chemical Engineering. 4th Mercosur Congress on Process Systems Engineering; 2005

UFRJ, IME, UERJ, UNS, UNL, OXITENO, PETROBRAS, ETC.

In this work it has been investigated the recovery of Nb, Ta, Fe and Mn from ferrocolumbite with hydrofluoric solutions. The experimental tests were carried out in a pressure reactor. The influence of several parameters has been studied in order to deduce the kinetic of the dissolution of a ferrocolumbite and each one of the oxides present in this mineral. The particle size of the mineral was -44 µm and the solid-liquid ratio was 1.82% wt/v; the temperature range was between 348 to 493 K. The reagents and products were characterised by means of X-ray fluorescence (XFR), X-ray diffraction (XDR), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), and BET specific surface area. From the experimental results it was determined that the stirring speed had not an important effect on the dissolution of the mineral. The leaching rate of ferrocolumbite increases with the concentration of HF and the reaction temperature. The diffractograms of the residues did not show any structural change respect to the mineral. The analysis by SEM and EDS, of some residues in which the conversion was approximately 50%, indicated a selective attack on certain particles of the mineral and on certain zones of a particle. This attack was an irregular located-type attack. The treatment of the experimental data was carried out using the MODELADO software. The better model that represent the dissolution of ferrocolumbite and each one of the oxides in the mineral is the following: ln (1-X)= -b1 [ln(1+b1) - ((b1 t)/(1+ b1 t))] The previous model is based on "nucleation and growth of nuclei" theory. This model physically represents the attack observed by SEM and EDS on the residues. Keywords: Kinetics; Hydrofluoric acid and Ferrocolumbite dissolution.