Acid leaching and thermal treatments in the obtaining of mixed oxides of Nb and Ta from ferrocolumbite

Abstract

In this paper, the study of an acid and thermal treatment in a mixture of niobium and tantalum oxides obtained from columbite mineral was performed. Initially, the mineral was physically prepared by milling and sifting, followed by characterization by X-ray diffraction (XRD), X-ray fluorescence (XRF) and Scanning Electron Microscope (SEM). Subsequently, the mineral performed an acid leaching in order to remove iron and manganese present in its composition. A second acid leaching was necessary to eliminate the persistent cassiterite impurity by precipitation of Nb and Ta hydrated oxides. These oxides were characterized by XRF, XRD and SEM. Then the oxides were calcined at 800 °C, 900 °C and 1000 °C at different heating rates and calcination times to study their crystallization. The mixed oxides were characterized by XRF, XRD, SEM and nitrogen adsorption (BET method). The influence of heating rate was verified at 800 °C. An increase in crystal size was observed when the rate was reduced from 10 °C.min−1 to 5 °C.min−1. Greater crystallinity and formation of peaks related to the change of phase from hexagonal to orthorhombic were observed when the temperature was raised from 800 °C to 900 °C. At the temperature of 1000 °C, intermediate and low peaks related to formation of monoclinic phase of niobium pentoxide were observed. The change in calcination time from 5 h to 10 h at 1000 °C caused reduction in Nb2O5 to NbO2 and a decrease in crystal size and hence an increase in the surface area. The oxides heated at 900 °C showed the largest surface area.