Extraction of tantalum and niobium from tin slags by chlorination and carbochlorination

Chlorination and carbochlorination of tantalum and niobium low-grade concentrate (LGC) and high-grade concentrate (HGC), obtained by leaching of tin slag, were studied using Cl₂ + N₂ and Cl₂ + CO + N₂ gas mixtures. Thermogravimetric analysis and conventional boat experiments were performed between 200 °C and 1000 °C. Chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to characterize the samples and reaction products. Chlorination of LGC led to the recovery of about 95 pct of tantalum and niobium compounds at 1000 °C. However, the tantalum and niobium chlorinated compounds were contaminated by chlorides of Fe, Mn, etc. For HGC, chlorination at 1000 °C allowed the extraction of about 84 and 65 pct of the niobium and tantalum compounds, respectively. The recovered condensates were composed of pure tantalum and niobium chlorinated compounds. The apparent activation energies E _a for the chlorination of LGC and HGC, between 850 °C and 1000 °C, were 166 and 293 kJ/mole, respectively. At temperatures lower than 650 °C, the apparent activation energies for the LGC and HGC carbochlorination were 116 and 103 kJ/mole, respectively. Total extraction of the tantalum and niobium compounds was achieved by the carbochlorination of the LGC at 1000 °C. The generated tantalum and niobium chlorinated compounds were contaminated by the chlorides of Fe, Mn, Al, and Ca. The carbochlorination of the HGC at 500 °C allowed complete extraction and recovery of pure tantalum and niobium compounds. These results confirm the importance of obtaining an HGC from tin slag before its subsequent chlorination. The carbochlorination of such a concentrate could be an efficient process for the recovery of relatively pure tantalum and niobium chlorinated compounds at low temperatures.