Chlorination and carbochlorination of tantalum and niobium low-grade concentrate (LGC) and highgrade concentrate (HGC), obtained by leaching of tin slag, were studied using Cl 2 ϩ N 2 and Cl 2 ϩ CO ϩ N 2 gas mixtures. Thermogravimetric analysis and conventional boat experiments were performed between 200 ЊC and 1000 ЊC. 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 ЊC. However, the tantalum and niobium chlorinated compounds were contaminated by chlorides of Fe, Mn, etc. For HGC, chlorination at 1000 ЊC 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 ЊC and 1000 ЊC, were 166 and 293 kJ/mole, respectively. At temperatures lower than 650 ЊC, 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 ЊC. 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 ЊC 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.

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of chlorination and carbochlorination of pure Nb 2 O 5 and Ta 2 O 5 were studied by thermogravimetric analysis between 385 ЊC and 1000 ЊC using Cl 2 -N 2 and Cl 2 -CO-N 2 gas mixtures. Standard free energy changes of the reactions and phase stability diagrams of Nb-O-Cl and Ta-O-Cl systems were calculated. The chlorination reaction order, for both oxides, with respect to Cl 2 in the Cl 2 -N 2 gas mixture was 0.82. The apparent activation energies (E a ) for Nb 2 O 5 chlorination were 208 and 86 kJ/mole for temperatures lower and higher than 850 ЊC, respectively. The experimental data could be described by a shrinking sphere model between 700 ЊC and 1000 ЊC. The chlorination mechanism, between 700 ЊC and 850 ЊC, was likely controlled by the chemical reaction. For T Ͼ 850 ЊC, the overall Nb 2 O 5 chlorination rate was affected by the allotropic transformation of the Nb 2 O 5 T form to M form. Between 925 ЊC and 1000 ЊC, E a for Ta 2 O 5 chlorination was 246 kJ/mole. In this case, the most appropriate model was also that of shrinking sphere suggesting that the chlorination of Ta 2 O 5 was controlled by the chemical reaction. For both oxides, the carbochlorination reaction order with respect to Cl 2 ϩ CO partial pressure, in the gas mixture, was about 2. The mathematical analysis of carbochlorination data indicates that Nb 2 O 5 and Ta 2 O 5 reactions could be described by shrinking sphere or cylinder, respectively. Below 600 ЊC, the E a values of Nb 2 O 5 and Ta 2 O 5 carbochlorination were 74 and 110 kJ/mole, respectively. Chemical reaction was probably the rate controlling step in both cases. An anomaly characterized by a decrease of the reaction rates occurs in the Arrhenius plots between 600 ЊC and 800 ЊC. This anomaly could be attributed to the thermal decomposition of COCl 2 formed in situ during the carbochlorination.

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