Abstract
The recovery of Nb(V) and Ta(V) from alkaline solutions was investigated using calcium-bearing reagents (CaCl2(aq), Ca(CH3COO)+(aq), Ca(NTA)−(aq), Ca(EDTA)2−(aq), CaCO3(s) and Ca(OH)2(s)) at 25°C. It was found that hexaniobate and hexatantalate ions (HxNb6O19x−8 and HxTa6O19x−8; 0≤x≤3) can be quantitatively precipitated with calcium chloride, calcium acetate or calcium hydroxide when the ratio (Ca/M)initial is at least 0.4mol/mol (M=Nb, Ta). Precipitation yields higher than 95% are obtained for solutions that contain, as low as, 3∗10−4mol/L of Nb and 1∗10−4mol/L of Ta. Moreover, the proposed precipitation method can be operated in a wide pH range and consumes two times less reactant than the classical way for recovering Nb and Ta which consists of neutralizing their alkaline solutions with a mineral acid. The amorphous calcium niobate concentrate was characterized by elemental analysis (ICP-OES), thermogravimetric analysis (TGA-MS) and Raman spectroscopy and the solid phase K3Ca2.2(H0.6Nb6O19)·nH2O was identified under specific conditions.
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