Tantalum recovery from alkaline leachates based on magnesium hexatantalate intermediate precipitate

A new approach for the recovery of tantalum (Ta(v)) from alkaline solutions is presented, with the expected environmental benefits. This method is based on magnesium-induced precipitation to extract tantalum present as polyoxotantalates (POTas) from alkaline leachates. We obtained a tantalum precipitation yield of over 99% by introducing a Mg/Ta₆ ratio of ≥4 into the solution. We show that Ta(v) ions, as hexatantalate species, precipitate in the presence of magnesium ions to form Mg₄Ta₆O₁₉·xH₂O crystalline phases with two different structures, with x = 16.1 or 24.4. The magnesium tantalate precipitate is then dissolved in ethylenediaminetetraacetic acid (EDTA) to release Mg(ii) in the form of an Mg(EDTA)^2- complex. The final product, amorphous hydrated tantalum pentoxide (Ta₂O₅·nH₂O), is obtained by neutralizing the Mg-EDTA-POTa solution to pH 7. After thorough washing with dilute acid and ultrapure water and calcination, tantalum pentoxide is obtained.