Selective recovery of niobium and tantalum from low-grade concentrates using a simple and fluoride-free process

Abstract

The current hydrometallurgical processes used for niobium and tantalum recovery are operated in strongly acidic and fluoride-containing solutions. To avoid the use of these highly toxic media, a fluoride-free process was developed to recover Nb and Ta from low-grade industrial concentrates. The process is based on the caustic conversion of the raw material with NaOH(aq) at atmospheric pressure and at relatively low temperature which then allows the selective dissolution of sodium hexaniobates. Finally, Nb is recovered as purified hydrous oxide by acidification of the hexaniobate solution. The influence of many industry-relevant parameters (temperature, initial NaOH concentration, residence time, impurity content in the initial concentrate, pH of precipitation) was studied in order to optimize the recovery and purification of the valuable metals. Finally, the process was validated in continuous operation at a pilot scale. High recovery yields for Nb and Ta (65%) were obtained as well as high separation factors toward Ti, Fe, P, S, Th and U. The results demonstrate that it is possible to recover and purify Nb and Ta from industrial concentrates without using fluoride solutions.