I. V. Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials of Russian Academy of Sciences of Kola Science Center (ICTREMRM KSC RAS), Apatity, Russia

V. G. Mayorov, Senior Researcher
A. I. Nikolaev, Deputy Director on Scientific Work, e-mail : nikol_ai@chemy.kolasc.net.ru
L. A. Safonova, Third Category Technologist

Commercial solvent extraction, separation and purification of tantalum and niobium are commonly based on fluoride systems. Due to scarcity of niobium and tantalum-rich resources, more attention nowadays is being paid to extracting tantalum and niobium from theprocesses of rare-earth titanium niobates and other unconventional minerals. It follows from the literature that many of the impurity elements, such as Ta and Nb, can form fluorometallate complexes of the H_xMeF_y and other types. These acids are strong and readily dissociating, which promotes the growth of hydrogen ions concentration. The latter improves the extraction of both Ta, Nb, and the impurities. Hence is the interest to the interference of niobium and tantalum fluoride complexes and associated impurities on niobium and tantalum extraction in complex systems. It has been shown that the extraction of P, Mo and W is considerably improved in the presence of Ti and Si. These elements are impurities hard to separate. Ti and Si are always present in unconventional rare-metal minerals; moreover, they are sually present in great quantities. It has been determined that in terms of the effect on P, Mo and W extraction, the Ti and Si fluorometallate acids are comparable with sulphuric acid, or exceed it. Solvent extraction of 0.05 mol/L molybdenum by tributylphosphate from fluoride solutions with titanium, niobium and tantalum contents up to 2 mol/L has been investigated. The molybdenum extraction from such solutions was found to diminish in the series titanium < niobium < tantalum, which agrees with increasing extraction level of these elements. At the contents of titanium 1 mol/L and niobium 0.5 mol/L, the maximal levels of molybdenum extraction were 90 and 28%, respectively. In the presence of titanium, the molybdenum extraction from niobium and tantalum solutions increased to 89 and 46%, respectively. These research findings are of practical interest for the niobium and tantalum solvent technology. At high titanium contents in mother solution, the molybdenum extraction can be suppressed by using solutions with a maximal tantalum and niobium concentration.

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