, Vol. 10, No.3, pp.245-256, 2011
and Folahan A. Adekola
Department of Chemistry, Faculty of Applied Sciences, Cape Peninsula University of
Technology, P.O. Box 652, Cape Town, South Africa.
Department of Chemistry, University of Ilorin, P.M.B 1515, Ilorin, Nigeria.
* Corresponding author:
Niobium is a rare, soft, grey and ductile transition metal with the symbol Nb. It was discovered
superconducting magnets, commemorative coins, medical device, jewelries, arc-tube seals,
capacitors, optical lens, barometer, nuclear applications, superconducting RF cavities,
electromagnetic radiation detector and it is used in nickel-, cobalt-, and iron-based super-alloys
which are used in jet engines components, rocket sub-assemblies, heat resistant and combustion
equipments [2, 3]. Tantalum was discovered by Anders Gustaf Ekeberg (1767-1813), in 1802 [1,
4]. It is a rare, hard, blue-gray, and lustrous transition metal, with the symbol Ta. Tantalum is
Olushola S. Ayanda and Folahan A. Adekola Vol.10, No.3
used in alloys and wires, surgical instruments, reaction vessels and pipes, ultra high frequency
used in capacitors as platinum substitute. Columbite, tantalite, columbite-tantalite (Coltan),
pyrochlore, and euxenite constitute the major primary sources for niobium and tantalum and are
located in Canada, Brazil, Nigeria, Zaire and Russia [5, 6].
These interesting elements are chemically similar and are associated with each other in nature.
oxides and due to their nearly identical atomic radii. For many years, the commercial technology
for separating tantalum from niobium involved the fractional crystallization of potassium
heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, a process
discovered by Jean Charles Galissard de Marignac in 1866. The method has been supplanted by
solvent extraction from fluoride-containing solutions .
A large number of chemical treatment procedures for the breakdown of primary sources have
been developed. Some of these have been adopted for commercial production while others have
been tested on a fairly large scale. There are yet a few others that have been tested only on a
laboratory scale. All these processes can essentially be divided into reduction to metallic or
compound form, chlorination, alkaline fusion and acid dissolution (leaching) .
One of the simplest methods for the breakdown treatment of primary concentrates of niobium
or carbon , with or without the addition of iron or iron oxides termed aluminothermic and
carbothermic reduction reaction.
2.1.1 Aluminothermic and carbothermic reduction reactions
Aluminothermic reduction reaction is highly exothermic and is thermodynamically feasible even
formation less negative than that of alumina are reduced to metallic state and join the ferroalloy,
whereas others report to the slag phase.
The carbothermic reduction reaction on the other hand, is thermodynamically feasible at high
C) and is highly endothermic in nature. Moreover, niobium
A Review of Niobium-Tantalum Separation 247
Thus, the product in the case of aluminothermic reduction reaction is usually a ferroalloy,
containing practically all of the niobium and tantalum, together with many of the other elements
that are present in the starting concentrate
Chlorination is a process for breakdown of ores and concentrates of many of the refractory
of chlorination, include the high reactivity of chlorine, relative ease in gasifying many of the
constituents of the concentrates due to high volatility of most of the chlorides, and high water
solubility of most of the chlorides. The chlorides formed can also be readily separated due to
differences in their vapour pressures, or due to differences in reactivity with oxygen and/or water
vapour and in their reducibility with hydrogen.
Thus, chlorination process is suitable not only for breakdown of the ore or concentrate but also
reduction to metallic form.
Alkaline fusion is also one of the processes used for the breakdown of mineral ores concentrate.
carbonate, and a mixture of these, with or without addition of oxidizing agent such as sodium
nitrate and sodium peroxide have been used by a large number of investigators .
Alkaline fusion in combination with acid leaching is one of the first methods to be adopted on an
upgrading of niobium and tantalum values by leaching out of iron, manganese, tin, titanium and
Leaching is the removal of material by dissolving them away from the solids. In chemical
solvents are often used. In industrial leaching, solvent and solids are mixed, allowed to approach
equilibrium, and the two phases are separated. Liquids and solids move counter currently to the
adjacent stages. The solvent phase, called the extract, becomes more concentrated as it contacts
in the stagewise fashion the increasingly solute-rich solids. The raffinate becomes less
concentrated in soluble material as it moves towards the fresh solvent phase .
3. EXTRACTION AND SEPARATION OF NIOBIUM AND TANTALUM
3.1 Processes of Extraction and Separation
After the breakdown treatment, the mixed oxides of tantalum Ta
] + 5 H
+ 10 HF → 2 H
] + 3 H
The first industrial scale separation, developed by de Marignac, used the difference in solubility
O) and dipotassium heptafluorotantalate (K
]) in water.
Newer processes use the liquid extraction of the fluorides from aqueous solution by organic
solvents like Octanol , bis(2-ethylhexyl)phosphoric acid (DEHPA) , Alamine 336 ,
methyl isobutyl ketone (MIBK) [14, 15, 16], tri-n-butyl phosphate (TBP) [17, 18] or
cyclohexanone . The complex niobium and tantalum fluorides are extracted separately from
the organic solvent with water and either precipitated by the addition of potassium fluoride to
produce a potassium fluoride complex, or precipitated with ammonia as the pentoxide :
] + 2 KF → K
]↓ + 2 HF
] + 10 NH
OH → Nb
F + 7 H
Several methods are used for the reduction to metallic niobium. The electrolysis of a molten
mixture of K
] and sodium chloride is one; the other is the reduction of the fluoride with
sodium. With this method niobium with a relatively high purity can be obtained. In large scale
production the reduction of Nb
aluminothermic reaction a mixture of iron oxide and niobium oxide is reacted with aluminium:
+ 12 Al → 6 Nb + 2 Fe + 6 Al
To enhance the reaction, small amounts of oxidizers like sodium nitrate are added. The result is
[21, 22]. The ferroniobium contains between 60 and 70% of niobium . Without addition of
iron oxide, aluminothermic process is used for the production of niobium. Further purification is
necessary to reach the grade for superconductive alloys. Electron beam melting under vacuum is
the method used by the two major distributors of niobium [11, 24].
A Review of Niobium-Tantalum Separation 249
A scheme of a proposed model by Amuda et al.  is presented in Figure 1. The figure
incorporates mainly gravity, magnetic and electrostatic separation techniques with leaching as
adjunct beneficiation technique to generate the various secondary ore concentrates.
Fig. 1 Proposed Multi-Ore Constituent Concentration Model 
process consists of the collective extraction of tantalum and niobium (5-7 extraction stages),
scrubbing (6-9 stages), niobium stripping (5-7 stages) and Tantalum stripping (4-6 stages). He
stated that sulphuric acid was added to Ta
(30g/l) solutions in order to
obtain an optimal acidity level.
Figure 2 below shows the extraction of tantalum and niobium versus H
It is evident from the graph that the optimal H
2.5-3.5M while niobium begins to move into the organic phase at an H
Vin and Khopkar  developed a method for the reversed-phase extractive chromatographic
separation of niobium and tantalum with bis(2-ethylhexyl)phosphoric acid (DEHPA). Niobium
was extracted from 1-10M hydrochloric acid and stripped with 3M sulphuric acid containing 2%
hydrogen peroxide while tantalum was extracted from 0.1-2M hydrochloric acid and was
Fig. 2 Extraction of tantalum and niobium versus H
El hussaini and Rice 
extracted niobium and tantalum from a leach liquor with tertiary amine,
Alamine 336, using kerosene and xylene as diluents and n-decanol as a modifier. He investigated
the effect of contact time, sulphate and fluoride concentrations in the aqueous phase, extractant
concentration and aqueous to organic phase ratio. Both elements were extracted to different
extents, with tantalum extraction slightly greater. The separation factor was greater for kerosene
diluent. Selective stripping was performed using either 50 g/L potassium hydroxide or 25 g/L
ammonium carbonate solutions for niobium and tantalum. Tantalum was stripped first and
was precipitated during the stripping process. The separation of niobium from tantalum
Damodaran et al  carried out solvent extraction studies of niobium and tantalum in Indian
the flouride solution at high acidities, and subsequently selectively stripped from the organic
phase. He reported that a solvent concentration of 50% TBP in kerosene gave optimum
extraction characteristics. A 2-stage scrubbing of the tantalum-laden organic phase with 0.5N
was said to reduce the niobium contamination in tantalum to less than 250ppm.
A Review of Niobium-Tantalum Separation 251
The pure tantalum in the form of H
was then finally stripped with de-mineralized water. On
completion of the extraction of tantalum, the aqueous raffinate was made up to 5.0N HF-9.0N
and equilibrated with fresh TBP to extract the niobium. Niobium was then stripped with
Konghak  also carried out solvent extraction studies of niobium and tantalum in Korea using
a mixer-settler with tributyl phosphate (TBP) as a solvent from the HF-H
performed scrubbing experiments to remove the impurities from the organic solution; the
scrubbing was found effective under the conditions that the concentration of H
is 9N and the
ratio of the volumetric flow rate of the organic feed to the aqueous feed in the mixer-settler is 5.
In the stripping of niobium from the organic solution, he stated that the phase separation was
much easier with 1N H
solution as a stripping medium than with water and proposed the
flow diagram for the extraction and purification of niobium and tantalum to be represented by
Figure 3 below:
Fig. 3 Flow diagram for the extraction and separation of niobium and tantalum (O: organic
Htet and Kay  studied the extraction of niobium oxide from columbite-tantalite concentrate
columbite-tantalite concentrate was leached with a mixture of hydrofluoric acid and sulfuric
acid. The variation of acid concentration and leaching time were studied.
The various concentrations of hydrofluoric acid and sulfuric acid were tested to obtain a
niobium in the residue. He likewise studied the effect of sulfuric acid, in which the concentration
was varied from 1-5N. According to his leaching tests, the concentration of 6N HF and
the concentration of 1NH
were chosen because these conditions gave minimum amount of
niobium oxide in the residue.
In order that he recovered niobium oxide from the pregnant solution, solvent extraction method
By adding NH
OH to the pregnant solution, precipitation took place until pH 11 was reached.
The precipitate and sodium hydroxide were put in a porcelain crucible and was placed in the
muffle furnace. HCl digestion was necessary to remove impurities. The fused mass from caustic
fusion was put in a beaker and leached for ½ hr. Calcinations was further performed for the
production of pure niobium oxide.
He established the flow diagram for the extraction of niobium oxide as shown in figure 4 below:
Fig. 4 Flow Diagram for the Extraction of Niobium Oxide
A Review of Niobium-Tantalum Separation 253
was subjected to solvent extraction (SX) treatment using the extractant MIBK or TBP. Both
niobium and tantalum extract at high concentration of H
(>8N), but only tantalum extracts
at lower acidity (3N-8N). Initially niobium and tantalum are extracted together in the organic
phase (MIBK) at greater than 8N H
iron, manganese and magnesium remain in the aqueous phase. Organic phase (MIBK)
containing niobium and tantalum was then brought into contact with fresh aqueous phase
containing less than 8N (preferably around 3N) H
back extracted in the aqueous phase keeping tantalum in the organic phase. The back extracted
aqueous niobium was again re-extracted with MIBK to remove traces of tantalum (i.e., to re-
extract traces of tantalum from niobium).
Then ammonia was added to the aqueous solution containing pure niobium to precipitate
calcined in heated chambers or rotary furnaces. Niobium oxide thus obtained is of high purity.
He reported that the extractants are amenable to degradation due to high concentrations of acids,
in particular HF.
Jainex Industrial Corporation  likewise reported that tantalum and niobium were extracted
are attacked by HF/H
acid solution was mixed thoroughly with MIBK (methyl-iso-butyl ketone) which dissolves the
tantalum and niobium compounds into the ketone while leaving impurities in the aqueous
solution. The organic and inorganic solutions form separate layers and the organic (ketone)
solution could be separated from the aqueous layer (liquid-liquid separation). The niobium was
then stripped with dilute acid, and the tantalum subsequently extracted by acid ammonium
fluoride. For tantalum, the metal could be produced in powder form by sodium reduction of the
Kigoshi  also developed a nitrofluor process for the extraction of niobium and tantalum from
non-aqueous inorganic solvent, purifying the niobium and tantalum and separating them by a
volatile separation technique. A niobium-tantalum separation was made possible by utilizing the
difference of volatility of the complex fluorides formed with an HF-N
disintegration of the ore. A general flowsheet for treating typical columbite or tantalite by a
nitrofluor process as proposed was represented in figure 5 below :
Fig. 5 Nitrofluor process for treating Nb and Ta ore
The World Intellectual Property Organization  described a process for the treatment of raw
material containing tantalum and/or niobium in which the raw material was processed by a
solution containing ammonium fluoride at the boiling point for not more than 10 hours, the
obtained mixture was leached using water or a solution containing ammonia at a temperature
below 100°C for not more than 1 hour. The obtained solution was filtrated giving a main filtrate
in not more
temperature not higher than 450°C for not more than 2 hours.
The sediment was then dissolved in a solution containing F and HF and the obtained solution
and/or niobium was achieved in the form of their complex fluoro acids and fluorosalts in an
aqueous solution. To the obtained fluoride containing solution of niobium and tantalum,
respectively, an ammonium solution was added. From the solution, oxide hydrates of niobium
and tantalum respectively were released and the released oxide hydrates were calcinated giving a
product containing more than 99% niobium and tantalum, respectively.
A Review of Niobium-Tantalum Separation 255
The extraction and separation of niobium and tantalum by solvent extraction has proven to be
simple, rapid and very efficient. Solvent extraction is largely applied in the purification
processes in chemical and metallurgical industries and it likewise provides selective extraction
and recovery of niobium and tantalum from aqueous solution. This present review also shows
that the extraction and separation of niobium and tantalum from their ores involves the
breakdown treatment of the source, extraction and separation by varying experimental
conditions, precipitation, filtration, washing, drying and calcinations. Other techniques such as
gravity, magnetic and electrostatic separation techniques may be coupled as adjunct to obtain a
purer niobium and tantalum.
1. TIC, Tantalum and Niobium-Early History. http://tanb.org/history, retrieved on 30/10/2009.
2. Wikipedia, the free encyclopedia, Niobium. http://en.wikipedia.org/wiki/Niobium, retrieved
3. V. Erick (2007) Coltan - Columbo tantalite,
http://www.eurosinolink.com/pdf/sdpm003v1coltan.pdf, retrieved 28/09/2009.
4. Tantalum, http://rsc.org/Chemsoc/VisualElements/pages/pdf/tantalum.PDF, retrieved
5. N. Thakur (2009) Niobium and Tantalum, http://knol.google.com/k/narayan-thakur/niobium-
and-tantalum/2kwb871ek26nr/66, retrieved on 23/09/2009.
6. Wikipedia, the free encyclopedia, Coltan. http://en.wikipedia.org/wiki/Coltan, retrieved on
7. C. K. Gupta, A. K. Suri (1994) Extractive Metallurgy of Niobium, CRC Press, pp. 1-16,
8. Wikipedia, the free encyclopedia, Reduction http://en.wikipedia.org/wiki/Reduction, retrieved
9. http//:email@example.com School of Engineering, Rensselaer Polytechnic Institute, Troy,
NY 12180, 2001
10. D. J. Soisson, J. J. McLafferty, J. A. Pierret (1961) Staff-Industry Collaborative Report,
Tantalum and Niobium Industrial and Engineering Chemistry, 53 (11), 861–868.
11. A. Agulyansky (2004) The Chemistry of Tantalum and Niobium Fluoride Compounds,
Elsevier, pp. 1–11. ISBN 9780444516046.
12. Y. Y. Vin , S. M Khopkar (1991) Separation of niobium and tantalum by extraction
chromatography with bis(2-ethylhexyl)phosphoric acid, Talanta, 38 (9), 971-5.
13. O. M. El hussaini, N. M. Rice (2004) Liquid-liquid extraction of niobium and tantalum from
14. H. H. Htet, T. L. Kay (2008) Study on Extraction of Niobium Oxide from Columbite–
15. Free patents online, Process for the recovery and separation of tantalum and niobium.
United States Patent 5209910 http://www.freepatentsonline.com/5209910.html, retrieved on
16. Jainex Industrial Corporation, Tantalum (Ta), http://jainexmetals.com/tantalum.htm,
retrieved on 30/10/2009.
17. A. D. Damodaran, S. G. Deshpande, A. A. Majmudar and M. S. Sastri (1969) Extraction and
Center, Trombay, Bombay, 36, No. 5, pp. 306-318.
18. H. Konghak (1991) Solvent Extraction of Tantalum and Niobium Using Mixer-Settler, Korea
Institute of Chemical Engineers, 29, 305-343.
19. N. Thakur (2009) Niobium and Tantalum, http://knol.google.com/k/narayan-thakur/niobium-
and tantalum/2kwb871ek26nr/66, retrieved on 23/09/2009.
20. N. Izabela; Z. Maria (1999) Niobium Compounds: Preparation, Characterization, and
Application in Heterogeneous Catalysis, Chemical Reviews, 99 (12), 3603–3624.
21. G. Tither (2001) Progress in Niobium Markets and Technology 1981–2001, Minerals, Metals
and Materials Society, Metals and Materials Society Minerals. Ed. Niobium Science &
Technology: Proceedings of the International Symposium Niobium 2001 (Orlando, Florida,
USA) (Niobium 2001 Ltd, 2002). ISBN 9780971206809.
22. C. Dufresne, G. Goyette (2001) The Production of Ferroniobium at the Niobec mine 1981–
Niobium Science & Technology: Proceedings of the International Symposium Niobium 2001
(Orlando, Florida, USA) (Niobium 2001 Ltd, 2002). ISBN 9780971206809.
23. J. Kouptsidis (2001) Niob für TESLA (in German), Deutsches Elektronen Synchrotron
24. A. Choudhury, E. Hengsberger (1992) Electron Beam Melting and Refining of Metals and
Alloys, The Iron and Steel Institute of Japan International, 32 (5), 673–681.
25. M. O. H Amuda, D. E. Esezobor, G. I. Lawal (2007) Adaptable Technologies for Life –
Characterization & Engineering, 6, No.1, pp 69-77.
26. A. Kigochi (1972) The extraction of Niobium and Tantalum from Columbite by the Nitrofluor
Process. The Research Institute of Mineral Dressing and Metallurgy, pp. 9.
27. World Intellectual Property Organization (2000) Treating Niobium and/or Tantalum