A review of Niobium-Tantalum Separation in Hydrometallurgy



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Journal of Minerals & Materials Characterization & Engineering

, Vol. 10, No.3, pp.245-256, 2011 

  

jmmce.org 



 Printed in the USA. All rights reserved 

245 


A Review of Niobium-Tantalum Separation in Hydrometallurgy 

 

 

 

Olushola S. Ayanda

1*

 and Folahan A. Adekola

 

 



1

Department of Chemistry, Faculty of Applied Sciences, Cape Peninsula University of 

Technology, P.O. Box 652, Cape Town, South Africa. 

2

Department of Chemistry, University of Ilorin, P.M.B 1515, Ilorin, Nigeria. 



 

* Corresponding author: 

holysholay04@gmail.com

   



 

 

ABSTRACT 

 

Niobium and tantalum are chemically similar and are associated with each other in nature 

which makes it very difficult to separate. For many years, the separation of tantalum from 

niobium involved the fractional crystallization of potassium heptafluorotantalate away from 

potassium oxypentafluoroniobate monohydrate, this method has been supplanted by solvent 

extraction from fluoride-containing solutions by the use of solvent extractants such as Octanol, 

bis(2-ethylhexyl)phosphoric acid (DEHPA), Alamine 336, methyl isobutyl ketone (MIBK), tri-n-

butyl phosphate (TBP) or cyclohexanone. A detailed review of the various processes involved in 

the breakdown treatment of niobium and tantalum primary sources, extraction and separation 

and newer processes of extraction  as well as the various technique involved were discussed. 

 

Keyword: Niobium, Tantalum, Columbite, Tantalite, Solvent extractant and Solvent extraction. 

 

 

 

1. INTRODUCTION 

 

Niobium is a rare, soft, grey and ductile transition metal with the symbol Nb. It was discovered 



by Charles Hatchett, an English chemist (1765-1847), in 1801 [1]. Niobium is used in 

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 



246 

                                        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 



electron tubes, lens, vacuum furnace parts, watches and tantalum being chemically inert is also 

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. 



Separaton of niobium from tantalum was very difficult due to the chemical similarities of their 

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 [7]. 



 

2. BREAKDOWN TREATMENT FOR PRIMARY SOURCES 

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) [7]. 



2.1 Reduction 

 

One of the simplest methods for the breakdown treatment of primary concentrates of niobium 



and tantalum, particularly pyrochlore and columbite-tantalite, is direct reduction with aluminum 

or carbon [8], 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 



at room temperature. During aluminothermic reduction, all the oxides that have free energy of 

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 



temperatures (generally over 1500

o

C) and is highly endothermic in nature. Moreover, niobium 



and tantalum react with excess carbon and form carbides.  

 



Vol.10, No.3 

                              A Review of Niobium-Tantalum Separation                                                   247

 

 

Thus, the product in the case of aluminothermic reduction reaction is usually a ferroalloy, 



whereas that ensuring from carbothermic reduction may be a ferroalloy or alloy carbide mass 

containing practically all of the niobium and tantalum, together with many of the other elements 

that are present in the starting concentrate 

 

2.2 Chlorination 

 

Chlorination is a process for breakdown of ores and concentrates of many of the refractory 



metals [7], and even some of the commonly used metals are very attractive, an important features 

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 



for the separation/purification of various elements co-occurring in the concentrate and for 

reduction to metallic form. 



 

2.3 Alkaline Fusion 

 

Alkaline fusion is also one of the processes used for the breakdown of mineral ores concentrate. 



A large number of alkaline fluxes, such as caustic soda, soda ash, caustic potash, potassium 

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 [7].  

 

Alkaline fusion in combination with acid leaching is one of the first methods to be adopted on an 



industrial scale to achieve simultaneous breakdown of columbite and tantalite concentrate and 

upgrading of niobium and tantalum values by leaching out of iron, manganese, tin, titanium and 

silicon. 

 

2.4 Leaching 

 

Leaching is the removal of material by dissolving them away from the solids. In chemical 



processes, industries use leaching but the process is usually called extraction, and organic 

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 [9]. 




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                                        Olushola S. Ayanda and Folahan A. Adekola                                  Vol.10, No.3 

 

 

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



2

O

5



 and niobium Nb

2

O



5

 are 


obtained. The first step in the processing is the reaction of the oxides with hydrofluoric acid [10]: 

 

Ta



2

O

5



 + 14 HF → 2 H

2

[TaF



7

] + 5 H


2

 



 

 

 



(1) 

Nb

2



O

5

 + 10 HF → 2 H



2

[NbOF


5

] + 3 H


2

 



 

 

 



(2) 

 

The first industrial scale separation, developed by de Marignac, used the difference in solubility 



between the complex niobium and tantalum fluorides, dipotassium oxypentafluoroniobate 

monohydrate (K

2

[NbOF


5

]·H


2

O) and dipotassium heptafluorotantalate (K

2

[TaF


7

]) in water. 

Newer processes use the liquid extraction of the fluorides from aqueous solution by organic 

solvents like Octanol [11], bis(2-ethylhexyl)phosphoric acid (DEHPA) [12], Alamine 336 [13], 

methyl isobutyl ketone (MIBK) [14, 15, 16], tri-n-butyl phosphate (TBP) [17, 18] or 

cyclohexanone [19]. 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 [20]: 

 

H

2



[NbOF

5

] + 2 KF → K



2

[NbOF


5

]↓ + 2 HF    

 

 

 



(3) 

 

Followed by: 



 

2 H


2

[NbOF


5

] + 10 NH

4

OH → Nb


2

O

5



↓ + 10 NH

4

F + 7 H



2

O   


 

(4) 


 

Several methods are used for the reduction to metallic niobium. The electrolysis of a molten 

mixture of K

2

[NbOF



5

] 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

2

O

5



 with hydrogen or carbon is used. In the process involving the 

aluminothermic reaction a mixture of iron oxide and niobium oxide is reacted with aluminium: 

 

3 Nb


2

O

5



 + Fe

2

O



3

 + 12 Al → 6 Nb + 2 Fe + 6 Al

2

O

3



   

 

 



(5) 

 

To enhance the reaction, small amounts of oxidizers like sodium nitrate are added. The result is 



aluminium oxide and ferroniobium, an alloy of iron and niobium used in the steel production 

[21, 22]. The ferroniobium contains between 60 and 70% of niobium [23]. 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].  



Vol.10, No.3 

                              A Review of Niobium-Tantalum Separation                                                   249

 

 

 



3.2 Newer Processes of Extraction and Separation of Niobium and Tantalum 

 

A scheme of a proposed model by Amuda et al. [25] 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 [25] 



Agulyanski [11] reported the use of 2-octanol for the separation of niobium and tantalum. The 

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

2

O

5



 (50-60g/l) and Nb

2

O



5

 (30g/l) solutions in order to 

obtain an optimal acidity level.  

Figure 2 below shows the extraction of tantalum and niobium versus H

2

SO



concentration.  

 

It is evident from the graph that the optimal H



2

SO

4



 concentration for tantalum extraction is about 

2.5-3.5M while niobium begins to move into the organic phase at an H

2

SO

4



 concentration of 4-

5M. 


 

Vin and Khopkar [12] 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% 




250 

                                        Olushola S. Ayanda and Folahan A. Adekola                                  Vol.10, No.3 

 

hydrogen peroxide while tantalum was extracted from 0.1-2M hydrochloric  acid and was 



stripped with 0.1M hydrochloric acid containing 2M tartaric acid. 

 

0



20

40

60



80

100


0

1

2



3

4

5



6

H2SO4 (M)

O

rg

a

nic p

h

ase co

nt

en

t, g

/L

Ta2O5


Nb2O5

 

Fig. 2 Extraction of tantalum and niobium versus H



2

SO



concentration 

 

El hussaini and Rice [13]



 

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 

Ta(OH)

5

 was precipitated during the stripping process. The separation of niobium from tantalum 



was achieved at this point and niobium was then precipitated by adding ammonia. 

 

Damodaran et al [17] carried out solvent extraction studies of niobium and tantalum in Indian 



with tributyl phosphate [TBP]. In his system niobium and tantalum were extracted together from 

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 

HF-2.0N H

2

SO



4

 was said to reduce the niobium contamination in tantalum to less than 250ppm. 




Vol.10, No.3 

                              A Review of Niobium-Tantalum Separation                                                   251

 

 

The pure tantalum in the form of H



2

TaF


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 

H

2



SO

4

 and equilibrated with fresh TBP to extract the niobium. Niobium was then stripped with 



de-mineralized water.  

Konghak [18] 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

2

SO



4

-H

2



O system. He 

performed scrubbing experiments to remove the impurities from the organic solution; the 

scrubbing was found effective under the conditions that the concentration of H

2

SO



4

 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

2

SO



4

 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 



phase; A: aqueous phase) [18] 

 

Htet and Kay [14] studied the extraction of niobium oxide from columbite-tantalite concentrate 



of Thayet Kon Area in Nay Phi Taw (Pyinmana) using methyl isobutyl ketone. He reported that 

columbite-tantalite concentrate was leached with a mixture of hydrofluoric acid and sulfuric 

acid. The variation of acid concentration and leaching time were studied.  

 



252 

                                        Olushola S. Ayanda and Folahan A. Adekola                                  Vol.10, No.3 

 

The various concentrations of hydrofluoric acid and sulfuric acid were tested to obtain a 



condition to extract maximum amount of niobium in the filtrate and minimum amount of 

niobium in the residue. He likewise studied the effect of sulfuric acid, in which the concentration 

of H

2

SO



was varied from 1-5N. According to his leaching tests, the concentration of 6N HF and 

the concentration of 1NH

2

SO



4

 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 



using MIBK was carried out. Two stages were employed. 

 

By adding NH



4

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 




Vol.10, No.3 

                              A Review of Niobium-Tantalum Separation                                                   253

 

 

 



Thakur [19] reported that a solution containing tantalum and niobium along with some impurities 

was subjected to solvent extraction (SX) treatment using the extractant MIBK or TBP. Both 

niobium and tantalum extract at high concentration of H

2

SO



4

 (>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

2

SO

4



. Under these conditions most of the impurities such as 

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

2

SO

4



. Under this condition only niobium was 

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 



niobium oxide hydrate. Oxide hydrate of niobium was then separated by filtration, dried and 

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 [16] likewise reported that tantalum and niobium were extracted 



from their ores after concentration by chemical means rather than by smelting. The concentrates 

are attacked by HF/H

2

SO

4



 which brings the tantalum and niobium compounds into solution. The 

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 

fluoride. 

 

Kigoshi [26] also developed a nitrofluor process for the extraction of niobium and tantalum from 



columbite. He reported that the nitrofluor process provides a method of dissolving columbite in a 

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

2

O

3



 azeotrope used for the 

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 [26]: 



254 

                                        Olushola S. Ayanda and Folahan A. Adekola                                  Vol.10, No.3 

 

 

Fig. 5 Nitrofluor process for treating Nb and Ta ore 



 

The World Intellectual Property Organization [27] 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 

containing Ta

2

0



5

 and/or Nb

2

0

5



 and the filtrate was processed by a solution of NH

3

 in not more 



than 30 minutes. A sediment was separated by filtering and was then dried and calcinated at a 

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 



undergoes a multistage liquid extraction, during which separation of components of tantalum 

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. 



 


Vol.10, No.3 

                              A Review of Niobium-Tantalum Separation                                                   255

 

 

4. CONCLUSION 



 

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. 

 

REFERENCES 

 

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 

on 05/10/2009. 

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 

28/09/2009 

5.   N. Thakur (2009) Niobium and Tantalum, http://knol.google.com/k/narayan-thakur/niobium-

and-tantalum/2kwb871ek26nr/66, retrieved on 23/09/2009. 

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23/09/2009. 

7.   C. K. Gupta, A. K. Suri (1994) Extractive Metallurgy of Niobium, CRC Press, pp. 1-16, 

ISBN 0849360714. 

8.  Wikipedia, the free encyclopedia, Reduction http://en.wikipedia.org/wiki/Reduction, retrieved 

on 23/09/2009. 

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NY 12180, 2001 

10. D. J. Soisson, J. J. McLafferty, J. A. Pierret (1961) Staff-Industry Collaborative Report, 

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