Raw materials

Sons of Gwalia, Overview of plant and infrastructure at Wodgina (Suzanna Hughes)

Tantalum ores are found primarily in Australia, Canada, Brazil, and central Africa, with some additional quantities originating in southeast Asia and in China. There is also interest in exploration for this element in various regions of the world, such as Canada, Egypt and Saudi Arabia. Tantalum minerals with over 70 different chemical compositions have been identified. Those of greatest economic importance are tantalite, microlite, and wodginite; however, it is common practice to name any tantalum-containing mineral concentrate as 'tantalite' primarily because it will be processed for the tantalum values and is sold on that basis. Tantalum mineral concentrates may contain from two to more than five different tantalum-bearing minerals from the same mining area. The sale of tantalum mineral concentrates is based on a certified analysis for the tantalum oxide they contain, with a range from 10 or 15 to over 60% depending on the mine source. The minerals are concentrated by physical means at or near the mine site to increase the percentage of tantalum oxide and niobium oxide by weight. The concentrates are transported to the processors' works for chemical processing.

The single largest source of tantalum mineral concentrates is the production by Sons of Gwalia Ltd. from its Greenbushes and Wodgina mines in Western Australia. These two mines combined produce over 50% of global demand, with production in 2003 reported at just over 2 million pounds Ta₂O₅ contained. The company has been in administration since September 2004, but production and supply of tantalite continue as usual. Additional operating mines are the Tanco Mine (Cabot) in Manitoba, Canada, the Kenticha Mine (Ethiopia Mineral Development Enterprise) in Ethiopia, the Yichun Mine in China, and the Pitinga Mine (Paranapanema) and Mibra Mine (Metallurg) in Brazil. Additional quantities are available from Brazil through collection from small alluvial deposits by prospectors and also in numerous countries in Africa, such as Rwanda, Namibia, Uganda, Democratic Republic of Congo, Nigeria, South Africa, and Burundi. Mining investment in Africa has been curtailed due to political instability and associated risk.

The central African countries of Democratic Republic of Congo and Rwanda and their neighbours used to be the source of significant tonnages. But civil war, plundering of national parks and exporting of minerals, diamonds and other natural resources to provide funding of militias has caused the Tantalum-Niobium International Study Center to call on its members to take care to obtain their raw materials from lawful sources. Harm, or the threat of harm, to local people, wildlife or the environment is unacceptable.

In southeast Asia the downsizing of the tin industry since 1980 has led to the reduction of tantalum oxide units available from tin slags, a by-product of the smelting of cassiterite ore concentrates for tin production. It should be noted that struverite concentrates have been available from this general area containing 9-12% tantalum oxide.

Scrap recycling generated within the various segments of the tantalum industry accounts for about 20 to 25% of the total input each year.

Extraction/refining

K2TaF7 Process, H.C. Starck GmbH, (Gerald Baehnish)

The extraction and refining of tantalum, including the separation from niobium in these various tantalum-containing mineral concentrates, is generally accomplished by treating the ores with a mixture of hydrofluoric and sulfuric acids at elevated temperatures. This causes the tantalum and niobium values to dissolve as complex fluorides, and numerous impurities that were present also dissolve. Other elements such as silicon, iron, manganese, titanium, zirconium, uranium, thorium, rare earths, etc. are generally present. The filtration of the digestion slurry, and further processing via solvent extraction using methyl isobutyl ketone (MIBK) or liquid ion exchange using an amine extractant in kerosene, produces highly purified solutions of tantalum and niobium. Generally, the tantalum values in solution are converted into potassium tantalum fluoride (K₂TaF₇) or tantalum oxide (Ta₂O₅). The niobium is recovered as niobium oxide (Nb₂O₅) via neutralization of the niobium fluoride complex with ammonia to form the hydroxide, followed by calcination to the oxide.

The primary tantalum chemicals of industrial significance, in addition to K₂TaF₇ and Ta₂O₅, are tantalum carbide (TaC), tantalum chloride (TaCl₅), and lithium tantalate (LiTaO₃).

Tantalum metal powder is generally produced by the sodium reduction of the potassium tantalum fluoride in a molten salt system at high temperature. The metal can also be produced by the carbon or aluminium reduction of the oxide or the hydrogen or alkaline earth reduction of tantalum chloride. Capacitor grade powder is produced by the sodium reduction of potassium tantalum fluoride. The choice of process is based on the specific application and whether the resultant tantalum will be further consolidated by processing into ingot, sheet, rod, tubing, wire, and other fabricated articles.

Capacitor grade tantalum powder provides about 60% of the market use of all tantalum shipments. Additional quantities are consumed by tantalum wire for the anode lead as well as for heating elements, shielding, and sintering tray assemblies in anode sintering furnaces.

The consolidation of metal powder for ingot and processing into various metallurgical products begins with either vacuum arc melting or electron beam melting of metal feedstocks, comprised of powder or high purity scrap where the elements with boiling points greater than tantalum are not present. Double and triple melt ingots achieve a very high level of purification with regard to metallics and interstitials. Ingots are used to produce the various metallurgical products named earlier. Ingot stock is also used for the production of such alloys as tantalum-10% tungsten. Ingot and pure tantalum scrap are used in the production of land and air-based turbine alloys.

Applications for Tantalum

Seco Tools, Eight different types of carbide cutting and grinding tools (Bo Holmblad)

Hitachi AIC, Tantalum capacitor tape reels (Kazuyuki Iida)