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Tantalum [Ta, 73]
46.1 INTRODUCTION
Tantalum (Ta), a blue-gray transition metal of group 5 in the periodic table of elements,
is hard and highly corrosion resistant. Its mean abundance in the Earth’s crust is
around 2  mg/kg, within the range of 1.5–2.2  mg/kg. Its content is the highest in
acidic magmatic rocks, about 4 mg/kg. In calcareous sedimentary rocks, its amounts
vary within <1–2 mg/kg. Coal contains Ta up to 0.3 mg/kg.
Oxidation states of Ta are from +3 to +5, but mainly at the highest value. It reveals both
chalcophilic and siderophilic affinity, and occurs in several minerals, mainly oxides. It is
associated with Nb, Tl, Y, and lanthanides (LAs). Its most common mineral is tantalite/
columbite [(Fe,Mn)(Ta,Nb) 2 O 6 ], also called coltan. Tantalum occurs mainly together with
chemically similar Nb and may form some other minerals, such as formanite (YTaO 4 ).
The chief Ta ores are tantalite, samarskite, and pyrochlore, which also contain Nb.
World mine Ta production (rounded), excluding the United States, in 2010 was
670 t, of which 180 t was mined in Brazil, 110 t in Mazambique, 100 t in Rwanda,
and 80 t in Australia (USGS 2011). Tantalum is used mainly for high-temperature
applications and aircraft engines, and as capacitors in electronic equipments, such as
mobile phones and computers. Metallic Ta dust is a fire and explosion hazard.
Tantalum is resistant to corrosion and to several chemical attacks. For this reason,
it has been employed in chemical industries, especially where strong acids are vaporized. It is rarely used as an alloying agent, because it tends to make metals brittle.
Due to chemical properties, Ta may substitute Pt in various tools. Its main use is
now in various electronic devices, mainly as capacitors. Due to Ta immune system
to impact of body liquids, it is widely used in surgical appliances (e.g., implants).
46.2 SOILS
The mean Ta content of soils worldwide is estimated to be 1.1  mg/kg (FOREGS
2005). Its contents vary within the range of 0.2–3.9 mg/kg, but are reported to reach
up to 5.3 mg/kg in soils of China (Govindaraju 1994). Agricultural soils of Sweden
contain Ta from 0.5 to 1.6 mg/kg, at an average value of 1.1 mg/kg (Eriksson 2001a).
The median levels of Ta in soils of Japan range from 0.7 to 1.4 mg/kg, being highest
in Gleysols (Takeda et al. 2004).
46.3 WATERS
Because Ta oxide is very insoluble, it is almost not found in natural waters. Thus,
there are few data on its concentration in river waters, which is within the range
between 0.1 and 148 ng/L, at an average of 1.1 ng/L (Gaillardet et al. 2003). The mean
Ta content of the North Pacific is <2.4 ng/L (Nozaki 2005).
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