Geology Reference
In-Depth Information
(Schlewitz, 2000). Tantalum can also be recovered from tantalum rich slag via the
smelting of tin concentrates through an identical procedure. This process accounts
for about 30% of the world tantalum production.
Tantalum powder metal, meanwhile, can be produced by reducing potassium
heptafluorotantalate with sodium in a molten salt system at high temperature. It
can also be produced by the carbon or aluminium reduction of the oxide (IPPC,
2009). As for niobium, its powder needs to be refined in an electric arc furnace where
most of the impurities volatilise during the high temperature melting process.
There are however alternative treatment routes. Chlorine gas may be used to
react with a mixture of coke and TiNbTaREE mineral concentrates (struverite
from Malaysia, for instance) to produce an oxychloride gas of titanium-niobium-
tantalum. The accompanying oxychlorides of iron, thorium and alkaline metals
precipitate out as the gas cools. The Ti oxychloride is distilled from the liquid
oxychlorides. The remaining Nb and Ta oxychlorides are further chlorinated to
produce NbCl
5
and TaCl
5
which are separated from each other by fractional dis-
tillation. Now, the chlorides can be converted with steam into hydroxide or with
ammonia hydroxide to form niobium and tantalum once the hydroxides are further
calcined and then reduced
19
.
Botero (2000) calculates an approximate value of the energy requirement needed
to obtain a tonne of tantalum based on the process involved in attaining tantalum
pentoxide. The calculations indicate that open pit mining requires around 800
GJ/t of ore. Furthermore, with consideration to the ore grade available in the mine,
leaching with sulphuric acid would require between 150 and 1,000 GJ/t of tantalum.
Botero (2000) uses the average value of this range at 575 GJ/t, meaning that some
1,375 GJ/t of Ta is required for its mining and concentration. Classen et al. (2007),
meanwhile, reports an average energy consumption for the beneficiation stage of
tantalum equal to 829 GJ/t plus a total of about 555 MWh/t (3,083 GJ/t) of Ta,
while for the refining stage this figure stands at 0.28 GJ/t of concentrate plus a
total of about 720 kWh/t (8.1 GJ/t) Ta.
8.11.8 Rhenium
Rhenium appears in the molybdenite fraction of porphyry copper ores with a typi-
cal concentration containing 0.001% to 0.2% Re in the molybdenite ore. Therefore,
unsurprisingly industrial rhenium is a byproduct of molybdenum and copper pro-
duction.
The roasting process of molybdenite concentrates produces dusts, off-gases rich
in SO
2
and minor amounts of selenium dioxide and rhenium heptoxide (Re
2
O
7
). As
rhenium heptoxide readily dissolves in water, it is removed from the waste gases via
19
Another possibility is to reduce the tantalum chloride with hydrogen or alkaline earth metals.
See the “Tantalum-Niobium International Study Center” http://tanb.org/niobium. Accessed Nov.
2011.
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