Geology Reference
In-Depth Information
As for energy requirements, Chapman and Roberts (1983) report consumption
in the mining and concentration stage at 157 GJ/t of mercury, which climbs at the
refining stage to 252 GJ/t.
8.11 Refractory metals
Refractory metals including Cr;Mn;Ti;V;Mo;W;Nb;Ta;Re;Zr are characterised
by their high melting point, good resistance to heat and corrosion, high density,
inertness and resistance to strong acid attack. They are used for special alloys in
a multiple of new high-tech devices ranging from electronics to high temperature
aerospace, industrial and medical appliances. New applications are found every day
and it is likely that there will be increased demand in the near future
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.
Due to this group's high melting points, pure metal production is a very energy
intensive operation because of its use, amongst others of electron beam furnaces.
In some cases refractory metals are produced under a vacuum or in other extreme
conditions. Their metal oxide reduction also requires extreme reducing agents such
as aluminium, magnesium, silicon, hydrogen or to a lesser extent, coke and all at
very high temperatures.
Their properties and the commonly low ore grades found in mining result in
the very high values of energy needed to generate one kilogram of refractory metal.
There is also a host of substantial direct and indirect environmental impacts to
consider. The Ullmann's Encyclopedia (Ullmann and Gerhartz, 2002) provides
data for the energy consumed in the electron beam furnaces used in the smelting
of different refractory metals. For niobium and tantalum the values all fall within
the range of 6,000 - 15,000 kWh/t-Me, whilst for molybdenum and tungsten it
is <5,000 kWh/t-Me. The value for titanium is 1,000 kWh/t-Ti. Such numbers
should give the reader an idea of the high energy impact of refractory metals. For
instance, Norgate et al. (2007) obtain a life cycle gross energy requirement for
titanium production of 361 GJ/t Ti which is a 70% higher than that of Al. They
also obtain a GWP of 35.7 tCO
2
e=t Ti.
Emissions to air are in concordance with the unit operations used. They are
conventional and metal specific. Dust and diffuse emissions may contain harmful
metals such as in chromium, cobalt or titanium and need to be specially treated
in some cases. In other cases such as those involving tantalum, zirconium and
hafnium, an additional radioactive control level is needed with wastewaters, process
residues and solid wastes needing to be treated accordingly and similarly to those
of conventional smelting.
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See: What Are Refractory Metals? http : ==www:pickpm:com=designcenter=refractory:pdf.
Accessed Nov. 2011.
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