Geology Reference
In-Depth Information
of aluminium metal as a reducing agent, lime fluorspar is added as a flux to im-
prove slag and metal separation. The reduction process can also be done with silicon
instead of aluminium. A smelting process produces a hot alloy block that once sepa-
rated from the slag, is cooled in air or by quenching in water. The cooled metal block
is crushed to a commercial size. The ferromolybdenum produced typically contains
60% molybdenum. Smelting as of this product emits dusts and fumes which can
be toxic, especially if ingested. Furthermore, low levels of prolonged exposure can
cause irritation to the eyes and skin. It is therefore important to prevent industrial
releases of the metal fumes and dust. They must be collected and extracted using
a reverse air jet cleaning baghouse. Dusts, specifically, are recycled back into the
smelting process (IPPC, 2009). On a side note, it is worth noting that molybdenum
is an important element for the full functioning of the body and is present in the
liver, kidneys and tooth enamel. Molybdenum also plays an important role in the
nitrogen fixation undertaken by certain bacteria.
According to Chapman and Roberts (1983), the energy requirement for the
production of molybdenum is 136 GJ/t of metal and 12 GJ/t of metal for the
concentration and refining stages, respectively. Kennecott Utah Copper (2006b)
undertook a life cycle assessment for molybdenum production as a byproduct of
copper mining and smelting. The energy proportion for each stage can be divided
as follows: 42% for roasting and another 42% in the concentration, 23% in the
mining, and 1% in the tailings (Fthenakis et al., 2007).
8.11.6 Titanium
Rutile (TiO
2
) and ilmenite (FeO TiO
2
) are the two main titanium ores. As an
example, a typical magnetite-ilmenite ore of northern Finland contains about 6.2%
titanium. Ilmenite often contains appreciable quantities of MgO and MnO too.
According to Barksdale (1968), the proportion of Ti in soils is approximately 0.5
to 1.5%
16
. This element is thus very frequent in the Earth's crust, so scarcity
is not an issue. However, its commercial production is very energy and material
intensive due to TiO
2
's high stability. A lowering of the energy requirement is
something which needs to be grappled seriously if titanium is ever going to be used
extensively. Melted titanium spontaneously reacts at 1200
o
C with the oxygen in air
and at the lower 610
o
C in cases where pure oxygen is used. It burns easily when
finely divided. It also readily reacts at high temperatures with nitrogen or carbon
to form the corresponding nitride or carbide and this is something which causes
embrittlement in the metal.
Currently, titanium is extracted from its ore via the Kroll process. This starts
with a carbochlorination reaction in which titanium oxide reacts at 1100 - 1200
o
C
with coke as a reducing agent to produce titanium tetrachloride and CO
2
gas (IPPC,
2009). It is done in a fluidised bed process and the feed employed can contain a
16
See also http : ==www:chemicool:com=elements=titanium:html. Accessed Sep. 2011.
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