Geology Reference
In-Depth Information
wet scrubbing. The liquor used is recirculated to increase rhenium concentration to
about 0.2 - 1.5 gr/l Re.
The production of rhenium metal consists of a reduction process and the re-
moval of rhenium heptoxide from the scrubbing liquor. The oxide is also easily
eliminated from the latter either by precipitation as a sulphide, an ion exchange or
solvent extraction procedure. Strong mineral acids then dissolve the oxide to form
perrhenic acid with a further addition of ammonium chloride given to precipitate
the perrhenate salt. Ammonium perrhenate is afterwards reduced with hydrogen
in a two stage process to obtain rhenium metal powder. In the first stage, the feed
is converted into rhenium dioxide at about 300 - 350 o C. The temperature rises to
800 o C for the second stage reducing the rhenium dioxide to powdered metal and
liberating ammonia and steam. The rhenium powder is further compressed, sin-
tered in a vacuum or in a hydrogen atmosphere and subsequently pelletised to fit
commercial requirements (IPPC, 2009).
There are few data on the energy requirements for the production of this metal.
However, from the description of the process in obtaining it, one can infer an ap-
proximate figure. The energy required to grind a typical tonne of ore to 100 m lies
somewhere in the range between 0.15 and 0.2 GJ/t. In the case of rhenium mining
for ore grades of 0.3% this figure is much higher at between 50 and 66.6 GJ/t. Also
the process of concentration by flotation of a generic sulphide ore requires between
0.1 and 0.18 GJ/t of ore, which in the case of rhenium is much higher at between
33.3 and 60 GJ/t. Assuming the intermediate value on both occasions and consid-
ering that the ore is subjected to a double process of concentration by flotation, it
is assumed that the concentration of rhenium requires around 156 GJ/t Re.
The pyrometallurgical process of rhenium is similar to other sulphide ores such
as molybdenite or lead from which molybdenum or galena are respectively obtained.
According to data presented by different authors, the process of extractive metal-
lurgy of molybdenum requires 12 GJ/t of metal obtained. In the case of lead,
as has already been described, a 18.9 GJ input is required per tonne of metal
obtained. Considering these approximate values for the energy requirements of rhe-
nium, Botero (2000) proposed a value of 15 GJ/t as representative of the energy
required for the pyrometallurgical treatment of rhenium ore.
8.11.9 Zirconium and Hafnium
Zircon (ZrSiO 4 ) is zirconium's main ore. It is found in the zircon bearing sands
of coastal waters and is associated with rutile and ilmenite titanium ores and tin
minerals. Zircon always occurs alongside hafnium. Indeed, commercial zirconium
can contain as much as 1% to 3% hafnium without affecting its properties, except
for where it is exploited for nuclear applications. Hafnium must be separated from
zirconium in nuclear reactor applications since Hf has a 600 times higher neu-
tron absorption cross-section than Zr. The beneficiating of zircon bearing sands
 
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