Geology Reference
In-Depth Information
with respect to the direct extraction of lithium from brines located in Bolivia, Salar
de Uyuni, Salar del Hombre Muerto, Argentina and Salar de Atacama, Chile
21
(Gru-
ber et al., 2011). Sedimentary rocks like clay and lacustrine evaporites are another
possible source of lithium. They may contain hectorite (Mg;Li)
3
Si
4
O
10
(OH)
2
and
jadarite Li
3
NaB
3
SiO
7
(OH) and thus constitute a potential option that can help
couple the future supply and demand for lithium batteries.
Natural brines contain elements like sodium, potassium, lithium, magnesium,
calcium, iron, boron, bromine, chlorines as anions, sulphates, carbonates and ni-
trates. They are located under the salar's surface and pumped to a series of evap-
oration ponds where lithium chlorine brines are concentrated by solar evaporation.
Boron and magnesium are then separated via precipitation. Boron precipitates and
crystallises as boric acid upon acidifying the brine. Magnesium precipitates as mag-
nesium carbonate upon adding sodium carbonate. The liquid is then pumped to a
recovery plant to produce lithium carbonate which is obtained by adding sodium
carbonate (soda ash) to the hot brine. The brines are used as a feedstock for potas-
sium chloride production, in addition to other salts which are produced as byprod-
ucts. Any residual brine is re-injected to underground salar deposits. Once this
occurs, the resulting lithium carbonate is filtered, dried and ready to be shipped as
the feed material for the further production of most industrial lithium compounds.
Lithium can also be obtained from pegmatite rocks. In this case, -spodumene is
separated by floatation. Subsequently it is converted at high temperature (1100
o
C)
into the less dense -spodumene. This concentrate is then leached with sulphuric
acid at 250
o
C to produce lithium sulphate which is further treated with sodium
carbonate to form lithium carbonate. Further, lithium carbonate forms the feed-
stock for producing lithium metal. Here the lithium carbonate is reverted back into
lithium chloride, which is concentrated and crystallised. A molten eutectic mixture
of lithium and potassium chloride is then electrolysed at 450
o
C with the voltage
(4-5 V) applied selectively electrolysing LiCl but leaving the KCl unaffected. The
electrodes involved in the process are made of a cylindrical anode and a concentric
steel cathode submerged in a rectangular bath. As the process proceeds, LiCl is fed
into the electrolytic cells (IPPC, 2009). The molten lithium metal is skimmed off
and cast into rectangular rods then immediately covered with mineral oil to prevent
oxidation.
Kellogg (1977) published information on the energy requirement for the produc-
tion of lithium hydroxide. Accordingly, 432.5 GJ are required to obtain a tonne
of product. The mining process demands between 1.8 and 12.5 GJ/t of treated
lithium. Given the high total energy consumption, Botero (2000) considered the
upper range value of 12.5 GJ/t as the energy required in the process of concentration
and subscribed 420 GJ/t to the metallurgical process.
21
See http : ==www:azom:com=article:aspx?ArticleID = 3503. Accessed Aug. 2011.
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