Geosynthetics June/July 2022 - 18

PVC geomembranes for South American lithium mining
will lose its mechanical properties faster,
especially properties critical at anchorage
points and slopes (Stark 2018). Even
with a high-quality geomembrane, the
evaporation ponds should be covered as
soon as possible in arid climates (Berube
2007). Crews use materials such as lowvalue
salts from the same geographic area
to cover the geomembrane. Protection
against UV degradation and other environmental
conditions are relevant design
parameters of the geomembrane.
Table 1 on page 15 shows wind speed:
all three salares in Bolivia, Chile and
Argentina experience wind velocity of a
minimum of 12.4 mph (20 kph). Once the
geomembrane is deployed onto the soil,
the wind speeds in the Lithium Triangle
create a significant risk of geomembrane
plasticizer loss. The MQC calendaring
process and the geomembrane's composition
are relevant in preventing this
loss. When the PVC geomembrane loses
plasticizer, mechanical properties-such
as tensile strength, tear resistance and
puncture resistance-increase, but flexibility
and impact resistance decrease.
Fractures may occur at night when the
temperature decreases. FGI notes the plasticizer
average molecular weight for arid
areas should be greater than 410 g/mol
(Fabricated Geomembrane Institute 2015).
The brine pressure exerted on the
watertight liner system is high due to
brine density, which typically has a value
of 76.2 pounds per cubic foot (1,220 kg/
m3) (Garc├ęs 2000). The geomembrane's
mechanical properties-particularly
for seams or near them-will maintain
optimal performance of the PVC
geomembrane under the brine. The
geomembrane offers strong chemical
resistance for water and, of course, for
salt solutions. The water extraction loss
can complement a quality index at this
stage. If the geomembrane passes through
all the described steps, site owners can
expect a life expectancy longer than 20
years (Figure 3).
Relevant properties
One of the most relevant properties is
the capacity of the PVC geomembrane
to dissipate wrinkles after unfolding and,
also, to function without tension during
the warm-cool temperature cycle (Rowe
2018). Flexibility is important at low temperatures,
both in storage and during
installation. The PVC resin quality and
the type/amount of plasticizer portends
such performance.
Another interesting standard introFIGURE
3 Pond already in service obtaining lithium salt crystals by evaporation
18
Geosynthetics | June July 2022
duced in the most-recent version of
FGI Specification 9119 (Fabricated
Geomembrane Institute 2019) is the
control of the lay-flat of the calendar
rolls. Having good lay-flat is important to
avoid wrinkles along the seams, so suppliers
who can comply with this specification
will have relatively flat, wrinkle-free,

Geosynthetics June/July 2022

Table of Contents for the Digital Edition of Geosynthetics June/July 2022

Geosynthetics June/July 2022 - Cover1
Geosynthetics June/July 2022 - Cover2
Geosynthetics June/July 2022 - 1
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Geosynthetics June/July 2022 - Cover3
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