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2.4.5 Adsorption characteristics of BA-based geopolymers
towards micropollutants
Micropollutants such as mercury, lead, copper, zinc, nickel, chromium and cad-
mium are a major concern in the world as they become hazardous for human health,
animals and the ecological environment. They are toxic and carcinogenic elements
which accumulate over time. Geopolymers have been investigated as an adsorbent
to remove these heavy metals from wastewater or aqueous solution (Kara et al.,
2017). This capacity is guaranteed by the considerable amount of meso-porosity in
geopolymers with size range of 10 50 nm ( . 40 vol%) (Landi et al., 2013) and
their ability to reduce the mobility of most heavy metals ions when contained
within their structure (Muˇ zek et al., 2014).
In the limited number of studies dealing with the use of geopolymers for heavy
metal removal from aqueous solutions, Novais et al. (2018) developed a highly
porous and lightweight BFA-based geopolymer used as an adsorbent for the
removal of methylene blue from synthetic wastewater. The results showed a value
in the absorption of 15.5 mg/g when the porosity was 80.6%, a threefold increase
that was observed in the geopolymer with 40.7% of porosity. Barbosa et al. (2018)
experimented with a meso-porous geopolymer made with MK and RHA as sources
of silica and alumina and soybean oil as a meso-structure-directing agent attaining
the adsorption equilibrium of methyl violet 10B dye from the aqueous solution val-
ued in 276.9 mg/g within 120 min.

2.4.6 Use of BA-based geopolymers for thermal and acoustic
insulation

Geopolymer concrete leads to an excellent new material that will save opera-
tional energy due to its low density and relatively lower thermal conductivity
than normal-weight concrete (Zhang et al., 2014). Moreover, Liu and his collea-
gues (Liuetal.,2014,2016) have introduced the foamed technique into geopoly-
mer materials to improve thermal insulation. In their initial investigation
regarding the behaviour of palm oil-shell foamed geopolymer concrete utilising
industrial wastes such as palm oil shell as lightweight coarse aggregate and
POFA and coal FA as binder mix in concrete, they produced a geopolymer with
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densities between 1300 and 1700 kg/m due its higher porosity. Despite the fact
of a reduction in compressive strength, they concluded that a thermal conductiv-
ity of about 0.47 W/m K was 22% and 48% lower than blocks and bricks as con-
ventional materials for walls. Hence this geopolymer could be categorised as
structural concrete Class I (compressive strength more than 15 MPa) and struc-
tural and insulating concrete Class II (compressive strength between 3.5 and
15 MPa and thermal conductivity less than 0.75 W/m K) according to the RILEM
(1983) classification.
From the point of view of the acoustic properties of BA-based geopolymer, it is
well-known that the sound absorption of a porous material is related to the loss of
noise by friction in the wall of its pores (Park et al., 2005), so that geopolymer