56
et al. 2015. It is comparable to activated carbon, which is the most widely used
adsorbent. But unlike activated carbon, biochar produced at certain pyrolysis conditions can be used directly without activation due to partitioning in the noncarbonized fractions or electrostatic attraction with O-containing carboxyl, hydroxyl, and
phenolic surface functional groups which could effectively bind with contaminants
(Uchimiya et al. 2012).
Generally, the functionality of biochar as a sorbent varies with pyrolysis temperature since the release of O- and H-containing functional groups changes its
surface polarity and aromaticity. Different types of contaminants also have varying
affinities with biochar. Organic contaminants can be removed from the soil and
aqueous solutions through adsorption, partitioning in the noncarbonized fraction, or
electrostatic attraction while inorganic pollutants can be removed by physical
adsorption, ion exchange, electrostatic attraction, or precipitation (Ahmad et al.
2014). Rice straw-derived biochar has also been found to be effective in treating
various soil and aqueous pollutants including pentachlorophenol, dyes, and lead
(Lou et al. 2011; Qiu et al. 2009; Jiang et al. 2012).
4.4.2 Slag, Vitrified Slag or Ash
Solid rock-like material, referred to as slag or vitrified slag, and greyish residue
called ash are considered to be byproducts of the gasification and combustion processes. These materials are derived from the inorganic fraction of the biomass.
Process conditions, such as temperature under which the inorganic materials from
the feedstock are being converted, determine the property of this material as to
whether a slag, vitrified slag, or ash will be formed. Heavy metals including chromium, lead, and mercury, which are considered as environmental hazards, may be
present in the slag, vitrified slag, or ash. Hence, the leachability of these metals from
the material should be tested. Slag, vitrified slag, and ash are typically disposed of
in landfills but these can potentially be converted into high-value products. Due to
its rock-like characteristics, slag or vitrified slag may be used as construction material, aggregates in asphalt or cement-concrete, pipe bedding material, decorative
tiles, and others if the Toxicity Characteristic Leaching Procedure (TCLP) standards
are being met. Ash, on the other hand, may be used as an additive for cement manufacturing (Young 2010).
Ash from gasification or combustion operations may also be utilized for cement
and concrete production, road pavement, glasses and ceramics, fertilizers, stabilizing agent,, and zeolite production (Lam et al. 2010). Furthermore, rice straw ash has
a high SiO 2 content ranging from 67.68 to 82.6% by weight as discussed in Chap. 1.
High silica content of about 73.65% SiO 2 of rice straw ash was also reported by
Chen et al. (2017). Silica from ash can be used to treat effluents containing heavy
metals (i.e. Pb
2+
, Cu
2+
, Cd
2+
, and Cr
2+
). Silica extraction from combustion ash has
already been studied by Caraos (2018) and Liu et al. (2014) via alkaline fusion and
hydrothermal desilication methods.
M. C. Maguyon-Detras et al.
et al. 2015. It is comparable to activated carbon, which is the most widely used
adsorbent. But unlike activated carbon, biochar produced at certain pyrolysis conditions can be used directly without activation due to partitioning in the noncarbonized fractions or electrostatic attraction with O-containing carboxyl, hydroxyl, and
phenolic surface functional groups which could effectively bind with contaminants
(Uchimiya et al. 2012).
Generally, the functionality of biochar as a sorbent varies with pyrolysis temperature since the release of O- and H-containing functional groups changes its
surface polarity and aromaticity. Different types of contaminants also have varying
affinities with biochar. Organic contaminants can be removed from the soil and
aqueous solutions through adsorption, partitioning in the noncarbonized fraction, or
electrostatic attraction while inorganic pollutants can be removed by physical
adsorption, ion exchange, electrostatic attraction, or precipitation (Ahmad et al.
2014). Rice straw-derived biochar has also been found to be effective in treating
various soil and aqueous pollutants including pentachlorophenol, dyes, and lead
(Lou et al. 2011; Qiu et al. 2009; Jiang et al. 2012).
4.4.2 Slag, Vitrified Slag or Ash
Solid rock-like material, referred to as slag or vitrified slag, and greyish residue
called ash are considered to be byproducts of the gasification and combustion processes. These materials are derived from the inorganic fraction of the biomass.
Process conditions, such as temperature under which the inorganic materials from
the feedstock are being converted, determine the property of this material as to
whether a slag, vitrified slag, or ash will be formed. Heavy metals including chromium, lead, and mercury, which are considered as environmental hazards, may be
present in the slag, vitrified slag, or ash. Hence, the leachability of these metals from
the material should be tested. Slag, vitrified slag, and ash are typically disposed of
in landfills but these can potentially be converted into high-value products. Due to
its rock-like characteristics, slag or vitrified slag may be used as construction material, aggregates in asphalt or cement-concrete, pipe bedding material, decorative
tiles, and others if the Toxicity Characteristic Leaching Procedure (TCLP) standards
are being met. Ash, on the other hand, may be used as an additive for cement manufacturing (Young 2010).
Ash from gasification or combustion operations may also be utilized for cement
and concrete production, road pavement, glasses and ceramics, fertilizers, stabilizing agent,, and zeolite production (Lam et al. 2010). Furthermore, rice straw ash has
a high SiO 2 content ranging from 67.68 to 82.6% by weight as discussed in Chap. 1.
High silica content of about 73.65% SiO 2 of rice straw ash was also reported by
Chen et al. (2017). Silica from ash can be used to treat effluents containing heavy
metals (i.e. Pb
2+
, Cu
2+
, Cd
2+
, and Cr
2+
). Silica extraction from combustion ash has
already been studied by Caraos (2018) and Liu et al. (2014) via alkaline fusion and
hydrothermal desilication methods.
M. C. Maguyon-Detras et al.