Agriculture Reference
In-Depth Information
Moreno et al., 2001a, 2001b; Ouki and Kavannagh, 1999; Pansini & Colella, 1990; Querol et
al., 1999, 2001, 2002; 2006; Rayalu et al., 2006; Stefanović et al., 2007; Torracca et al., 1998;
Woolard et al., 2000; Wu et al., 2008). All this is strictly connected with their ability to
exchange cations, their large surface area, and their typical structural characteristics (such as
porosity), which facilitate pollutant absorption and encapsulation.
This mineral can be synthesized from different source materials and fly ash is one of the
most used (Berkgaut & Singer, 1996; Querol et al., 2002; Shih & Chang, 1996; Shigemoto et
al., 1993). Numerous methods have been suggested for the zeolite synthesis including
hydrothermal reaction (Holler & Wirsching, 1985; Murayama et al., 2002; Querol et al., 1995;
1997a; 2001; Shih and Chang, 1996; Tanaka et al., 2003), hydrothermal reaction with a fusion
pre-treatment (Berkgaut & Singer, 1996; Chang & Shih, 1998; Rayalu et al., 2000; Shigemoto
et al., 1993, 1994), molten-salt methods (Park et al., 2000a; 2000b), methods employing
microwaves (Inada et al., 2005; Katsuki et al., 2001; Querol et al., 1997b; Slangen et al., 1997)
and ultrasonic treatments (Belviso et al., 2011; Lie et al. 1995; Park et al., 2001; Wang et al.,
2008). Distilled water is used in most of the experiments conducted with these different
methods, whereas the synthesis of zeolite with seawater is described in very few articles
(e.g. Belviso et al., 2009; 2010a; Lee et al, 2001).
The authors carried out experiments on zeolite synthesis at low temperature in a soil
artificially contaminated with heavy metals (in separate experiments) and treated with fly
ash. The role played by this mineral in the immobilization of heavy metals was investigated
(Belviso et al. 2010b; c). The results obtained show that the direct synthesis of zeolite takes
place readily after a month and the amount of the newly-formed mineral increases during
the entire experimentation period. The presence of heavy metal does not exert any influence
on zeolite formation which, on the contrary, plays a leading role in the mechanism of the
toxic element immobilization. In fact, a reduction in toxic element availability characterizes
the soil samples in which zeolite was synthesized. In particular the data about Ni (Belviso et
al., 2010b) and Pb suggest that the mobilization of this elements takes place only after zeolite
structure is destroyed. This causes the availability of the metals, previously trapped in the
mineral and/or co-precipitated on its surfaces in the oxidable and hydroxide form
respectively. In all cases synthetic zeolite forms complexes with the toxic metals which are
broken by a strong chemical attack but are stable under normal environmental conditions.
4. Conclusion
Soil pollution is a worldwide environmental problem and the current technologies used for
remediation are generally very expensive. In this context, the development of low cost
remediation methods using various industrial residues which do not alter the physical and
chemical properties of soils plays a leading role. This would also reduce waste disposal
giving new value to industrial wastes through converting them into industrial by-products.
Particularly fly ash and red muds could be cost-effective materials capable of treating a
variety of contaminants.
A deeply characterization of this waste materials by multi-technique approach is
fundamental for their application. In particular, in this study the application of field and
laboratory imaging spectroscopy for identifying and mapping soils containing pollutants,
such as red dust, was successfully used in a multi-technique approach for waste material
detection and soil quality and remediation strategies assessment.
