62
Phytotechnology with Biomass Production
arsenic, selenium) from the environment as one option of phytoremediation
(Pilon-Smits, 2005), the aim of phytomining processes is to extract commercially valuable elements from sources where the concentration of these
elements is too low for economic activities applying conventional mining
technologies, such as subeconomic ore bodies, mineral wastes (mine tailings), metal-bearing, or polluted soils, e.g., in (post-)mining areas (Heilmeier
& Wiche, 2020; Naila et al., 2019; Sheoran et al., 2009). Most prominent examples in phytomining applied “hyperaccumulator” plants, particularly for
nickel (e.g., Anderson et al., 1998; Kidd et al., 2018; Li et al., 2003) or gold
(e.g., Wilson-Corral et al., 2011). The term “hyperaccumulator” had been proposed by Brooks et al. (1977) for plant taxa that accumulate above 1000 mg
kg −1 of nickel (Ni) in their aboveground dry biomass. In the meantime, the
term “hyperaccumulator” has been applied to a number of different elements, with respective adjustments of the concentration level (Jaffré et al.,
2018; Rascio & Navari-Izzo, 2011; Van der Ent et al., 2013). Hyperaccumulator
plant species were first suggested by Chaney (1983) for the purpose of phytomining. Nicks & Chambers (1995, 1998) were the first to perform field trials
on phytomining of Ni, using the naturally occurring Ni-hyperaccumulator
Streptanthus polygaloides. Brooks et al. (1998) argued that phytomining of Ni
should be generally feasible due to a number of plants which accumulate
Ni to high shoot concentrations (>10,000 mg kg −1 ) and produce high biomass
(> 10 t ha −1 ). Soon, other elements such as thallium, copper, cobalt, and particularly gold have been tested for their phytomining potential (Anderson
et al., 1998; Sheoran et al., 2013; Wilson-Corral et al., 2011, 2012).
In this chapter advantages and limitations of phytomining will be discussed, followed by a description of field experiments, particularly for phytomining of gold and Ni applying the so-called “hyperaccumulator plants”
and recommendation for agronomic practices as derived from these experiments. Problems of economic viability and environmental implications will
be addressed, based on the outcomes of various modelling studies. Examples
on options of commercial application include phytomining for Ni from ultramafic soils, production of nanoparticles as catalysts, and extraction of valuable elements such as rare earth elements (REEs) from secondary sources for
raw materials such as mine tailings.
4.2 Advantages and Limitations of Phytomining
In comparison to conventional mining technologies phytomining has
several advantages. The two most important advantages are the fact that
phytomining offers the option to exploit ores that are not economic for
conventional mining approaches (Anderson et al., 1999), and the low cost
of operation (Robinson et al., 2003). Further advantages are the use of