69
Phytomining
were studied by Novo et al. (2015) for phytomining potential of Rhenium with
Indian mustard (expected profit ca. 4000 US-$ ha −1 ) and Shi et al. (2020) for platinum group metals to obtain nanoparticles, both under controlled conditions.
One of the earliest extended field experiments on phytoremediation of a former
Uranium mining site (plot size 2 m×2m, 1m deep) was performed by Willscher
et al. (2013) at Ronneburg (Thuringia, Germany). Soil improvement (amendment
with calcareous top soil, mycorrhiza+bacteria) reduced the concentration of
contaminants in seepage water, and rates and loads of seepage water. Neither
ethanol fermentation nor biogas production was inhibited by uranium or heavy
metals accumulated in low concentrations in the plant biomass; thus, the plant
material from phytoremediation could be used for winning of bioenergy.
Another large-scale experiment for remediation of polluted soils via phytotechnologies has been carried out in Southwestern Europe (PhytoSUDOE,
2019). Nonfood crops, supported by soil amendments such as compost and
bioaugmentation (inoculation with beneficial microorganisms), have been
cultivated for rehabilitation of contaminated sites and production of useable
biomass in Portugal, Spain, and France.
As shown by Harumain et al. (2017) and Midula et al. (2017), mine tailings
are a huge reservoir of secondary resources, not only of elements considered traditionally in phytomining such as gold and nickel but also of less
common elements such as palladium (Pd), germanium (Ge), and REEs. The
phytomining potential for Ge and REEs has been investigated for a number
of herbaceous plant species (both forbs and grasses) at experimental field
sites close to Freiberg (Saxony, Germany), with the option to generate bioenergy either via fermentation or combustion. Whereas grasses such as Ph.
arundinacea, Avena sativa, or Zea mays proved to be good accumulators for Ge
due to their high capacity for uptake of the chemically similar Silicium, forbs
like Fagopyrum esculentum or Brassica napus turned out to accumulate high
amounts of REEs (Wiche & Heilmeier, 2016). Intercropping of A. sativa (oat)
with Lupinus albus (white lupine), a leguminous plant with a high capacity for
exudation of organic acids (e.g., citric acid) which can increase bioavailability
of elements in the soil, increased accumulation of REEs in oat (Wiche et al.,
2016). According to an economic analysis by Rentsch et al. (2016), both the
accumulation of target elements in the plants and the high costs of extraction
of target elements from fly ash after combustion of fermentation residues
from biogas production are key factors for economic feasibility.
4.7 Conclusions and Perspectives
Although there are still major challenges to be passed for an economically viable application of phytomining on a broad scale, such as selection and improvement of promising target plants and the low bioavailability of target elements
Phytomining
were studied by Novo et al. (2015) for phytomining potential of Rhenium with
Indian mustard (expected profit ca. 4000 US-$ ha −1 ) and Shi et al. (2020) for platinum group metals to obtain nanoparticles, both under controlled conditions.
One of the earliest extended field experiments on phytoremediation of a former
Uranium mining site (plot size 2 m×2m, 1m deep) was performed by Willscher
et al. (2013) at Ronneburg (Thuringia, Germany). Soil improvement (amendment
with calcareous top soil, mycorrhiza+bacteria) reduced the concentration of
contaminants in seepage water, and rates and loads of seepage water. Neither
ethanol fermentation nor biogas production was inhibited by uranium or heavy
metals accumulated in low concentrations in the plant biomass; thus, the plant
material from phytoremediation could be used for winning of bioenergy.
Another large-scale experiment for remediation of polluted soils via phytotechnologies has been carried out in Southwestern Europe (PhytoSUDOE,
2019). Nonfood crops, supported by soil amendments such as compost and
bioaugmentation (inoculation with beneficial microorganisms), have been
cultivated for rehabilitation of contaminated sites and production of useable
biomass in Portugal, Spain, and France.
As shown by Harumain et al. (2017) and Midula et al. (2017), mine tailings
are a huge reservoir of secondary resources, not only of elements considered traditionally in phytomining such as gold and nickel but also of less
common elements such as palladium (Pd), germanium (Ge), and REEs. The
phytomining potential for Ge and REEs has been investigated for a number
of herbaceous plant species (both forbs and grasses) at experimental field
sites close to Freiberg (Saxony, Germany), with the option to generate bioenergy either via fermentation or combustion. Whereas grasses such as Ph.
arundinacea, Avena sativa, or Zea mays proved to be good accumulators for Ge
due to their high capacity for uptake of the chemically similar Silicium, forbs
like Fagopyrum esculentum or Brassica napus turned out to accumulate high
amounts of REEs (Wiche & Heilmeier, 2016). Intercropping of A. sativa (oat)
with Lupinus albus (white lupine), a leguminous plant with a high capacity for
exudation of organic acids (e.g., citric acid) which can increase bioavailability
of elements in the soil, increased accumulation of REEs in oat (Wiche et al.,
2016). According to an economic analysis by Rentsch et al. (2016), both the
accumulation of target elements in the plants and the high costs of extraction
of target elements from fly ash after combustion of fermentation residues
from biogas production are key factors for economic feasibility.
4.7 Conclusions and Perspectives
Although there are still major challenges to be passed for an economically viable application of phytomining on a broad scale, such as selection and improvement of promising target plants and the low bioavailability of target elements