Current status and challenges in developing nickel phytomining: an agronomic perspective
Résumé
Background Nickel (Ni) phytomining operations
cultivate hyperaccumulator plants (‘metal crops’)
on Ni-rich (ultramafic) soils, followed by harvesting
and incineration of the biomass to produce a
high-grade ‘bio-ore’ from which Ni metal or pure
Ni salts are recovered.
Scope This review examines the current status,
progress and challenges in the development of
Ni phytomining agronomy since the first field
trial over two decades ago. To date, the agronomy
of less than 10 species has been tested, while
most research focussed on Alyssum murale and
A. corsicum. Nickel phytomining trials have so
far been undertaken in Albania, Canada, France,
Italy, New Zealand, Spain and USA using ultramafic
or Ni-contaminated soils with 0.05–1 %
total Ni.
Conclusions N, P and K fertilisation significantly increases
the biomass of Ni hyperaccumulator plants, and
causes negligible dilution in shoot Ni concentration.
Organic matter additions have pronounced positive effects
on the biomass of Ni hyperaccumulator plants, but
may reduce shoot Ni concentration. Soil pH adjustments,
S additions, N fertilisation, and bacterial inoculation
generally increase Ni phytoavailability, and consequently,
Ni yield in ‘metal crops’. Calcium soil
amendments are necessary because substantial amounts
of Ca are removed through the harvesting of ‘bio-ore’.
Organic amendments generally improve the physical
properties of ultramafic soil, and soil moisture has a
pronounced positive effect on Ni yield. Repeated ‘metal
crop’ harvesting depletes soil phytoavailable Ni, but
also promotes transfer of non-labile soil Ni to
phytoavailable forms. Traditional chemical soil
extractants used to estimate phytoavailability of trace
element s are of limited use to predict Ni
phytoavailability to ‘metal crop’ species and hence
Ni uptake.
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