Current status and challenges in developing Ni phytomining: An agronomic perspective

Authors: NKRUMAH, PHILIP - University Of Queensland; BAKER, ALAN - University Of Melbourne; Chaney, Rufus; ERSKINE, PETER - University Of Queensland; ECHEVARRIA, GUILLAUME - Université De Lorraine; MOREL, JEAN LOUIS - Université De Lorraine; VAN DER ENT, ANTONY - University Of Queensland

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2016
Publication Date: 3/19/2016
Citation: Nkrumah, P.N., Baker, A.J., Chaney, R.L., Erskine, P.D., Echevarria, G., Morel, J., Van Der Ent, A. 2016. Current status and challenges in developing Ni phytomining: An agronomic perspective. Plant and Soil. 406:55-69. doi: 10.1007/s11104-016-2859-4.

Interpretive Summary: Phytomining is a new technology in which unusual plants which can accumulate over 1% nickel are grown as a farmed crop accumulate soil metals into the plant shoots where they can be recovered and marketed. With the expiration of the initial patents on this technology, the commercial application of nickel phytomining is being considered for many locations where soils naturally contain high levels of nickel from geological enrichment, or from industrial contamination such as mine and smelter contamination. This review paper summarizes the characteristics of plant species which accumulate over 1% Ni (hypernickelophores), their physiology and biochemistry, and the agronomic practices needed to grow high annual yields on nickel rich soils. Most extensive arable ultramafic soils rich in nickel, enough to support phytomining, occur in the Mediterranean region, or in tropical nations. These locations were also found to have evolved plant species which hyperaccumulate nickel and promise to support commercial phytomining. hese soils are commonly extremely deficient in phosphorus and calcium for normal plant growth, but with meager fertilization can produce high yields of the phytomining crops. Although some have suggested that crop plants could be used for phytomining or phytoremediation, it is evident from the information summarized in this paper that crop plants have no role in phytomining. Other agronomic practices are discussed including inoculation with rhizosphere or endophytic microbes or plant hormone sprays which might stimulate growth or accumulation of metals. Last, the conversion of biomass into nickel products is discussed. One of the complications of evaluating soils for potential value in nickel phytomining is that most soil extraction methods show much higher extractable nickel at lower pH of a soil, while the studied Alyssum species show lower accumulation of nickel at lower pH; no reliable predictive chemical extraction of phytominable Ni has been identified yet.

Technical Abstract: This review examines the current status, progress and challenges in Ni phytomining agronomy undertaken since the first field trial two decades ago. To date, over 400 Ni hyperaccumulators have been documented (of which >30% are in Cuba) including approximately 50 species with potential for use in Ni phytomining. Of these, the agronomy of <10 species has been tested with most research focusing on Alyssum murale and A. corsicum. Nickel phytomining pot or field trials have been undertaken in Albania, Canada, Italy, New Zealand, Spain, USA and Zimbabwe using ultramafic or Ni refinery contaminated soils with 0.05–1% total Ni. Soil and plant management practices, including nutrient amendment, soil pH adjustment, phytohormone application and bacterial inoculation, have been undertaken to increase biomass production, Ni uptake and accumulation. Biomass is harvested either manually or mechanically and dried in the open air. Field and laboratory agronomic trials are pre-requisites to large-scale demonstration and commercial operation which are likely to be established in Albania, Turkey, Indonesia, Malaysia, New Caledonia and the Philippines.