The Long Road to Developing Agromining/Phytomining

The concept of phytomining is a natural extension of botanical prospecting and the study of metal biochemistry and biogeography of metal hyperaccumulator plants. Some elements may be phytoextracted to remediate soils, but the recovered biomass would have little economic value (e.g. Cd, As, etc.) and disposal of the biomass would be a cost. A few elements may have sufficient economic value in phytomining biomass to support commercial practice (Ni, Co, Tl and Au). The development of agro/phytomining requires (i) selection of high-biomass hyperaccumulator plant species; (ii) evaluation of genetic diversity and breeding of improved strains with higher yields of the phytoextracted element; (iii) development of agronomic practices to maximize economic return; and (iv) development of methods to recover the agromined element(s) from the plant biomass. Plant species and methods for agromining of soil Ni have been demonstrated for several species and locations (temperate and tropical climates). Production of Ni metal in an electric-arc furnace smelter, and of Ni(NH4)2SO4 using a hydrometallurgical method, and other metals (e.g. Zn, REEs) have been demonstrated. Full commercial agromining of Ni is underway in Europe (e.g. the Balkans, France) using Brassicaceae (notably Odontarrhena chalcidica—formerly Alyssum murale), and major trials in Malaysia are underway using Phyllanthus rufuschaneyi. Variable prices of commodity metals add constraints on the development of commercial agromining.