Characterisation and hydrometallurgical processing of nickel from tropical agromined bio-ore
Résumé
Hyperaccumulator plants ("metal crops") can be used for selective extraction of Ni from low-grade resources, thereby producing a high-grade "bio-ore". This so-called agromining (or phytomining) technology involves farming select metal crops on ultramafic soils, mineral wastes, or overburden that are sub-economic Ni resources for conventional extractive technology. Key to profiting from agromining is the efficient recovery of Ni and by-products from the bio-ore, either directly from freshly harvested biomass or from the ash after incineration. Bio-ore of wild grown specimens of the Ni hyperaccumulator plants Rinorea bengalensis and Phyllanthus securinegoides were collected in Malaysia. After incineration, the ash composites contained 5.5.and 12.7 wt% Ni for Rinorea and Phyllanthus respectively, along with substantial amounts of Ca, K, C, Mg, P, Na, S and Cl. Other minor impurities included Si, Fe, Al, Mn and Zn. The solids were characterised in detail by SEM-EDS, XRD and XANES. The effect of solution chemistry on the leaching behaviour of the bio-ore (dried biomass and ash) was also assessed. A hydrometallurgical process for recovering Ni from the bio-ore was then demonstrated. The processes involves the bio-ore (ash) being water-washed, yielding >90% recovery of K to solution. After water washing, >95% Ni recovery was achieved by H2SO4 leaching at 60 degrees C, although long residence times and high acid concentrations were required. Ni(OH)(2) was then precipitated from solution using the K2CO3 rich wash-water. The bio-ore generated precipitant was compared with NaOH and MgO used industrially.