Processing of Hyperaccumulator Plants to Nickel Products

Hyperaccumulator plants may contain valuable metals at concentrations comparable to conventional ore and can be significantly upgraded by incineration. There is an incentive to recover these metals as products in order to counterbalance the cost of disposing the contaminated biomass from contaminated soils, mine tailings, and processing wastes. Metal recovery has become an essential challenge as conventional ore grades decrease. Metal recovery is included in the agromining chain, which has been developed over the past two decades for Ni. More than 520 Ni hyperaccumulator species are currently known and some of these grow quickly providing a high-farming yield. Nickel recovery has been investigated at the laboratory scale and some processes have been upscaled. Most often, dry plants are burnt to produce ash, which has a very high Ni content, then the Ni in the ash is leached into aqueous solution. From there, the Ni is recovered by precipitation to obtain Ni salts or oxide. This hydrometallurgical route has now been scaled up. Other studies have aimed to obtain catalysts from ash or direct extraction of Ni from the plants. In the latter case, further processing requires complicated purification steps. Finally, the plants have also been treated by pyrometallurgical processes to produce Ni metal; initial studies have been carried out using pyrolysis. Interest in the production of carbon-supported Ni catalyst materials is increasing day by day, owing to the potential capacities of these products for use in bio-refineries. Finally, economic and environmental considerations are proposed here for supporting the interest of Ni recovery by agromining.