Evaluation of the performance of nickel hyperaccumulator plants as combustion fuel

Abstract

Agromining is an emerging technology aiming at recovering metals from soils using hyperaccumulator (HA) plants. Plant cultivation and pyro- and hydrometallurgical processes have been designed for nickel (Ni) recovery. In this chain of processes, dry plants are burnt to obtain Ni-rich ashes that are subsequently treated. To ensure the sustainability and the profitability of the process, energy recovered at the combustion stage would add some value. The combustion of three Ni HA plants (Odontarrhena chalcidica, Leptoplax emarginata and Berkheya coddii) was investigated. Namely the higher and lower heating values (HHV and LHV) were measured with a calorimeter bomb and calculated with correlations, thermo-gravimetric analysis was performed, dry plants and ashes were characterized, and gas emissions were monitored during combustion at two temperatures. In a complementary approach, the self-heating behaviour of plants and ashes were compared, and the activation energy of such phenomenon was determined. These results allowed the identification of the step limiting the self-inflammation of the plants, which gives relevant information for their safe storage.