Ni recovery from serpentine soils by phytomining has proved feasible. Phytomining involves the crop of hyperaccumulating plants with high Ni contents and the valorization of Ni by pyro or hydrometallurgical process. In order to evaluate the Ni content of different plants, we analyzed the organs of 14 hyperaccumulators from three genera: Alyssum, Leptoplax and Bornmuellera. The highest concentration was recorded in the leaves of Leptoplax (34.3 +/- 0.7 mg g(-1)DM). Additionally, we investigated biomass combustion which is the first step of the process we designed to obtain a nickel salt. We showed that temperature and duration were important parameters to ensure a good quality of ashes. At the bench scale, the best conditions were 550 degrees C and 3 h. In this way, we obtained ashes in which Ni could reach 20 wt%. Biomass ashes can be considered as a bio-ore for recovering metal value.

International audiencePhytomining, now called agromining, consists of growing hyperaccumulator plants in order to farm metals and recover them from the biomass. This technology enables us to extract metals from secondary resources (e.g. metal containing-soils, mineral wastes, polluted soils) and manufacture high-value products. It has proved feasible for nickel, since more than 400 hyperaccumulators have been identified worldwide, able to accumulate at least 1% Ni in their tissues. Moreover, Ni is a target metal with a relatively high economic value.We have recently designed and patented a method for the synthesis of a nickel salt, ammonium nickel sulfate hexahydrate (ANSH: Ni(NH4)(2)(SO4)(2)center dot 6H(2)O), from the biomass of the hyperaccumulator plant Alyssum murale, grown in the Balkans. In this contribution, the process has been improved in order to save water, energy and chemicals, while producing a high purity salt. The biomass is dried and ashed, potassium is removed by washing ash with pure water following a cross-current pathway, nickel is extracted by acid leaching (2 M H2SO4, 95 degrees C, 2 h, mass fraction of 10%). The leachate is neutralized by Ca(OH)(2) to reach a pH of 4-5 and magnesium is removed by precipitating MgF2 after addition of NaF. Then volume is reduced by evaporation and ANSH crystallization is run at 2 degrees C for 4h. The crystals are dissolved and a second crystallization is run. The final ANSH was characterized by combined techniques (ICP-AES, XRD and gravimetric analysis), and the purity was 99.1 +/- 0.2