Increasing purity of ammonium nickel sulfatehexahydrate and production sustainability in anickel phytomining process
2016
Zhang, Xin | Laubie, Baptiste | Houzelot, Vivian | Plasari, Edouard | Echevarria, Guillaume | Simonnot, Marie-Odile
Phytomining, now called agromining, consists of growing hyperaccumulator plants in orderto farm metals and recover them from the biomass. This technology enables us to extractmetals 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 400hyperaccumulators have been identified worldwide, able to accumulate at least 1% Ni intheir 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)2·6H2O), from the biomass ofthe hyperaccumulator plant Alyssum murale, grown in the Balkans. In this contribution, theprocess has been improved in order to save water, energy and chemicals, while producinga high purity salt. The biomass is dried and ashed, potassium is removed by washing ashwith pure water following a cross-current pathway, nickel is extracted by acid leaching (2 MH2SO4, 95◦C, 2 h, mass fraction of 10%). The leachate is neutralized by Ca(OH)2to reach a pHof 4–5 and magnesium is removed by precipitating MgF2after addition of NaF. Then volumeis reduced by evaporation and ANSH crystallization is run at 2◦C for 4 h. The crystals are dis-solved and a second crystallization is run. The final ANSH was characterized by combinedtechniques (ICP-AES, XRD and gravimetric analysis), and the purity was 99.1 ± 0.2%.
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