A new process for nickel ammonium disulfate production from ash of the hyperaccumulating plant Alyssum murale

The extraction of nickel (Ni) from ultramafic soils by phytomining can be achieved using Alyssum murale cultures. This study presents a new process for the valorization of Ni accumulated by this plant through the production of a Ni ammonium disulfate salt (Ni(NH4)2(SO4)2.6H2O). The process comprises an initial leaching of the ashes of A. murale with a sulphuric acid solution (1.9 M H2SO4, T = 95 °C, t = 240 min, TS = 150 g ash L− 1), producing a leachate rich in Ni (10.2 g Ni L− 1; 96% Ni solubilisation), Mg, P, K, Fe, Ca and Al. The pH of the acid leachate is increased to 5.0 with NaOH (5 M), followed by an evaporation step which produced a purified solution rich in Ni (21.3 g Ni L− 1) and an iron hydroxide precipitate. The cold crystallization (T = 2 °C, t = 6 h) of this solution by the stoichiometric addition (× 1.2) of ammonium sulfate generates a Ni ammonium disulfate salt, containing 13.2% Ni, that is potentially valuable to industry.

► Ni accumulated by phytomining is solubilized by H2SO4 leaching at 95 °C.
► Ni solubilized is recovered after iron precipitation and cold crystallization.
► Ni ammonium disulfate salt (Ni(NH4)2(SO4)2·6H2O) produced contains 13.2% Ni.