CHARACTERIZATION OF THE NICKEL-RICH EXTRACT FROM THE NICKEL HYPERACCUMULATOR DICHAPETALUM-GELONIOIDES

Following the discovery of the hyperaccumulation of nickel by the Philippine plant Dichapetalum gelonioides subsp. tuberculatum, the nature of the nickel in aqueous plant extracts has been investigated by gel chromatography, ion exchange chromatography, high voltage electrophoresis and GC-MS. The purified extract contained 18% Ni, 24% citric acid and 43% malic acid (mole ratio 1:0.4:1), the remainder consisting of small amounts of Ca, Mg, K, Na and a trace of tartaric acid. Experimental observations are discussed in terms of the stabilities of complexes of citrate and malate with Ni. By using X-ray crystallography it was shown that crystals obtained from a Ni-citrate-malate solution simulating the extract, contain Ni exclusively in the form of an anionic Ni(II)-citrato complex.