| Author(s): Chaney, Rufus L. (Beltsville, MD); J.S. Angle (Ellicot City, MD); Y.-M. Li (Potomac, MD); Assigned to the United States of America as represented by the Secretary of Agriculture (Washington, DC) & University of Maryland (College Park, MD) |
U.S. Patent & Trademark Office, Washington, DC. U.S. Patent 6,786,948, 7 Sep 2004
|
| Abstract: This patent describes a method of extracting nickel, cobalt, and other metals, including the platinum and palladium metal families, from soil by cultivation of the soil with hyperaccumulating plants that concentrate these metals in above-ground portions of the plants. The plants can be harvested, dried, and smelted to recover the metal in a process known as metal phytomining. The applicants have screened a large wild-type collection of germplasm to identity hyperaccumulating plants. Plants of the Brassicaceae family, particularly naturally occurring plants as opposed to those with induced mutations, are known to be Ni+Co accumulators. Alyssum species that are preferred candidates for use concentrate and hyperaccumulate nickel, show an enhanced uptake of cobalt, and may be useful in accumulating other metals. Preferred species have a preference for, and a high toxicity resistance to, these metallic elements. Rather than relying on the unpredictable process of mutagenesis, the applicants have screened a large library of wild-type germplasm and have identified several Alyssum species, including A. murale, A. pintodasilvae (A. serpyllifolium ssp.), A. malacitanum, A. lesbiacum, A. tenium, and A. fallacinum as suitable hyperaccumulators of nickel and useful in the enhanced uptake of cobalt. The same plants may also accumulate Pd, Rh, Ru, Pt, Ir, Os, and Re. While these platinum and palladium metals are accumulated in lower concentrations, their greater value per unit weight makes phytomining of these metals economically attractive as well. By definition, hyperaccumulator plants accumulate over 1000 mg Ni or Co/kg dry weight growing in the soils where they evolved. The identified metal species are accumulated by growing the Alyssum in nickel-rich soil under specific soil conditions, i.e., (1) lowering the soil pH, which increases the phytoavailability of nickel, (2) maintaining moderate levels of Ca in the soil by appropriate treatments and by use of Ca, (3) using ammonium-constraining or ammonium-generating nitrogen fertilizers to improve plant growth and to increase Ni hyperaccumulation due to rhizosphere acidification, and (4) applying chelating agents to the soil to improve nickel uptake by the roots of the hyperaccumulating Alyssum species. Examples of suitable chelating agents include nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid, and ethylene glycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid. |
