Author
 |
Chaney, Rufus |
|
Submitted to: Proceedings of the International Minerals Processing Congress
Publication Type: Proceedings Publication Acceptance Date: 4/29/2016 Publication Date: 9/11/2016 Citation: Chaney, R.L. 2016. Phytomining of Ni from mineralized or contaminated soils available to industry. Proceedings of the 28th International Minerals Processing Congress, Quebec City, Quebec, Canada, September 11-16, 2016. Proceedings ISBN: 978-1-926872-29-2. Paper 479:1-9. Interpretive Summary: Soils with high levels of plant available nickel (Ni) require remediation to protect the environment. This can be achieved by either phytostabilization or phytomining. In phytostabilization, after agronomic soil analysis, soil amendments needed to persistently prevent Ni phytotoxicity and to improve soil fertility are assessed. Both greenhouse pot experiments and field tests have shown that making soils fertile and calcareous can restore normal fertility for diverse plant species on such previously barren Ni phytotoxic soils. The alternative to phytostabilization is phytomining in which plants which accumulate very high concentrations of shoot Ni when grown on Ni mineralized or contaminated soils are grown to produce a crop of nickel. Rare nickel "hypernickelophores" accumulate over 1% Ni in their shoot dry matter, and can yield as high as 400 kg Ni per ha on soils where normal crop plants give poor yields. Fertilizer and cropping management practices needed to maximize annual yield of biomass Ni were determined by experiment, and diverse genotypes evaluated to allow breeding of improved cultivars of Alyssum murale and Alyssum corsicum. Basic studies have clarified the mechanisms used by Alyssum roots to obtain soil Ni, and to transport to the shoots and store the Ni in non-toxic forms in epidermal cell vacuoles. One of the remarkable aspects of Ni phytomining is that Alyssum species accumulate higher concentration of shoot Ni as soil pH rises, but the dissolved Ni in soil solution falls as pH rises. The quite low concentration of Ni in soil solution of serpentine soils cannot supply all that Ni by convection of soil solution to the roots; rather, diffusion from soil solid phases to the root surface, and extensive root length in the soils allows the hyperaccumulation to occur. The expiration of our existing patents on the phytomining technologies offer new opportunities for commercial Ni phytomining. Technical Abstract: A new technology is available to the Ni mining and remediation community to "phytomine" Ni from mineralized or contaminated soils using rare plants which hyperaccumulate Ni to over 1% of shoot dry matter. Research has identified useful plant species, and even bred improved cultivars of Alyssum murale and Alyssum corsicum for commercial phytomining in temperate regions. All agronomic practices (fertilization, soil amendments, planting and harvest methods) needed for economic phytomining were identified to attain high yields and high Ni concentration in the biomass. In tropical regions, other species are available such as Phyllanthus which accumulate over 1% Ni in dry shoots. These species are perennial so they re-grow after annual cutting to harvest biomass. Expiration of our patents on the technology opens the opportunity for other organizations which control Ni rich natural soils or contaminated soils requiring remediation to commercialize the technologies. Inexpensive methods to remediate/revitalize Ni contaminated phytotoxic soils using agronomic approaches have also been developed and demonstrated at Port Colborne, Ontario, but adoption is delayed until formal agreements with government are completed. These new simple remediation and profitable phytomining technologies can obtain Ni from soils which contain Ni well below levels considered economic for current mining technologies, and the plants biopurify the Ni so it is easy to recover Ni metal from plant ash by pyrometallurgical or hydrometallurgical technologies. Although increasing pH decreases the solubility of Ni in all soils, raising pH increases Ni accumulation by Alyssum species. Hence usual chemical extraction methods for phytoavailable soil metals such as the DTPA- or ammonium acetate-extraction cannot predict Ni accumulation by Alyssum species. |
