Aerial deposition of Ni from a refinery in Port Colborne, Ontario, Canada has resulted in the enrichment of 29 km2 of land with Ni concentrations exceeding the Canadian Ministry of the Environment's remedial action level of 200 mg kg-1. Several studies on these soils have shown that making the soils calcareous was effective at reducing chemically extractable Ni, as well as alleviating Ni phytotoxicity symptoms in vegetable crops grown in the vicinity of the refinery. Conversely, dolomitic limestone additions resulted in increased uptake of Ni in the Ni hyperaccumulator Alyssum murale 'Kotodesh', a plant whose use was proposed as a remediation strategy for this area. In this paper we use multiple techniques to directly assess the role soil type and lime treatments play in altering the speciation of Ni in the Welland loam and Quarry muck soils around the refinery and relate these findings to Ni mobility and bioavailability. Stirred-flow dissolution experiments using pH 4 HNO3 showed that Ni release from the limed Quarry muck and Welland loam soils was reduced (∼0.10%) relative to the unlimed soils (∼2.0%). Electron microprobe analysis (EMPA) identified approximately spherical NiO and Ni metal particles, which are associated with no other metals, and range from 5 to 50 μm in diameter. Synchrotron micro-X-ray absorption fine structure and X-ray fluorescence spectroscopies showed that Ni and Al layered double hydroxide (Ni-Al LDH) phases were present in both the limed and unlimed mineral soils, with a tendency towards more stable (e.g., aged-LDH and phyllosilicate) Ni species in the limed soil, possibly aided by the solubilization of Si with increasing pH. In the muck soils, Ni-organic complexes (namely fulvic acid) dominated the speciation in both limed and unlimed soils. The results reported herein show that both soil type and treatment have a pronounced effect on the speciation of Ni in the soils surrounding the Port Colborne refinery. We provide the first evidence that Ni-Al LDH phases can form in anthropogenically enriched mineral field soils at circumneutral pH, and can lead to a reduction in Ni mobility. In the organic soils Ni is strongly complexed by soil organic matter; a property enhanced with liming. Interestingly, increased accumulation of Ni by A. murale grown in the limed muck and loam soils indicates that the plant may be capable of removing Ni from those fractions typically considered unavailable to most plants.
|Number of pages||19|
|Journal||Geochimica et Cosmochimica Acta|
|State||Published - May 1 2007|
Bibliographical noteFunding Information:
The authors would like to thank Kirk Scheckel, Andreas Scheinost, Ted Peltier, Maarten Nachtegaal and Timothy Strathman for supplying XAFS spectra for selected references. We would like to thank Matthew Marcus for assistance with μ-XAFS data collection at the Advanced Light Source beamline 10.3.2 and the staff of beamline X11A at the National Synchrotron Light Source (NSLS) for their assistance in the collection of the EXAFS standards spectra. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886. We would also like to thank Ken Livi of the Department of Earth and Planetary Sciences at Johns Hopkins University for help with EMPA data collection, analysis and interpretation. The authors would also like to thank all reviewers for their constructive comments and advice.
ASJC Scopus subject areas
- Geochemistry and Petrology