title: Leaching potential of geogenic nickel in serpentine soils from Taiwan and Austria.
abstract: Serpentine soils may be natural sources of metal leaching and pollution. In this study, two contrasting serpentine soils from Taiwan and Austria were selected to evaluate the leaching potential of geogenic nickel (Ni). We applied selective sequential extractions and dissolution kinetics with three inorganic acids (HCl, HNO3, and H2SO4) and three organic acids (citric, acetic, and oxalic acids) in concentrations ranging from 0.05 to 10 mM to determine the release rate of Ni in the soils with respect to pH and acid types. Chlorite and serpentine were the major Ni-bearing minerals in the studied soils. Ni was dominantly bound in unavailable forms within these silicate minerals, but smaller fractions of acid-soluble, Fe-Mn oxide-bound, and organically bound Ni represented more labile Ni sources in the soils. The release rate of Ni from the soils increased with decreasing pH in all acids. However, the organic acids caused stronger pH dependences than the inorganic acids, likely because of ligand-promoted dissolution. The maximum total rate of Ni dissolution occurred with citric acid in both soils. The dissolution of Ni strongly increased when the ionic strength in the background solutions increased. We observed marked differences in dissolution rates and ligand effects between the Austrian and Taiwanese soils, which reflect differences in labile Ni pools, especially in the organically bound fraction. Our results demonstrate that labile fractions control the leaching potential of Ni in serpentine soils and that Ni associated with soil organic matter may contribute to leaching at moderately acidic pH levels.
authors.affiliation: Department of Agricultural Chemistry, National Taiwan University, Taipei 10617, Taiwan. Electronic address: zyhseu@ntu.edu.tw.
authors.forename: Zeng-Yei
authors.initials: ZY
authors.lastname: Hseu
authors.affiliation: Department of Environmental Science and Engineering, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan.
authors.forename: Ying-Ching
authors.initials: YC
authors.lastname: Su
authors.affiliation: Institute of Soil Research, University of Natural Resources and Life Sciences, A-1190 Vienna, Austria.
authors.forename: Franz
authors.initials: F
authors.lastname: Zehetner
authors.affiliation: Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: Hsing-Cheng
authors.initials: HC
authors.lastname: Hsi
mesh_terms: D001317:Austria; D001682:Biological Availability; D005591:Chemical Fractionation; D002712:Chlorides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009532:Nickel / Q000032:analysis* / Q000493:pharmacokinetics; D009994:Osmolar Concentration; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis* / Q000493:pharmacokinetics; D013624:Taiwan
chemical_list: D002712:Chlorides; D012987:Soil; D012989:Soil Pollutants; D009532:Nickel; C001599:chlorite
keywords: Acid rain; Bioavailability; Leaching; Nickel; Serpentine soil