Changes in zinc speciation in field soil after contamination with zinc oxide.
Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn-phyllosilicate phases. However, no information on the kinetics of the formation of those phases under field conditions is currently available. In the present study, the transformation of Zn in a field soil artificially contaminated with ZnO containing filter dust from a brass foundry was monitored during 4 years using extended X-ray absorption fine structure (EXAFS) spectroscopy. Soil sections were studied by micro-X-ray fluorescence (micro-XRF) and micro-EXAFS spectroscopy. EXAFS spectra were analyzed by principal component analysis (PCA) and linear combination fitting (LCF). The results show that ZnO dissolved within 9 months and that half of the total Zn reprecipitated. The precipitate was mainly of the Zn-LDH type (>75%). Only a minor fraction (<25%) may be of Zn-phyllosilicate type. The remaining Zn was adsorbed to soil organic and inorganic particles. No significant changes in Zn speciation occurred from 9 to 47 months after the contamination. Thermodynamic calculations show that both Zn-LDH and Zn-phyllosilicate may form in the presence of ZnO but that the formation of Zn-phyllosilicate would be thermodynamically favored. Thus, the dominance of Zn-LDH found by spectroscopy suggests that the formation of the Zn precipitates was not solely controlled bythermodynamics but also contained a kinetic component. The rate-limiting step could be the supply of Al and Si from soil minerals to the Zn-rich solutions around dissolving ZnO grains.
Voegelin
Andreas
A
Institute of Terrestrial Ecology, Swiss Federal Institute of Technology (ETH) Zurich, Switzerland. voegelin@env.ethz.ch
Pfister
Sabina
S
Scheinost
Andreas C
AC
Marcus
Matthew A
MA
Kretzschmar
Ruben
R
D000042:Absorption; D000535:Aluminum / Q000032:analysis / Q000737:chemistry; D011232:Chemical Precipitation; D004784:Environmental Monitoring / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007287:Inorganic Chemicals / Q000032:analysis / Q000737:chemistry; D007700:Kinetics; D009930:Organic Chemicals / Q000032:analysis / Q000737:chemistry; D010316:Particle Size; D025341:Principal Component Analysis; D012822:Silicon Dioxide / Q000032:analysis / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis*; D013057:Spectrum Analysis; D013816:Thermodynamics; D013997:Time Factors; D017967:Zinc Compounds / Q000032:analysis*; D015034:Zinc Oxide / Q000737:chemistry*
D007287:Inorganic Chemicals; D009930:Organic Chemicals; D012989:Soil Pollutants; D017967:Zinc Compounds; D012822:Silicon Dioxide; D000535:Aluminum; D015034:Zinc Oxide