TY - JOUR
T1 - Iron Isotopes in Acid Mine Drainage
T2 - Extreme and Divergent Fractionation between Solid (Schwertmannite, Jarosite, and Ferric Arsenate) and Aqueous Species
AU - Burton, Edward D.
AU - Karimian, Niloofar
AU - Hamilton, Jessica L.
AU - Frierdich, Andrew J.
N1 - Funding Information:
Funding was provided by the Australian Research Council under grant number FT200100449, with additional funding provided by Southern Cross University. X-ray absorption spectroscopy (XAS) analyses at the Australian Synchrotron was funded by the Australian Nuclear Science and Technology Organization.
Publisher Copyright:
© 2022 American Chemical Society.
PY - 2022/11/28
Y1 - 2022/11/28
N2 - Examination of stable Fe isotopes is a powerful tool to explore Fe cycling in a range of environments. However, the isotopic fractionation of Fe in acid mine drainage (AMD) has received little attention and is poorly understood. Here, we analyze Fe isotopes in waters and Fe(III)-rich solids along an AMD flow-path. Aqueous Fe spanned a concentration and δ56Fe range of ∼420 mg L-1 and + 0.04‰ at the AMD source to ∼100 mg L-1 and -0.81‰ at ∼450 m downstream. Aqueous As (up to ∼33 mg L-1) and SO42- (up to ∼2000 mg L-1), like aqueous Fe, decreased in concentration down the flow-path. X-ray absorption spectroscopy indicated that downstream attenuation in aqueous Fe, As, and SO42- was due to the precipitation of amorphous ferric arsenate (AFA), schwertmannite, and jarosite. The Fe(III) in these solids displayed extreme variability in δ56Fe, spanning +3.95‰ in AFA near the AMD source to -1.34‰ in schwertmannite at ∼450 m downstream. Similarly, the isotopic contrast between solid Fe(III) precipitates and aqueous Fe (Δ56Feppt-aq) dropped along the flow-path from about +4.1 to -1.1‰. The shift from positive to negative Δ56Feppt-aq reflects divergence between competing equilibrium versus kinetic fractionation processes.
AB - Examination of stable Fe isotopes is a powerful tool to explore Fe cycling in a range of environments. However, the isotopic fractionation of Fe in acid mine drainage (AMD) has received little attention and is poorly understood. Here, we analyze Fe isotopes in waters and Fe(III)-rich solids along an AMD flow-path. Aqueous Fe spanned a concentration and δ56Fe range of ∼420 mg L-1 and + 0.04‰ at the AMD source to ∼100 mg L-1 and -0.81‰ at ∼450 m downstream. Aqueous As (up to ∼33 mg L-1) and SO42- (up to ∼2000 mg L-1), like aqueous Fe, decreased in concentration down the flow-path. X-ray absorption spectroscopy indicated that downstream attenuation in aqueous Fe, As, and SO42- was due to the precipitation of amorphous ferric arsenate (AFA), schwertmannite, and jarosite. The Fe(III) in these solids displayed extreme variability in δ56Fe, spanning +3.95‰ in AFA near the AMD source to -1.34‰ in schwertmannite at ∼450 m downstream. Similarly, the isotopic contrast between solid Fe(III) precipitates and aqueous Fe (Δ56Feppt-aq) dropped along the flow-path from about +4.1 to -1.1‰. The shift from positive to negative Δ56Feppt-aq reflects divergence between competing equilibrium versus kinetic fractionation processes.
KW - AMD
KW - arsenic
KW - iron isotopes
KW - jarosite
KW - schwertmannite
UR - http://www.scopus.com/inward/record.url?scp=85143423795&partnerID=8YFLogxK
U2 - 10.1021/acs.est.2c05999
DO - 10.1021/acs.est.2c05999
M3 - Article
C2 - 36442144
AN - SCOPUS:85143423795
SN - 0013-936X
VL - 56
SP - 18060
EP - 18068
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 24
ER -