TY - JOUR
T1 - Acid Erosion of Carbonate Fractures and Accessibility of Arsenic-Bearing Minerals
T2 - In Operando Synchrotron-Based Microfluidic Experiment
AU - Deng, Hang
AU - Fitts, Jeffrey P.
AU - Tappero, Ryan V.
AU - Kim, Julie J.
AU - Peters, Catherine A.
N1 - Funding Information:
This work is supported by the National Science Foundation under Grant CMMI-0919140, NSF Grant CBET-1134397 to Princeton University, and Laboratory Directed Research and Development (LDRD) funding from Berkeley Lab, provided by the Director, Office of Science of the U.S. Department of Energy (DOE) under contract no. DE-AC02-05CH11231. It is also supported by Princeton Environmental Institute at Princeton University. Portions of this work were performed at the National Synchrotron Light Source under the U.S. DOE contract no. DE-AC02-98CH10886 and at the XFM (4-BM) Beamline of the NSLS II under the U.S. DOE contract no. DE-SC0012704 operated by Brookhaven National Lab. Portions of this work were performed at GeoSoilEnviroCARS (The University of Chicago, Sector 13), at the Advanced Photon Source, which is operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. GeoSoilEnviroCARS is supported by the National Science Foundation - Earth Sciences (EAR—1634415) and DOE GeoSciences (DE-FG02-94ER14466).
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/10/6
Y1 - 2020/10/6
N2 - Underground flows of acidic fluids through fractured rock can create new porosity and increase accessibility to hazardous trace elements such as arsenic. In this study, we developed a custom microfluidic cell for an in operando synchrotron experiment using X-ray attenuation. The experiment mimics reactive fracture flow by passing an acidic fluid over a surface of mineralogically heterogeneous rock from the Eagle Ford shale. Over 48 h, calcite was preferentially dissolved, forming an altered layer 200-500 μm thick with a porosity of 63-68% and surface area >10× higher than that in the unreacted shale as shown by xCT analyses. Calcite dissolution rate quantified from the attenuation data was 3 × 10-4 mol/m2s and decreased to 3 × 10-5 mol/m2s after 24 h because of increasing diffusion limitations. Erosion of the fracture surface increased access to iron-rich minerals, thereby increasing access to toxic metals such as arsenic. Quantification using XRF and XANES microspectroscopy indicated up to 0.5 wt % of As(-I) in arsenopyrite and 1.2 wt % of As(V) associated with ferrihydrite. This study provides valuable contributions for understanding and predicting fracture alteration and changes to the mobilization potential of hazardous metals and metalloids.
AB - Underground flows of acidic fluids through fractured rock can create new porosity and increase accessibility to hazardous trace elements such as arsenic. In this study, we developed a custom microfluidic cell for an in operando synchrotron experiment using X-ray attenuation. The experiment mimics reactive fracture flow by passing an acidic fluid over a surface of mineralogically heterogeneous rock from the Eagle Ford shale. Over 48 h, calcite was preferentially dissolved, forming an altered layer 200-500 μm thick with a porosity of 63-68% and surface area >10× higher than that in the unreacted shale as shown by xCT analyses. Calcite dissolution rate quantified from the attenuation data was 3 × 10-4 mol/m2s and decreased to 3 × 10-5 mol/m2s after 24 h because of increasing diffusion limitations. Erosion of the fracture surface increased access to iron-rich minerals, thereby increasing access to toxic metals such as arsenic. Quantification using XRF and XANES microspectroscopy indicated up to 0.5 wt % of As(-I) in arsenopyrite and 1.2 wt % of As(V) associated with ferrihydrite. This study provides valuable contributions for understanding and predicting fracture alteration and changes to the mobilization potential of hazardous metals and metalloids.
UR - http://www.scopus.com/inward/record.url?scp=85092681543&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85092681543&partnerID=8YFLogxK
U2 - 10.1021/acs.est.0c03736
DO - 10.1021/acs.est.0c03736
M3 - Article
C2 - 32845141
AN - SCOPUS:85092681543
SN - 0013-936X
VL - 54
SP - 12502
EP - 12510
JO - Environmental Science & Technology
JF - Environmental Science & Technology
IS - 19
ER -