Modeling Precipitation and Sorption of Al, U and Co-contaminants during Titration of Acidic Sediments in Recirculation Flow-Through Experiments

Journal Article · Tue Jan 01 04:00:00 EST 2013 · Environmental Science & Technology

DOI:https://doi.org/10.1021/es400169y· OSTI ID:1082991

Tang, Guoping ^[1]; Luo, Wensui ^[2]; Brooks, Scott C ^[1]; Watson, David B ^[1]; Gu, Baohua ^[1]

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1. ORNL
2. Institute of Urban Environment, Chinese Academy of Sciences

We conducted batch and recirculating column titration tests with contaminated acidic sediments with controlled CO2 in the headspace, and extended the geochemical model by Gu et al. (2003, GCA) to better understand and quantify the reactions governing trace metal fate in the subsurface. The sediment titration curve showed slow pH increase due to strong buffering by Al precipitation and CO2 uptake. Assuming precipitation of basaluminite at low saturation index (SI=-4), and decreasing cation exchange selectivity coefficient (kNa\Al=0.3), the predictions are close to the observed pH and Al; and the model explains 1) the observed Ca, Mg, and Mn concentration decrease by cation exchange with sorbed Al, and 2) the decrease of U by surface complexation with Fe hydroxides at low pH, and precipitation as liebigite (Ca2UO2(CO3)3:10H2O) at pH>5.5. Without further adjustment geochemical parameters, the model describes reasonably well previous sediment and column titration tests without CO2 in the headspace, as well as the new large column test. The apparent inhibition of U and Ni decrease in the large column can be explained by formation of aqueous carbonate complexes and/or competition with carbonate for surface sites. These results indicated that ignoring labile solid phase Al would underestimate base requirement in titration of acidic aquifers.

• Research Organization: Oak Ridge National Laboratory (ORNL); Center for Computational Sciences
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1082991
• Journal Information: Environmental Science & Technology, Journal Name: Environmental Science & Technology Journal Issue: 11 Vol. 47; ISSN 0013-936X
• Country of Publication: United States
• Language: English