Numerical Simulations of Urea Hydrolysis and Calcite Precipitation in Porous Media Using STOMP
Subsurface radionuclide and trace metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of DOE’s greatest challenges for long-term stewardship. One promising in situ immobilization approach of these contaminants is engineered mineral (co)precipitation of calcite driven by urea hydrolysis that is catalyzed by enzyme urease. The tight nonlinear coupling among flow, transport, reaction and reaction-induced property changes of media of this approach was studied by reactive transport simulations with systematically increasing level of complexities of reaction network and physical/chemical heterogeneities using a numerical simulator named STOMP. Sensitivity studies on the reaction rates of both urea hydrolysis and calcite precipitation are performed via controlling urease enzyme concentration and precipitation rate constant according to the rate models employed. We have found that the rate of ureolysis is a dominating factor in the amount of precipitated mineral; however, the spatial distribution of the precipitates depends on both rates of ureolysis and calcite precipitation. A maximum 5% reduction in the porosity was observed within the simulation time period of 6 pore volumes in our 1-dimensional (1D) column simulations. When a low permeability inclusion is considered in the 2D simulations, the altered flow fields redistribute mineral forming constituents, leading to a distorted precipitation reaction front. The simulations also indicate that mineral precipitation occurs along the boundary of the low permeability zone, which implies that contaminants in the low permeability zone could be encapsulated and isolated from the flow paths.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- DOE - EM
- DOE Contract Number:
- DE-AC07-05ID14517
- OSTI ID:
- 1012404
- Report Number(s):
- INL/JOU-10-20563; TRN: US1102262
- Journal Information:
- Earth Science Frontiers, Vol. 17, Issue 6
- Country of Publication:
- United States
- Language:
- English
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in situ Calcite Precipitation for Contaminant Immobilization
Final report for DOE Grant No. DE-FG02-07ER64404 - Field Investigations of Microbially Facilitated Calcite Precipitation for Immobilization of Strontium-90 and Other Trace Metals in the Subsurface
Related Subjects
58 GEOSCIENCES
CALCITE
ENZYMES
HYDROLYSIS
PERMEABILITY
POROSITY
PRECIPITATION
RADIOISOTOPES
REACTION KINETICS
SENSITIVITY
SIMULATION
SIMULATORS
SPATIAL DISTRIBUTION
TRANSPORT
UREA
UREASE
calcite precipitation
in situ remediation
numerical simulation
STOMP
urea hydrolysis