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Reactive Solute Transport in Heterogeneous Porous Media

Title: Reactive Solute Transport in Heterogeneous Porous Media: Numerical Simulation of Urea Hydrolysis and Calcite Precipitation Using STOMP.
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Name(s): Guo, Luanjing, author
Hu, Bill X., professor directing thesis
Kish, Stephen A., committee member
Ye, Ming, committee member
Department of Earth, Ocean and Atmospheric Sciences, degree granting department
Florida State University, degree granting institution
Type of Resource: text
Genre: Text
Issuance: monographic
Date Issued: 2009
Publisher: Florida State University
Place of Publication: Tallahassee, Florida
Physical Form: computer
online resource
Extent: 1 online resource
Language(s): English
Abstract/Description: Department of Energy (DOE) proposed an in situ remediation approach to radioactive metal contaminants in DOE complex through calcite mineral precipitation facilitated by hydrolysis of urea (ureolysis). One of the ureolysis products, aqueous ammonium, can desorb metal contaminants and calcium ions from solid phase of the subsurface medium through cation exchange. The other ureolysis product, bicarbonate, is a mineral-forming constituent that participates in both coprecipitation of contaminants into calcite and encapsulation and isolation of contaminants through calcite precipitation to enhance the capture of the contaminants in a more stable solid phase. In this study, numerical modeling is used to simulate the above processes. The transport of species undergoing complicated chemical reactions is simulated using STOMP to better understand the coupling of various geochemical processes. Sensitivity studies on the reaction rates of urea hydrolysis and calcite precipitation are conducted by adjusting two parameters in the rate models used for urea hydrolysis and calcite precipitation: urease concentration [E0] and the kinetic reaction constant k. Urease concentration determines the rate of urea hydrolysis. The higher the [E0], the more urea gets hydrolyzed. For example, when [E0]=1.0e-3 mol/L, more than 80% of injected urea is hydrolyzed; while for a lower concentration of urease, [E0]=1.0e-5 mol/L, only 4% of urea is hydrolyzed. The rate of ureolysis has a dominant impact on the mineral precipitation. However, the spatial distribution of the precipitates depends on not only the rate of ureolysis but also calcite precipitation rate. In a simulation (or laboratory) study, a maximum 5% reduction in porosity is observed within the simulation time period of 6 pore volumes due to mineral precipitation in the scope of this study. The simulation results indicate that the effect of calcite precipitation rate constant on the rate of urea hydrolysis is trivial. This can be explained by the fact that the pH value is the only parameter in the rate model of ureolysis through which calcite precipitation can contribute; however, pH has a much smaller impact than urease concentration on the rate of ureolysis. Cation exchange results in more aqueous calcium that could potentially form more precipitates. The precipitation magnitude will depend on the cation exchange capacity available in the system. Physical heterogeneity of a low permeability inclusion alters the flow field and emphasizes the advection of transport locally, thus the disturbed distribution of mineral forming constituents leads to a distorted front of decreasing precipitation from boundaries to the center. The distribution of hydrogen concentration implies that there is precipitation along the boundary of the low permeability zone, which indicates that contaminants in the low permeability inclusion could be immobilized by isolating them.
Identifier: FSU_migr_etd-3898 (IID)
Submitted Note: A Thesis submitted to the Department of Geological Sciences in partial fulfillment of the requirements for the degree of Master of Science.
Degree Awarded: Spring Semester, 2009.
Date of Defense: March 31, 2009.
Keywords: STOMP, In Situ Remediation, Calcite Precipitation, Urea Hydrolysis, Reactive Transport
Bibliography Note: Includes bibliographical references.
Advisory Committee: Bill X. Hu, Professor Directing Thesis; Stephen A. Kish, Committee Member; Ming Ye, Committee Member.
Subject(s): Earth sciences
Geology
Persistent Link to This Record: http://purl.flvc.org/fsu/fd/FSU_migr_etd-3898
Owner Institution: FSU

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Guo, L. (2009). Reactive Solute Transport in Heterogeneous Porous Media: Numerical Simulation of Urea Hydrolysis and Calcite Precipitation Using STOMP. Retrieved from http://purl.flvc.org/fsu/fd/FSU_migr_etd-3898