Abinash Agrawal (Advisor), Mark Goltz (Advisor), Robert Ritzi (Committee Member)
Master of Science (MS)
Nanoscale particles of zero valent iron stabilized with carboxymethylcellulose (CMC-nZVI) have been shown to degrade chlorinated hydrocarbons efficiently in bench-scale investigations. The remediation of contaminated sites by subsurface injection of stabilized nZVI in a slurry form has been investigated at pilot scale and field scale with conflicting results concerning transport of stabilized nZVI and its long-term stability for in situ degradation of chlorinated hydrocarbons. Changes in the hydraulic conductivity in porous media have also been reported following injection of stabilized nZVI slurry in both large tank experiments and in field studies. This study investigated the leaching behavior of CMC-nZVI post-emplacement at a variety of CMC concentrations (1 g/L, 2 g/L, 4 g/L, and 8 g/L) in a sand-filled flow-through reactor (30 cm long x 5 cm diameter). The goal was to identify changes in total iron mass eluted and changes to the hydraulic properties of the column post-emplacement of CMC-nZVI for different CMC concentrations. Experiments were also conducted to determine the amount of unreacted CMC-nZVI that would elute the column post-emplacement. Prior to injection of the CMC-nZVI, tracer breakthough studies were analyzed using the Method of Moments to determine velocity, resulting in calculation based estimations for pore volume (PV) and porosity. CXTFIT, a parameter estimation based on the physical non-equilibrium convection-dispersion equation, was used to demine initial conditions within the column for longitudinal dispersivity, mobile porosity, and the rate of mass transfer from mobile to immobile zones. The CMC-nZVI slurry was emplaced by rapid injection into the sand column through the base at a rate of ~120 mL/min and then flushed with a 10 mM NaCl solution at a velocity of 1 m/d (0.5 mL/min). After CMC-nZVI emplacement, the effluent samples exiting the flow-through reactor were collected with fraction collector for 15 min sampling period over 48 hours to determine total iron mass eluted through application of the zeroth moment. 48 hours post-injection, another tracer was applied to identify possible changes in PV and above mentioned parameters in CXTFIT. In a separate experiments, anaerobically sealed vials for subsequent analysis using laboratory techniques to quantify the amount of unreacted nZVI particles in each sample. Results showed that with an increase in CMC concentration, and increase in total iron mass elution resulted. Under all concentrations of CMC, some iron mass was retained within the column. Losses in PV showed a similar trend, where lower concentrations of CMC (<3g/L) resulted in an increase in the loss of pore volume. Immediately after emplacement, an increase in the discharge rate of the effluent was observed, disallowing any modeling for the flushing of the CMC-nZVI that required steady state conditions. CXTFIT results showed: that a reduction in mobile porosity was seen with all concentrations, some injections resulted in an increase in the mass transfer rate suggesting a reduction in size and highly dispersed regions of low, and the lowest concentration of CMC resulted in an increase in longitudinal dispersivity. This may suggest that post-emplacement CMC-nZVI particles that are modified with a low concentration of CMC may agglomerate, resulting in clogged pore spaces and a reduction in transportability. Reactivity tests results showed that a majority of the iron leaving the column was unreacted within 8 hours post-emplacement. After 8 hours, which was slightly beyond 1 PV of flushing, H2 gas bubbles created erratic results.
Department or Program
Department of Earth and Environmental Sciences
Year Degree Awarded
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