Field Scale Mobility and Transport Manipulation of Carbon-Supported Nanoscale Zerovalent Iron in Fractured Media

Abstract

In field applications, mostly in porous media, transport of stabilized nano zerovalent iron particles (nZVI) has never exceeded a few meters in range. In the present study, the transport of Carbo-Iron Colloids (CIC), a composite material of activated carbon as a carrier for nZVI stabilized by carboxymethyl cellulose (CMC), was tested under field conditions. The field site lies within a fractured chalk aquitard characterized by moderately saline (∼13 mS) groundwater. A forced gradient tracer test was conducted where one borehole was pumped at a rate of 8 L/min and CMC-stabilized CIC was introduced at an injection borehole 47 m up-gradient. Two CIC-CMC field applications were conducted: one used high 100% wt CMC (40 g/L) and a second used lower 9% wt loading (∼2.7 g/L). Iodide was injected as a conservative tracer with the CIC-CMC in both cases. The ratio between the CIC-CMC and iodide recovery was 76% and 45% in the high and low CMC loading experiments, respectively. During the low CMC loading experiment, the pumping rate was increased, leading to an additional CIC recovery of 2.5%. The results demonstrate the potentially high mobility of nZVI in fractured environments and the possibility for transport manipulation through the adjustment of stabilizer concentration and transport velocity.

The Role of Stabilizer Concentration in the Mobility of Carbon‐Supported Nanozerovalent Iron (nZVI) in Fractured Media

“…In previous work, we showed very high potential CIC mobility in fractures and the possibility for CIC transport manipulation (Cohen & Weisbrod, 2018a, 2018b. nZVI transport manipulation is beneficial for efficient 10.1029/2019WR025553…”

“…Particle stability was assessed by measuring the particle sedimentation rate in a closed cuvette. The change in optical density was measured using a UV‐VIS spectrophotometer (BioMate 5, Thermo Scientific, Waltham, MA, USA) at a wavelength of 508 nm (Cohen & Weisbrod, , ) every 20 s for 120–200 min. The settling behavior of the stability tests can be expressed by an exponential decay model (equation ; Phenrat, Saleh, Sirk, Tilton, et al, ) where I is the absorbance intensity at time t , I 0 is the initial absorbance intensity, t is time ( t ), and A and α are fitting parameters.…”

“…The AC carrier acts as a physical barrier to prevent nZVI interactions, and CIC's lower effective density and zeta potential, compared with bare nZVI, results in its increased stability (Bleyl et al, ; Busch et al, ; Mackenzie et al, ). When supplemented with CMC, CIC was shown to have high‐mobility potential in porous and fractured environments (Busch et al, ; Cohen & Weisbrod, , ; Mackenzie et al, ), depending on the stabilizer loading used (Cohen & Weisbrod, ).…”

Mobility of Radionuclides in Fractured Carbonate Rocks: Lessons from a Field-Scale Transport Experiment

“…It further prevented mixing of sediments from the bottom of the injection borehole during the experiment. 35 A 3″ submergible pump (Grundfos) was installed at a depth of 24 m for water recirculation. Water was pumped into the top 1 m of the water column (water level was 4.8 m below land surface) during the experiment to ensure tracer homogeneity in the injection borehole.…”

Injection of Zerovalent Iron Gels for Aquifer Nanoremediation: Lab Experiments and Modeling

“…Green polymers, such as guar gum (GG) [21,22], xanthan gum (XG) [23], starch, and carboxymethyl-cellulose [24], are commonly used to improve the colloidal stability of iron particles. When dosed in concentrations of few g/L [17], these polymers provide steric repulsion among particles and increase the slurry viscosity, thus preventing iron sedimentation for several hours [25].…”