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

Abstract

The mobility of nanozerovalent iron (nZVI) particles is of major importance when assessing their effectiveness for use in contaminated sites. Here, the influence of the stabilizer loading on nZVI mobility was investigated in fractured media. nZVI in the form of Carbo‐Iron Colloids (CIC), a composite material of activated carbon as a carrier for nZVI, was used for the tests. CIC was supplemented with carboxymethyl cellulose stabilizer, at three different loadings: 5% wt., 20% wt., and 80% wt., in a moderately saline solution of 250 mM. Transport experiments were conducted in a fractured chalk core, and the characteristics of the solutions and particles were analyzed. The effect of ionic strength was investigated by application of the 80% loading, also in a lower salinity solution of ~3 mM. Transport experiments were modeled, and all results were compared with especially high 1,600% wt. stabilizer loading, from a previous study. Among the different carboxymethyl cellulose loadings, significant differences in mobility and a correlation between mobility and stability were observed. Though, differences in stability were found insignificant. Higher stabilizer concentration and, to a greater extent, a higher number of free stabilizer molecules in solution enhance particle stability and, hence, mobility. A good fit was obtained between the transport experiment results and a model of solute and colloid transport in a single fracture. The model attachment parameters showed a good correlation with the decay rate constants of the stability tests, indicating yet again the significant role played by stability in CIC mobility and the possibility for mobility prediction.

Simulation of Colloid Transport and Retention Using a Pore‐Network Model With Roughness and Chemical Heterogeneity on Pore Surfaces

“…However, there is presently no accepted method to predict k det . Experimental observations commonly indicate that k det is a few orders of magnitude smaller than k att (Cohen et al., 2019). Consequently, the value of k det is set to be 0.01× k att for each pore throat.…”

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

“…For microparticles, instead, the sedimentation is induced by their high density and relatively large size [20]. 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].…”

Laboratory experiment of iron nanoparticle transport in a rock fracture with online concentration detection probes

“…Only few studies have been made compared to soil materials. Experiment in [13,14] injected nZVI into a chalk core with a single fracture in longitudinal direction, detecting the concentration commonly at the output by discrete sampling and analyses.…”