TY - JOUR

T1 - Retention of sulfidated nZVI (S-nZVI) in porous media visualized by X-ray μ-CT - the relevance of pore space geometry

AU - Schiefler, Adrian A.

AU - Bruns, Stefan

AU - Muter, Dirk

AU - Uesugi, Kentaro

AU - Sorensen, Henning Osholm

AU - Tobler, Dominique J.

PY - 2022

Y1 - 2022

N2 - Obtaining pore scale knowledge about retention mechanisms of nanoparticles (NP) is inherently difficult and can in turn restrict accurate forward prediction. Herein, an X-ray microcomputed tomography (mu-CT, 0.5 mu m pixel size) approach is described which is capable of resolving sulfidated nanoscale zerovalent iron (S-nZVI) retention at the pore scale, by using difference images of pre- and post-injection scans to account for local background variations around grains on a per pixel basis. The type of information that can be obtained from this approach including its limitations is discussed based on a first set of S-nZVI transport experiments performed in columns filled with irregular fine sand, where mu-CT images were obtained before and after S-nZVI injection at three positions along the column. A total of 5 column experiments were performed testing the effect of three different superficial injection velocities (5.8 x 10(-4) m s(-1), 2.9 x 10(-4) m s(-1) and 1.5 x 10(-4) m s(-1)) and three different S-nZVI concentrations (5.0 g L-1, 10 g L-1 and 20 g L-1) on S-nZVI retention behaviour, while the total injected S-nZVI mass was kept constant across experiments. The results clearly show that S-nZVI retention is determined by physical straining. Column depth and S-nZVI aggregate size dependency during straining appears to play a role, yet depth extension seems limited. Ripening deposition likely also occurred and increased with a decrease in injection velocity and/or increase in S-nZVI concentration. The local pore geometry and the flow regime strongly impacted S-nZVI attachment and retention behaviour, which suggests that pore space descriptors and velocity should be included in future predictive models. Together these results provide new perspectives for further studies of nZVI-based particle retention and transport in porous media.

AB - Obtaining pore scale knowledge about retention mechanisms of nanoparticles (NP) is inherently difficult and can in turn restrict accurate forward prediction. Herein, an X-ray microcomputed tomography (mu-CT, 0.5 mu m pixel size) approach is described which is capable of resolving sulfidated nanoscale zerovalent iron (S-nZVI) retention at the pore scale, by using difference images of pre- and post-injection scans to account for local background variations around grains on a per pixel basis. The type of information that can be obtained from this approach including its limitations is discussed based on a first set of S-nZVI transport experiments performed in columns filled with irregular fine sand, where mu-CT images were obtained before and after S-nZVI injection at three positions along the column. A total of 5 column experiments were performed testing the effect of three different superficial injection velocities (5.8 x 10(-4) m s(-1), 2.9 x 10(-4) m s(-1) and 1.5 x 10(-4) m s(-1)) and three different S-nZVI concentrations (5.0 g L-1, 10 g L-1 and 20 g L-1) on S-nZVI retention behaviour, while the total injected S-nZVI mass was kept constant across experiments. The results clearly show that S-nZVI retention is determined by physical straining. Column depth and S-nZVI aggregate size dependency during straining appears to play a role, yet depth extension seems limited. Ripening deposition likely also occurred and increased with a decrease in injection velocity and/or increase in S-nZVI concentration. The local pore geometry and the flow regime strongly impacted S-nZVI attachment and retention behaviour, which suggests that pore space descriptors and velocity should be included in future predictive models. Together these results provide new perspectives for further studies of nZVI-based particle retention and transport in porous media.

KW - NANOSCALE ZEROVALENT IRON

KW - GUAR GUM SOLUTIONS

KW - ZERO-VALENT IRON

KW - PARTICLE CONCENTRATION

KW - IMPROVED DELIVERY

KW - TRANSPORT

KW - NANOPARTICLES

KW - NANOMATERIALS

KW - REMEDIATION

KW - SUSPENSIONS

U2 - 10.1039/d2en00224h

DO - 10.1039/d2en00224h

M3 - Journal article

VL - 9

SP - 3439

EP - 3455

JO - Environmental Science: Nano

JF - Environmental Science: Nano

SN - 2051-8153

IS - 9

ER -