The recent spark in the interest for the usage of nano zero valent iron (nZVI) as a remediation tool for contaminated land and groundwater is mainly due to its higher reactivity in comparison to micro ZVI, cost effectiveness, and potential to treat a broad range of contaminants. The authors review the recent developments and approaches made on synthesis on nZVI, strucuture and characterization of nZVI, the challenges faced in the transport of nZVI in the subsurface environment, and the augmentation of the motility of nZVI. The effective use of nZVI in remediating organic pollutants (halogenated organic compounds, pharmaceutical waste, and azo dyes) and inorganic pollutants (Ni2+, PO43−, Co2+, Cu2+) carried out in recent studies is discussed. The potential risks and limitations of this emerging nanotechnology are also addressed.

A review on synthesis, characterization, and applications of nano zero valent iron (nZVI) for environmental remediation

One of the recent In-Situ groundwater remediation techniques under development uses reactive zero valent iron (ZVI) to turn highly toxic chlorinated hydrocarbons (CHCs) into harmless compounds. CHCs are non miscible and characterized by a low solubility which determines their slow dissolution (over decades or centuries) into groundwater, forming plumes that can target drinking water wells, rivers and lakes. Injection of nano sized zero valent iron (nZVI) suspension into the subsurface could target the contaminants directly in the source zone. The high reactivity of nZVI together with the injection into the source fastens the depletion of the contaminant and interrupts the plume generation. The presented work focused on the transport of nZVI during the injection. To make quantitative descriptions of transport possible, an effective detection technique was developed. Exact concentrations of nZVI inside the porous medium was measured through changes in susceptibility detected with electromagnetic induction sensors. Mobility tests with different suspension concentrations were performed in a 1-D horizontally orientated two meter long column. Continuous concentration measurements were performed over the whole length of the column. In a near field scale container experiment a confined aquifer with a radial flow field over a radius of almost two meters was simulated. Different injection rates and pumping techniques were tested inside this experimental set up. A discretization method to represent all effects of a radial flow field using sets of columns was developed. The method could be verified successfully by comparing the concentration profiles to the results obtained from the container experiments. A mathematical model, developed by starting from the classic colloid filtration theory and by considering the transport of primary colloids and aggregates separately, was able to be fitted on the 1-D results. After implementation in a numerical solver, the model was furthermore capable of providing a very good fit on the results of the radial geometry tests while using exclusively the fitted parameters obtained from the 1-D tests. Throughout the work a better understanding of the transport of nZVI during the injection was developed. It was demonstrated that transport of nZVI without modification was possible over a distance of two meters in both 1-D and radial geometry flow fields. An extrapolation of the work for field application was furthermore described. By applying the methods developed in this work the necessary suspension concentration, the volume of suspension and the injection rate could be determined in advance. The presented work showed promising results and could be a sound scientific basis for further investigations and case studies on nZVI based remediation. 
Der Einsatz von Nano-Eisen ist ein vielversprechendes Verfahren zur Sanierung von verunreinigten Aquiferen. Das Ziel eines solchen Einsatzes ist die Entfernung des Schadensherdes in-situ, also direkt im Untergrund. Das Transportverhalten von Nano-Eisen wahrend der Injektion wurde in dieser Arbeit im Detail untersucht und es konnte ein deutlicher Fortschritt im Verstandnis des Transportverhaltens verzeichnet werden. 

Es gab bis zum Anfang der Arbeit noch keinen verfugbaren Messtechnik.
Deshalb wurde im Rahmen der Arbeit eine neue Messtechnik entwickelt mit Hilfe derer die Nano-Eisen-Konzentration zerstorungsfrei gemessen werden kann.

Die Grose der Kolloide wurde als Hauptfaktor fur den Transport bestimmt. Beim betrachteten Nano-Eisen-Material (RNIP 10-E, Toda Kogyo, Japan) wurde festgestellt, dass die Kolloide zur Bildung von Aggregaten neigen und der angelieferte Schlamm fur eine direkte Einbringung in den Untergrund zu hoch konzentriert ist. Ein vorrangiges Ziel dieser Arbeit war es, die minimal notige Vorbehandlung der Suspension fur eine erfolgreiche Injektion zu ermitteln. Die kolloidalen Aggregate konnen unter Einsatz hoher Scherkrafte mittels eines Dispergiergerates in kleinere Aggregate aufgebrochen werden. Die Primarkolloide konnen aber selbst damit nur bedingt wiederhergestellt werden. Zusatzlich muss der angelieferte Schlamm runterverdunnt werden, um den Transport im Untergrund moglich zu machen.

In dieser Arbeit wurde erstmalig ein Transport von fast zwei Metern in einem radialen Stromungsfeld nachgewiesen.

Es wurde ein Fliesschema erstellt, um bei der Einschatzung der Machbarkeit einer Injektion zu helfen. Es wurden zwei alternative Methoden entwickelt, um den Transport im radialen Stromungsfeld vorhersagen zu konnen.
Der Einsatz einer dieser Methoden kann in der Planungsphase helfen, die richtigen Entscheidungen zu treffen und die benotigten Ablaufbedingungen festzulegen.

Die Ergebnisse dieser Arbeit sind vielversprechend und stellen eine gute Basis fur weitere Forschung bezuglich des Einsatzes von Nano-Eisen bei der Sanierung von kontaminierten Aquiferen dar. Des Weiteren konnen die hier vorgestellten Ergebnisse bei der Beurteilung von entsprechend gelagerten Fallbeispielen helfen.

Transport of nano sized zero valent iron colloids during injection into the subsurface

Successful in situ groundwater remediation relies on the adequate distribution of treatment materials within the subsurface. Zero-valent iron (ZVI) is widely used for the remediation of soils contaminated with chlorinated organic compounds. Because ZVI is a solid, various tech-niques are used to distribute ZVI in the subsurface; however, a major uncertainty in this process involves determining the distribution of the iron during emplacement. A method of mapping the distribution of ferromagnetic material such as ZVI is by magnetic susceptibility (MS), a novel approach that is highly sensitive, quantitative, objective, and easily applied in field. The method has been tested in the laboratory on synthetic cores containing EHC ® , an organic amendment containing 40 to 50% ZVI, using an MS meter with two types of sensors (loop and handheld). Both sensors have high sensitivity (e.g., 1% disseminated EHC is easily detected), whereas the hand-held sensor has greater spatial resolution (e.g., differences are notable on a scale of 1 cm). Following the laboratory studies, the handheld instrument was us ed to perform field measurements for multiple pilot studies and a full-scale application of EHC using various delivery methods (pneumatic fracturing, hydraulic fracturing, and direct injection) to construct a biobarrier at a field remedial site. The MS method has proven invaluable in quantifying amend-ment distribution and ensuring appropriate application of this remedial technology.

Evaluating the Subsurface Distribution of Zero‐Valent Iron Using Magnetic Susceptibility

The concentration of nano sized zero valent iron (nZVI) is an important criterion for the in-situ remediation of ground water contaminations. To measure the magnetic susceptibility of nZVI, two specified cylindrical coils with the desired measuring range and the corresponding post-processing algorithm (PPA) are presented to determine the concentration change of nZVI during the remediation process. To accurately calculate the concentration of nZVI, numerical simulations are required to evaluate the actual magnetic susceptibility of nZVI filled in the column and the change of the self-inductance of each coil because of nZVI. To improve the efficiency of the presented algorithm, an optimal frequency for the measurement is determined by taking into account the equivalent capacitance of the coil and the cable. Moreover, two special boundary conditions for the efficient calculation of the parasitic capacitances are presented. Finally, two experiments have been performed to verify the developed sensor and the measurement method.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-smt.2014.0259

Optimisation of a concentration measurement sensor for nano sized zero valent iron using numerical simulation

The purpose of this work was to develop and validate a rapid, non-destructive, real-time measurement system for nanoscale zero-valent iron (nZVI) particles determination in sand-packed columns. This aims to provide an approach to analyse for nZVI particle transport and nZVI induced contaminant degradation reactions in 1-dimensional aquifer experiments. The inductive measurement system (IMS) was developed and tested by measuring columns filled with varying portions of nZVI and sandy aquifer material. Method validation was conducted for this innovative approach in accordance with several guidelines in disciplinary areas. The linearity of ZVI concentration and measurement signal was confirmed. Calibration curves were determined to be linear over the range of 0.11–53.50 g/L for nZVI NANOFER STAR, 0.10–81.67 g/L for nZVI BASF 1, 0.12–58.26 g/L for nZVI Carbo-Iron, 0.12–69.70 g/L for nZVI NANOFER 25DS ORM, 0.12–50.69 g/L for nZVI NANOFER 25DS, and 0.21–1613.39 g/L for nZVI Höganäs 1* (dry). This method was determined to be sensitive in nZVI, accurate (101.63 % within-run recovery, 101.85 % between-run recovery covering 76 days), and precise (0.46 % repeatability RSD, 0.85 % intermediate precision RSD covering 76 days). LOQ was determined ranging from 0.10 to 0.21 g/L for nZVI used in experiments and regression through origins was selected as the calibration model. Quality control processes were performed to assure the reliability of the results and the long-term stability. Additional data processing steps allowed to compensate for measurement deviations resulting from different liquid phase compositions, e.g. dispersants used for nZVI suspensions. This method is now successfully validated in single-laboratory conditions. 

Method validation of an inductive measurement system (IMS) for nanoscale zero-valent iron (nZVI) particles determination in sand-packed columns

The injection of colloidal nano sized zero valent iron (nZVI) into a contaminated aquifer is a promising new in-situ groundwater remediation technique. An inductive sensor is presented to directly detect and measure the concentration of nZVI in the subsurface. The method is based on the inductive measurement of magnetic material properties of nZVI within an alternating magnetic field. The change of magnetic flux density generated by one coil is determined by measuring an induced voltage in a second coil. Numerical simulations with the finite element software COMSOL Multiphysics were performed to optimize the sensor design. Furthermore, these components were used to analyze the possible measuring range, taking into account the accuracy of the measuring device to be used. Since the susceptibility of nZVI in the aquifer is very small, it is necessary to use a background measurement to improve the sensitivity of the measurement system. Finally, the measuring concept was experimentally verified.

Development of an inductive concentration measurement sensor of nano sized zero valent iron

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Development of an inductive concentration measurement sensor of nano sized zero valent iron