Determining ZVI Emplacement using Magnetic Separation
During a recent FEROXSM application, soil cores were collected to qualitatively delineate and confirm the emplacement of FEROXSM powder in the subsurface.
Due to the small size of the iron powder particles, visual identification of iron within soil cores was extremely difficult. ARS' engineers developed a novel magnetic separation test to assist in identifying iron powder within the soil cores. Samples from each soil core were removed and allowed to dry. The sample was then crushed and spread over a magnet wrapped in plastic. The distribution of FEROXSM powder within the subsurface was confirmed relying upon the magnetic properties of the individual zero-valent iron particles, as well as mixed iron and soil that adhered to the magnet.
Figure 1, shows magnetically separated soil particles at depths of 22 to 22.5 ft bgs adhering to the magnet.
In addition, to the magnetic separation test, an iron filled fracture was visually identified at 17.9 feet bgs during the analysis (Figure 2). This fracture was horizontally orientated and bisected the core. Confirmation of this iron filled fracture was accomplished by using the magnetic separation test.
 |  | | Figure 1, magnetically separated soil particles | Figure 2, iron filled fracture |
The magnetic separation test not only provided direct evidence of emplaced iron powder in the subsurface, but also delineated the distribution pattern. Further research and testing with this method is ongoing as we continue to standardize the test for field performance assessment.
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