The objectives of this research were to prepare an environmentally benign nanoscale zero-valent iron (also known as nanoiron) and then to apply it to remediate a simulated soil/groundwater contamination. Trichloroethylene (TCE) was selected as the target pollutant in this study. First, nanoiron was prepared by the borohydride reduction method. During the growth of iron nuclei in the solution, a soluble starch (3 wt%) among other dispersants was determined to be the best to form the stabilized nanoiron slurry (“nanoiron slurry” for short) for later uses. X-ray diffraction (XRD) analysis has identified iron as the single crystalline substance. The image of transmission electron microscopy (TEM) indicated that the particle size of nanoiron ranged from 10 to 20 nm. This size range is in accord with that of calculated by Scherrer formula. Due to the aggregation of nanoiron, a size distribution of secondary particles was determined to be 40-60 nm as shown in the micrograph of scanning electron microscopy (SEM). A fluffy substance over the surface of nanoiron (as shown in TEM image) was confirmed to be starch by SEM mapping of elements on the surface of nanoiron. In the batch tests the nanoiron slurry (nanorion dose: 1.25 g/L; soluble starch: 3 wt%) was found to be capable of removing TCE in aqueous solution. For the initial TCE concentrations of 10 mg/L and 0.1 mg/L, after a reaction time of 150 min, the respective TCE degradation efficiencies were determined to be about 60 % and 75 %. After the above preliminary tests, such nanoiron slurry was further verified for its capability of degrading TCE in soil and groundwater. In this series of tests, laboratory-prepared, saturated TCE-bearing soil was firmly packed in horizontal soil columns to simulate the groundwater flow in the subsurface. Soil specimens of sandy clay loam and sand were selected to compare the transport behaviors of nanoiron slurry in the simulated subsurface environment as driven by electrokinetics (EK) and pumping using a peristaltic pump, respectively. In the EK tests, 20 mL of nanoiron slurry was injected to the selected electrode (anode or cathode) reservoir daily with a constant applied electric potential gradient of 1 V/cm and for a reaction time of 7 days. The initial TCE concentration in sandy clay loam was in the neighborhood of 285 mg/kg, whereas about 68 mg/kg in sand. Experimental results have shown that the anode reservoir is a better injection spot as compared with its counterpart. Under the circumstances, a TCE degradation efficiency of about 99 % could be obtained. In the pumping tests, however, it is only applicable to sand with a flow rate of 0.29 mL/min. Further, even for an operation time of 25 h it was unable to transport nanoiron slurry from the influent reservoir to the effluent reservoir. The soil fraction near the effluent reservoir was found to have a high residual TCE concentration. As compared with the pumping tests, the EK tests were found to be much capable of transporting nanoiron slurry in the simulated groundwater system resulting in a much greater TCE removal. Moreover, the number of microorganism colony in soil was found to be increased as a result of the injection nanoiron slurry. This might be ascribed to the fact that starch molecules surrounding iron nanoparticles have provide a good carbon source for the growth of microorganism colony in the neighborhood. Based on the research findings obtained above, it might be claimed that the nanoiron slurry prepared in this study is an environment-friendly one. By combining the injection of such nanoiron slurry with EK, a green environmental nanotechnology has been developed for the remediation of TCE in the subsurface.

Nanoscale Zero-Valent Iron Slurry, Electrokinetic Method, In Situ Remediation