Synthesized and Commercial Iron Sulfide Particles as Contaminant Sorbents

Radioactive contaminants like technetium and iodine are highly mobile in groundwater, posing long-term environmental risks. Washington State University researchers synthesized and evaluated iron sulfide (Fe-S) nanoparticles, particularly greigite, for their ability to sorb and magnetically separate these contaminants from liquid waste. This guide outlines the process of preparing and utilizing these magnetic Fe-S particles for effective contaminant removal.

1. Synthesize Iron Sulfide Nanoparticles via Hydrothermal Method. This method produced Fe-S particles (primarily greigite) with the highest saturation magnetization, making them ideal for magnetic separation. Combine FeCl3-6H2O and thiourea in a 2:1 ratio of deionized water and ethylene glycol, stirring constantly under N2 purging. Transfer the amber solution to a PTFE-lined hydrothermal autoclave and react at 180 °C for 20 hours, then wash, centrifuge, dry, and store the resulting grayish-black powder.
2. Characterize Synthesized Particles. Verify the phase assemblage using X-ray diffraction (XRD) to confirm greigite as the dominant phase, along with minor pyrite and magnetite. Examine particle morphology and size using scanning electron microscopy (SEM) and measure magnetic properties via vibrating sample magnetometry (VSM). Hydrothermally synthesized particles should exhibit high saturation magnetization (e.g., 32.44 emu/g) and low coercivity for efficient magnetic separation.
3. Prepare Contaminant Solution. For demonstration, prepare an aqueous solution of a contaminant surrogate, such as perrhenate (ReO4-) for technetium (TcO4-), at a known concentration (e.g., 20,000 ppm). Ensure the solution is free of other anions that might interfere with the sorption process.
4. Introduce Iron Sulfide Sorbent. Add varying aliquots (e.g., 0.1 g, 0.2 g, 0.4 g) of the hydrothermally synthesized iron sulfide particles to separate closed vials containing the contaminant solution. Allow the mixture to react for 24 hours to facilitate contaminant sorption onto the particle surfaces.
5. Perform Magnetic Separation. After the reaction time, apply an external magnetic field (e.g., using a rare-Earth hand magnet) to the vials. The magnetic Fe-S particles, now laden with contaminants, will be drawn to the magnet, allowing for their physical separation from the aqueous solution. 6.  Quantify Contaminant Removal. Analyze the remaining aqueous solution using Raman spectroscopy to measure the concentration of the contaminant (e.g., the perrhenate symmetric stretch band at ~971 cm⁻¹). Compare the post-separation concentration to the initial stock solution to determine the percentage of contaminant removed.