An initial study into the use of microwave remediation of hexachlorobenzene treated soil using selected oxidants and coated graphite rods

Abstract

Microwave remediation has become an established method to treat contaminated soils, sediments, and sludges. Chlorinated contaminants are of particular interest due to their widespread industrial use in the past and current potential health hazards. Literature reports the use of microwave heating and oxidants for various reactions, but no work could be found combining microwave heating, persulfate, and coated graphite rods for remediation of halogenated hydrocarbon treated soil. Therefore, this research focused on combining microwave energy combined with oxidants, potassium hydroxide and potassium persulfate, and, coated and uncoated, graphite rods to remove hexachlorobenzene (HCB) from treated soil samples. Soil collected from a local pond was dried, sieved, and cleaned by extraction with methylene chloride. Samples were spiked with hexachlorobenzene, then depending on experimental parameters, heated in a microwave oven, had an oxidant added, and had a coated or uncoated graphite rod added. The samples were then extracted with methylene chloride using a Soxhlet extraction setup. The methylene chloride volume was then reduced and analyzed by gas chromatography/mass spectrometry (GC/MS). Additional analysis on the soil and rods was done with powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The data show that heating alone remediated the soil, but the addition of graphite rods and oxidants enhanced the remediation amount. The oxidant alone removed 200% more HCB than just heating the sample. Using coated graphite rods caused the removal of 125% more than the uncoated graphite rod did. SEM and XRD data show no decomposition of the graphite rods. Thermal and chemical effects are likely causes for the enhanced removal. The maximum particle size increased after heating due to vitrification. Although an initial study, this research shows that microwave heating and the addition of oxidants and coated or uncoated graphite rods removed HCB from the treated soil. The removal is due to thermal, microwave and graphite rods, and chemical, oxidants, effects. Hexachlorobenzene remediation of soil was enhanced by microwave heating, insertion of a coated or uncoated graphite rod, and addition of oxidants. Therefore, these procedures could provide a method for solving a widespread problem and returning once contaminated soil back to its natural environment.