Effects of Persulfate Activation with Pyrite and Zero-Valent Iron for Phthalate Acid Ester Degradation

Phthalic acid esters (PAEs) are often detected in remediated groundwater using appropriate oxidant materials by in situ groundwater treatment. The study compares zero-valent iron-persulfate with a pyrite-persulfate system to degrade three PAEs di(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), and dimethyl phthalate (DMP). Column experiments were conducted, and rapid oxidation occurred in a pyrite-persulfate system due to sulfate radical generation. DMP concentration was found at about 60.0% and 53.0% with zero-valent iron (ZVI) and pyrite activation of persulfate, respectively. DBP concentration was measured as 25.0-17.2% and 23.2-16.0% using ZVI-persulfate and pyrite-persulfate systems, respectively. However, DEHP was not detected. The total organic carbon concentration lagged behind the E3 PAEs. Persulfate consumption with ZVI activation was half of the consumption with pyrite activation. Both systems showed a steady release of iron ions. Overall, the oxidation-reduction potential was higher with pyrite activation. The surface morphologies of ZVI and pyrite were investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and XPS. Intensive corrosion occurs on the pyrite surface, whereas the ZVI surface is covered by a netting of iron oxides. The pyrite surface showed more oxidation and less passivation in comparison with ZVI, which results in more availability of Fe2+ for persulfate activation. The pyrite-persulfate system is relatively preferred for rapid PAE degradation for contamination.