Factors affecting p-nitrophenol removal by microscale zero-valent iron coupling with weak magnetic field (WMF)

Abstract

The effect of WMF on the kinetics of p-nitrophenol (PNP) removal by six commercial zero-valent iron (ZVI) samples from different origins were studied at pH 4.0. The pseudo-first-order rate constant (k_obs) of PNP removal by ZVI with WMF were 2.9–5.4-fold greater than those without WMF. The strong correlation between the specific reaction rate constants (k_SA) of PNP removal by various ZVI samples and the specific rate constant of Fe(II) release (k_{Fe(II) release SA}) during these processes indicated that enhancement of PNP removal by ZVI in the presence of WMF was mainly ascribed to the improved Fe⁰ corrosion and Fe(II) generation. Effects of pH value (4.0–7.0), ZVI loading (100–1000 mg L⁻¹), PNP concentration (5–100 μM), magnetization time (1–120 min), and various anions (at 1–50 μM concentration) on PNP removal by ZVI with and without the presence of WMF was investigated. The presence of WMF significantly accelerated PNP removal at pH 4.0–7.0, especially at neutral pH values. The k_SA and k_{Fe(II) release SA} linearly increased with increasing ZVI loading, and the enhancement factor is stable with increasing ZVI loading. PNP concentration exhibited a very slight effect on PNP removal with and without WMF. The k_obs of PNP removal increased with increased magnetization time and trended to be consistent for more than 5 min of magnetization by WMF. WMF exhibited a positive effect on PNP removal in the presence of sulfate, chlorate, and nitrate. Although perchlorate could inhibit PNP removal by ZVI, WMF decreased the negative effect of perchlorate on PNP removal by ZVI. Furthermore, the possible degradation pathway of PNP degradation by ZVI was proposed according to the detected intermediates.