Interactions of synthetic Fe(II)-Fe(III) green rusts with pentachlorophenol under various experimental conditions

Sorption of pentachlorophenol (PCP) to three different green rusts (GRs) was studied versus time and initial PCP concentration at neutral pH. A competitive adsorption occurred when salicylate or silicate was present in the reaction medium. The monitoring of chloride formation and PCP byproducts indicated the absence of any possible reductive pathway in the PCP removal. All solid characterization showed that the PCP sorption in the presence or absence of foreign ligands did not alter the GR structure. Addition of nitrate (weak oxidant) involved a gradual release of PCP in solution from the sorbent solid. This is probably due to the oxidative transformation of GR into magnetite that sorbs less PCP. However, reaction with a strong oxidant (H₂O₂) involved both dechlorination and mineralization of PCP via oxidation reaction. HPLC and ion chromatography analysis, TOC and dissolved iron measurements showed that PCP had been degraded by heterogeneous Fenton-like reaction. Both X-ray diffraction analysis and Raman spectroscopy showed that the oxidation of GR may lead to magnetite (Fe₃O₄) or goethite (α-FeOOH), depending on the oxidant type. As green rusts have considerable potential in environmental applications, the influence of naturally occurring ligands and/or oxidants on the reactivity of green rusts should be considered.