RESEARCH ARTICLE Pentachlorophenol dechlorination with zero valent iron: a Raman and GCMS study of the complex role of surficial iron oxides Buddhika Gunawardana 1,2 & Peter J. Swedlund 3 & Naresh Singhal 1 & Michel K. Nieuwoudt 3 Received: 7 September 2017 /Accepted: 11 April 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract The dechlorination of chlorinated organic pollutants by zero valent iron (ZVI) is an important water treatment process with a complex dependence on many variables. This complexity means that there are reported inconsistencies in terms of dechlorination with ZVI and the effect of ZVI acid treatment, which are significant and are as yet unexplained. This study aims to decipher some of this complexity by combining Raman spectroscopy with gas chromatography-mass spectrometry (GC-MS) to investigate the influence of the mineralogy of the iron oxide phases on the surface of ZVI on the reductive dechlorination of pentachlorophenol (PCP). Two electrolytic iron samples (ZVI-T and ZVI-H) were found to have quite different PCP dechlorination reactivity in batch reactors under anoxic conditions. Raman analysis of the Bas-received^ ZVI-T indicated the iron was mainly covered with the ferrous oxide (FeO) wustite, which is non-conducting and led to a low rate of PCP dechlorination. In contrast, the dominant oxide on the Bas-received^ ZVI-H was magnetite which is conducting and, compared to ZVI-T, the ZVI-H rate of PCP dechlorination was four times faster. Treating the ZVI-H sample with 1 N H 2 SO 4 made small change to the composition of the oxide layers and also minute change to the rate of PCP dechlorination. However, treating the ZVI-T sample with H 2 SO 4 led to the loss of wustite so that magnetite became the dominant oxide and the rate of PCP dechlorination increased to that of the ZVI-H material. In conclusion, this study clearly shows that iron oxide mineralogy can be a contributing factor to apparent inconsis- tencies in the literature related to ZVI performance towards dechlorination and the effect of acid treatment on ZVI reactivity. Keywords Dechlorination . Iron oxides . Magnetite . Pentachlorophenol . Raman . Wustite . ZVI Introduction Pentachlorophenol (PCP) is a restricted use biocide which is utilized as a wood preservative for applications such as power poles and fence posts. PCP has been identified as a persistent contaminant that can enter surface and groundwater from im- proper disposal, accidental spills, evaporation from treated wood products, and incineration of chlorinated wastes (ATSDR 1999; Sun et al. 2015). PCP is also a probable human carcinogen (IARC 1991; USEPA 2010) and has been desig- nated as a priority pollutant by the USEPA (2017a, b) and the European Commission (EC 2016). Due to PCP’s toxicity and resistance to natural degradation, the USEPA has imposed a maximum contaminant level in drinking water for PCP of 1 ppb (USEPA 2017a, b). For these reasons, an effective and efficient technology for the degradation of PCP and its remov- al from water is important to eliminate the potential risk of PCP to the environment and people. The dechlorination of chlorinated organic pollutants in the presence of zero valent iron (ZVI) is an important process with a complex dependence on many variables. Dechlorination of PCP using ZVI has been extensively studied; however, there are inconsistencies in the literature which are significant and are as yet unexplained. For example, some studies have re- ported minimal or no PCP degradation (Hou et al. 2009; Morales et al. 2002) while Kim and Carraway (2000) have reported almost complete removal of PCP by ZVI. In this study, we demonstrate how the nature of the iron oxides Responsible editor: Philippe Garrigues * Buddhika Gunawardana buddhi75@yahoo.com 1 Department of Civil and Environmental Engineering, University of Auckland, Auckland, New Zealand 2 Department of Civil Engineering, University of Moratuwa, Moratuwa, Sri Lanka 3 School of Chemical Sciences, University of Auckland, Auckland, New Zealand Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-2003-5