2-Chloronaphthalene Dehalogenation by High-Carbon Iron Filings: Formation of Corrosion Products on High-Carbon Iron Filings Surface

Abstract

Long-term temporal behavior of permeable reactive barriers used for remediation of subsurface contamination is of ongoing research interest. This study was designed to investigate the impact of formation of surface oxide coatings on the performance of high-carbon iron filings (HCIF) used for dehalogenation of 2-chloronaphthalene (2-CN). Three types of HCIF, viz. HCIF-S1, HCIF-S2, and HCIF-S3, with no oxide coating, Fe(II)/Fe(III) oxide coating, and pure Fe(III) oxide coatings, respectively, were prepared and characterized by X-ray diffraction and Mössbauer spectroscopy. The HCIF samples were contacted with 2-CN in completely mixed batch systems. During interaction with HCIF-S1, 2-CN was observed to partition substantially to the HCIF surface, whereas the residual aqueous 2-CN underwent reductive dehalogenation. Results were similar during 2-CN interaction with HCIF-S2. However, during 2-CN interaction with HCIF-S3, both 2-CN dehalogenation and adsorption were severely diminished. Reduction in sorption was attributed to the concealment of carbon present on HCIF-S3 surface by the oxide coating, as confirmed by scanning electron microscopy and energy dispersive X-ray spectroscopy studies. Reduction in dehalogenation rate was attributed to the insulating effect of the surface oxide coating. Addition of ferrous ions led to the enhancement of the rate of dehalogenation of 2-CN by HCIF-S3 by almost an order of magnitude.