LONG-TERM stability of arsenic in iron amended contaminated soil.

Jurate Kumpiene,Alfreda Kasiuliene,Michel Mench,Annabelle Austruy,Ivan Carabante

doi:10.1016/j.envpol.2020.116017

Abstract

This study aimed at elucidating the long-term efficiency of soil remediation where chemical stabilization of arsenic (As) contaminated soil using zerovalent iron (Fe) amendments was applied. A combination of chemical extraction and extended X-Ray absorption fine structure (EXAFS) spectroscopy technique was applied on soils collected from five laboratory and field experiments in Sweden and France. All soils were treated with 1wt% of zerovalent Fe grit 2-15 years prior to the sampling. The results indicate that all studied soils, despite the elapsed time since their amendment with Fe grit, had substantial amounts of ferrihydrite and/or lepidocrocite. These metastable and the most reactive Fe (oxyhydr)oxides (mainly ferrihydrite) were still present in substantial amounts even in the soil that was treated 15 years prior to the sampling and contributed most to the As immobilisation in the amended soils. This increases confidence in the long-term efficiency of As immobilisation using zerovalent Fe amendments. Both applied methods, sequential extraction and EXAFS, were in line for most of the samples in terms of their ability to highlight As immobilisation by poorly crystalline Fe phases.

Highlights

Nowadays the established concept that bioavailability of contaminants, and not their total soil concentrations, is one of the main environmental risk-defining factors has led to a broader application of in situ stabilization technique for remediating metal(loid)contaminated soils
A combination of chemical extractions and extended X-Ray absorption fine structure (EXAFS) spectroscopy technique was applied on soils collected from laboratory and field experiments in Sweden and France
The fraction of crystalline Fe oxides remained in general unchanged and only in some samples was slightly smaller than in the untreated samples. These results suggest that zerovalent Fe added to the soils increased the fraction of poorly crystalline Fe oxides, which are the most reactive towards sorption of many trace elements

Summary

Introduction

Nowadays the established concept that bioavailability of contaminants, and not their total soil concentrations, is one of the main environmental risk-defining factors has led to a broader application of in situ stabilization technique for remediating metal(loid)contaminated soils. The formation of insoluble phases leads to a reduction of metal(loid) mobility, bioavailability, and pollutant linkages in line with risks to the environment and to metastable oxyhydroxides, which will slowly transform into more crystalline Fe oxides (e.g. goethite, hematite) that have lower specific surface area. This might cause a release of sorbed TE and increase their leaching over time; or (2) various sorbates (e.g. silicates, phosphates, and organic compounds) can influence Fe crystallization by passivating Fe oxide surfaces (Schwertmann and Cornell, 2000). Sorbed TE themselves can inhibit further crystallization and dissolution of Fe-(hydr)oxide minerals (Paige et al, 1997; Melitas et al, 2002), by this maintaining TE immobilisation efficiency over prolonged time periods

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