Chemical Engineering Journal 172 (2011) 689–697 Contents lists available at ScienceDirect Chemical Engineering Journal j ourna l ho mepage: www.elsevier.com/locate/cej Improvement soil remediation by using stabilizers and chelating agents in a Fenton-like process F. Vicente ∗ , J.M. Rosas, A. Santos, A. Romero Dpto Ingenieria Quimica, Facultad de Ciencias Químicas, Universidad Complutense Madrid. Ciudad Universitaria S/N. 28040 Madrid, Spain a r t i c l e i n f o Article history: Received 4 April 2011 Received in revised form 15 June 2011 Accepted 15 June 2011 Keywords: Chelating agent Fenton-like Hydrogen peroxide ISCO Stabilizer a b s t r a c t In situ chemical oxidation (ISCO) is a powerful technology for soil remediation. However, one of the main drawbacks of an in situ Fenton-like treatment (H 2 O 2 + natural Fe species present in soil) relies in the instability of H 2 O 2 when is in contact with soil. Besides, organic pollutants can be strongly entrapped on the soil organic matter (SOM) diminishing the efficiency of the ISCO technology. The H 2 O 2 stabilization was evaluated, in this work, using KH 2 PO 4 and six different chelating agents (EDTA, l-ascorbic acid, gallic acid, citric acid, sodium citrate mono-hydrate (CITRm), sodium citrate 2-hydrate (CITRt), at different experimental conditions, in three different calcareous loamy sand soils, with different SOM, iron and manganese amounts. A negligible stabilization effect is noticed using KH 2 PO 4 in soils with the highest SOM content, probably due to SOM coating the iron and manganese minerals. EDTA did not produce any relevant effect on the H 2 O 2 decomposition in neither of the soils analyzed. A certain decrease of the hydrogen peroxide conversion was observed for the l-ascorbic, gallic and citric acids. While CITRm and CITRt produced a significant stabilization effect of H 2 O 2 . Higher efficiencies are obtained with CITRm due to the acidification of the soils produced by chelating agent. The influence of the chelating agent addition on remediation of soil contaminated with 2,4-dimethylphenol (2,4-DMP) was also analyzed. The addition of EDTA or CITRt as chelating agents produced an increase of the 2,4-DMP degradation. This could be explained because chelating agents stabilize the hydrogen peroxide, enhance desorption of the entrapped pollutant and solubilize part of the iron from the soil. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The remediation of contaminated soils is becoming a problem of great importance. In situ chemical oxidation (ISCO) is an increas- ingly popular method for the remediation of contaminated soils and groundwater. Four oxidants have been used for ISCO remedi- ation: ozone, permanganate, activated persulfate, and H 2 O 2 . This last is one of the most commonly used reagents for ISCO and is based on the property of hydrogen peroxide to generate hydroxyl radicals by reacting with ferrous ions in the well known Fenton’s reaction. Acidic pH has been often used to optimize Fenton oxida- tion efficiency in aqueous phase. The pH of many soils is often near neutral or slightly alkaline, and an acidic soil environment might cause dramatic ecological impacts. Naturally occurring iron minerals can be used in a heteroge- neous Fenton process, where iron minerals serve as catalysts in place of soluble iron. This allows obtaining an in situ Fenton-like treatment of contaminated soils without pH adjustment. ∗ Corresponding author. Tel.: +34 913944106. E-mail address: fervicen@quim.ucm.es (F. Vicente). The use of hydrogen peroxide in this treatment is relatively inex- pensive, nonpersistent, and is unlikely to be a health hazard if is used properly. However, one of the main drawbacks of an in situ Fenton-like treatment relies in the instability of hydrogen peroxide to water and oxygen via non-radical-producing pathways, when it gets in touch with inorganic compounds, such as iron and man- ganese oxyhydroxides catalysts, as well as other transition metals resulting from mineral dissolution, or with organic compounds, which are widespread in surface soils [1,2]. In most cases, hydro- gen peroxide travels no more than 3–4 m, and often decomposes within 1–2 m of the injection well [3]. Hydrogen peroxide is typ- ically stabilized at acid pH. Therefore, it is desirable to have an additive which buffers at a high pH and acts as an effective stabilizer without compromising the natural pH of the soil. Some attempts have been made to stabilize hydrogen peroxide in the subsurface, primarily through the addition of phosphates to bind transition metals [4–7]. The increase in H 2 O 2 stability with KH 2 PO 4 , the most effective phosphate specie [6], probably resulted from the inacti- vation of the primary catalysts (e.g., transition elements such as iron, manganese), either by precipitation reactions or by conver- sion to relatively inactive complexes [5]. Phosphate also functions as a radical scavenger because it quenches hydroxyl radicals and terminates chain decompositions reactions [1]. 1385-8947/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2011.06.036