Novel chelant‐based washing method for soil contaminated with Pb and other metals: A pilot‐scale study

Abstract

Remediation with chelants can restore metal‐contaminated soils for use as a natural resource. Calcareous soil from Meza Valley, Slovenia, and acidic soils from Arnoldstein, Austria, and Pribram, Czech Republic (with 1,028, 862, and 926 mg ∙Pb∙kg−1, respectively), were washed with 60–100 mmol EDTA per kilogram of air‐dried soil in series of 30 batches (50 kg soil batch−1). The approach involves a novel reaction that incorporates alkaline substitution, precipitation and adsorption of toxic metals on polysaccharides, and chelant acidic precipitation via 83% EDTA (on average) and complete process water recycling (no wastewater was generated). The pH gradient was imposed by Ca(OH)2 and H2SO4, and excess reagent was removed with the remediated soil as CaSO4, thereby preventing the salification of the recycled waters. Remediation removed 60%, 78%, and 71% of the Pb from the Meza, Arnoldstein, and Pribram soils, respectively, and reduced the Pb bioaccessibility levels in the simulated human gastrointestinal phase by 5.0, 7.7, and 8.1 times. Residual emissions (EDTA, toxic metals) were reduced with soil aging and remediated soil deposition on a reactive permeable barrier. The solid waste generated from the process totaled 10.8 kg tons−1 of the air‐dried soil, and the material/energy costs of remediation reached 20.6 € tons−1. These results demonstrate the robustness, efficiency, and safety of this novel approach.

Effect of soil washing with biodegradable chelators on the toxicity of residual metals and soil biological properties

“…S1), which facilitates more efficient ligand-metal ion complexation and formation of metal-chelate complexes (Yip et al, 2010). Previous works have confirmed that EDTA possess strong chelating ability for multi-heavy metals even over a wide pH ranges (Udovic and Lestan, 2012;Deng et al, 2017;Lestan, 2017). The Cd, Pb, and Zn removal efficiencies obtained in this work for farmland soil were 93, 71, and 62% after washing with EDTA, respectively, but washing the mine soil removed less metals (62% of Cd, 56% of Pb, and 32% of Zn).…”

Changes in Organic Matter Composition Caused by EDTA Washing of two Soils Contaminated with Toxic Metals

“…Similarly, Tsang et al (2007) observed the dissolution of native Fe/Al oxides, Ca carbonates and organic matter in soils that have been ushed with Na 2 EDTA. It was reported that CaEDTA, as used in this study, has a less negative effect on soil properties (Lestan 2017;Theodoratos et al 2000). Indeed, the soil washing solution provides Ca 2+ ions that effectively promote the formation of cationic bridges.…”

“…Remediation of contaminated soils (ReSoil®) was carried out in the pilot scale chelate washing plant described by Lestan (2017). Brie y, soil (40 kg per batch), at about 18% moisture content, was washed with recycled EDTA solution (50 L) for 18 h in a concrete mixer.…”

Soil Washing Technology for Removing Heavy Metals from a Contaminated Soil: A Case Study

“…Thus, soil remediation is necessary to attain more acceptable environmental conditions [8]. In this concern, ethylene di amine tetra acetic acid (EDTA) forms water-soluble complexes with heavy metals in soil [9,10] and therefore is considered an efficient soil-washing liquid for extracting these metals from soils [11,12]. This amendment can also be used for inducing phytoextraction of heavy metals [13] and probably metalloids from polluted soils by grown plants [14].…”