Remediation of hexavalent chromium-contaminated soils using zero-valent magnesium
Abstract
Hexavalent chromium (Cr[VI]) is hazardous because it has high mobility, toxicity and strong oxidizing properties. Cr(III) is less toxic than Cr(VI) and is relatively immobile in soils and sediments because of its extremely low solubility. Many remediation strategies focus on the chemical or microbiological reduction of Cr(VI) to produce immobile Cr(III) phases. Zero-valent iron (ZVI) is the most commonly used reductant to remediate contaminants in soil or groundwater. However, the reactivity of ZVI decreases over time, due to the surface passivation caused by corrosion products. Several recent studies have examined the feasibility of using zero-valent magnesium (ZVMg) as a reductant in remediation processes. ZVMg is a potential alternative for the reductive remediation of various classes of pollutant due to its high solubility and high redox potential. This study evaluated the effectiveness of Cr(VI) removal from Cr(VI)-contaminated soils using ZVMg. In this study, 16 samples of residual soil from representative geologic bedrock in Korea were collected, characterized physicochemically, and then artificially contaminated with 100 mg Cr(VI) per kg soil. The initial concentration of the soil samples ranged from 24.7 to 92.9 mg/kg of Cr(VI) depending on the characteristics of the soil samples. The addition of ZVMg at 0, 0.01, 0.02, 0.04, 0.06, 0.08, and 0.1 g increased the pH and electrical conductivity (EC) of the soil solutions (soil 1 g, deionized water 40 mL) to pH 10.6 and 13.2 μS/cm, respectively, and equilibrium was reached within 4 h. The Cr(VI) concentration of the soil residuals after the reaction ranged from 4.2 to 13.8 mg/kg. The removal efficiency of Cr(VI) in soils ranged from 48.6% to 93.0% (average 75.0%) at a ZVMg dosage of 0.04 g/g soil. We confirmed that ZVMg can be used for the removal of adsorbed Cr(VI), as well as water-soluble Cr(VI), in contaminated soils. ZVMg had high Cr(VI) removal efficiency in samples with a relatively low soil pH. The reduction mechanism of Cr(VI) from the contaminated soil using ZVMg was related to Mg solubility, the chemical species of Cr(VI) in soil, and physicochemical properties of soil, such as soil pH, EC, and mineralogical characteristics. The reactivity of ZVMg and removal efficiency of Cr(VI) could be improved by comprehensive, continuous pH control during treatment.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H21M1838C
- Keywords:
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- 0409 Bioavailability: chemical speciation and complexation;
- BIOGEOSCIENCESDE: 1832 Groundwater transport;
- HYDROLOGYDE: 1865 Soils;
- HYDROLOGYDE: 1871 Surface water quality;
- HYDROLOGY