Leaching behavior of Cr(III) in stabilized/solidified soil

Area of Science:

• Environmental Science
• Geochemistry
• Soil Science

Background:

• Chromium contamination in soil poses significant environmental and health risks.
• Effective remediation strategies are crucial for managing contaminated sites.
• Understanding chromium speciation and leaching behavior is key to developing successful treatment methods.

Purpose of the Study:

• To investigate the leaching behavior of chromium in contaminated soil.
• To evaluate the effectiveness of stabilization/solidification (S/S) techniques for chromium remediation.
• To determine the influence of pH on chromium leachability and identify controlling mechanisms.

Main Methods:

• Batch leaching tests were performed on untreated and S/S-treated soil samples.
• Surface complexation modeling was employed to understand Cr(III) release mechanisms.
• X-ray absorption near edge structure (XANES) spectroscopy was used to identify chromium species.
• Toxicity Characteristic Leaching Procedure (TCLP) was utilized to quantify leachate chromium concentrations.

Main Results:

• XANES analysis confirmed Cr(III) as the predominant species in all samples.
• The leachate chromium concentration was reduced from 5.18 mg/L to 0.84 mg/L with 25% cement treatment.
• Chromium leachability decreased with increasing pH from 3 to 5, remained stable between pH 5-10.5, and further decreased at pH > 10.5.
• Modeling indicated Cr(III) adsorption on iron oxides controlled release below pH 10.5, and precipitation governed it above pH 10.5.

Conclusions:

• Stabilization/solidification, particularly with 25% cement, is an effective method for reducing chromium leaching from contaminated soils.
• Chromium leachability is strongly pH-dependent, with optimal reduction observed at higher pH values.
• The study elucidates the geochemical mechanisms controlling chromium release, aiding in the design of effective soil remediation strategies.