Most soil remediation studies investigated single contaminants or multiple contaminants of the same type. However, in field conditions, soils are often contaminated with potentially both toxic metals and organic pollutants, posing a serious technical challenge. Here, batch experiments were conducted to evaluate the performance of combining in situ solidification/stabilization (ISS) and in situ chemical oxidation (ISCO) for the simultaneous removal of aniline (1000 mg/kg) and Cd (10 mg/kg). All four tested ISS amendments, especially quick lime and Portland cement, promoted in situ chemical oxidation with activated persulfate in contaminated soil. Combined ISS/ISCO remediation effectively removed aniline and reduced the bioavailable Cd content at optimal initial persulfate and ISS amendment concentrations of 1.08 mol/kg and 30 wt% with a seven-day curing time, and significantly reduced leaching. Persulfate inhibited the reduction of the bioavailable Cd content, and ISS amendment with persulfate did not synergistically remediate Cd in co-contaminated soil. Strong alkalinity and high temperature were the main mechanisms driving rapid pollutant removal and immobilization. The reaction of CaO with water released heat, and Ca(OH)₂ formation increased the pH. The relative contributions of heat vs. alkaline activation, as well as the contaminant removal efficiency, increased with ISS amendment CaO content. Combined treatment altered the soil physicochemical properties, and significantly increased Ca and S contents. Activated persulfate-related reactions did not negatively impact unconfined compressive strength and hydraulic conductivity. This work improves the selection of persulfate activation methods for the treatment of soils co-contaminated with both potentially toxic metals and organic pollutants.

A novel composite of montmorillonite-supported carboxymethyl cellulose-stabilized nanoscale iron sulfide (CMC@MMT-FeS), prepared using the co-precipitation method, was applied to remediate hexavalent chromium (Cr(VI))-contaminated soil. Cr(VI)-removal capacity increased with increasing FeS-particle loading. We tested the efficacy of CMC@MMT-FeS at three concentrations of FeS: 0.2, 0.5, and 1 mmol/g, hereafter referred to as 0.2 CMC@MMT-FeS, 0.5 CMC@MMT-FeS, and 1.0 CMC@MMT-FeS, respectively. The soil Cr(VI) concentration decreased by 90.7% (from an initial concentration of 424.6 to 39.4 mg/kg) after 30 days, following addition of 5% (composite–soil mass proportion) 1.0 CMC@MMT-FeS. When 2% 0.5 CMC@MMT-FeS was added to Cr(VI)-contaminated soil, the Cr(VI) removal efficiency, as measured in the leaching solution using the toxicity characteristic leaching procedure, was 90.3%, meeting the environmental protection standard for hazardous waste (5 mg/kg). The European Community Bureau of Reference (BCR) test confirmed that the main Cr fractions in the soil samples changed from acid-exchangeable fractions to oxidable fractions and residual fractions after 30 days of soil remediation by the composite. Moreover, the main complex formed during remediation was Fe(III)–Cr(III), based on BCR and X-ray photoelectron spectroscopy analyses. Biotoxicity of the remediated soils, using Vicia faba and Eisenia foetida, was analyzed and evaluated. Our results indicate that CMC@MMT-FeS effectively immobilizes Cr(VI), with widespread potential application in Cr(VI)-contaminated soil remediation.