Sustained release and self activation of peroxydisulfate intercalated Ca/Al-layered double hydroxide in the remediation of organic contaminated soil

To keep the sufficient effective concentration of oxidants during the in-situ chemical oxidation (ISCO) for organic polluted soil, peroxydisulfate (S ₂O ₈ ²⁻, PDS) intercalated Ca/Al-layered double hydroxide (LDH) was employed as sustainable released and self-activated material of PDS. In the simulated diesel contaminated soil (1000 mg/kg) column with Ca/Al-PDS LDH dosage of 1 wt% and a water flow rate of 0.2 mL/min, PDS released sustained around 50 d, and the final removal rate of diesel could reach 70%, which mainly attributed to Ca/Al-PDS LDH for the oxidation decomposition of diesel. A coupled mechanism between PDS release from Ca/Al PDS LDH and organics oxidation process was proposed according to the concentration of Ca ²⁺ and Al ³⁺ in solution and the X-ray diffraction (XRD) analysis of the solid residue. The generated organic acids and SO ₄ ²⁻ after the oxidation promoted the dissolution of LDH layers and ion exchange of PDS with SO ₄ ²⁻ respectively, thereby enhancing the release of PDS. The result of electron paramagnetic resonance (EPR) showed that the oxidative species (•OH, SO ₄ ⁻• and ¹O ₂) were generated both in the reaction solution and on LDH, resulting from the activation of PDS by the aqueous OH ⁻ and the Lewis basicity on Ca/Al-PDS LDH, respectively. Thus the oxidation process occurred both in the homogeneous and heterogeneous pattern. This study provided a novel design strategy of sustained-released and self-activated oxidants for the remediation of organic contaminated soil.