Remediation effectiveness of aging diesel-contaminated soil using thermochemical treatment: Soil microstructure transformation and reusability

Abstract

This study investigated the microstructure transformation observed in an aging diesel-contaminated soil after thermochemical treatment (DT150°C+PS) to explore its impact on engineering reusability. Three thermal remediation procedures (i.e., DT150°C, DT350°C, and DT550°C) were selected as the control group. The results show that: (a) Pyrolytic carbon was produced in the DT350°C and DT550°C, while none was produced in DT150°C and DT150°C+PS; (b) Iron-based minerals and organic matter in DT150°C+PS, DT350°C, and DT550°C were combusted and decomposed to release the Fe(II) substances; under stronger oxidation environments, Fe(II) substances would further transform into more stable Fe(Ⅲ) substances; and (c) Halloysites and illites were formed in DT350°C, palygorskites and cordierites were formed in DT550°C, and oxidation in DT150°C+PS produced the sulfate minerals. The formed sulfate minerals in the DT150°C+PS sample filled pores and provided the skeleton strength, resulting in high unconfined compressive strength and poor permeability. Using a self-developed assessment model, only the DT150°C+PS sample showed an improvement (calculated as 2.96×10−5) in engineering performance and other methods led to the deterioration of soil mechanical properties. Thermochemical treatment is more suitable for engineering reuse, and this study can provide a theoretical basis for evaluating the greener reusability of contaminated soil after thermal or thermochemical remediation.