Effects of Different Desorbing Agents on the Desorption and Oxidative Degradation of Naphthalene in Soil Media

To develop efficient remediation technologies for naphthalene (NAP)-contaminated soil, this study systematically investigates the desorption behavior of NAP in various soil media, analyzes the effects of soil aging on NAP retention, and compares the desorption performance of three categories of desorbents toward NAP, including inorganic salt (CaCl₂), low-molecular-weight organic acids (Citric acid (CA), Oxalic acid (OA), Aspartic acid (ASP)), and surfactants (Tween-80, sodium dodecyl sulfate (SDS), alkyl polyglycoside (APG)). The influences of the three desorbent categories on NAP degradation in the ferrous ion (Fe(II))-activated persulfate (PDS) oxidation system are also evaluated. The results reveal that NAP desorption becomes more difficult with increasing soil clay content and longer aging duration. Weakly alkaline conditions (pH = 9.0) facilitate NAP desorption, and the desorption process conforms to the pseudo-second-order kinetic model. Significant differences are observed in the NAP desorption efficiency of the three desorbent groups. Low-molecular-weight organic acids exhibit the optimal desorption capacity; specifically, 1 mmol/L CA achieves a NAP removal rate of 36.1% after 48 h of desorption, which is markedly superior to OA and ASP. All tested surfactants substantially improve NAP desorption, among which Tween-80 delivers the best performance owing to its low critical micelle concentration (CMC) and suitable hydrophobicity, with desorption efficiency rising evidently as Tween-80 concentration increases. Low-concentration CaCl₂ ( <10 mmol/L) promotes NAP desorption by competing for soil adsorption sites, while high-concentration CaCl₂ (100 mmol/L) inhibits desorption by inducing flocculation and precipitation of soil organic matter. In the subsequent oxidative degradation stage, surfactants and CaCl₂ suppress NAP degradation via competing for reactive oxygen species (ROS), whereas all three low-molecular-weight organic acids exert positive promotional effects on NAP removal. When the molar ratio of PDS/Fe(II)/CA/NAP is set to 15∶5∶1∶1, the NAP removal rate reaches 97.5% within 120 min. This study verifies that CA possesses dual functions: Efficiently desorbing soil-sorbed NAP and enhancing subsequent oxidative degradation. The present work provides theoretical support for the green and efficient remediation of organic-contaminated sites using CA.