Kinetics and Solid Effect Investigations During Oil Droplet Desorption from Oil-Contaminated Soil Using the Chemical Cleaning Method

Considering the implications for the environment and human health, oil-contaminated soil generated in the petroleum industry requires treatment. Chemical cleaning represents an effective treatment approach for oil-contaminated soil and has attracted considerable attention. In this study, sodium d-gluconate (C₆H₁₁NaO₇), trisodium citrate (C₆H₅Na₃O₇), and L-arginine (C₆H₁₄N₄O₂) were employed as detergents to remove oil from oily sludge. The impacts of sludge (solid) concentration (<i>C</i>_S), types of detergents, temperature (<i>T</i>), and pH value on the deoiling efficiency (<i>D</i>_e) were systematically investigated. The results indicated that at a given detergent concentration (<i>C</i>_DG) and <i>C</i>_S, <i>D</i>_e followed the order C₆H₁₁NaO₇ > C₆H₅Na₃O₇ > C₆H₁₄N₄O₂. When <i>C</i>_S was 3.86 g·L^-1 and <i>C</i>_DG was 10.0 g·L^-1, sodium d-gluconate achieved a maximum <i>D</i>_e of approximately 85%. Additionally, at a fixed <i>C</i>_S, <i>D</i>_e decreased as the pH value increased, while it increased with increasing temperature. Interestingly, during the deoiling equilibrium, an obvious "solid effect" (or <i>C</i>_S-effect) was observed. The "solid effect" refers to the phenomenon where the oil distribution coefficient (<i>K</i>_D) changes with an increase in <i>C</i>_S. The observed <i>C</i>_S effect was described using the surface component activity (SCA) model. The values of the intrinsic distribution coefficient (KD0) and <i>C</i>_S-effect constant (<i>γ</i>), which are the model parameters of the SCA model, were derived from three detergent-sludge systems under different temperatures (<i>T</i>) and pH values. The strength of the <i>C</i>_S effect (or <i>γ</i> value) was found to be independent of detergent type and increased as <i>T</i> and pH value increased. This study broadens the application range of the SCA model and contributes to a deeper understanding of the adsorption and desorption behavior of oil droplets at the solid-liquid interface.