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 (CS), types of detergents, temperature (T), and pH value on the deoiling efficiency (De) were systematically investigated. The results indicated that at a given detergent concentration (CDG) and CS, De followed the order C6H11NaO7 > C6H5Na3O7 > C6H14N4O2. When CS was 3.86 g·L-1 and CDG was 10.0 g·L-1, sodium d-gluconate achieved a maximum De of approximately 85%. Additionally, at a fixed CS, De decreased as the pH value increased, while it increased with increasing temperature. Interestingly, during the deoiling equilibrium, an obvious "solid effect" (or CS-effect) was observed. The "solid effect" refers to the phenomenon where the oil distribution coefficient (KD) changes with an increase in CS. The observed CS effect was described using the surface component activity (SCA) model. The values of the intrinsic distribution coefficient (KD0) and CS-effect constant (γ), which are the model parameters of the SCA model, were derived from three detergent-sludge systems under different temperatures (T) and pH values. The strength of the CS effect (or γ value) was found to be independent of detergent type and increased as T 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.