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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 (C_S), types of detergents, temperature (T), and pH value on the deoiling efficiency (D_e) were systematically investigated. The results indicated that at a given detergent concentration (C_DG) and C_S, D_e followed the order C₆H₁₁NaO₇ > C₆H₅Na₃O₇ > C₆H₁₄N₄O₂. When C_S was 3.86 g·L⁻¹ and C_DG was 10.0 g·L⁻¹, sodium d-gluconate achieved a maximum D_e of approximately 85%. Additionally, at a fixed C_S, D_e decreased as the pH value increased, while it increased with increasing temperature. Interestingly, during the deoiling equilibrium, an obvious “solid effect” (or C_S−effect) was observed. The “solid effect” refers to the phenomenon where the oil distribution coefficient (K_D) changes with an increase in C_S. The observed C_S effect was described using the surface component activity (SCA) model. The values of the intrinsic distribution coefficient ($K_D^0$) and C_S−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 C_S 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. Full article