Insight into the Thermal Washing Mechanism of Sodium Lignosulfonate Alkyl/Sodium Persulfate Compound on Oily Sludge

The thermal washing of oily sludge using sodium persulfate (SD) assisted by sodium lignosulfonate surfactant has been demonstrated to be an effective method for oily sludge remediation. To further explore the underlying mechanisms of this process, a systematic study was conducted by simulating oily sludge systems consisting of saturated hydrocarbons (SaH), aromatics hydrocarbons (ArH), resins (Res), and asphaltenes (Asp). The effects of reaction conditions, such as pH, sodium lignosulfonate alkyl (LSA) concentration, SD concentration, and washing temperature, were analyzed. Furthermore, the oxidative kinetic mechanism during the reaction process was investigated. The results demonstrated that neither petroleum hydrocarbons nor SD underwent significant chemical transformations when exposed to LSA, while SD exhibited a marked oxidative degradation effect on all four types of hydrocarbons. Oxidation kinetics indicated that sodium hydroxide played a catalytic role, with SD being the main oxidant and particularly efficient in degrading Asp and Res. Meanwhile, LSA contributed to the removal of hydrocarbons by reducing the surface tension of the solution, enhancing solubilization. This study not only elucidates the central role of SD in the thermal washing process but also provides a solid theoretical foundation for the practical application of this technology in oily sludge treatment.