Co-pyrolysis of oily sludge and lignin for fabrication of high-performance adsorbent for oily wastewater treatment

Oily sludge, a hazardous by-product of the petroleum industry, poses significant environmental risks due to its elevated levels of hydrocarbons and heavy metals. As conventional disposal methods often lead to secondary pollution or inefficient resource recovery, this study investigates the synergistic pyrolysis of oily sludge with lignin to produce high-performance adsorbents for oily wastewater treatment. Thermogravimetric analyses demonstrated complementary properties and a synergistic co-pyrolysis effect between the two feedstocks. Kinetic analysis employing the Coats–Redfern method revealed that the co-pyrolysis of oily sludge and lignin significantly decreased the apparent activation energy while increasing the pre-exponential factor, confirming the lignin’s catalytic role in enhancing pyrolysis efficiency. The optimal adsorbent, produced at an oily sludge-to-lignin mass ratio of 1:5, exhibited a specific surface area of 1324.5 m 2 /g, abundant micropores, and diverse surface functional groups, as confirmed by SEM and FT-IR analyses. Under optimized conditions—an adsorbent dosage of 1.0 g/L, contact time of 40 min, and pH 7—this material effectively removed residual oil from synthetic oily wastewater and maintained over 70% removal efficiency after five regeneration cycles, highlighting its reusability. Finally, the chemical transformations of various components during the co-pyrolysis of oily sludge and biomass materials are elucidated.