Characteristics of changes in hazardous elements and heavy metals during pyrolysis treatment of oily sludge

Oily sludge is a hazardous solid waste, hazardous ingredients (hazardous elements and heavy metals) in pyrolysis products have the potential for secondary pollution. The distribution of hazardous elements (N/S/Cl) during the pyrolysis of oily sludge was determined at different pyrolysis temperatures (350–750°C), and the potential ecological risk of heavy metals (Zn/Cu/Cd/Cr/Pb) in the solid residue was evaluated. The results showed that N-pollutants in oily sludge were mainly distributed at higher pyrolysis temperatures (550°C), S and Cl-pollutants were mainly distributed at 450°C. The leaching concentration of Zn metal in oily sludge was 119.73 mg/L, which has exceeded the concentration limit (100 mg/L) stipulated by GB 16,889–2008. The pyrolysis treatment could reduce the leaching rate of Zn metal to 18.39 mg/L Moreover, the risk assessment code (RAC) values for Zn showed a very high risk environmental risk level. Pyrolysis treatment could reduce the RAC value of Zn and change the environmental risk level of Zn to low risk. The results of this study provide a theoretical basis for the pyrolysis treatment of oily sludge and the control of harmful ingredients.