Palm oil fuel ash blended cement for solidification stabilization of petroleum sludge and heavy metal immobilization and waste valorization

The petroleum industry produces a significant quantity of solid waste referred to as petroleum sludge (PS) as a result of several refining, storage, and transportation procedures. PS typically contains a variety of heavy metals that could threat environment even to the human. Fortunately, PS can be effectively managed using a variety of treatment techniques. The solidification/stabilization (S/S) technique was applied to treat PS, with ordinary Portland cement (OPC) partially replaced by palm oil fuel ash (POFA). The study began with the characterisation of raw materials, including OPC, POFA, and PS, using X-ray fluorescence (XRF) and scanning electron microscopy (SEM). POFA substitution levels of 5%, 10%, 15%, and 20% were evaluated for their effectiveness in encapsulating heavy metals within the cementitious matrix. Two leaching assessments were conducted: the Toxicity Characteristic Leaching Procedure (TCLP) and the Synthetic Precipitation Leaching Procedure (SPLP). Heavy metal concentrations in the leachates were measured by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The results indicate that heavy metal concentrations decreased progressively with increasing POFA content up to 15%; a slight increase was observed at 20% substitution. All results were compared against USEPA regulatory guidelines, and the heavy metal concentrations in all treated samples complied with the applicable limits. The optimal POFA substitution level was 15%. The TCLP and SPLP results suggest that the treated material may warrant further investigation for potential reclassification from hazardous to non-hazardous waste; however, this conclusion requires validation through long-term durability assessment and compressive strength testing, which were not within the scope of the present study.