Acid tar treatment—the transformation of organic waste into “organic core—inorganic shell” structure particles

Acid tar (AT) is a distinct black viscous waste from the petrochemical industry that retains hazardous characteristics decades after creation. It is defined as an emulsion of various organic compounds, sulfuric acid, and water. Due to specific chemical composition and physical properties, the best available technique for the treatment of AT is not determined. This paper investigates the treatment of AT by CaO, resulting in its complete physicochemical transformation into a dry powder with the characteristics of inorganic material. Waste characterization of AT and obtained powder (including metals, PAH, BTEX, total hydrocarbon content, and EN12457-4 leaching test), their comparative FT-IR and SEM–EDS analyses, and XRD analysis of the powder revealed that the transformation is a complex process involving Ca(OH)₂ formation, evaporation of water and BTEX, and degradation of aromatic and unsaturated hydrocarbons. The remained organic phase is encapsulated under Ca(OH)₂ and CaCO₃ layers forming “organic core—inorganic shell” micron-sized particles, rendering the powder suitable for further treatment. This was confirmed by solidification/stabilization treatment of AT and obtained powder using the same amount of cement and pozzolanic binder. In contrast to AT solidificates, the powder solidificates possess unconfined compressive strength above the required value and characteristics of inert waste.