| Summary: | Used lubricating oil (ULO), commonly known as black oil, is the used or excess oil produced from different equipment, machineries, and motor vehicle in day to day operation. ULOs are extremely contaminated materials and it is harmful to nature owing to existing impurities resulting from the degradation of additives. The presence of the metals additives along with wear and tear makes waste lubricant oils as hazardous waste. ULOs are classified as hazardous and waste materials, and they lead to severe environmental issues as well as harm population well-being. Contaminants, for instance, poly-aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), carcinogenic elements, and heavy toxic metals which make black oil as a serious threat to human life and the environment. Handling of waste lube oils reduces waste toxicity and complexity while producing useful goods including fuels, solvents, and base oils for fresh lube oil manufacturing. There are a number of techniques are reported to re-refining used lubricant oil to remove impurities and obtain base oil from waste lubricant oil. Some of these techniques include the acid/clay method, vacuum distillation, solvent extraction, thin film evaporation method, thermal deasphalting process, pyrolysis using microwave heating, membrane technology, and other modern techniques. Additionally, advanced methods are developed in the recent times such as membrane technology; pyrolysis process and its significant application in refining in waste lubricant oil are also discussed. Adsorption is a simple, inexpensive, and easy method for re-refining old lubricating oil. A variety of adsorbing agents were employed in the adsorption process. Polymers with high conductivity are known as conducting polymers also possess great adsorption capacity and suitable electrical and electrochemical properties. As a result, conducting polymers should be investigated as a viable adsorbent material for pre-treatment of waste oil in order to decrease the development of acidic sludge generated from the acid/clay method. To minimize pollution, the research states that waste oil regeneration is a more sustainable and environmentally beneficial option than the traditional refinery method. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022.
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