In this study, the conventional acid-clay method was used to evaluate its potential for recycling waste crankcase lubricating oil (WCLO). The results showed that the acid-clay method was effective in re-refining the WCLO and returning the oil to a quality comparable to oils produced from fresh lube oil stocks. This method has been reported to account for around 90% of the global waste crankcase lubricating oil treatment and is considered to be an inexpensive process. The results revealed that the acid-clay method improved the viscosity of the oil at 40°C from 104 cSt to 105.6 cSt. The flash point of the oil was also increased from 192°C in the WCLO to 204°C in the re-refined crankcase lubricating oil (RCLO). The water content reduced from 0.01% in the WCLO to 0% in the RCLO, indicating the effectiveness of the acid-clay method in removing water traces from the WCLO. Additionally, the contaminants present in the WCLO were reduced drastically, with iron and aluminum content reduced from 23.0% and 21.0% to 0.0% and 0.0%, respectively. The fuel ingress in the WCLO reduced from 4.0% to 1.0%. However, it was observed that the acid-clay method did not significantly impact the viscosity index, TBN, and density of the oil. The re-refined base oil produced by the acid-clay method can be fortified with appropriate additives and reused in vehicles, reducing environmental pollution, depleting fossil resources, and saving the country’s foreign exchange used in importing fresh lubricating oil.

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