Enhancing lignite flotation via ultrasound: the potential of waste motor oil as an eco-friendly collector

Waste motor oil (WMO) is considered one of the major pollutants in the automotive sector that poses significant risks to both environmental and human health. The present study investigated the potential application of WMO as a collector in the flotation of low-grade coal, supported by an ultrasonic pretreatment process. The results of Fourier Transform Infrared (FTIR) spectroscopy analyses revealed that waste motor oil (WMO) contains adsorbed hydrocarbons and oxygen-containing compounds on the surface of coal. When waste motor oil (WMO) was employed as a collector in coal flotation without any ultrasonic pretreatment, a clean coal recovery of 76.03% and an ash content of 13.21% were achieved at a dosage of 10 kg/t. These results indicate a significant performance improvement as compared to the conventional collector, diesel oil. Furthermore, the application of ultrasonic pretreatment prior to the use of WMO was found to enhance the process efficiency even further, reducing the ash content to 11.23% and increasing the clean coal recovery to 86.09%. Finally, ultrasonic treatment resulted in higher contact angle values for both WMO and diesel oil collectors, thereby further enhancing surface hydrophobicity. This effect was consistent with the observed improvements in combustible recovery and ash reduction. Taken together, the results of the present study indicate that WMO can be considered a sustainable alternative collector from both economic and environmental perspectives. WMO outperformed diesel in enhancing lignite flotation efficiency.Ultrasound process improved the flotation recovery of lignite in presence of WMO.Ultrasonic treatment led to an increase in the contact angle of lignite suspension.Ultrasonic treatment changed the surface roughness of lignite particles. WMO outperformed diesel in enhancing lignite flotation efficiency. Ultrasound process improved the flotation recovery of lignite in presence of WMO. Ultrasonic treatment led to an increase in the contact angle of lignite suspension. Ultrasonic treatment changed the surface roughness of lignite particles.