The high cost of low rank coal flotation using diesel as the collector significantly restricts the improvement in economic efficiency of the coal plant. Waste colza oil (WCO) from the catering industry was used as a renewable and alternative collector for ultrafine low rank coal flotation in this investigation. Scanning electron microscopy (SEM) test was carried out to check the surface morphologies of the coal sample. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) tests were performed to examine the coal chemical compositions. The flotation yield using WCO was always higher than that of using diesel, especially at a high dosage. When 6 kg/t dosage was used, 35.68% yield was obtained with WCO, 5.54% higher than that with diesel. The mechanism of WCO used as an alternative collector was discussed based on the induction time, FTIR, and XPS tests. The induction time of the low rank coal after conditioning with 6 kg/t diesel and WCO were 200 ms and 100 ms, respectively, indicating that WCO was a more effective collector for improving the floatability of low rank coal compared with traditional diesel. XPS tests confirmed the adsorption of WCO on coal surface as the WCO has a large amount of C=O groups according to FTIR results. The hydrogen bonding between oxygen-containing groups in WCO and low rank coal surface was responsible for the improvement of floatability and flotation recovery. (C) 2018 Elsevier B.V. All rights reserved.