In this work, blast furnace dust (BFD), a steel industry waste, was used as a demulsifier for highly efficient removal of the organic oil contaminant of metal working wastewater. Batch experiments showed that a simple mixture and stirring of BFD with stable emulsified wastewater containing metalworking oil (TOC ca. 15,000 mg L-1 and 1500 NTU) led to 90-98% TOC removal at pH lower than 7. Scanning electronic microscopy, X-ray diffraction, Mossbauer, thermogravimetric analysis, and Raman analyses suggest that the removal of the stable oil micelles is a combination of two synergic processes: (i) an electrostatic capture of the stable negatively charged oil droplets by the positive BFD particles followed by (ii) a strong interaction with the oil and the hydrophobic carbon surface. Preliminary results showed that BFD can be regenerated and reused by simple extraction or thermal treatment. (C) 2015 Elsevier B.V. All rights reserved.