Production of cleaner mill scale by dynamic separation of the mill scale from the fast-moving flume water at a hot rolling mill

High oil concentration in mill scale can have detrimental effects on environment, production and equipment when the oily mill scale is recycled in the ironmaking and steelmaking process. Therefore, it is of great importance to develop cost-effective technologies of producing clean mill scale. In this research, an in-process separation technology has been developed to produce the clean mill scale by dynamic separation from the fast-moving flume wastewater. An industrial trial was carried out to capture mill scale particles from the fast-moving flume wastewater with a strong magnet at an ArcelorMittal hot rolling plant. The results show that the dynamically-separated flume mill scale is much cleaner, containing about 6-30 time less oil than the conventional statically-separated pit mill scale. Oil concentrations in the flume mill scale samples are all significantly less than 0.5%, the commonly recognized oil limit in the mill scale for recycling in iron ore sintering. Size-by-size analysis shows that in every size fraction, the oil concentration in the flume mill scale particles is significantly less than that in the pit mill scale particles, and hence the cleaner flume mill scale is not due to coarser particle sizes. The much shorter residence time of the flume mill scale particles in the oily wastewater and the much stronger turbulence of the flume wastewater could be two of the main reasons why the flume mill scale is cleaner than the pit mill scale. (C) 2017 Elsevier Ltd. All rights reserved.