An experimental study and regression analysis to estimate the reduction time of mill scale by coal

Mill scale is one of the solid co-products in steel industries containing free iron with different types of iron oxides, traces of non-ferrous elements and other compounds. Reduction of mill scale by solid reductants is a widespread method to convert it into valuable products. In this study, effect of three process variables: temperature (1000 °C, 1050 °C, 1100 °C), coal/mill scale ratio (0.8, 1.0, 1.2) and bed depth (35 mm, 40 mm, 45 mm) on the reduction kinetics of mill scale were studied. The activation energy was found to be nearly identical in evaluation by both integral and differential approach at around 70 KJ/mol. It was found in the study that increasing temperature and coal/mill scale ratio contributes in decreasing the reduction time of mill scale while increasing the bed depth results in an increase in the reduction time. An empirical correlation among these three variables was developed for degrees of reduction (0.4 to 0.6) by regression analysis and was validated by a set of test data.