Fast Assessment of Total Iron Contents in Steelmaking Slags by Means of Water Displacement Test for Recycling of the Iron in the Ironmaking and Steelmaking Process

Abstract

Steelmaking slags are usually processed to recover iron for recycling in the ironmaking and steelmaking process which replaces high-cost purchased steel scrap and iron ores. It is crucial to quickly determine the total iron content in an iron-bearing slag product for prompt and accurate quality control of the slag product. The water displacement test has been widely adopted in the slag processing industry as an industrial method to quickly assess the total iron contents in iron-rich slag products. However, this industrial method is often misused, and serious disparities exist between total iron contents evaluated using water displacement densities and by chemical analysis. Such disparities have resulted in the generation of great amounts of non-recyclable “iron-rich” steelmaking slag products with actual low levels of iron. In this research, we aimed to resolve this disparity. A total of 40 steelmaking slag samples were tested for water displacement densities and were chemically analyzed for total iron contents. The total iron contents in the slag samples were also evaluated using the measured water displacement densities with assumed parameters from two references. The research results suggest that the current industrial method for evaluating the total iron contents in the steelmaking slag products via the water displacement test cannot deliver precise but rather approximate results. Using assumed parameters from one reference to evaluate the total iron contents in the tested slag samples, the maximum error is about 12% and the average error is about 5%. While using assumed parameters from the other reference to evaluate the total iron contents in the tested samples, the maximum error is about 19% and the average error is about 10%. In order to decrease the evaluation error, a formula relating the total iron contents in the steelmaking slag samples via chemical analysis to the water displacement densities of the samples was developed by data fitting. Compared to the current industrial method of assessing the total iron contents in steelmaking slags via water displacement densities with assumed parameters from the references, the best fit formula gives the least error. Therefore, in order to quickly evaluate the total iron contents in a steelmaking slag product, a correlation formula between the total iron contents measured via chemical analysis and the water displacement densities should be developed in the first place. The formula then can be used to quickly determine the total iron content in the slag product with measured water displacement densities of the product for quality control when the product is being produced. Procedures were proposed in this paper for correctly measuring water displacement densities of slag samples and for correctly preparing the slag samples for chemical analysis.