Characterization of gypsum synthesized from LD slag fines generated at a waste recycling plant of a steel plant

The present work is devoted to the characterization of gypsum synthesized on the laboratory scale by the atmospheric leaching of -60 mesh LD slag fines generated from a waste recycling plant (WRP) during the Linz-Donawitz process of steel making at the Tata Steel plant, Jamshedpur, India. The main objective of the present work was to synthesize and characterize gypsum which is a value added product from LD slag which is a waste product of the steel industry. The techniques used for the characterization were X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and thermogravimetry (TG) techniques. The XRD analysis revealed the presence of the anhydrite and gypsum phases in the product material as well as the presence of silica in the form of coesite. This observation was further correlated by the TG analysis which indicated that the synthetic gypsum was a mixture of gypsum (dihydrate), hemihydrate, soluble γ-anhydrite and insoluble β-anhydrite phases of gypsum. The morphology of the material was found to be like tabular crystals along with the presence of intermittent needle-like and rod like structures as observed from the SEM micrographs. The chemical composition was further confirmed by SEM-EDS analysis. The purity of the product was also estimated to be 86.12% calcium sulphate by the estimation of sulphur trioxide content. These findings have been discussed in detail in the subsequent sections of the paper. Tabular, needle-shaped and rod-like morphology of synthesized gypsum crystals can be observed in the SEM micrographs at different magnifications.