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The influence of the Fe 3؉ /Fe 2؉ ratio on the crystallization of iron-rich glasses was investigated in this study. The glass batches were made from two hazardous industrial wastes: mud (goethite and jarosite) originating from the zinc hydrometallurgical process and electric arc furnace dust (EAFD). Glass compositions were prepared by adding different percentages of carbon powder. The crystallization process was investigated by a combined thermogravimetry/differential thermal analysis technique, in air or nitrogen atmospheres, using powder and bulk glass samples. The crystalline phases formed, i.e., pyroxene and spinels, and their relative ratio were determined by X-ray diffractometry. The experimental results indicated that melting temperature and crystallization behavior were influenced by the initial Fe 3؉ /Fe 2؉ ratio and by the amount of carbon added to the glass batch. For goethite and jarosite glass compositions, decreasing the Fe 3؉ /Fe 2؉ ratio increased the crystallization rate by favoring magnetite formation. For EAFD glass compositions, the addition of carbon to the batch inhibited chromite-magnetite spinel formation and favored the attainment of an amorphous glassy phase.

In this study, sintered glass-ceramics made up of jarosite (a hazardous industrial waste) have been obtained by sintering high-iron-content glasses. Thermal gravimetry and differential thermal analysis, carried out in different atmospheres, have been utilized to explain the phase formations in the volume and iron oxidation on the surface of the glass particles. Low-angle XRD technique has been used to investigate the distribution of the phases formed on the surface of the glass during heating. The variation of density of the powder and bulk samples has been used to investigate the kinetics of phase transformation. The value of the Avrami constant, n, has been obtained as 1.33, which corresponds to the three-dimensional diffusion growth on a fixed number of nuclei. The sinter-crystallization process has been defined to yield a 40 wt% crystal phase. The results of this study have opened the possibility of preparing glass-ceramics with an original appearance, somewhat similar to that of granite, by reevaluating industrial wastes.