Thermal process and mechanism of phase transition and detoxification of glass-ceramics from asbestos tailings

Abstract

Based on the chemical and mineral composition of asbestos tailings, the asbestos tailings powder was pre-fired, formed into green body and finally heat-treated to prepare glass-ceramics through the processes of crystallization and sintering. The main crystal phases of the sample were forsterite and enstatite, and the minor crystal phases were magnesioferrite and diopside. The effects of crystallization temperature (787–867 °C) and sintering temperature (1150–1250 °C) on crystallization and phase change, micromorphology and physical-chemical properties of glass ceramics were investigated by means of thermogravimetry-differential scanning calorimetry analysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM-EDS) and mechanical properties tests. The results showed that the toxic phase chrysotile was almost converted into forsterite when the asbestos tailings powder was pre-fired at 700 °C for 1 h. During the sintering process of the green body, with the increase in the crystallization temperature, the content of the forsterite firstly increased and then decreased, and the enstatite increased gradually. After crystallizing at 850 °C for 1 h and holding at different sintering temperatures for 1 h, the glass-ceramics samples were obtained. With the increase in sintering temperature, the content of diopside in the samples gradually decreased, the hematite gradually disappeared and magnesioferrite precipitated at the same time. The crystal morphology was transformed from aggregates of spherulites and ellipse into intertwined bodies of spherulites, ellipse and round bar-like shape. The glass-ceramics achieved optimum compactness at the sintering temperature of 1200 °C with the water absorption rate being 0.026%, the bulk density being 3.164 g/cm3, and the flexural strength being 88 MPa, which reached the standard of glass ceramics for construction. In the process of preparing glass-ceramics from asbestos tailings, the phase transition and detoxification in asbestos tailings were realized, which had certain practical value for the utilization of asbestos tailings and the preparation of high value-added materials.