Investigating the effects of intensive milling on the production of synthetic calcium silicate from marble industry wastes, by using ceramic materials

In this thesis, it was concerned on the synthetically production of wollastonite (CaSiO3), one of the calcium silicate minerals, through thermal methods, by using calcium carbonate (CaCO3) obtained from marble processing plant waste sludge and quartz (SiO2) obtained from silica sand. Determining the effects of co-milling of the raw materials at prolonged periods on the roasting temperature at which wollastonite forms, when accomplished before the roasting procedure where the waste marble is contacted with silica sand to manufacture wollastonite was aimed. Marble dusts with white colour, purchased from marble processing plant waste depositing areas were mixed with silica sand powder at different stoichiometric ratios and mixtures were milled by jet ball mill at different periods. The milled mixtures obtained were characterized using various physical and physicochemical analysis methods such as particle size distribution analysis (PSD), X-ray powder diffractometry analysis (XRD), scanning electron microscopy analysis (SEM and EDX), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and the results were compared to the characteristics of the unmilled mixtures. By applying intensive XRD analysis for numerous of mixture samples, temperatures for conversion from CaCO3 to CaO and for manufacturing of CaSiO3 through sintering of CaO with SiO2 in the silica sand were determined by roasting the unmilled and milled mixtures at temperatures between 900°-1200°C. By characterizing the roasting products especially through the XRD and SEM analyses, wollastonite contents were examined. Moreover, performance of the synthetically produced wollastonite in traditional floor tile ceramics was comparatively determined as regard to natural wollastonite. Traditional floor tile ceramic masses which synthetic wollastonite were added at different ratios between 5-20% by weight were fired at various temperatures between 1000°-1200°C; a wide variety of the tests such as water absorption analysis, firing shrinkage analysis, colour index measurement, thermal dilatation behaviour analysis, mineralogical phases analysis, microstructure analysis, autoclave tests, and acid-base resistance tests were applied to the ceramics. The manufactured floor tile ceramics tablets were also glazed and then fired again and their glaze holding properties were determined. Thus, impact of the produced wollastonite and other calcium silicate additives on the technical properties of floor tiles were comparatively brought out. At the end of studies conducted in this thesis, it was determined that intensive milling achieved before the roasting process causes mechanical activation giving rise to a decrease both at the formation temperature of CaO from CaCO3 found in the marble and the sintering temperature of CaO with SiO2 during wollastonite production using marble waste dust and silica sand. KEY WORDS: Marble wastes, intensive milling, mechanical activation, synthetic wollastonite, ceramics material