| With the rapid development of industry, large amounts of solid wastes have been produced. These solid wastes not only occupy land but also cause various pollutions to environment, which seriously restrict the sustainable development of society. The ceramics appear a promising solution because it is able to convert, at a relatively low cost, complex chemical compositions into useful materials with good technological properties. Ceramics industry also has the ability to consume these bulk solid wastes, and is facing with the demand of utilizing low grade minerals or industry wastes as the decreasing of high-quality raw materials.The traditional ceramics belong to K2O(Na2O)-Al2O3-SiO2 ternary system. Clay, feldspar and quartz are its main raw materials. In this system. Fe2O3 and CaO are required less than 0.8 wt.% and 3wt.% in the raw materials respectively. As steel slag and red mud hve a composition of more than 35wt.% CaO and 10wt.% Fe2O3. utilization of such solid wastes in ceramics with large proportion requires a new ceramics system with high CaO and/or Fe2O3 content. It is reported that ceramics based on CaO-MgO-SiO2-Fe2O3-Al2O3 (CMSFA) were feasible to utilize Ca-rich and iron-rich industrial wastes and in the meanwhile had excellent properties. However, little systematic research has been conducted on the mechanism of sintering and densification of the new ceramics, which restricts the application of its industrialization.The main purpose of this paper was to study utilizing Ca-rich and iron-rich solid wastes to prepare Ca-Si system ceramics using steel slag as main raw materials. Techniques such as FactSage software, x-ray diffraction, scanning electric microscope, phase diagram were used for a series of research, including the mechanism of sintering and densification of the new CMSFA ceramics, effects of alumina and iron on the sintering process and properties, optimization of sintering process and properties and so on. What is more, industrialization experiments were carried out on the basis of these studies. Research achievements are as follows:(1) According to the studies of the differences of main crystal phases and physical and mechanical properties of ceramics, the division rules of CMSFA system ceramics were determined. The CMSFA system could be divided as pyroxene ceramic system, pyroxene-anorthite ceramic system and anorthite ceramic system. When MgO>10wt.%, pyroxene ceramic with pyroxene minerals as the main phase, sintered between 1180?1220?, were formed and its flexural strength was 90-150MPa; when MgO<10wt.% and 10wt.%<Al2O3<15wt.%, pyroxene-anorthite ceramics with pyroxene and anorthite as the main phases, sintered between 1130?1180?, were formed and its flexural strength was 60-1 OOMPa; when MgO<5wt.% and 15 wt.%<Al2O3<40 wt.%, anorthite ceramics with anorthite as the main phase, sintered between 1100?1130?, were formed and its flexural strength was 30-75MPa; when MgO<5 wt.% and Al2O3<5 wt.%, pyroxene-quartz ceramics with pyroxene and quartz as the main phases, sintered between 1220?1250?, were formed and its flexural strength was 50-90MPa.(2) Iron component contributed to promote densification and enhanced crystals during sintering process of pyroxene ceramics. In the CMASF ceramics system, iron component replaced alkali metal component as the role of flux, which promoted the formation of liquid and the densification process. At the same time part of iron ions dissolved into diopside, which promoted diopside transferred into more excellent performance augite phases. However, too much iron ions would cause generation of an excess volume of liquid and then cause deformation before densification process, which is detrimental for sintering and properties. It is proved that<10wt.% Fe2O3 addition in pyroxene ceramics system could promote sintering process and improve the physical and mechanical properties of products. Under the same experiment conditions, flexural strength of sample with 5 wt.% Fe2O3 is 132.9MPa, which is 83.35MPa and 68.45 MPa higher than the without and 10 wt.% Fe2O3 addition samples.(3) The sintering mechanism of pyroxene ceramics is quite different from the traditional clay-feldspar-quartz ceramics. The sintering process of pyroxene ceramics is divided into three stages:dehydration and decomposition of raw materials stage (<800?), primary crystallization stage (700?1100?) and densification &secondary crystallization stage. CaO and Fe2O3 components play key roles in the sintering process of pyroxene ceramics. Anothite and diopside phases formed at 700?1100?, before densification, by reaction between CaO and decomposition products of the clay and talc raw materials. The resulting crystals played an important role of framework during the densification process. Melting of iron-rich phases, such as andradite, at temperature between 1150? to 1180? promoted liquid sintering and densification process. Liquid formation promoted the main phases transferred from diopside, quartz and protoenstatite to sole pyroxene phases, which was contributed to excellent mechanical performances of final production.(4) The sintering temperature interval of pyroxene ceramics narrower than anorthite ceramics. The main reason for this phenomenon is that the temperature of liquid formation in pyroxene ceramics system is close to formation temperature of main crystals and the sharp increase of the liquid phase content with the increase of the sintering temperature. The results show that the addition of B2O3 had the best effect on improving the sintering temperature interval of pyroxene ceramics. The sintering temperature interval of sample with 5 wt.% B2O3 was broadened to 50? and the sintering temperature was down to 1100?1150? but attained flexural strength of 102.5MPa, which was excellent results.(5) Industrialization experiments of preparation of pyroxene ceramics and anorthite ceramics were successfully conducted. Pyroxene ceramics with steel slag as the main raw materials were successfully prepared in traditional ceramics production line. The sintering temperature is 1180? and the whole sintering time is 75min. The resulting products attained the average flexural strength of 93.4MPa and water absorption of 0.045%. It is indicated that pyroxene system ceramics adapted the existing ceramics production process and had excellent performance. What is more, the glazing effect of the products is good, which is conducive to promotion and application of the products. Industrialization experiments of anorthite system ceramics with low-quality minerals and tailings as the main raw materials were successfully carried out. The amount of low-quality minerals and tailings in ceramics reached 83 wt.%. The sintering temperature is 1130? and the whole sintering time is 36min. The resulting products attained the average flexural strength of 35.2MPa and water absorption of 0.2%. The success of the industrialization experiments showed that the theoretical system of calcium silicate ceramics based on the steel slag as the main raw material has strong applicability of raw materials and extensive popularization and provides a basis for large-scale utilization of industrial solid wastes and low-quality minerals in the ceramic industry. |
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