Preparation of Magnesium Carbonate Whisker from Magnesite Tailings

Transcription

1 IOP Conference Series: Materials Science and Engineering Preparation of Magnesium Carbonate Whisker from Magnesite Tailings To cite this article: N Wang et al 2011 IOP Conf. Ser.: Mater. Sci. Eng View the article online for updates and enhancements. This content was downloaded from IP address on 17/03/2019 at 02:08

2 Preparation of Magnesium Carbonate Whisker from Magnesite Tailings N Wang 1, M Chen 1, and H W Ni 2 1 School of Materials and Metallurgy, Northeastern University, Shenyang , China 2 Wuhan University of Science and Technology, Wuhan , China chenm@smm.neu.edu.cn Abstract. Magnesium carbonate whisker was prepared by thermal decomposition of Mg(HCO 3 ) 2 solution that was prepared through hydration and carbonation of light burnt magnesia derived from magnesite tailings. The effects of thermal decomposition conditions on the morphology of magnesium carbonate crystal were investigated. The results showed that thermal decomposition product was MgCO 3 3H 2 O, and its crystal morphology was appreciably influenced by the additives added to Mg(HCO 3 ) 2 solution. Magnesium carbonate whiskers were successfully prepared when a kind of soluble magnesium salt was added, and magnesium carbonate whiskers with the length of 20 to 60μm and aspect ratio of 10~20 were obtained under the condition of 50 C thermal decomposition temperature and 200 rpm stirring intensity. 1. Introduction The magnesite resource is abundant in China which is also a main refractory production base. However, as for the mining and utilization of magnesite in China, the utilization ratio of low-grade magnesite tailing is low, which not only restricts the effective utilization of magnesite resource but also causes the problems of land occupation and environmental impact. Magnesium carbonate whisker is widely used as filler, reinforcing agent of rubber and high temperature thermal insulating refractory in terms of its high purity and strength. It s also used for the production of glass and chemical materials and the preparation of high grade magnesium hydroxide, magnesium sulfate, magnesium chloride and precursor of MgO whisker for its good properties [1,2,3]. Based on the previous work, the preparations of magnesium carbonate whiskers have been reported, and most of the preparation methods of magnesium carbonate whisker were according to coprecipitation technology through the reaction of soluble magnesium salts with carbonate salts in water solution [4,5,6]. For example, magnesium carbonate whisker could be prepared through the reaction of MgCl 2 with (NH 4 ) 2 CO 3 in water solution, but the generated by-product of NH 4 Cl gives rise to unavoidable environment problems. Therefore, the existing preparation methods of magnesium carbonate whisker have the disadvantages such as complicated technology, higher cost as well as byproduct problems. The present work investigated the preparation of magnesium carbonate whiskers from magnesite tailings by using a novel eco-friendly technique. 2. Experimental procedures c 2011 Ceramic Society of Japan. 1 Published under licence by Ltd

3 The starting material was magnesite tailings (particle size<40mm) from Dashiqiao of Liaoning province, China, and with the chemical composition shown in table 1. Reagent grade potassium dihydrogen phosphate (KH 2 PO 4 ), ammonium carbonate((nh 4 ) 2 CO 3 ) and a kind of soluble magnesium salt were used as additives for the preparation of magnesium carbonate whisker during pyrolysis process. Table 1. Chemical composition of magnesite [%] MgO CaO SiO 2 A1 2 O 3 Fe 2 O 3 LOI* * the mass loss percentage by soaking magnesite powder at 850 C for enough time. The preparation procedure of magnesium carbonate whisker is shown in figure 1. Magnesite tailing with the chemical composition as shown in table 1 was firstly fired at 850 C to obtain light burnt MgO, which was then mixed with water under the condition of stirring and CO 2 gas bubbling in order to realize hydration and carbonation. Consequently, magnesium bicarbonate (Mg(HCO 3 ) 2 ) solution was obtained after resting and filtration. Then, Mg(HCO 3 ) 2 solution was heated at 40~80 C with stirring and different additives added. After filtration, the obtained precipitated product was dried at 120 C for 24h. The chemical composition of the prepared samples were evaluated by fluorometric analysis and thermal gravity analysis (TGA), and the phase composition was characterized by X-ray diffraction (XRD). The morphology of the sample was observed by scanning electron microscopy (SEM). magnesite tailings clcination magnesia hydration and carbonation filter cake filtrate filtration pyrolysis Figure 1. Flow chart of preparing magnesium carbonate whisker MgCO 3 3H 2 O whisker 3. Results and discussion Figure 2 shows the XRD pattern of precipitated product after heating magnesium bicarbonate solution at 50 C. It can be seen that the obtained powder was well crystallized. By chemical and TGA analysis, it is known that the obtained whisker was MgCO 3 3H 2 O, and chemical analysis of the prepared powder after heating at 850 C showed that the content of MgO was more than 99.6%, indicating that the obtained product has a high purity due to the effective separation of magnesium bicarbonate solution from gangue and other insoluble compositions in the tailings. Thus, it is considered that the present method for the preparation of MgCO 3 3H 2 O powder can achieve an effective utilization of low-grade magnesite tailings. In addition, the filter cake after carbonation and solid-liquid separation could be reused for the hydration and carbonation processes, which is favorable to promote the yield ratio of magnesite. MgCO 3 3H 2 O Intensity / a.u θ / Figure 2. XRD pattern of pyrolysis product 2

4 Fig. 3 shows the effects of different additives on the morphology of MgCO 3 3H 2 O crystals. Without any addition, the mixtures of flaky and rod-like precipitated products were obtained, shown as Fig. 3(a). On the other hand, petal-like magnesium carbonate crystals were obtained when potassium dihydrogen phosphate was added, shown as Fig. 3(b). Spherical magnesium carbonate ones were obtained with the addition of ammonium carbonate, shown as Fig. 3(c). MgCO 3 3H 2 O whiskers with the length of 20~60μm and aspect ratio of 10~20 were obtained while a kind of soluble magnesium salt was added, shown as Fig. 3(d). Figure 3. Effects of different additives on the crystal morphologies (a) without addition;(b) potassium dihydrogen phosphate; (c) ammonium carbonate;(d) soluble magnesium salt Figure 4 shows the effect of stirring intensity on the crystal morphology of MgCO 3 3H 2 O. A proper stirring intensity is required for the formation of magnesium carbonate whisker. The well-grown magnesium carbonate whisker was obtained when the thermal decomposition temperature was 50 C at the stirring intensity of 200 rpm. (a) (b) (c) 20µm 10µm 20µm Figure 4. SEM images of the magnesium carbonate obtained for various stirring intensity. (a) without stirring, (b) 200 rpm, (c) 400 rpm 4. Conclusions (1) Magnesium carbonate powder with high purity MgCO 3 3H 2 O could be prepared from magnesite tailings by the present method. (2) The well-grown magnesium carbonate whisker was successfully prepared when a kind of soluble magnesium salt was added. 3

5 (3) Stirring intensity had an appreciable effect on the formation of magnesium carbonate whisker, and the magnesium carbonate whiskers with the length of 20 to 60 μm and aspect ratio of 10~20 were successfully prepared when the thermal decomposition temperature was 50 C at the stirring intensity of 200 rpm. Acknowledgments This research work was supported by the Open Research Fund of Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology. References [1] Xue D F and Wang X L 2006 Matter. Lett [2] He Y L, Wang J K and Deng H Y 2008 Ceram. Int [3] Chen R, Luo K B, and Tan Y X 2007 Ceram. Int [4] Wang Y, Li Z B and Demopoulos G P 2008 J. Cryst. Growth [5] Kloprogge J T, Martens W N, Nothdurft L and Duong L V 2003 J. Mater. Sci. Lett [6] Wang W P and Zhang Y 2002 Mater. J. Chin. Ceram. Soc