Comparison of Thermal Decomposition Kinetics of Magnesite and Limestone Lei Su 1, a, Gang Zhang 2,b, Yu Dong 1,c, Jian Feng 3,d and Dong Liu 3,e

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1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Comparison of Thermal Decomposition Kinetics of Magnesite and Limestone Lei Su 1, a, Gang Zhang 2,b, Yu Dong 1,c, Jian Feng 3,d and Dong Liu 3,e 1 Northeastern University Research Academy, Shenyang, Liaoning, , China 2 Department of Chemistry of Northeastern University, Shenyang, Liaoning, , China 3 Yingkou Dongji Technology Group Co., LTD, Yingkou, , China a sulei6026@yahoo.com.cn, b gangzhang99@126.com, c dongyu4253@163.com, d f860826z@163.com, e liuyitong4448@sina.cn Keywords: magnesite; limestone; kinetics; activation energy; reaction order. Abstract. The thermal decomposition kinetics of magnesite and limestone, which are alkaline earth metal carbonates, were investigated using thermal analysis method. The research results showed that their kinetic decomposition characteristics and apparent decomposition activation energy have the comparability. Based on the thermodynamic/thermogravimetric data, the industrial production process of magnesite and limestone can draw on the experience of each other because of their similar decomposition thermodynamics and kinetics. Introduction Magnesite, the most important minerals contained magnesium, which has 3.05 billion tons of probed reserves in Liaoning province taking up 85 percent of the whole national reserves, whose main application is used for manufacturing fire-resistant materials[1]. Limestone belongs to steel materials most in use whose consumption accounts for 8~9 percent of total steel production and their annual consumption is 500~600 million tons[2]. At present, many large-scale production processes are applied to lime metallurgy such as 1000 t/d rotary kiln, Maerz kiln, suspension furnace, large vertical kiln. However, the calcination of magnesite mainly relied on small vertical kiln (with annual output below than 10 thousand tons)is a little behindhand. MgCO 3 and CaCO 3 are main chemical compositions of magnesite and limestone respectively, and thermal decomposition of them belong to thermal decomposition of alkaline earth metal carbonates. There are a large number of studies about thermal decomposition of limestone[3,4] and some reports about thermal decomposition of magnesite[5], nevertheless the same material differs greatly in their own research results. And, there is lack of thermal decomposition study results of magnesite and limestone under similar experimental conditions. The kinetics of thermal decomposition of limestone has received considerable attention, but kinetics of thermal decomposition of magnesite has received much less attention. If kinetic parameters of magnesite pyrolysis process such as activation energy and reaction order can be obtained, which will be useful in reasonablely designing conditions of fused magnesium production as well as will be useful in researching reaction mechanism and influenced conditions of reaction rate of magnesite and dealing with the problem of reaction yield. Limestone and magnesite stored in Liaoning province are studied by the means of thermal analysis and dynamic theory analysis and simulation. A series of kinetic parameters of thermal decomposition reaction are obtained which stated clearly that the thermal decomposition reaction of the two minerals had comparability. The research results will have a better clinical significance to use for reference between magnesite and limestone production processes. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-06/03/16,19:45:38)

2 Y Advanced Materials Research Vols Experimental and Data Analysis Materials. Magnesite samples are supplied by Great Stone Bridge, Yingkou, Liaoning province. Limestone samples are supplied by Tuchengzi, Ansteel Group. Their chemical components are showed on table 1. Analysis instruments and experimental conditions. Magnesite samples are analysed by NETZSC STA 449 F3 (German) including Kinetics Analysis software package. The instrument is running at: ±0.1 o C temperature accuracy, 0.1 μg balance sensitivity, alumina crucible, temperature from 25 o C to 1200 o C and nitrogen flow velocity of 30 ml/min. Thermogravimetric analysis experiments of limestone samples are performed using a Shimadzu DT-30 Differential Thermal Analyser[6]. Thermogravimetric analysis experiments are performed on 29 mg limestone samples running at: platinum crucible, heating rate of 10 o C/min, ±10 mg measurement range, differential rangen of 4 mv.min-1, temperature from room temperature to 950 o C, flowing air atmosphere (filtered by drying apparatus) and air flow velocity of 30 ml/min. Methods and data analysis. This work choose magnesite samples with porosity less than 0.5 for its not exploding upon heating Equation y = a + b*x Adj. R-Square Value Standard Error B Intercept B Slope Fig. 1 Thermal decomposition kinetics fitting curve of magnesite of Great Stone Bridge 1/T When heated to above 500 o C, magnesite begin to break down into magnesium oxide and carbon dioxide, and its decomposition chemical equation is MgCO 3 MgO+CO 2. In the atmosphere of nitrogen, redidual mass of magnesite from temperature to 1200 o C is 47.82% (10K/min). The activation energy and mechanism function of decomposition (Fig. 1) is obtained by thermo-kinetics software analysing TG curve. The most probable mechanism of magnesite is f(α)= 3(1-α)2/3 (correlation coefficient =0.9997). Atmosphere has an effect on decomposition temperature and decomposition kinetic parameters, and activation energy is kj/mol in the atmosphere of nitrogen. Table 1 The chemical components of limestone and magnesite Components CaO SiO 2 Al 2O 3 Fe 2O 3 MgO MnO P Na 2O K 2O S CO 2 (combustion loss) Limestone[%] Magnesite[%] Limestone analysis samples supplied by Tuchengzi of Ansteel Group are screened to 130 mesh of particle size. And difference reduce differential method (i.e. Freeman-Carroll formula[7] )which is one of the most common methods used to calculate kinetics data of thermal analysis is adopted to process kinetics data.

3 log(dα/dt)/ log(1-α) 2582 Advances in Materials and Materials Processing The reaction equation of limestone decomposition: CaCO 3 CaO+CO 2 (1) According to the Arrhenius formula, the kinetic equation of the weightlessness rate α in relation to the time (t) and temperature (T) is established: (2) we take the logarithm on both sides of the equation: (3) The data of limestone mine is imported in the Eq. 3. Then the straight line which is plotted by / as X-axis and as Y-axis can be obtained by using least square method. According to the Eq. 3, we discover the gradient of the straight line is and the intercept term is n, so that we can calculate E and n easily. After that, we import E and n into the equation of =log so that we can calculate the frequency factor A. Thus all the kinetic parameters of limestone have been calculated. Fig. 2 is the fit curve of kinetics of limestone decomposition. The equation is Y= X The table 2 is the result of kinetics data of limestone and magnesite. sample weight [mg] Table 2 The result of kinetics data of limestone and magnesite Weightle ssness [%] decomposition temperature [ C] reaction order [n] activation energy E [kjmol -1 ] frequency factor loga [S -1 ] correlation coefficient [r] limestone ~ magnesite experimental result and analysis. It can be seen from the data and result of table 2 that weightlessness of limestone is 42% and weightlessness of magnesite is 51.37%, which is in accordance with the assay value. The ranges of temperature for limestone and magnesite are 622~838 o C and 350~820 o C respectively. Reaction orders of limestone and magnesite are 0.1 and 0.66 respectively. Frequency factors of limestone and magnesite are 9.24 and 7.12, while activation energy is kj/mol and 177 kj/mol (1/T)/ log(1-α) Fig. 2 The fit curve of kinetics of limestone decomposition

4 Advanced Materials Research Vols Reaction heat of magnesium carbonate and calcium carbonate decomposition is 5.89 kj/g and 5.73 kj/g[8] respectively, which is almost identical. As previously mentioned, decomposition reactions of limestone and magnesite are similar in kinetics and thermodynamics because of their similar activation energy. From the fit curve of kinetics of Fig. 1 and Fig. 2 as well as relative information[9], we can find the most probable mechanism for limestone is f(α)=2(1-α)1/2, which is similar with limestone since they are both alkaline earth carbonate. It can be inferred that their reaction process parameters are similar for their semblable mechanisms in kinetics and thermodynamics. As a result, productive technology of limestone burning is also suited to magnesite burning after a minor correction. Of course, a specific application need more production tests. Conclusions The reaction order of limestone and magnesite are 0.1 and 0.66 respectively. Frequencyfactor of limestone and magnesite are 9.24 and 7.12, while activation energy are kj/mol and 177 kj/mol. The results are similar to related information which had been reported abroad. Since decomposition reactions of limestone and magnesite are similar in kinetics and thermodynamics, the results are significant for magnesite mine production. Acknowledgements This work was supported by a grant from the National High Technology Research and Development Program of China (863 Program) (No. 2011AA060103) References [1] Yue Quan: Magnesia Material Production and Application (Metall. Ind. Press, Beijing, China 2008). [2] Shengying Li, Zhihui Fan, Tianyi Yuan, Shaokang Li, Xuewen Chen, Shuisheng Wen and Fang Liu: Metall. Collect. (in Chinese) Vol. 2 (2010), p [3] J. Khinast, G.F. Krmmer, Ch. Brunner and G. Staudinger: Chem. Eng. Sci. Vol. 51 (1996), p. 623 [4] Mei Li and Hong Zhang: Coal Conver. (in Chinese) Vol. 29 (2006), p.25 [5] Xinwei Liu, Yali Feng and Haoran Li: Inorg. Chem. Ind. (in Chinese) Vol. 11 (2011), p.15 [6] Lei Su and Qinglin Zhan: Res. Iron & steel (in Chinese) Vol. 2 (1997), p. 17 [7] Yuzeng Li: Thermo Analysis (Tsinghua University Press, Beijing, China 1987). [8] Tianyou Song, Peng Cheng, Xingqiao Wang and Jianing Xue: Inorganic Chemistry (Higher Education Press, Beijing, China 2009). [9] Shijie Wang, Jidong Lu and Hu Zhou: J. Eng. Therm. (in Chinese) Vol. 24 (2003), p.699

5 Advances in Materials and Materials Processing / Comparison of Thermal Decomposition Kinetics of Magnesite and Limestone / DOI References [3] J. Khinast, G.F. Krmmer, Ch. Brunner and G. Staudinger: Chem. Eng. Sci. Vol. 51 (1996), p / (95)