Investigating the Kinetics, Mechanism, and Activation Energy of Limestone Calcination Using Isothermal Analysis Methods
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Investigating the Kinetics, Mechanism, and Activation Energy of Limestone Calcination Using Isothermal Analysis Methods Meisam Ghiasi 1 & Mahmoud Abdollahy 1
&
Mohammadreza Khalesi 1
Received: 22 December 2019 / Accepted: 1 September 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract In the current research, isothermal experiments of kinetic analysis were performed at different temperatures (800–1050 °C) and particle sizes (885 to 10,763 μm) to investigate the calcination kinetics of high-purity limestone. Thermal analyses were carried out in a zirconia crucible, 1 cm in height, for different temperatures and particle sizes. The reaction rate coefficients were varied in the 2.2 × 10−5-1.62 × 10−3-m0.6.s−1 range. Moreover, various isothermal kinetic analysis methods were applied to assess the decomposition mechanism and the calcination function governing the process. The modified shrinking core model was found as the best representation of the high-purity limestone kinetic data. The activation energy was evaluated using the Arrhenius curve, and an average value of 86 kJ.mol−1 was obtained. Keywords Calcination . High-purity limestone . Isothermal methods . Kinetic analysis . Shrinking core model
1 Introduction Quicklime (CaO) is a widely used raw material in many industries, including the production of precipitated calcium carbonate (PCC) [1–4], water treatment [5, 6], color and surface coatings [7, 8], oil refining [9–11], the manufacture of fertilizers [12, 13], and as a slag-refining agent for the steel industry [14, 15]. Quicklime is highly reactive to water and even reacts with moisture in the air. Therefore, it is rarely found naturally in nature, and its production in most cases requires limestone to be initially calcined, which produces lime and CO2 as a result of thermal decomposition [16]. The calcination reaction [Eq. (1)] is endothermic, which means that the forward reaction is favored by higher temperatures. CaCO3 → CaO þ CO2 ¼ þ182:1 kJ=mol
ΔH900°C ð1Þ
The reaction will proceed only if the partial pressure of CO2 in the gas above the solid surface is less than the decomposition pressure of the CaCO3. The decomposition pressure is determined by equilibrium thermodynamic equations [17]. * Mahmoud Abdollahy [email protected] 1
Department of Mining Engineering, Tarbiat Modares University, Tehran, Iran
Silokh et al. [18] proposed the following expression [Eq. (2)] for the equilibrium pressure Peq (in the atmosphere), where T is the temperature (K): 20474 Peq ¼ 4:137 107 exp − ð2Þ T Several kinds of research have shown that the CaCO3 decomposition occurs in a well-defined border (known as the reaction front) between CaO and CaCO3 phases. The border progresses continually into the core of particles [19, 20]. Duc et al. [19] applied a shrinking core model to predict their experimental results, whereas Borgwardt [21] assumed a homogeneous reaction for particles smaller than 90 μm. A shrinking core model was developed for high-purity limestone in a study by Milne et al. [22
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