Preparation of Calcined Kaolin by Efficient Decarburization of Coal-Series Kaolinite in a Suspended Bed Reactor

Abstract

The reaction process, mechanism, and kinetics of the decarbonation of coal-series kaolinite (CSK) were investigated using the thermal analysis (TG)–infrared spectrum analysis (IR) coupling method. A pilot test was performed using a suspended calcination system. Further, the carbon content, phase composition, whiteness, oil-absorbed value, and micromorphology of calcined kaolin were characterized. Results showed that the decarburization reaction of CSK was a two-step reaction that mainly occurred in the ranges of 593 °C–836 °C. The mechanism of the decarburization reaction was a phase-boundary reaction (unreacted-core shrinking model) with an activation energy of 214.56 kJ/mol. Calcination at 900 °C or 950 °C for ~3.3 s in a suspension reactor resulted in the decarburization rate of CSK becoming >99.9%. The whiteness of calcined kaolin was mainly positively associated with the decarburization rate, and increasing the calcination temperature aided in increasing the whiteness. The oil-absorbed value of calcined kaolin was positively correlated with the specific surface area. Insufficient or over-calcination decreased the oil-absorbed value of calcined kaolin products. The calcined kaolin product with a whiteness of 89.3% and an oil-absorbed value of 76.1 g/100 g was obtained via suspension calcination process, which meets the requirements of calcined kaolin for paper-making.

Activation of Low-Quality Coal Gangue Using Suspension Calcination for the Preparation of High-Performance Low-Carbon Cementitious Materials: A Pilot Study

“…The main processes corresponded to Reactions (1) and ( 2). Reaction (1) represents the decomposition of kaolinite and is mainly affected by the temperature and diffusion of H 2 O (g) during suspension calcination [16]. Reaction (2) represents the combustion of coal in the gangue, requires a long time at later stages, and is influenced by O 2 content, temperature, and CO 2 diffusion [16].…”

“…Methods of the first type, which rely on the calcination, beneficiation, and ultrafine grinding of raw materials, involve chemical reactions, beneficiation, and enrichment or mechanochemistry to Processes 2024, 12, 550 2 of 14 remove harmful components and improve the reactivity of active minerals [11][12][13][14]. Calcination is typically conducted in muffle furnaces, vertical furnaces, and rotary kilns [15,16]. This type of equipment is difficult to popularize and apply because of its low calcination efficiency.…”

“…However, in-depth research on the applicability of our system to the activation of low-quality coal gangue is still lacking. According to previous studies, low-quality coal gangue is very different from highquality gangue in terms of composition, reaction characteristics and kinetics, the hydration mechanism of the corresponding cementitious materials, and product properties [16,[29][30][31]. Thus, the results of research on the suspension calcination of high-quality coal gangue and its conversion to cementitious materials cannot be directly applied to low-quality coal gangue.…”

Research on Resource Recovery and Disposal of Copper-Containing Sludge

“…In terms of suspension decomposition, the study by Zhang H et al [ 24 ] successfully activated low-quality gangue to prepare high-performance low-carbon cement through the suspension state calcination technology, demonstrating the high efficiency and potential commercial value of this technology in industrial-scale applications. Simeng C et al [ 25 ] investigated the highly efficient decarbonisation and calcination process of coal-based kaolin by means of a suspended-bed reactor and thermal infrared analysis. A new kinetic model was developed to optimise the calcination parameters and high-quality calcined kaolin was successfully prepared.…”