The morphology of limestone-based pellets prepared with kaolin-based binders Firas N. Ridha a, b , Vasilije Manovic a , Edward J. Anthony a, b, * , Arturo Macchi b a CanmetENERGY, Natural Resources Canada, 1 Haanel Drive, Ottawa, Ontario K1A 1M1, Canada b Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada highlights < Limestone-based pellets with kaolin-based binders were prepared and characterized. < Kaolin is unsuitable binder for use in high temperature applications. < Al(OH) 3 binder (from acid leaching of kaolin) is a suitable binder for pellets. < Acetification of limestone produced a highly porous fluffy structure. < Pellets prepared from acetified limestone and Al(OH) 3 binder are a promising sorbent. article info Article history: Received 11 June 2011 Received in revised form 26 October 2012 Accepted 1 November 2012 Keywords: Microporous materials Adsorption Chemical synthesis Oxides abstract Modifications and pelletization of limestone were investigated in order to improve the utilization of CaO- based materials for different catalytic reactions and environmental applications. Attempts to purify the limestone by ion-exchange with CaCl 2 solution did not result in significant removal of impurities. On the other hand, acetification with 10 vol.% acetic acid enhanced pore surface area and pore volume of the sorbent by 42% and 3-fold, respectively. The acetification was found to widen small pores, and thus create a beneficial pore size distribution with more pores in the range of 25e100 nm. In order to utilize such powdered materials in fluidized beds, pelletization is the next step. Unfortunately, pelletization results suggested that natural kaolin is an unsuitable binder for preparing CaO-based pellets due to its negative impact on pellet morphology. By contrast, Al(OH) 3 binder obtained from kaolin leaching had a strong positive effect on the porous texture of the pellets, demonstrated by pore surface area and volume of 22.48 m 2 g 1 and 0.051 cm 3 g 1 for 1 mm pellets with CaO/binder ratio of 5.5, compared to 10.92 m 2 g 1 and 0.039 cm 3 g 1 for natural materials. The enhancement in pellet morphology is mainly attributed to transformation of Al(OH) 3 to the highly porous Al 2 O 3 at high temperatures. Pellets synthesized from limestone modified with 10 vol.% acetic acid with Al(OH) 3 binder (ratio of 5.5) exhibited high pore surface area and volume, represented by 1.3-fold and 44% increase over those for natural limestone. It was concluded that the combination of acetified limestone with Al(OH) 3 binder is a promising approach for synthesis of CaO-based pellets with enhanced morphology. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Limestone is a sedimentary rock composed of calcium carbonate (CaCO 3 ) which, upon calcination, yields lime (CaO). The resultant CaO comprises a range of chemical and physical properties that are of interest for many chemical and environ- mental applications [1]. Included among these properties are: high melting temperature, low vapor pressure, altered porous structure when it is calcined, thermodynamic stability at high temperatures, and also low cost and widespread availability worldwide. In the field of catalytic reactions, CaO is a suitable catalyst in the oxidation of volatiles like HCN and NH 3 to NO and N 2 at temperatures up to w950  C [2,3]. The use of CaO in environ- mental applications has been expanding rapidly, such as for in situ SO 2 capture from flue gases, which has been commercially applied for many years [4,5], co-capture of SO 2 and CO 2 [6e8], in situ CO 2 capture from flue gas [9e11], CO 2 capture from syngas for H 2 enrichment [12e14], N 2 O decomposition and capture [15],H 2 S capture [16,17], potential co-capture of H 2 S and CO 2 [18e20]. * Corresponding author. CanmetENERGY, Natural Resources Canada, 1 Haanel Drive, Ottawa, Ontario K1A 1M1, Canada. Tel.: þ1 613 996 2868; fax: þ1 613 992 9335. E-mail address: banthony@nrcan.gc.ca (E.J. Anthony). Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys 0254-0584/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matchemphys.2012.11.007 Materials Chemistry and Physics 138 (2013) 78e85