Geopolymer synthetized from bottom coal ash and calcined paper sludge Rozineide A. Antunes Boca Santa a , Adriano Michael Bernardin b, * , Humberto Gracher Riella a , Nivaldo Cabral Kuhnen a a Chemical Engineering Department, Santa Catarina Federal University, P.O. Box 476, Trindade, Florianópolis, SC 88.040-900, Brazil b Ceramic Materials Group, Santa Catarina Extreme South University, Av. Universitária 1105, Criciúma, SC 88.806-000, Brazil article info Article history: Received 1 October 2012 Received in revised form 4 May 2013 Accepted 14 May 2013 Available online 27 May 2013 Keywords: Bottom ash Calcined paper sludge Alkaline activation Aluminosilicates Geopolymer abstract This study deals with the development of geopolymers synthetized from industrial waste containing aluminosilicates. Geopolymers are inorganic polymers formed by the activation of amorphous alumi- nosilicates (Al 2 O 3 .SiO 2 ), which react in a strongly alkaline medium. Bottom ash (SiO 2 /Al 2 O 3 ¼ 3.3e4.5) was used as source of aluminosilicate and sodium hydroxide (NaOH ¼ 5, 10 and 15 M) and sodium silicate (Na 2 SiO 3 , SiO 2 /Na 2 O ¼ 1.58) were used as alkaline medium. Calcined paper sludge was used to increase the reactivity of the partially crystallized bottom ash. The solid waste was characterized by XRF and XRD and the geopolymer samples were characterized by XRF, XRD, SEM, FTIR and compressive strength tests. The best results were obtained with a solution of 15 M NaOH and sodium silicate and a mixture of 2:1 bottom ash and calcined paper sludge. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The increasing industrial development induced by a constant demand for new products has resulted in an exponential growth of waste generated at the end of the manufacturing processes as well as post-consumer disposal. Therefore, the best way to solve the problem of waste generation, besides the consumption reduction, is the use of those as raw materials for the production of high quality and valuable products. In addition, there is the saving of natural resources because the environmental aspect must be considered and evaluated when thinking about social and eco- nomic development, in other words, sustainability (McLellan et al., 2011; Castro-Gomes et al., 2012). In this study, bottom ash from coal and calcined paper sludge from paper sludge were used as raw materials for the synthesis of geopolymer, an inorganic polymeric material formed by the acti- vation of aluminosilicates in strongly alkaline medium formed by the activation of aluminosilicates in strongly alkaline medium, resulting in poly(sialates) with the structure of phyllosilicates. The term “geopolymer” was created by J. Davidovits in 1979 to describe the chemical properties of inorganic polymers based on aluminosilicates. Geopolymers present cementitious properties and, therefore, great potential for use in the construction industry. They can be formed using natural raw materials or industrial wastes from several sources, provided that the wastes are rich in amorphous or semi-crystalline aluminosilicates or have passed through heat treatment, making them more reactive and suitable to alkaline activation. The alkaline activation is a chemical process that transforms amorphous, partially amorphous or metastable vitreous structures into a compacted cementitious material (Palomo et al., 1999). The aluminosilicates can dissolve in contact with an alkaline solution because leaching of the Al 3þ and Si 4þ species occurs. The concentration of the activator should be high (Rattanask and Chindaprasirt, 2009). When mixing an aluminosilicate with an alkaline solution a reaction is triggered and in few seconds there is the dissolution of the particles, reorganization of the structure and gelation, resulting in a three-dimensional aluminosilicate network. The Si and Al species released on the surface are responsible for the geo- polymerization reaction. The dissolution of the amorphous alumi- nosilicate is rapid at high pH resulting in a supersaturated solution of Si and Al. Concentrated solutions result in the formation of a gel with increasing oligomers. The aqueous gel forms large networks by condensation (Duxson et al., 2007). The Si 4þ and Al 3þ in the solution are coordinated by oxygen bridges. The negative charge of the AlO 4 is responsible for balancing the alkaline cations. * Corresponding author. Tel./fax: þ55 48 34312669. E-mail addresses: amb@unesc.net, adriano.bernardin@pq.cnpq.br (A.M. Bernardin). Contents lists available at SciVerse ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro 0959-6526/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jclepro.2013.05.017 Journal of Cleaner Production 57 (2013) 302e307