Upgrading the rice husk char obtained by flash pyrolysis for the production of amorphous silica and high quality activated carbon Jon Alvarez, Gartzen Lopez, Maider Amutio, Javier Bilbao, Martin Olazar ⇑ Department of Chemical Engineering, University of the Basque Country UPV/EHU, P.O. Box 644, E48080 Bilbao, Spain highlights  Rice husk char is valorised for the joint production of silica and activated carbons.  Na 2 CO 3 extraction for the recovery of high amorphous silica rates (88%).  15 min activation for BET surface areas of up to 1365 m 2 g 1 .  Long activation times cause growth and eventual destruction of micropores.  Promising results for the viability of rice husk flash pyrolysis. graphical abstract article info Article history: Received 10 June 2014 Received in revised form 18 July 2014 Accepted 19 July 2014 Available online 28 July 2014 Keywords: Activated carbon Char Rice husks Steam activation Adsorbent abstract The overall valorization of rice husk char obtained by flash pyrolysis in a conical spouted bed reactor (CSBR) has been studied in a two-step process. Thus, silica has been recovered in a first step and the remaining carbon material has been subjected to steam activation. The char samples used in this study have been obtained by continuous flash pyrolysis in a conical spouted bed reactor at 500 °C. Extraction with Na 2 CO 3 allows recovering 88% of the silica contained in the rice husk char. Activation of the silica-free rice husk char has been carried out in a fixed bed reactor at 800 °C using steam as activating agent. The porous structure of the activated carbons produced includes a combination of micropores and mesopores, with a BET surface area of up to 1365 m 2 g 1 at the end of 15 min. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Rice husk is an agricultural waste material abundantly available in rice-producing countries. According to recent estimations the global production of rice is around 685 MT (including rice, straw and husk), and rice husk means between 0.2 and 0.33 kg per kg of rice harvested (Lim et al., 2012). Rice husk is usually burnt in open fields, and this practice involves energy waste and, moreover, causes a serious environmental problem. Fast pyrolysis is an interesting option for the valorization of rice husk, as shown in a previous study (Alvarez et al., 2014) in which the excellent performance of a bench scale plant provided with a conical spouted bed reactor was proven to be suitable for high bio-oil production (70%). However, the economic viability of the rice husk pyrolysis process requires the valorization of the char fraction (continuously withdrawn from the reactor). Thus, the aim of this work is to study the combined production of amor- phous silica and high quality activated carbon from rice husk char. Given the interesting applications of silica, its recovery improves the perspectives of the pyrolysis process and, moreover, avoids http://dx.doi.org/10.1016/j.biortech.2014.07.073 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +34 946012527; fax: +34 946 013 500. E-mail address: martin.olazar@ehu.es.es (M. Olazar). Bioresource Technology 170 (2014) 132–137 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech