Licorice residue and Pistachio-nut shell mixture: A promising precursor for activated carbon T. Kaghazchi *, N. Asasian Kolur, M. Soleimani Department of Chemical Engineering, Amirkabir University of Technology, No. 424, Hafez Ave., Tehran, PO Box 15875-441, Iran 1. Introduction Activated carbons can be produced from any carbonaceous solid precursors which may be either natural or synthetic. The selection of precursor essentially determines the range of adsorptive and physical properties that can be attained in the activated carbon products. Due to environmental considerations, agricultural by-products are gaining great importance as pre- cursors for activated carbon production, because they are cheap, renewable, safe, available at large quantities and easily accessible sources; in addition they have high carbon and low ash content [1– 6]. In our previous works, the preparation of activated carbons from different kinds of agricultural wastes such as hard shells of apricot stones, almond, walnut and pistachio-nut shells, and also softer materials such as rice hulls, sugarcane bagasse and residues of licorice has been put under investigation [7–15]. In previous studies, it was understood that some kinds of these materials have several deficiencies and drawbacks; for instance, the results of chemical analysis revealed that soft agricultural wastes have relatively high ash contents that is not a favorite property and subsequently result in high ash content activated carbons with low mechanical strength. Another weakness of these materials is their low hemicellulose contents that lead to activated carbons with low apparent density. Instead, hard shells with their low ash and high hemicellulose contents are more suitable in some applications for producing adsorbents with higher surface area. So it was thought that one of the ways for modification of activated carbon properties, to reach a product with all of such advantages as low ash content, high bulk density and high surface area, may be the use of mixture of two or several kinds of raw materials, each kind having special and unique properties that another one does not. Therefore, they can cover each other’s deficiencies and frailties, and can also strengthen the other’s beneficial capabilities. Hence in the present work, mixtures of two kinds of agricultural wastes; residues of licorice (soft material) and pistachio-nut shells (hard material) were used as feedstock. The activation of the parent mixture was performed using H 3 PO 4 and ZnCl 2 , separately. These two chemicals have been chosen for some reasons. Among the plenty of chemical reactants that could be used, H 3 PO 4 is a low efficient activator in terms of microporosity development, but it is the only one which is industrially acceptable due to the possibility of recycling the unused reactant fraction in the process [16]. ZnCl 2 has been used as an activating reagent increasingly, because it results in high surface areas and relatively high yield. Although using of this reactant, due to the problems of environmental contamination caused by zinc compounds has somewhat declined [4,16,17]. In this research, it is focused on applying two kinds of local agricultural wastes as a parent mixture to prepare activated carbons, which have better properties in comparison with the ones made of each of the agricultural wastes, separately. Since mercury Journal of Industrial and Engineering Chemistry 16 (2010) 368–374 ARTICLE INFO Article history: Received 14 February 2009 Accepted 6 October 2009 Keywords: Activated carbon Agricultural by-products Chemical activation Characterization Wastewater treatment ABSTRACT As a continuation of previous research concerning preparation of activated carbon from agricultural by- products, applying a mixture of two kinds of lignocellulosic by-products with complementary properties as the parent material is investigated. Two kinds of activated carbons are prepared by chemical activation of the parent mixture – including residues of licorice and pistachio-nut shells – with H 3 PO 4 and ZnCl 2 solutions, separately. The produced activated carbons have the surface areas comparable to the commercial ones. The lower ash content, higher bulk density and surface area of mix-based activated carbons in comparison with licorice-based ones, and also the highest mercury adsorption capacity of the mix-based ones confirm that it would be possible to modify the properties of an activated carbon using several complementary raw materials. The comparison of mercury adsorption capacities among mixed- based and the commercial activated carbons reveals that mix-based ones are effective and economical adsorbents for industrial wastewater treatment. ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +98 21 66405847; fax: +98 21 66405847. E-mail address: kaghazch@aut.ac.ir (T. Kaghazchi). Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1226-086X/$ – see front matter ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2009.10.002