Separation and Purification Technology 65 (2009) 331–336 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Evaluation of wheat straw and barley straw carbon for Cr(VI) adsorption Rumi Chand, Takanori Watari ∗ , Katsutoshi Inoue, Toshio Torikai, Mitsunori Yada Department of Applied Chemistry, Saga University, Honjo 1, Saga 840-8502, Japan article info Article history: Received 7 July 2008 Received in revised form 4 November 2008 Accepted 5 November 2008 Keywords: Wheat straw Barley straw Carbonization Adsorption Chromium abstract The present study deals with the adsorption of Cr(VI) on carbonized wheat straw (CWS) and barley straw (CBS). Carbon materials, prepared at different carbonization temperatures, were investigated for the adsorptive removal of Cr(VI). These carbonized materials prepared from agro-waste were found to have a high affinity for chromium as represented by very high adsorption capacities of 1.67 and 1.68 mol/kg for wheat and barley straws, respectively, carbonized at 800 ◦ C at pH 2. Equilibrium was reached within 1 h of contact time which suggests high efficiency of the carbonized materials for Cr(VI) removal. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Chromium is a redox active element, with oxidation states from -2 to +6, but only the +3 and +6 states are prevalent in aqueous solution [1]. Hexavalent chromium is highly toxic pollutant [2] gen- erated from many industrial processes like manufacturing pigment in paints, inks, and plastics, as an anti-corrosion agent in protective coatings, and in chrome plating, leather tanning, etc. [3]. Consider- ing its hazardous risks for human health, the treatment of industrial effluents to reduce or remove the pollutant before discharge into the environment becomes inevitable. A wide range of physical and chemical processes is available for the removal of Cr(VI) from water, such as electrochemical precipita- tion [4], ultrafiltration [5], ion exchange [6] and adsorption [7]. The adsorption process is one of the efficient methods for chromium removal [8] due to its clean operation and complete removal of heavy metal ions even from dilute solutions. Activated carbon is the most widely used adsorbent for this purpose because of its large surface area, microporous structure, high adsorption capac- ity and high degree of surface reactivity. However, commercially available activated carbons are expensive, which has led to a search for cheaper substitutes. Consequently, a number of low-cost adsor- bents have been prepared for Cr removal. These include those prepared from rice husks [9], sawdust [10], apricot stones [11], cow dung [12], etc. However, since the adsorption capacities of these carbon materials are unsatisfactory or their preparation is not easy, new adsorbents are still under development. ∗ Corresponding author. Tel.: +81 952 28 8683; fax: +81 952 28 8548. E-mail address: watarit@cc.saga-u.ac.jp (T. Watari). Carbonization of carbon containing raw materials is the prereq- uisite step for preparation of carbon but the porosities of carbon is not sufficiently developed to match the need for practical uses. Thus generally carbonization is simultaneously followed by thermal acti- vation (carbonization under flow of CO 2 or steam) or chemical activation (carbonization after chemical treatment with reagent like ZnCl 2 ,H 3 PO 4 or KOH) or combination of both. Consequently, the preparation procedure of highly porous carbon becomes difficult and expensive. In the present work, porous carbon materials was prepared from low-cost agro-waste like barley straw and wheat straw for the first time by applying very simple method of carbonization without using any activation process. Thus prepared carbon have been tried as adsorbents for the removal of Cr(VI) from aqueous solutions. 2. Experimental 2.1. Preparation of carbonized materials Carbon from wheat and barley straws was prepared by employ- ing very simple method of carbonization without using any activation process. Wheat and barley straws were ground in an alumina vibration mill. The resulting samples were then put in an alumina crucible with an alumina cover. This crucible was put in a larger alumina crucible and covered with graphite powder and capped with an alumina cover in order to prevent oxidation. The crucible set was put into a furnace with a heating rate of 5 ◦ C/min and then heated up to the carbonization temperature. The straw was carbonized at different carbonization temperatures (600, 700, 800, 900 and 1000 ◦ C) for 1 h. After 1 h the electric furnace was automatically switched off. The door of the electric furnace was 1383-5866/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2008.11.002