Industrial Crops and Products 33 (2011) 409–417 Contents lists available at ScienceDirect Industrial Crops and Products journal homepage: www.elsevier.com/locate/indcrop Adsorbents from Schinopsis balansae: Optimisation of significant variables J. Sánchez-Martín ∗ , J. Beltrán-Heredia 1 , C. Carmona-Murillo Universidad de Extremadura, Department of Chemical Engineering and Physical Chemistry, Avda. de Elvas, s/n, 06071 Badajoz, Spain article info Article history: Received 22 September 2010 Received in revised form 25 October 2010 Accepted 30 October 2010 Available online 14 December 2010 Keywords: Tannins Schinopsis balansae Design of experiments Gelification Natural adsorbents Adsorption abstract The current article presents the study of the influencing variables in gelification process of Schinop- sis balansae tannin extract. This product is an adsorbent for wastewater remediation since it retains cationic pollutants such as heavy metals, surfactants or dyes. Design of experiments procedure was used in order to evaluate the influence of two main factors involved in the immovilization process: temperature and formaldehyde-tannin ratio. The complete statistical protocol has confirmed an optimal temperature of 75 ◦ C and the fact that minimum amount of formaldehyde leads to a more efficient adsorbent. The theoretical predicted results through the design of experiments were experimentally confirmed. © 2010 Elsevier B.V. All rights reserved. 1. Introduction One of the most interesting procedures for wastewater remedi- ation has to do with the adsorption of pollutants onto adsorbents. There are many examples of how natural and modified mate- rials can act as adsorbents in the removal of dyes (Lee et al., 2006; Hameed and Daud, 2008; Karagöz et al., 2008), heavy met- als (Vázquez et al., 1994; Aoyama et al., 2000; Aroua et al., 2008) or surfactants (Ayranci and Duman, 2007; Cotoruelo et al., 2009). Therefore, adsorption is recommended as an advisable procedure for this kind of purification (Cooney, 1998). Although many types of adsorbents have been recently developed (Liu et al., 2010) the search is not over because of the multiplicity of circumstances where wastewater treatment processes are involved. Effluents from textile, chemical or mining industries repre- sent harmful and noxious menaces nowadays and they should be treated before dumping into the environment. Life equilibrium is so fragile that minimum concentrations of contaminants such as sur- factants, dyes or heavy metals can cause a great damage in fauna and flora (Ryan and Elimelech, 1996). Water treatment has become a very important researching task therefore. For many years scientific community has been test- ing new methods for water treatment. Some processes are rather well known, such as filtration, disinfection or coagulation, but new ∗ Corresponding author. E-mail addresses: jsanmar@unex.es (J. Sánchez-Martín), jbelther@unex.es (J. Beltrán-Heredia), cristinacm87@gmail.com (C. Carmona-Murillo). 1 Tel.: +34 924289300x89033; fax: +34 924289385. cheaper and affordable water treatment processes are needed (Alila and Boufi, 2009). Tannins are mostly vegetal water-soluble polyphenolic com- pounds. Their molecular weight is ranged between 500 and some thousands Daltons. Trees such as Acacia mearnsii de Wild, Castanea sativa or Schinopsis balansae are traditional tannin sources. This last one is also known as Quebracho colorado. From a chemical point of view, there are three kinds of tannins: hydrolysable, condensed and complex tannins (Haslam, 1989). These products are rather chem- ically complex and they are usually taken from a natural matrix, without a very exhaustive purification. Because of that, it is rather difficult to know their structure exactly. A full study about tannins, chemical structure and properties can be found in previous scien- tific literature (Pizzi, 2008) and structural tannin unit is shown in Fig. 1. Regarding water treatment, tannins can be used in two main ways: gelified and cationized. Tannin gelification is a chemical pro- cedure that immovilizes tannins inside an insoluble matrix (Pizzi, 1994) so their properties involving, e.g. metal quelation, are avail- able. A rather efficient adsorbent agent is produced then. This procedure has been previously presented either in scientific liter- ature or in patents. Experimental conditions of gelification involve the use of formaldehyde (or other aldehyde) in a basic or acid aqueous solution. Examples of basic gelification are shown in pre- vious scientific papers (Nakano et al., 2001; Kim and Nakano, 2005; Tondi et al., 2009) and in patents such as US patent 5,158,711 (Shirato and Kamei, 1992). Acid gelification is also presented by other researchers (Vázquez et al., 1994, 2002). Mainly, the chemical basis of the tannin gelification are widely reported (Pizzi, 2008). Formaldehyde and other aldehydes react 0926-6690/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2010.10.038