Removal of cationic dyes by kaolinite M. Hamdi Karaog ˘lu a , Mehmet Dog ˘an b, * , Mahir Alkan b a Mug ˘la University, Faculty of Science and Literature, Department of Chemistry, Mug ˘la, Turkey b Balikesir University, Faculty of Science and Literature, Department of Chemistry, 10145 Balikesir, Turkey article info Article history: Received 3 August 2008 Received in revised form 25 January 2009 Accepted 1 February 2009 Available online 20 February 2009 Keywords: Adsorption Dyes Isotherm Enthalpy abstract The removal of cationic dyes such as maxilon yellow 4GL (MY 4GL) and maxilon red GRL (MR GRL) on kaolinite from aqueous solutions has been studied according to the adsorption method. The adsorbed amount of dyes on kaolinite surface was investigated as a function of pH, ionic strength, temperature, acid activation, and calcination temperature. It was found that: (i) the adsorbed amount of cationic dyes increased with increase in pH and decreased with increase in temperature, ionic strength, acid activation, and calcination temperature; (ii) the adsorption process was an exothermic process; (iii) the experimen- tal data were correlated reasonably well by the adsorption isotherm of the Langmuir; and (iv) the inter- actions between adsorbate and adsorbent from adsorption heat data were physical in nature. Ó 2009 Elsevier Inc. All rights reserved. 1. Introduction Colored organic effluents are produced in the textile, paper, plastic, leather, food, and mineral processing industries [1,2]. Wastewater containing pigments and/or dyes can cause serious water pollution problems. In addition, dyes are toxic to some organisms and hence, harmful to aquatic animals. Furthermore, the expanded uses of dyes have shown that some of them and their reaction products, such as aromatic amines, are highly carcino- genic [1,3]. Therefore, removal of dyes before disposal of wastewa- ter is necessary. In general, there are five main methods used for the treatment of dye-containing effluent: adsorption, oxidation– ozonation, biological treatment, coagulation–flocculation, and membrane processes [4,5]. The adsorption process is one of the most efficient methods of removing pollutants from wastewater. The ability of adsorption to remove toxic chemicals without disturbing the quality of water or leaving behind any toxic degraded products has augmented its usage in comparison to electrochemical, biochemical or photo- chemical degradation processes [6,7]. Recovery of costly toxic sub- stances from the wastewater is an added advantage of the adsorption procedure. Also, the adsorption process provides an attractive alternative treatment, especially if the adsorbent is inex- pensive and readily available [8]. Activated carbon has been widely used as an adsorbent for the removal of various pollutants due to its high adsorption capacity. However, it has relatively high opera- tion costs, regeneration problems, and is difficult to separate it from the wastewater after use. Therefore, a number of low-cost adsorbents have been tried for treatment of wastewaters [9].A wide variety of materials, such as clay minerals [10], activated car- bon, bagasse pith [11], wood [12], maize cob [13], and peat [14], are being evaluated as viable adsorbents to remove dyes from col- ored effluents. However, the adsorption capacity of the adsorbents is not very large. For the past few years, the focus of the research is to utilize cheap materials as potential adsorbents and the pro- cesses developed so far are based on exploring those solid waste products, which can prove economic and bring cost effectiveness [7]. Kaolinite is one of the most common phyllosilicate clay miner- als with the chemical composition Al 2 Si 2 O 5 (OH) 4 . It is a layered sil- icate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra. Successive 1:1 layers are held together by hydrogen bonding of adjacent silica and alumina layers. The tetrahedral sheet carries a small perma- nent negative charge due to isomorphous substitution of Si 4+ by Al 3+ , leaving a single-negative charge for each substitution. Both the octahedral sheet and the crystal edges have a pH-dependent variable charge caused by protonation and deprotonation of sur- face hydroxyl (SOH) groups. Kaolinite has a low shrink–swell capacity and a low cation exchange capacity (1–15 meq/100 g). It is a soft, earthy, usually white mineral. Kaolin is used in ceramics, medicine, coated paper, as a food additive, in toothpaste, as a light diffusing material in white incandescent light bulbs, and in cos- metics. It is also used in most paints and inks. The largest use is in the production of paper [15–18]. In our previous works, we have investigated the electrokinetic properties of kaolinite suspensions [19]; and also the adsorption 1387-1811/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2009.02.013 * Corresponding author. Tel.: +90 266 612 10 00; fax: +90 266 612 12 15. E-mail addresses: mdogan@balikesir.edu.tr, mdogan7979@yahoo.com (M. Dog ˘an). Microporous and Mesoporous Materials 122 (2009) 20–27 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso