Preparation, characterisation of thermally treated Algerian dolomite powders and application to azo-dye adsorption Fatima Boucif a , Kheira Marouf-Khelifa b , Isabelle Batonneau-Gener c , Jacques Schott d , Amine Khelifa a, ⁎ a Laboratoire de Structure, Elaboration et Applications des Matériaux Moléculaires, (S.E.A.2M.), Département de Chimie, Université de Mostaganem, B.P. 981, R.P., Mostaganem 27000, Algeria b Laboratoire S.T.E.V.A., Département de Chimie, Université de Mostaganem, Algeria c Laboratoire LACCO – UMR 6503, 40 avenue du Recteur Pineau, 86022 Poitiers, France d Géochimie: Transferts et Mécanismes, Laboratoire LMTG (UMR 5563)-OMP-, Université Paul-Sabatier, Toulouse, France abstract article info Article history: Received 4 September 2009 Received in revised form 31 March 2010 Accepted 9 April 2010 Available online 24 April 2010 Keywords: Dolomite Thermal treatment X-ray powder diffraction SEM Adsorption Dolomite powder from Ouled Mimoun, Tlemcen (western region of Algeria) was thermally treated within the temperature range 450–1000 °C. The modifications undergone by dolomite, inherent to thermal treatment, were investigated from X-ray diffraction patterns. The results were also discussed using scanning electronic microscopy and nitrogen adsorption. The XRD data, analysed from X Pert Plus program, showed that the dolomite phase ceases at 700 °C and is relayed by the formation of in situ calcite and periclase. The crystallographic parameters of these two phases tend towards that of pure periclase and calcite at 1000 and 900 °C, respectively. SEM analysis indicated that the morphological properties were profoundly affected. SEM images of D-1000 (sample treated at 1000 °C) indicated that the original particle shape of dolomite (presence of discrete grains having sharp edges with presence of cleavages) was totally destroyed, leading to small spherical particles with a diameter of 0.1 μm. The specific surface area value of D-1000 increased more than 6 times against that of the raw dolomite. Adsorption of azo-dye Orange I from aqueous solutions onto untreated and treated dolomites was also reported. The isotherms were of L-type. The interaction was explained by electrostatic considerations between sulfonate groups of the dye (D-SO 3 Na), which are dissociated in the aqueous system, and positively charged adsorption sites. The affinity of orange I for the dolomitic solids follows the sequence D-900 N D-1000 N D-800 NN D-600 N raw dolomite. The maximum retention capacity shown by D-900 was explained and correlated with its crystallographic properties. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Dolomite is an inexpensive material. Its structure contains alternat- ing planes of Ca 2+ and Mg 2+ cations with ideal formula CaMg(CO 3 ) 2 . Occasionally one element may have a slightly greater presence than the other [1]. Dolomite is an important industrial mineral. It is used as a source of both magnesium metal and magnesia in different branches of industry such as the food and pharmaceutical industries and the production of fertilizers, glass, and building materials. One of the main applications is in the field of refractory materials, in order to produce fire-resistant products, used in metallurgy, chemical and ceramic industries [2–4]. Dolomite was also used as transesterification catalyst for palm kernel oil [5] and adsorbents for substances such as iodine [6], dyes [7], copper(II) [8], lead(II) and cadmium(II) [9], CO 2 [10] and so on. The majority of these applications implies the decomposition of dolomite, from where the necessity and interest of studying its stability as a function of temperature. This thermal processing is accompanied by structural changes within the solid product [11], causing a significant change of the crystallographic, morphological and textural properties. Obviously, the modification in the interfacial properties of dolomitic solids improves their adsorption properties. The objectives of this study were to investigate the modifications undergone by Algerian dolomite owing to thermal treatment and apply the decomposition products for removing azo-dye orange I from aqueous solutions. The dolomite was treated over the range 450– 1000 °C. The thermally modified samples are called dolomitic solids. The powder XRD data were measured by fitting with pseudo-Voigt function through the X Pert Plus program. The results were also discussed using scanning electronic microscopy and nitrogen adsorp- tion. Despite evidence in the literature of increased interest in low- cost adsorbents, no adsorption study of azo-dye on dolomitic solids has yet been published, in which the treatment temperature is considered as a pertinent parameter. 2. Experimental The dolomite used in this study was supplied from the Ouled Mimoun deposit in Tlemcen (western Algeria). The composition of Powder Technology 201 (2010) 277–282 ⁎ Corresponding author. E-mail address: aminekhelifadz@yahoo.fr (A. Khelifa). 0032-5910/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2010.04.013 Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec