Adsorption Equilibria of L-(+)-Tartaric Acid onto Alumina Hasan Uslu* ,† and I ˙ smail I ˙ nci ‡ Department of Chemical Engineering, Engineering & Architecture Faculty, Beykent University, Ayazag ˘a Ko ¨yu ¨, I ˙ stanbul, Turkey, and Department of Chemical Engineering, Engineering Faculty, I ˙ stanbul University, 34850, I ˙ stanbul, Turkey The adsorption equilibria of L-(+)-tartaric acid onto alumina from wastewaters of wineries were studied, and it has been found that the equilibrium adsorption fits the Langmuir and Freundlich isotherms. Adsorption experiments were carried out at three different temperatures (298, 310, and 325) K. The adsorption of L-(+)- tartaric acid is dependent on the acid concentration and the amount of alumina. The maximum percentage removal of L-(+)-tartaric acid was 22 % by alumina at 298 K. The Langmuir and Freundlich constants have been found to be 0.023 g · g -1 and 0.014 (g · g -1 )/(L · g -1 ) -1/n , respectively, at 298 K. The thermodynamic parameters ΔH ads 0 and ΔS ads 0 for the adsorption of tartaric acid on alumina have been calculated to be -5.62 kJ · mol -1 and 50.65 J · mol -1 · K -1 , respectively. Introduction Wastewaters from wineries contain tartaric acid. This acid is used in food processing and the pharmaceutical industry. The wastewaters from the winemaking process are the only industrial source for tartaric acid production. 1 Many methods have been investigated to separate organic acids from aqueous solution. Solvent extraction has been used for purification of carboxylic acids, 2,3 but the toxicity of the solvents used is always a problem. Electrodialysis has been used as a technique for the isolation and purification of carboxylic acids from fermentation media. Because other anions also go with the acid and other broth components end up in the product stream by diffusion, further processing is necessary to remove these impurities. The sorption of carboxylic acids on ion exchange resins has also been studied. This latter method requires additional chemicals to recover the acid from the resin. An alternative method of recovery of carboxylic acids from fermentation broth is based on adsorp- tion. 2 The adsorption of carboxylic acids by a number of substrates has been examined. For example, Aljundi examined the silicalite molecular sieve for adsorption of lactic acid. 3 Inci investigated the adsorption of two carboxylic acids with activated carbon. 4,5 In this study, the adsorption of L-(+)-tartaric acid on alumina is investigated. Adsorption processes are operative in most natural physical, biological, and chemical systems, and adsorption operations that employ solids such as alumina and synthetic resins are widely used in industrial applications and for purification and separation. 6,7 The adsorption of carboxylic acids on alumina is very strong with adsorption energies much larger than those of other organic compounds. This is because most carboxylic acids are weak acids, and their degrees of dissociation in aqueous solutions are affected by the acidity of the medium. For example, the adsorption of aromatic acids on alumina is a strong function of the solution acidity. Although the adsorption of medium- and long-chain aliphatic carboxylic acids on alumina has been of considerable interest because their property of forming self- assembled monolayers, the adsorption of water-soluble car- boxylic acids on alumina has not been extensively studied. 6 The nature of the interaction between the carboxylic group and hydroxyls on the surface has been studied by many investigators. In particular, the adsorption of aromatic acids on alumina has been studied. It is generally recognized that both oxygen atoms in the carboxylic group are anchored on the alumina surface, but two models have been proposed for the interaction. The bridging model considers that both oxygen atoms of the carboxylic group involved in the interaction are linked to Al-O sites on the surface through hydrogen bonding. The chelating model considers that the carboxylic group is dissociated and forms a bidentate linkage with a single Al-O-H site. The adsorption of carboxylic acids from aqueous solution onto the alumina surface is a dissociative adsorption process. 8 The adsorbed carboxylic acids may interact with the alumina surface in such a way that a hydrogen atom is shared between each oxygen atom in the carboxylic group with an oxygen atom on the alumina surface forming a strong hydrogen bond. 5 L-(+)-Tartaric acid is the dextro form of 2,3-dihydroxysuc- cinic acid. It has been known since antiquity in the form of its potassium salt, which occurs in grapes. In the fermentation of grape juice, the salt deposits in the fermentation vessels. The free crystallized L-(+)-tartaric acid was first obtained from such fermentation residues by Scheele in 1769. Tartaric acid is employed in the preparation of carbonated drinks, especially those that are grape flavored. It is widely used in effervescent tablets and powders and is frequently mixed with citric acid. 9,10 There are many studies about the separation of tartaric acid from aqueous solution. In particular, activated carbon, 11 cop- per, 12 nickel, 13 and oxidized nickel 14 have been used to separate tartaric acid from wastewater streams. As ¸ci 15 removed some carboxylic acids from aqueous solution by using hydrogels. Ramsier et al. 16 reported adsorption of phosphorus acids on alumina. Chakraborty et al. 17 provided a theoretical insight into physical adsorption for a single-component adsorbent + adsor- bate system. In this work, systematic studies of the adsorption of L-(+)- tartaric acid from aqueous solutions have been investigated using alumina. Experimental results for the adsorption of L-(+)-tartaric * Corresponding author. E-mail: hasanuslu@gmail.com. † Beykent University. ‡ I ˙ stanbul University. J. Chem. Eng. Data 2009, 54, 1997–2001 1997 10.1021/je800976d CCC: $40.75  2009 American Chemical Society Published on Web 05/01/2009