Journal of Hazardous Materials A119 (2005) 13–18 Solubility of chlorine in aqueous hydrochloric acid solutions Mahir Alkan a ,M¨ unir Oktay b , M. Muhtar Kocakerim c , Mehmet C ¸ opur c,∗ a Department of Chemistry, Faculty of Science and Literature, Balikesir University, Balikesir, Turkey b Department of Chemistry, K.K. Faculty of Education, Atat¨ urk University, Erzurum, Turkey c Chemical Engineering Department, Engineering Faculty, Atat¨ urk University, Erzurum, Turkey Received 23 April 2004; received in revised form 2 November 2004; accepted 6 November 2004 Available online 15 December 2004 Abstract The solubility of chlorine in aqueous hydrochloric acid solutions was studied. The effects of HCl concentration and temperature on the solubility were evaluated, and the thermodynamic parameters of the dissolution were calculated. It was found that the solubility isotherms had a minimum at about 0.5 M HCl concentration at all the temperatures studied and that solubility decreased with the increase of temperature at all the HCl concentration range investigated. © 2004 Elsevier B.V. All rights reserved. Keywords: Solubility; Chlorine; Hydrochloric acid; Thermodynamic parameters 1. Introduction Chlorine is an element of the halogen family, but it is never found uncombined in nature. It is estimated to ac- count for 0.15 percent of the earth’s crust in the form of soluble chlorides such as common salt (NaCl), carnallite (KMgCl 3 ·6H 2 O) and sylvinite (KCl) [1]. Chlorine gas is especially produced as a by-product in the electrolysis of sodium chloride in the chloroalkali industry. Generally, most producers operate their plants to make chlorine since it is hard to store and is used to product derivatives such ethy- lene dichloride, phosgene and epichlorhydrine. Caustic soda is generally sold on the merchant market and consumed in a myriad of uses. Little chlorine is traded among countries, but a considerable amount of caustic soda is traded, especially in aqueous form [2]. Chlorine is a very effective disinfectant and has been used in drinking water supplies for nearly 100 years. Risks for certain types of cancer are now being correlated to the use of chlorinated drinking water. Suspected carcinogens make ∗ Corresponding author. Tel.: +90 442 2314573; fax: +90 442 2361129. E-mail address: mcopur@atauni.edu.tr (M. C ¸ opur). the human body more vulnerable through repeated ingestion and research indicates the incidents of cancer are 44% higher among those using chlorinated water [3]. On the other hand, chlorine released to atmosphere causes depletion of the ozone layer which absorbs most of the harm- ful ultraviolet-B radiation from the sun. To prevent the de- pletion of ozone shield, developed countries have made pro- tocols and some international regulations have arranged. For that reason, new and applicable uses must be found to con- sume chlorine [4]. When chlorine gas is dissolved in water, it is rapidly hy- drolysed and a special type of oxidation–reduction reaction takes place. The chlorine molecule with the sum valence of zero enters into the reaction known as disproportion reaction with water as following [1]: Cl 2 + H 2 O ⇔ H + + Cl - + HOCl (1) This reaction is reversible. It was found that the forward reaction is first order [5]. The rate of this reaction was stud- ied by Lifthitz and Perlmutter-Haymen [6], Shilov and Solo- dushenkov [7] and Brian et al. [8]. The equilibrium constant 0304-3894/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2004.11.001