Coupled transport of cyanide ions through liquid membranes C. Aydiner,* M. Kobya* and I. Koyuncu** *Department of Environmental Engineering, Gebze Institute of Technology, 41400, Cayirova-Gebze, Turkey **Department of Environmental Engineering, Istanbul Technical University, 80626, Maslak-Istanbul, Turkey Abstract In this study, the transport kinetics of coupled transport of cyanide ions through liquid membrane (trichloromethane) containing tetraoctylammonium chloride as a carrier was examined at different temperatures. The kinetics of cyanide transport could be analyzed in the formalism of two consecutive irreversible first order reactions. The influence of the temperature on the kinetic parameters (k 1d , k 2m , k 2a , R m max , t max , J d max , J a max ) has been established. For maximum membrane entrance and exit fluxes, J d max and Jamax, the activation energies were found from the slopes of the two linear relationships: 9.02 kcal/mol and 11.20 kcal/mol, respectively. The values of the found activation energy indicate that in the first step the transport process of cyanide ions through liquid membrane is difussional controlled, whereas in the second step it is most probably controlled by species diffusion and the rate of the reversible chemical reaction. Keywords Coupled transport;cyanide ion transport; kinetics; liquid membranes; temperature effects Introduction Interest in the development of new and improved techniques for the separation of ions and molecules has increased in the recent years. It is well known that ions and molecules can be transported across polymeric and liquid type membranes. With an ever increasing aware- ness of our energy demands, energy efficient membrane technology is proving to be a valu- able approach in separation processes. The effectiveness of a membrane separation process is determined by the flux of species through the membrane and by the selectivity of the membrane (Noble and Way, 1987; Mulder, 1991; Winston and Sirkar, 1992). At this point, it can be seen that liquid membrane technology has attracted increasing attention for its potential capability in the field of separation and has been demonstrated as an effective tool in many applications, such as resource recovery, purification of polluted wastewater, toxic pollutant removal and bioseparation (Kitagawa et al., 1977; Noble and Way, 1989). Almost all research work on liquid membranes is done on systems in which metal ions are being recovered, obviously for economical reasons. Besides hundreds of cation separa- tion systems published in literature, only a few examples are known for the separation of anions. Molnar et al. (1978) used the counter-transport of hydroxide ion to remove chloride ions from the water phase. Another example of a counter-transport process, between chro- mate ions and chloride ion, is given by Loiacono et al. (1986). In this later article the trans- port mechanism was not entirely clear and some complexities in the chemistry of facilitated diffusion were observed. Anions can also be removed by a co-transport mechanism. In this way, systems were developed for the concentration of chloride ion by Kataoka et al. (1980), picrate ion by Sugiura and Yamaguchi (1983), and nitrate ion (Neplenbroek et al., 1992). In addition, the kinetics of coupled transport of thiocyanate ions by Kobya et al. (1997, 1998) and nitrite and nitrate ions by Demircioglu et al. (2000a, b) through liquid membranes has been investigated. The removal of toxic elements such as cyanide anions by liquid membranes has been of great interest in recent years. Cyanide ion is an environmentally significant pollutant in industrial wastewater, because cyanide is generated industrially on a large scale for use in gold and silver extraction, electroplating, synthetic fiber production, coal cooking and coal Water Science and Technology Vol 41 No 10–11 pp 125–133 © IWA Publishing 2000 125