Equilibrium Data for the Exchange of Cu 2+ , Cd 2+ , and Zn 2+ Ions for H + on the Cationic Exchanger Amberlite IR-120 Jose ´ L. Valverde, Antonio de Lucas, Marcela Gonza ´ lez, and Juan F. Rodrı ´guez* Department of Chemical Engineering, University of Castilla-La Mancha, Avenida de Camilo Jose ´ Cela 10, 13004 Ciudad Real, Spain Equilibrium ion-exchange isotherms of H + /Cu 2+ ,H + /Cd 2+ , and H + /Zn 2+ on a strong acid resin, Amberlite IR-120, in an aqueous medium at (283 and 303) K have been determined in order to assess the possibility of using ion exchange to eliminate heavy-metal ions from industrial aqueous liquid streams. The experimental equilibrium data have been satisfactorily correlated using the homogeneous mass action law model (LAM). This model assumes nonideal behavior for both the solution and solid phases. Wilson and Pitzer equations have been used to calculate activity coefficients in the resin and liquid phases, respectively. The values of the thermodynamic equilibrium constants show a temperature dependence. Introduction Disposal of hazardous ions in aqueous waste streams is a significant industrial problem. Basic metals such as aluminum, cadmium, chromium, cobalt, copper, iron, lead, mercury, nickel, and zinc have been classified as the 10 metals of primary importance for recovery from industrial waste streams. 1 The main drawback of the treatment of the mentioned waste effluents charged with toxic metals is the generation of a concentrated reject or regeneration stream using whatever removal procedures (precipitation, ion exchange, solvent extraction, adsorption, osmosis, etc.). This concentrated effluent must be minimized and reduced in order to reach the ideal objective of “zero discharge”. 1 In this way, the regeneration process must be optimized to minimize the volume of the concentrated residual stream. The affinity of the strong acid resins for metallic ions is not as high as that of the chelating resins. Even so, it has been found that the affinity of those resins for such ions could be suitable for its use in the removal of these metallic ions from water streams, 2 with its advantages being easier regeneration and simpler working conditions. In this work, equilibrium data of the systems H + /Cu 2+ ,H + /Cd 2+ , and H + /Zn 2+ are obtained and used to evaluate the behavior of the systems if an acid is used for regeneration. Experimental Section Chemicals. Zinc, copper, and cadmium nitrates were PRS grade (99%), and nitric acid (65%, w/w) was PA grade, supplied by Panreac. Demineralized water was used with a conductivity value lower than 5 µS/cm. The cationic resin Amberlite IR-120, supplied by Rhom & Haas, was used as the ion exchanger. The resin was pretreated and regener- ated to convert it to the H + form, as described by de Lucas et al. 3 Procedure. The experimental set consisted of nine 0.25 L Pyrex containers, hermetically sealed and submerged in a temperature-controlled thermostatic bath. The temper- ature was kept constant within (0.1 K. The suspension formed by the resin and solution was vigorously agitated by means of a multipoint magnetic stirrer. Equilibrium resin loading data were generated for H + / Cu 2+ ,H + /Cd 2+ , and H + /Zn 2+ systems. To obtain these data, samples of 0.1 L of an ionic solution of known composition were weighed and added into each of several flasks. 4 Different known masses of resin, in H + form, had previ- ously been added to each flask. The accuracy of weighing was (0.0001 g. The solution and resin were maintained at a fixed temperature ((0.1 K) under vigorous stirring, until equilibrium was achieved (24 h). 4 At the end of this period, the mixtures were filtered to remove the ion- exchange resin and the filtrate was analyzed for the metal content. The resin-phase composition was determined by mass balance from initial and equilibrium compositions of the liquid phase, according to eq 1, where c 0 and c* are the metal ion initial concentration and the metal ion equilibrium concentration in the liquid phase, respectively, and q* denotes the resin-phase equilibrium concentration of metal. V and m are the volume of solution and the mass of the dry ion-exchange resin, respectively. The solutions were analyzed for their metal content by atomic absorption spectrophotometry in a Varian 220 AS spectrophotometer. The standard uncertainty and repro- ducibility of measurements was found to be (0.1%. To improve the reproducibility of the results, the resin was preconditioned (several regeneration cycles and finally treated with a 1 mol‚L -1 solution of clorhidric acid). Model and Prediction Ion-exchange equilibrium is attained when an ion ex- changer is placed in an electrolyte solution containing a counterion which is different from that in the ion ex- changer. Consider the ion exchanger (r) initially in the A form and the counterion in the solution (s) is B. Counterion exchange occurs, and the ion A in the ion exchanger is partially replaced by B: * To whom correspondence should be addressed. E-mail: juanfran@ inqu-cr.uclm.es. Fax: 3426295318. q* ) V m (c 0 - c*) (1) 613 J. Chem. Eng. Data 2002, 47, 613-617 10.1021/je010299g CCC: $22.00 © 2002 American Chemical Society Published on Web 04/17/2002