Transport Number Determination of Copper Ions in a Heterogeneous Membrane for Electrodialysis

Kayo Santana Barros, Jorge Alberto Soares Tenório, Denise Crocce Romano Espinosa

In the last decades, the number of separation processes that use ion-exchange membranes has increased due to their important environmental and economic benefits. In the wastewater field, ion exchange membranes are usually used in electrodialysis cells in order to remove ionic contaminants from aqueous solutions, for example, in the electroplating industry. However, it is useful to know the transport number of the ions present in the solution to assure a good performance of electrodialysis and guarantee its viability, since the transport number refers to the fraction of current carried by the ions and depicts the selectivity of the membrane. Among the dynamic characterization electrochemical methods, the chonopotentiometry allows a direct access to the voltage contributions in different states of the membrane/ solution system. The scope of the present study is to determine the transport number of copper ions in the heterogeneous cationic membrane HDX 100 using the chronopotentiometry with a synthetic effluent solution of the galvanizing industry prepared with copper sulfate and sulfuric acid in different concentrations (0.1 g/L, 0.5 g/L and 1.0 g/L of Cu2+) and pH (2.0, 2.6, 3.0 and 4.0). The fraction of the conductive area of the membrane was determined with KCl solution (0.1 mol/L), since the permselectivity value of this system is already known. According to the results, the chronopotentiometric curves were effectively constructed, the fraction of the conductive area of the cationic membrane obtained was 80.8 % and the transport number was determined in all conditions tested. It was verified that the increase of copper concentration at a constant pH causes an increase of the transport number, since the transport of current carried by copper is improved by the amount of ions in solution. The increase of pH for a constant concentration also causes an increase of the transport number, which can be explained by the reduction of H+ concentration and the consequent reduction of the competition between protons and Cu2+.