Solubility of Cl2 Gas in Aqueous Chloride Solution

The electrowinning of zinc is currently practiced using acidic sulfate solutions. This process is characterized by a large anodic overvoltage, required to discharge oxygen at a lead anode. If acidic zinc chloride solution can be used in the electrowinning, the dimensional stable anodes originally developed for the chloroalkali industry may find further application. These anodes discharge chlorine with the operation of low overvoltages and high current densities, permitting energy savings and an increase in plant productivity.For this reason, a fundamental study was undertaken to establish the solubility of chlorine gas in various chloride solutions at 298 K. The solubility of chlorine gas in aqueous HCl solutions decreases drastically with increasing HCl concentration up to 0.2 kmol·m−3, and then it increases gradually with a further increase in HCl concentration. In aqueous HCl solutions containing MClx (M: Na, K, Ca, Ba, Mg, Ni, Co, Zn, and Fe(III)), the solubility of chlorine gas decreases steadily with increasing MClx concentration. Chlorine exists as Cl2(aq), HClO, and Cl3− in aqueous solutions. Based on the speciation of chlorine in aqueous solutions, it was found that the decrease in solubility of chlorine in aqueous HCl solutions in the concentration range of 0–0.2 kmol·m−3 is due to a decrease in HClO and that the gradual increase in solubility with further additions of HCl is due to an increase in Cl3−. Moreover, the addition of MClx in aqueous solutions decreases the solubility in response to a decrease in Cl2(aq).