塩化物水溶液中の塩素ガスの溶解度

抄録

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