Facilitated OH¯ diffusion via bubble motion and water flow in a novel electrochemical reactor for enhancing homogeneous nucleation of CaCO3

Abstract

Electrochemistry is a potential method for water softening. An essential disadvantage is OH¯ ions from water electrolysis accumulate on cathode surface, inducing the generation of the insulating CaCO₃ layer and then interrupting the electrochemical reaction. In order to propel OH¯ diffusion into the bulk solution instead of aggregation at cathode, we designed an electrochemical reactor, whose electrodes were placed horizontally in the middle of the reactor, and the bubbles created by water electrolysis move upward, while the water flows downward. The visual evidence displayed that the unique reactor structure allowed OH¯ to spread to almost all the solution rapidly. Average pH value of bulk solution reached 10.6 in only 3 min. Therefore, homogeneous nucleation of CaCO₃ in bulk solution would take primary responsibility for water softening, and the softening efficiency is up to 212.9 g CaCO₃/h/m², higher than reported results. The reactor is easy to scale up, providing a new idea for the softening of circulating cooling water.

Keywords: Electrochemistry; Homogeneous nucleation; OH¯ diffusion; Softening efficiency; Water softening.