Continuous Purification of Molten Chloride Salt: Electrochemical Behavior of MgOHCl Reduction

Abstract

We present a study on the electrochemical behavior of magnesium hydroxide (MgOH+) reduction on a tungsten (W) cathode in molten chloride salt (MgCl2-KCl-NaCl) across the temperature range of 475-525℃. MgOH+, which forms within the salt upon exposure to moisture, is a leading cause of corrosion. Corrosion is a major barrier to deployment of chloride salts across a number of applications, including concentrating solar power plants and nuclear power plants. While pre-purification protocols have been developed to ensure MgOH+ is removed from molten chloride salts prior to deployment, MgOH+ forms in-situ during operation of chloride-salt based plants. Thus, methods for continuous purification during plant operation are needed. Continuous electrochemical purification via electrolysis using a Mg anode and W cathode has been proposed, but little has been done to assess scalability. Here, we assess fundamental properties of electrochemical removal of MgOH+ to enable future scale up of this method.

Rare Earth Chlorides in Low-Hydration Magnesium Chloride Electrolysis: Mechanistic Insights

“…This issue still requires further research. [26][27][28] Figure 1 presents the CV curve acquired from a tungsten electrode in the MgCl 2 -KCl-NaCl melt at 773 K, with MgCl 2 absorbing H 2 O. Peak C observed near −1.7 V represents the deposition of Mg, and Peak C' corresponds to the dissolution of magnesium.…”