Electrochemical Behavior of MgOH+ in Molten MgCl2-KCl-NaCl Salt

Abstract

Research on molten chloride salts as a high-temperature (500-800 ℃) heat transfer fluid has been reinvigorated in recent years. Its abundance, low cost, and good thermohydraulic properties have drawn attention from the nuclear and concentrated solar power industry. Specifically, a ternary MgKNa chloride salt (45.98/38.91/15.11 wt.%) has been considered a prime candidate for commercial application. However, economic risk remains due to high corrosion of containment alloys.The rate of corrosion in ternary MgKNa chloride salt has been primarily attributed to the impurity MgOH+, stemming from the reaction of MgCl2 with moisture. Extensive research has been conducted to purify chloride salts, but little attention has been given to on-line purification strategies once the salt is molten and circulating in the plant. One proposed strategy is continuous electrochemical purification via electrolysis using a Mg anode and W cathode. This strategy has been successfully demonstrated at the laboratory scale. Work done in our group indicate significant opportunity for the electrochemical process to be scaled up commercially as an electrochemical purification unit.Here, we present a study on the electrochemical behavior of MgOH+ reduction on a W cathode in molten MgCl2-KCl-NaCl across the temperature range of 475-525 ℃. The kinetic parameters from this study aid in modeling and scaling up an electrochemical purification cell at industrially relevant scales.