Analysis of Anhydrous Calcium Chloride Production for Pyrochemical Processes: Drying Procedures and Moisture Detection Methods

Calcium chloride (CaCl2) has applications in thermochemical storage, as a desiccant, for molten salt nuclear reactors, and in pyrochemical processing. The deliquescent nature of CaCl2 poses significant challenges for its use in pyrochemical processes, particularly in molten salt electrorefining, where residual moisture can adversely affect metal coalescence, process yields, and current efficiencies. In this study, we present a reliable vacuum oven drying procedure for converting CaCl2·2H2O to anhydrous CaCl2. Exposure experiments showed that dried CaCl2 absorbs water much more rapidly at a relative humidity of 67.3% than at relative humidities below 36.3%. Water uptake of salt samples in a container was also shown to depend more on the exposed surface area than sample mass, highlighting the importance of minimizing the exposed surface area-to-mass ratio during handling and storage. After establishing the reliability of the drying procedure, residual moisture was quantified using various analytical techniques to compare their performance, including oven-based volumetric and coulometric Karl Fischer (KF) titration, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Raman spectroscopy. Oven-based KF titration, both coulometric and volumetric, provided the most accurate measurement of trace moisture levels, detecting residual water as low as 0.04 wt % in dried CaCl2 samples.