ELECTROREFINING OF ZIRCONIUM METAL IN ALKALI CHLORIDE AND ALKALI FLUORIDE ELECTROLYTES AND THERMODYNAMIC PROPERTIES OF SOME ALKALI-METAL HEXACHLOROZIRCONATE AND HEXACHLOROHAFNATE COMPOUNDS
Abstract (summary)
The stoichiometric compounds Na(,2)ZrCl(,6), Na(,2)HfCl(,6), Cs(,2)ZrCl(,6) and Cs(,2)HfCl(,6) have been prepared by the reaction of ZrCl(,4) and HfCl(,4) vapours with the appropriate alkali chlorides. The X-ray diffraction powder patterns of Na(,2)HfCl(,6) and Cs(,2)HfCl(,6) were indexed.
Equilibrium vapour pressure measurements representing the reactions
A(,2)MCl(,6(,(S,l))) (DBLARR) 2ACl(,(S,l)) + MCl(,4(,(V)))
where A(,2)MCl(,6) represents the pure stoichiometric compounds Na(,2)ZrCl(,6), Na(,2)HfCl(,6), Cs(,2)ZrCl(,6) and Cs(,2)HfCl(,6) were conducted. The measurements were carried out at temperatures up to 950(DEGREES)C using a spiral Bourdon fused quartz gauge as a null point detector.
The electrochemical properties of dilute solutions of Cs(,2)ZrCl(,6) in molten CsCl, (KCl-LiCl)(,eut.) or (KCl-NaCl)(,eut.), were investigated by EMF-measurements using cells of the type:
(UNFORMATTED TABLE FOLLOWS)
Cs(,2)ZrCl(,6) (X(,1)) AgCl (X(,2))
Zr Ag
ACl (1-X(,1)) ACl (1-X(,2))
(TABLE ENDS)
Reducibility experiments were conducted in an attempt to investigate the formation of the lower valence zirconium chlorides in melts containing CsCl, KCl-NaCl (1:1 mole), CsCl-Cs(,2)ZrCl(,6) and KCl-K(,2)ZrCl(,6). The experiments consisted of equilibrating the melts with zirconium metal and determining the zirconium metal loss which is attributed to the formation of lower valence zirconium chlorides. The effects of variables such as alkali chloride solvent present, the temperature of the melt, the concentration of zirconium tetrachloride in the melt, and reaction time, have been considered.
The electrorefining of zirconium metal in alkali halide melts has been investigated. Variables affecting the electrodeposition process such as the composition of the electrolyte, the current density, cell potential and the configuration of the electrodes were investigated. Two types of electrolytes were studied: the alkali chloride-rich and the alkali fluoride-rich electrolytes.
Based on the results of this study, it is predicted that industrial application of electrorefining of zirconium in fused salt baths should utilize a zirconium-bearing solute which is complexed with potassium ion. A schematic flowsheet of an integrated zirconium process is proposed and consideration is given to further studies needed to extend the process to electrowinning of zirconium from fused salt baths.