Development of Inert Anode Materials for Electrowinning in Calcium Chloride Melts

Abstract

The electroreduction of solid titanium dioxide in a calcium chloride melt is an attractive method for the production of titanium metal. Several groups have proposed versions of this route, but no commercial process yet exists. In laboratory studies, consumable carbon anodes are used, and these can give rise to a number of cell design and operational issues. The replacement of the carbon anode with an inert anode offers numerous benefits that include: elimination of carbon dioxide emissions; more efficient cell operation and reduced electrode costs. We have evaluated a wide range of candidate inert anode materials, including metals, alloys and conductive ceramics. The studies examined the chemical stability of these materials in a calcium chloride-based melt, and also performance in laboratory-scale electrolysis tests. All metals and alloys tested were either dissolved in the melt and/or formed a thick, highly resistive crust. A conductive ceramic, chromium titanate, was the best-performed candidate and gave an acceptable cell voltage during a 24 h electrolysis test. This work was undertaken as part of the CSIRO Light Metals Flagship.