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.

Beyond CO2Reduction: Vistas on Electrochemical Reduction of Heavy Non-metal Oxides with Very Strong E—O Bonds (E = Si, P, S)

“…Details of the electrochemical analyses revealed that a growth of 1 μm Si nanowire per unit area is equivalent to 1.56 C charge consumed at a cell voltage of 2.2 V. 65 In a similar direction, Bard et al used the highly conducting Magneĺi phase Ti 4 O 7 as electrode material, 72 which has been previously used for the electroreduction of TiO 2 to elemental Ti. 73 Unlike the carbon anode, where CO 2 is produced during the electrolysis herein with Ti 4 O 7 anode and graphite as the 4). 74…”

“…In a similar direction, Bard et al used the highly conducting Magnéli phase Ti 4 O 7 as electrode material, which has been previously used for the electroreduction of TiO 2 to elemental Ti . Unlike the carbon anode, where CO 2 is produced during the electrolysis herein with Ti 4 O 7 anode and graphite as the cathode in two-electrode cell, only O 2 is liberated with ca.…”

Electrochemical Production of Si without Generation of CO2 Based on the Use of a Dimensionally Stable Anode in Molten CaCl2

“…To reduce environmental impacts and labor, one must find a non‐consumable anode material that is stable in the molten salt with oxygen evolution as the anode reaction . Until now, several types of materials, including oxides and noble metals, have been considered as potential inert anode candidates in molten‐CaCl 2 electrolysis, but none demonstrate the rigorous requirements for practical implementation …”

“…This material was first investigated as an anode by McGregor et al. for the electrochemical reduction of titanium oxide to titanium metal in molten CaCl 2 . However, anode deterioration caused by oxidation formed a less conductive layer on the anode surface, limiting the duration of its use to a few hours.…”

Development of a niobium-doped titania inert anode for titanium electrowinning in molten chloride salts

“…However, the process suffers from low current efficiency due to the occurrence of parasitic side reactions involving the consumable carbon anode. As previously noted, 7 the disadvantages of carbon anodes are as follows:…”