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

Abstract

The direct electrochemical reduction of solid titanium dioxide in a chloride melt is an attractive method for the production of titanium metal. It has been estimated that this type of electrolytic approach may reduce the costs of producing titanium sponge by more than half, with the additional benefit of a smaller environmental footprint. The process utilises a consumable carbon anode which releases a mixture of CO2 and CO gas during electrolysis, but suffers from low current efficiency due to the occurrence of parasitic side reactions involving carbon. The replacement of the carbon anode with a cheap, robust inert anode offers numerous benefits that include: elimination of carbon dioxide emissions, more efficient cell operation, opportunity for three-dimensional electrode configurations and reduced electrode costs. This paper reports a study of Nb-doped titania anode materials for inert anodes in a titanium electrolytic reduction cell. The study examines the effect of niobium content and sintering conditions on the performance of Nb-doped TiO2 anodes in laboratory-scale electrolysis tests. Experimental findings, including performance in a 100 h laboratory electrolysis test, are described.

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

“…[14] Until now,s everal types of materials,i ncluding oxides and noble metals,h ave been considered as potential inert anode candidates in molten-CaCl 2 electrolysis,but none demonstrate the rigorous requirements for practical implementation. [15][16][17][18][19][20][21][22] Here we report on an anode material-MagnØli phase, mixed titanium oxide,s uitable for silicon deposition without CO 2 emissions-with good stability under optimized operating conditions compared to previously proposed anodes. These MagnØli-phase titanium oxides have the general formula Ti n O 2nÀ1 (n = 4-9), known commercially as Ebonex , [23] and have an electrical conductivity approaching that of graphite.…”

“…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 …”

Molten salts and energy related materials

“…94 Other groups have reported the use of calcium titanate that has been doped with metallic elements and this is described by Kathie McGregor in this Faraday discussion. 95 Fig. 5 Photograph of Ca (1Àx) Ru x O 3 anodes after electrolysis x ¼ 0.28 (top) and x ¼ 019 (bottom).…”

A perspective on liquid salts for energy and materials

“…For example, providing an inert anode for electro-winning a metal from an oxide is a fairly stringent test. To achieve this, the following material properties are required: 3 1. Insolubility in a molten salt electrolyte up to 1000 C Efficient electro-reduction of Ta 2 O 5 to Ta has been achieved at a graphite electrode in a MgCl 2 -NaCl-KCl melt at 700 C via a TaO 2 intermediate.…”