Ole Sigmund Kjos

New Method for Low-Cost Titanium Production

The present work deals with the investigation of an electrolytic method for titanium production that uses TiO2 enriched titania slag as raw material. The process involves two steps: i) carbothermal reduction of the slag to form titanium oxycarbide powder; and ii) electrolysis in a molten chloride-based electrolyte using a titanium oxycarbide consumable anode. Electrochemical studies show the stability of the different Ti species in the equimolar NaCl-KCl melt at 850oC. These results, together with previous work about the anodic oxidation mechanism of a consumable titanium oxycarbide anode in molten chlorides, allow us to optimize the anode and cathode voltages in the electrolysis experiments. The results show that best quality titanium deposits are obtained when the reduction occurs in a single electrochemical step, i.e. directly from di-valent titanium species to Ti metal. Then, the complete conversion of the Ti(III) ions released from the consumable oxycarbide anode to Ti(II) species by adding Ti sponge to the electrolyte, must be fulfilled.

Electrochemical Production of Titanium from Oxycarbide Anodes

The aim of this work was to improve the quality of the produced titanium at the cathode in electrolysis experiments using a titanium oxycarbide anode, which is made of a solid solution of TiC and TiO. Two different approaches were tested: solid titanium deposition from a NaCl-Na3AlF6 electrolyte, and a standard NaCl-KCl electrolyte with a liquid metal cathode producing a titanium alloy.

Titanium Production from Oxycarbide Anodes

The aim of this work is to investigate the new possibilities for electrochemical titanium production as a way of reducing the production costs of the primary metal. The oxycarbide process is a process which involves electrodeposition of Ti at a cathode substrate, and using anodes of a TiC-TiO solid solution made from TiO2 and C. It looks promising, with cheap raw materials, and with a simpler production route than todays process.

Electrochemical Behavior of Dissolved Titanium Species in Molten Salts

INTRODUCTION Titanium has many attractive properties and the use of titanium and its alloys can be greatly increased if a new and less expensive process for the production of pure titanium were developed. Electrolysis in a molten salt electrolyte is a possible way to produce titanium, and many attempts to develop an electrolysis process have been reported. Large cells and pilot plants have been run, but no commercial electrolysis production has been achieved. Of importance is the work by Ginatta [1] which resulted in the successful development of a pilot cell for the electrowinning of titanium from TiCl4 dissolved in a molten NaCl based electrolyte. A more recent approach is due to Fray et al. [2] who suggested a new electrolysis method, later known as the FFC Cambridge method. Similar methods have been proposed by Suzuki et. al [3] and Okabe and Waseda [4].

PFC evolution characteristics during aluminium and rare earth electrolysis

In addition to aluminium electrolysis, the electrolysis of rare earth (RE) metals from fluoride melts is a significant source of perfluorocarbon (PFC) emissions to the atmosphere. These processes have many similarities, they are both based on molten fluoride salt electrolysis at temperatures around 1000 °C, and are utilizing carbon materials as the anode. Although PFC emissions from aluminium industry and rare earth electrolysis have similar overall reactions, they are often reported to have different characteristics. In order to get a better understanding of these differences and similarities, different laboratory experiments focusing on anode reactions and gas compositions in Al2O3 saturated cryolite and REF3-LiF melts during aluminium and rare earth metal electrolysis were studied. The results obtained, combined with thermodynamic data analysis allowed to better understand onset, evolution and termination behaviour of PFC evolution in molten fluoride systems of different chemistries.

Electrochemical Processing of Rare Earth Alloys

The light rare earth metals Nd, Pr, La, Ce as well as some alloys with Fe, are today produced in China by electrolysis in molten fluorides using oxide raw materials. A major challenge is to obtain a good cell operation without de-composing the electrolyte leading to emissions of perfluorinated carbon (PFC) green-house gases to the atmosphere. This work is focused on understanding the fundamental requirements to run the electrolysis cells for DyFe alloy production in an efficient and environmental friendly way. Electrolysis experiments was carried out in DyF3-LiF melts at 1050 °C. A Fe rod was used as consumable cathode and the (consumable) anode was made of graphite. To establish at which anode potential PFC occurred and thus enabling optimisation of the oxide batch feed rate, analysis of the anode gases was performed with Fourier Transform Infrared Spectrometer (FTIR). The produced DyFe alloy was characterised by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS).

Anode Effect Initiation during Aluminium Electrolysis in a Two-Compartment Laboratory Cell

Most laboratory cells used in the investigation of the alumina reduction process use a single anode. When investigating the initiation of the anode effect an approach with more than one anode might give better results, as the probability of obtaining partial anode effect is higher. Additionally, the design is closer to the industrial, where several anodes are connected in parallel. The system constructed consisted of two anodes in separate electrolyte compartments connected in parallel with a single combined cathode. The results indicate that an anode can go in and out of partial anode effect with little influence on the current, although, kept untreated a full anode effect is likely imminent. The results also show that under certain current and alumina conditions, with only two anodes in parallel, an anode can handle approximately the whole load of a fully passivated anode for a certain time.

A study of anode baking gas composition

A method has been developed to measure gas composition inside the pit in open anode baking furnaces. The gas composition can be used to understand attack on and degradation of the refractory lining, baking behavior and combustion energy contribution through the baking cycle. A probe was installed in the packing coke near the bottom of the pit while extracting gas over several days with continuous analysis with an FTIR spectrometer. The results show a clear temperature dependence of CO and CO2 composition. Methane was found to be the dominating gas species at the beginning of the measuring cycle. Fluoride gases was also present, indicated by reactions with the glass wool filter to yield SiF4 that was detected in small amounts. PAH condensates were observed but not systematically determined in the present campaign. Earlier results from PAH measurements before the scrubbing, showing large fluctuations, will be discussed in relation to present findings.

Perfluorocarbon Formation During Rare Earth Electrolysis

A challenge during rare earth (RE) electrolysis is to avoid emissions of perfluorocarbon (PFC) green-house gases. The objective of this work was to study how to operate the RE electrolysis process with neither PFC formation nor anode effect. Linear Sweep Voltammetry was carried out at 1050 and 1100 °C, and electrolysis was performed in REF3-LiF melts at ca. 1050 °C during on-line off-gas analysis. To avoid anode effect, the current density values must be strictly less than 0.43 and 0.68 A cm−2 at working temperatures of 1050 and 1100 °C, respectively. The optimal REO batch feed rate for avoiding PFC formation could be established by correlating the onset of PFC with the values and the changes that occurred in the anode potential.

Gas Anodes Made of Porous Graphite for Aluminium Electrowinning

One of the major downsides of the current aluminium production process is the high CO2 emission. One alternative is to replace the consumable carbon anodes with inert anodes so that oxygen evolves instead of CO2. Also PFC emissions will be eliminated by using inert anodes. However, so far a sufficiently inert anode has not been found. Another option is to utilize natural gas through porous anodes in order to change the anode process. This will decrease CO2 emission remarkably and also eliminate PFC emissions and anode effect. The porous anode could be made of carbon or it can be inert. However, the as-mentioned problem still exists regarding porous inert anodes. Therefore, at the moment porous carbon anodes seem to be the best practical option. In this study, porous anodes made of different grades of graphite were used for electrolysis experiments in a laboratory cell. Also, off-gas analysis was performed to get an insight of the ongoing reactions. Our results show that for some types of graphite anodes, methane participates effectively in the anodic reaction.