Foreword

Acknowledgments

Summary

Introduction

Recent technology developments

Recent developments in the world titanium market

Medium term outlook for the world titanium market

Some economic aspects of the technology innovation process

Implications for the TiRO pilot plant project and an australian titanium metal industry

Appendix

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A Kroll and TiRO production processes

Industrial production of titanium started in the early 1950s. Only two titanium production processes have been commercialised — the Hunter process and the Kroll process. The Alta Group’s 500 tonne a year plant in the United States is the only facility that still uses the Hunter process.

The kroll process

The Kroll process is a batch process that was developed in 1940 and involves a number of steps, some of which are labour intensive and all of which are discrete (figure i). A batch of approximately 10 tonnes takes around two weeks to complete. The process is also energy intensive owing to the high temperatures required in some of the steps. The initial feedstock for the Kroll process is titanium dioxide (TiO2) of at least 85 per cent purity — this is most commonly synthetic rutile. Once the titanium dioxide has been purified, it is combined with chlorine gas and high purity coke at 1000°C. This reaction produces titanium tetrachloride (TiCl4), which must then be distilled. The purified TiCl4 is added to a steel reactor that contains magnesium and has been sealed, evacuated and filled with inert argon gas. The introduction of the TiCl4 is a gradual process in order to maintain a temperature in the reactor of 850–950°C. If the temperature falls below 712°C the magnesium chloride solidifies, while if the temperature rises above 1025°C the titanium will begin to react with the iron present in the reactor itself. Over a number of days, liquid magnesium forms and floats over a layer of magnesium chloride while a spongy mass of titanium accumulates on the floor of the reactor. The reaction consumes the magnesium and produces magnesium chloride, which is periodically removed and reprocessed into pure magnesium and chlorine. After the mixture is cooled, the sponge is jack hammered from the floor and walls of the reactor. It is then put through a process where it is first cut with a guillotine, then a shearing machine and then crushed with a jaw crusher. Finally, the processed sponge must be purified to remove any remaining magnesium salts. This is commonly done using vacuum distillation. Vacuum distillation takes place over 85 hours at temperatures between 1000 and 1060°C. From this point the sponge must be melted to produce ingot. Scrap and waste products are also added to the melt at this stage and make up a significant proportion of inputs. In the traditional approach the sponge is melted up to three times, depending on the desired level of purity, to produce ingot. A newer approach, the cold hearth process, melts sponge under pressure from helium. The cold hearth process produces some titanium powder as a byproduct of drawing out the ingot. This titanium powder can be remelted into ingot or processed into finished products using powder metallurgy.

The TiRO process

CSIRO has recently developed the TiRO process as an alternative method for producing titanium. It relies on the same chemistry as the Kroll process but allows TiCl4 to be turned directly into titanium powder. In the TiRO process, TiCl4 is reacted with magnesium in a gas–solid contacting reactor. The reaction is slow at the start but as liquid magnesium chloride begins to form it is able to host the reaction and increase the reaction speed. TiRO uses a narrow operating temperature window of 62°C to allow the process to take place in a fluid bed reactor. In fluidised bed reduction solid particles are suspended in gas and behave like a fluid. This technique allows for the production of titanium powder in a continuous not a batch manner. As titanium powder, and not titanium sponge, is produced, many of the interim steps from the Kroll process are avoided. These include the labour intensive removal of sponge from the reactor and the cutting, crushing and vacuum distillation of the sponge. The TiRO process also permits flexibility in the shape and size of the particles it produces. This allows the packing density, surface area and roughness of particles to be altered to suit different needs. The current TiRO process operated on the laboratory scale is producing metal with an oxygen content that is above the 0.25 per cent mandated for grade 2 commercially pure titanium, the goal of the project. Promising research addressing this issue is in progress and the CSIRO believes that this problem can be fixed in a larger scale pilot plant (CSIRO 2006).