Fluoride compounds play a vital role in the electrowinning of aluminium. AlF3 added to the electrolyte controls the temperature at which the bath freezes, dictates the cells operating temperature, and influences the solubilties of alumina (to be reduced to aluminium metal) and aluminium (whose oxidation back to alumina we want to avoid). Keeping the fluoride concentration stable proves the most energy efficient way to run the cell. However, HF and particulate fluoride emissions lead to fluoride escaping the system. Currently, these are effectively returned to the cell by capture on alumina, an efficient adsorbent for fluorides, as well as being the metal feedstock. However, as cells are pushed to ever-higher currents to maximise metal production and cell gas temperatures increase, a new source of fluoride loss is becoming important. Particulate fluorides (for example, frozen electrolyte) react with humid air at elevated temperatures to regenerate HF. However, this can occur after dry scrubbing and therefore this fluoride is lost from the cycle. This drives both the emission of harmful compounds to the environment and cell instabilities that cost energy.

This PhD project will likely involve:

(1) Materials characterization: fluorinated alumina will be explored in terms of the microstructural and textural properties of smelter generated and lab generated materials. Their surface chemistry, and the distribution, nature and quantities of the fluorinated species present will be characterised.

(2) Experiment design and implementation: the rate of HF regeneration will be studied as a function of parameters such as fluoride speciation, reaction temperature, humidity, alumina microstructure etc.

(3) Multivariable data analysis: the final aim is to understand the interplay of all parameters studied on the rate of HF regeneration.

A fully funded PhD studentship (a stipend of $30k NZD per year for three year, and course fees) is available, with work to be undertaken under the supervision of Dr Grant McIntosh and Professor Jim Metson of the University of Auckland, New Zealand. The project is to commence by the 1st of December 2016 at the latest. We are accepting applications from capable and motivated students with an interest in materials and surface science with either a chemistry or chemical engineering background. If you are looking for an exciting research project with real-world applications, please contact either Dr McIntosh or Prof Metson for further information.

Dr Grant McIntosh: g.mcintosh@auckland.ac.nz

Prof Jim Metson: j.metson@auckland.ac.nz