Introduction
Crystallisation is a separation technique ubiquitous in hydrometallurgy and many other industries. Whilst crystallisation is literally as old as the hills from which many ore bodies are mined, there is plenty to be learned through the application of modern scientific research methods. Most current industrial practices are based on empirical rather than fundamental understandings of the chemistry and physics that are operating.

Generally, and specifically in the industrial context, the formation of crystals can be classified into two areas: desired (product) and undesired (scale). In the case of product, increasing market pressures are pushing manufacturers to increase productivity (rate and yield) whilst maintaining or improving quality (purity, phase, particle size and shape).

The Crystallisation Program is studying model systems to develop an understanding of the principles that underlie and ultimately control crystallisation in an industrial plant. It also aims to generate innovative ideas that may lead to new processes. In parallel, the program is undertaking a range of industry-funded crystallisation projects, both short and long term. The overall objective is technology transfer, namely the implementation of fundamental scientific discoveries for the improvement of industrial operations.

Specific Areas of Research
The Crystallisation Program has many different projects concentrating on the various aspects of crystallisation, from growing better crystals to inhibiting unwanted crystals. The CRC-funded and WA State Government-funded research focuses on uncovering and characterising the fundamental processes of crystallisation that are of generic value across the different commodity streams addressed by the Parker Centre:

Optimisation of Crystal Growth
The growth of highly ordered and pure crystals from disordered and frequently impure solutions is a marvel and a mystery. What, for example, determines the rate of growth and the shape of crystals? This research aims to:

• develop fundamental models that accurately describe how microscopic crystal growth mechanisms depend on macroscopic variables and properties eg solution concentration, temperature and additives.
• apply discoveries made with model systems to selected industrial crystallisation processes.

Control of Scale Formation
Scaling caused by the crystallisation of impurities or the very products or intermediates of a process is a universal and costly problem throughout hydrometallurgy. Scale formation results in lost production, poor heat transfer and downtime for equipment cleaning and repair. Current scale control strategies frequently use expensive additives, many of which are ineffective. The objectives of this work are:

• to develop a fundamental understanding of the chemistry and hydrodynamics (flow related processes) of supersaturated solutions that favour and hinder the formation of crystalline deposits as scale.
• to develop a theoretical understanding of how existing approaches to scale prevention do and do not work.
• to develop novel scale control strategies based on fundamental understanding of scaling.

Unwanted Silica and Iron Precipitation in Hydrometallurgical Operations
Dissolved iron and silica impurities are troublesome impurities in a wide range of hydrometallurgical processes. These impurities can cause problems such as scale build-up, unpredictable precipitation during processing, product loss and difficulty in disposal of waste streams. For example, the production of very fine particles or a gelatinous precipitate can render solid-liquid separation almost impossible. This can readily occur when iron or silica are precipitated rapidly from solution. This project aims to:

• gain a fundamental understanding of the chemistry underlying iron and silica precipitation in mineral processing.
• gain a fundamental understanding of the action of additives currently used to control these precipitations.
• use the acquired fundamental knowledge to recommend strategies for controlling iron/silica precipitation in specific hydrometallurgical processes.

Expertise/Capabilities

• Surface chemistry
• Solution chemistry
• Crystal growth mechanisms
• Computer molecular modelling of crystal growth
• Atomic resolution imaging
• In situ atomic force microscopy for studying crystal growth processes
• The MACMode technique (high resolution technique for fluids) for nanoscale surface characterisation
• Crystal growth modification
• Additive design and synthesis
• Chemical engineering

Facilities and Equipment
The world-class facilities available within the Program are:

The Scanning Probe Microscopy Facility

• contains microscopes and other instruments for studying crystal growth that provide very high resolution, 3D surface topographic "maps" of surface features.
• microscopes include:
  
  
  Scanning tunnelling microscope (STM)
• 
  Atomic force microscope (AFM)
  - uses the sense of touch and measures the topography by mechanically moving a sharp probe across the sample to "feel" the surface contours, acting like the needle of a record player tracking across the grooves of a record.
  - produces surface images in air or liquids, including the corrosive solutions frequently encountered in industry, and at high temperatures (up to about 100^oC).
  - applications include studying gibbsite (alumina hydrate) crystals growing in hot caustic alumina liquors ie under the conditions found in Bayer liquors in alumina refineries.

The Molecular Modelling Facility

• for large scale computations of surface structure and energetics to simulate surface and crystal growth processes, as well as visualising the results.
• consists of:
  Six Silicon Graphics workstations
  A Beowulf class parallel computer with supercomputer performance
  Commercial software (MSI and Spartan) and in-house software for simulating bulk and surface structures

For further information, contact
Mrs Elisabeth Grant (Projects Coordinator)
Ph: + 61 8 9266 7203
e-mail: E.Grant@curtin.edu.au

The Crystallisation Group at Curtin University (Nanochemistry Research Institute)

Program Manager: Professor Gordon Parkinson