Coal Preparation » Fine Coal
Since Project C18041 was completed, the CSIRO image analysis software has been transitioned and more detailed information is able be generated by further extending and re-coding the software calculations. This allows previous images to be re-analysed to extract additional information of tremendous value to coal characterisation, washability and liberation behaviour.
Liberation information will be critical to the future development of the coal industry. New commercial forms of thermal coal utilisation need to be developed, and the reality of ultraclean coal is likely to be pivotal. CGA offers immense benefits for the purpose of characterising coals and their potential beneficiation routes.
It was however evident that further development of the image analysis software was necessary to determine component maceral and mineral size (within each grain/particle), for each grain type. Such development has facilitated a more fundamental characterisation of the components in each particle size and grain class, and consequently provides direct information as to any liberation potential from any specific particle sizes.
This project focussed on composite grains defined as '-rich' (less than 65% of any one component) or '-dominant' (65-95% of any one component) in the CGA classifications.
In respect of the potential to liberate coal material from mineral matter, the Sinks 1.40 RD fractions were investigated.
In respect of the potential to liberate mineral matter from coal matter, the Floats 1.80 RD fractions were investigated.
This project has found that, for the three coals investigated:
- Mineral matter is generally very finely disseminated in composite coal grains, such that fine grinding to smaller than 0.125 mm would be required in order to start to liberate significant mineral.
- Composite dark mineral predominates in the minus 0.038 mm particle size fraction, with its major component in the minus 0.008 mm fraction.
- Composite vitrinite and inertinite occur mainly in the minus 0.50 plus 0.063 mm particle size fractions.
- Component mass distribution relative to particle (grain) size is not materially different to component mass distribution relative to the component size itself.
- Different coals exhibit subtle differences as to how the composite components are distributed.
- A Liberation Index has been defined whereby the numerical value of the Index directly provides the mass of pure component which may be expected to be liberated at a given size.
- The image analysis software has been augmented to enable the particle surface composition to be quantified. The option to procure particle surface composition will be invaluable to fine coal processes such as flotation, coagulation and flocculation.