Beneficiation of Collie fly ash for synthesis of geopolymer: Part 1 – Beneficiation

Beneficiation of the fly ash was conducted in a three stage procedure using sieving, milling and magnetic separation to improve fly ash homogeneity and reactivity. Sieving was effective in reducing large carbon particles and free primary quartz content. Most of the carbon was found to be small and finely dispersed throughout the material, making it unfeasible to remove by sieving. Sieving in conjunction with milling increased surface area from 9.83 m2/g to 10.7 m2/g. Magnetic separation revealed that amorphous iron was not magnetic and the complete removal of crystalline iron phases is not possible without a robust separation technique. The removal of magnetic phases increased the surface area of the sieved and milled fly ash to 12.9 m2/g. oportion of reactive amorphous material increased at each stage of beneficiation, resulting in increased reactivity. The increase in reactivity necessitated changes in solids:liquids ratio in order to maintain a workable geopolymer mixture which will be discussed in Part 2 of this set of papers. The outcomes from this research clearly identifies that different levels of fly ash beneficiation leads to different geopolymer properties, which in turn extend the range of applications for which geopolymers can be used.