Coal Ash Variability and Its Potential Utilisation as a Treatment Layer for Acid Mine Drainage Remediation

Coal incineration for power generation in South Africa generates an average of 25 Mt of coal ash annually, with only 7 % being utilised, hence there is growing advocacy for coal waste utilisation. A multi-technique approach was used to analyse the variability of coal fly ash and legacy coal ash, assessing its suitability for acid mine drainage remediation. Legacy coal ash samples were collected from 3 South African power stations and cola fly ash samples from the fourth power station. The variability studies were carried out in 3 phases, i.e. daily, weekly, and monthly to assess if there are any significant changes in the physical and chemical properties of the coal ash over time. All the samples were classified as Class F, having a SiO2, Al2O3, and Fe2O3 wt. % of > 70 %. The highest net neutralising potential (NNP) value of 151 CaCO3 kg/t was obtained over a coal fly ash sample, while 87.1, 77.9, and 30.3 CaCO3 kg/t were the highest obtained from each of the three respective power stations where legacy coal ash was sampled. The acid neutralising properties of legacy coal ash, coupled with its good civil engineering properties, make it a feasible option for use as a reactive barrier or mine backfilling material for acid mine drainage treatment.