On the feasibility of South African coal waste for production of 'FabSoil', a Technosol

Appropriate handling and disposal of coal waste is key to maximizing a sustainable approach towards coal processing activities. This paper investigates the feasibility of using the desulfurised fraction of coal processing slurry (<500 µm) streams from a colliery in the eMalahleni coalfields of South Africa as the main component for the manufacture of 'FabSoil', a fabricated soil or technosol, for use as topsoil in the rehabilitation of mine sites. Compost and anaerobic digester sludge were added as organic matter and nutrient source, whilst malt residue was used as physical ameliorant. Native soil from the study area was used as control. Validation of the potential of the fabricated soils was conducted through germination and growth experiments using the grass species Teff (Eragrotis tef), an indigenous grass from the Mpumalanga region of South Africa commonly cultivated on degraded mine land. Results showed that soils produced with coal waste and native soil in a 3:1 ratio amended with compost or anaerobic digester sludge and malt residue had the highest biomass production after 90 days. According to this study, the use of these soil substitutes can reduce the amount of topsoil used in coal mine restoration, while also reducing the amount of fine coal disposed in dump deposits significantly. This minimises the land-use footprint and the social and environmental impact of mining activities as part of circular economy and zero-waste strategies.