Dewatering of Ultra-fine Coal

Stockpiling degraded every soil property measured across four Witbank area mines. Clay content of topsoil and subsoil rose by 50 to 60 per cent, surface bulk density increased from stockpiling through to rehabilitation, and effective depth on rehabilitated areas was under 17 cm in most cases. Topsoil organic carbon fell by almost half and microbial species numbers dropped in the stockpiles.

Sets out good practice for planning, implementing, monitoring and adaptively managing land rehabilitation at surface coal mines, with generic rehabilitation objectives, implementation actions and suggested relinquishment criteria for each component. It updates guidance first issued in 1981 and revised in 2007, reflecting later changes to South African rehabilitation legislation.

Geophysical logging of boreholes above three Witbank seams identified clay rich matrices, stiffness changes, bedding planes and the principal stress direction, and picked up fractures in 30 to 75 per cent of cases. Core logging found most of the same features faster, so routine use was not recommended unless stiffness and stress direction matter.

Sustainability in mining is still framed in neoclassical economic terms, measured by profit, shareholder value and growth, with social and environmental dimensions added in response to regulation. Six air quality and waste minimisation projects run over seven years were assessed against seven dimensions of the biosphere and fell well short. A collaborative model is proposed for a sector built on mining waste residues.