Dewatering of Ultra-fine Coal

Recharge factors of 23.5 per cent and 12.9 per cent were calculated at the two rehabilitated pits with complete data. The higher value reflected surface drainage towards the pit centre and eroded topsoil; the lower one, a deep pit floor with well compacted spoil and intact cover. The rates are site specific and no generic formula could be derived.

Heat exchanger material governs how fast ice scale forms during eutectic freeze crystallisation of dilute brine. Induction time fell as thermal conductivity rose, so copper scaled first, while aluminium gave the lowest scaling rate because its low surface energy pushed ice crystallisation into the bulk. Stainless steel delayed onset but scaled heavily once nucleation started.

Geotechnical factors affecting secondary extraction were identified from interviews with collieries already re-mining pillars and with people experienced in stooping, then quantified and ranked against the different aspects of the work. No single factor governs the outcome. Factors interact, so choosing a method and working safely in old workings depends on managing them together across disciplines.

Ion exchange treatment of acid mine drainage from a closed KwaZulu-Natal colliery was piloted and shown to give effluent free processing, converting the salts into saleable products rather than sludge and brine. Reverse osmosis had previously produced water of discharge standard but left both. Combined flow from the two mine compartments averaged 4.6 megalitres a day.