Publications

Shallow reflection seismic surveys failed on South African collieries mainly because too little preliminary data, from vertical seismic profiles and noise spreads, was gathered before the surveys were designed. Following the field procedures set out here produces usable data for mine planning. For target depths under about 150 m, exploration drilling stays cheaper, because shot holes must be drilled below the weathered layer.

Dolerite intrusion mechanisms and their metamorphic effect on coal were examined across four collieries in the south eastern Witbank Coalfield. In decreasing order of importance, intrusions cut safety by raising the risk of roof, pillar and floor failure, raise mining costs, reduce saleable tonnage, and increase waste generation and environmental risk.

Three modes of intervention were found in coal company procurement: preferential procurement rules, segmentation of goods and services by suitability for transformation, and support programmes for small suppliers. Progress stalled where supplier development was handled by staff carrying other duties, since work not tied to production loses time and has no target. The remedy proposed is procurement targets linked down through commercial and production management.

Hydrogen for biological sulphate removal can be generated on site by electrolysis more cheaply than it can be bought. Stainless steel electrodes in acid mine drainage gave hydrogen at about a third of the bought in price while oxidising ferrous iron to ferric, which helps downstream treatment. Iron and zinc electrodes dissolved too quickly to be viable.

The separator handled fine coal and produced a 28 MJ/kg product, but its measured separation efficiency was lower than that of conventional dense medium cyclones and it was harder to operate. Two efficiency tests produced no evidence that the unit outperforms cyclones on fine coal, so cyclones were recommended when the plant was rebuilt at its next site.

A stand-alone device was built that detects micro-seismicity within 100 m of the roof and raises an alarm when preset thresholds are exceeded, giving early warning of goafing. Input parameters proved not to vary with geotechnical setting. Man-made noise triggering false alarms remained the main obstacle, addressed by signal conditioning and sensor placement.

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.

Failures continued after the safety factor approach was adopted, in pillars created both before and after it, so the record of failed workings has kept growing since the original 27 cases. The database was updated and re-analysed to revise the strength formula and to set out the probability of failure associated with pillar designs.

Four centrifugal concentrators all cut ash in fine coal, with desliming the decisive step. The best unit took ash from 35.2% to 18.47% and sulphur from 0.68% to 0.36% in a single stage, raising calorific value from 23.78 to 26.16 MJ/kg. Pilot work reached 19% ash on thickener underflow and reconstituted spiral feed.

Laboratory testing showed coal specimen strength rising linearly with width to height ratio and falling exponentially with specimen size, the size effect becoming insignificant beyond about 2 m diameter. The slope of that relationship was the same for coals from different mines, while the intercept varied with specimen size.