Integrated Mining and Processing

Run of mine and discard coal carried total rare earth contents of 260 and 265 ppm, above the 130 ppm cut off grade used for coal. Flotation with an emulsion binder did not raise those concentrations in either the product or the tailings streams. Calcination did, lifting totals to between 285 and 289 ppm, with most rare earths leaching within the first fifteen minutes.

South African underground sections average about 60 000 t a month, against 130 000 to 160 000 t for single pass bolter miner units on continuous haulage, while the better sections target 1.4 to 1.6 Mt a year. Australian longwalls deliver 5 to 7 Mt a year from one face, compared with 3 to 5 Mt at the two local wall operations.

Finite element simulation reproduced the rapid collapse of bord and pillar workings in the 2 Seam at a Witbank colliery, showing that progressive pillar deterioration triggers snap through of a strong sandstone plate in the overburden. Too little was known about the chosen collapse to back out a real pillar safety factor, so the calibration goal was not met.

Sets out the steps to establish a small scale coal mine in South Africa, from mineral rights and regulatory approvals through finance, mining and processing choices, marketing, and environmental management and closure. The information a new entrant needs sits in many separate places, so the guideline draws it together from practitioners rather than from any single published source.

Testing of 28 coal and coal-shale samples showed the coals to be more liable to spontaneous combustion than the shales, though reactive coal-shales still self-heat and pyrite in them speeds the process. Higher carbon, moisture, hydrogen, volatile matter and nitrogen with lower ash all raised proneness to self-heating, so proximate and ultimate analysis can serve as a screening tool.

Nine bituminous coals from the Witbank, Waterberg and Soutpansberg coalfields all formed compacts without a binder, and the process worked better with coking coals. Reactive maceral content, free swelling index and Hardgrove grindability index governed briquette strength, with ash and kaolinite contents also contributing to bonding. Briquetting pressure, feed moisture and particle size distribution controlled the outcome.

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.

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.