Integrated Mining and Processing

Co-treating coal discards with sewage sludge by hydrothermal carbonisation gave hydrochars with better physicochemical properties than treating either waste alone. The blended hydrochar reached a surface area of 20.35 m2/g and a pore volume of 0.38 cm3/g, and removed 97.19% of nevirapine and 93.32% of lamivudine from recycled water. Routes to activated carbon and hydrogen storage were also assessed.

Shallow coal suitable for small scale opencast working was mapped in the northern Witbank and Highveld coalfields, using a limit of 30 m from surface to the top of the first seam. Most outcrop areas examined proved already mined out, and depth to the top seam increases southwards, though some ground remains available. Obtaining resource data was the main obstacle.

About 3.19 billion tons of coal now sits underground in pillars, growing by roughly 110 million tons a year under current bord and pillar practice. Pillars with a safety factor of about 1.8 or higher can be extracted successfully, and 1.5 is permissible in thin seams where the pillar width to height ratio exceeds 10.

Sub-seams within the No 2 Seam were characterised at a single test site using lithology, seam thickness, proximate analysis, petrography and geophysical logs, and a paleoenvironmental model was built from them. Wireline logs separated coal from interburden but could not resolve the individual zones, because the physical differences are too subtle. Better sedimentological models gave better reserve and resource estimates.

No single global standard governs refuge bay design, and the collieries surveyed differ widely in construction, location, equipment and operating practice, which made ranking them impractical. Areas needing attention were identified in design, construction and maintenance of the facilities that keep people alive until rescue, drawn against local law and overseas practice.

Mapping abandoned, inaccessible bord and pillar workings comes down to two options: borehole deployed laser or sonar scanning, or sensors carried in by unmanned vehicles. Drone mounted laser scanning for air filled voids and sonar carried by small submersibles for flooded workings were judged the most promising, but intrinsic safety, deployment and the risk of losing equipment still favour borehole methods for occasional use.

Dust masks worn by load haul dump operators passed 200 mg of filter loading in an average of 1.7 hours, and continuous miner, shuttle car and roofbolt operators reached the same point within two to five hours. Every mask failed laboratory fit testing. An eight hour service life is too long.

Government and industry aeromagnetic data over the Witbank Coalfield were merged into one set of maps and GIS compatible files, and roughly 1200 dyke traces were interpreted from them. Purchase of a 200 m line spacing government survey removed the need for infill flying. One participating company valued advance knowledge of a single underground dyke at about R15 million.

Employee share ownership participation schemes are presented as a route to spreading mining wealth more widely after apartheid. They differ from profit sharing and pension arrangements in holding only the employer's own equity and in enlarging the company's capacity to borrow. Acceptance of such schemes in the South African mining industry was tested through an attitude survey of workers.

Dolerites in the study area differ in mineral content, geometry, thickness, grain size and degree of alteration. Plagioclase textures indicate fractionation at different depths in the crust for the Witbank and Sasolburg intrusions, and the olivine content points to separate magma sources for two of the sills. Fine crystalline dolerite, including chilled margins and bifurcations, alters most readily.

Computational fluid dynamics, checked against underground measurements, mapped ventilation flow and methane concentration around continuous miner headings for straights and splits, single and double scrubbers, side and straight scrubber discharges, jet fans, brattices and force columns. It showed the earlier physical test work cannot predict contaminant flow for larger machines or altered scrubber layouts.

No single method gives a continuous, real time report on how a coal preparation plant is performing. Mass meters converted to yield values, on-line ash and moisture monitors, load cell chutes and automatic medium density control together supply most of what is needed. Measuring discard and slimes tonnages, particularly slimes disposal, remains the weakest point in plant accounting.