Integrated Mining and Processing

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.

Coal can feed products well beyond combustion. The study sets out routes to rare earth elements held in particular seams, building materials made with carbon fibre and carbon char, coal foam and graphene composites, carbon black and activated carbon, including a coal derived activated carbon reported to hold four times the gas of compressed natural gas at lower pressure.

A high internal phase water in oil emulsion binder upgraded weathered ultra fine coal discard. At 5 kg/ton on a feed of 29.34 per cent ash and 20.94 MJ/kg, flotation gave a clean coal of 11.76 per cent ash and 28.61 MJ/kg at 15.61 per cent mass yield. Calorific value rose with agitation speed and fell with binder dosage.

Practical guidance for opencast operations covers early detection with low cost thermal cameras, prevention, and the treatment methods in current use: water sprays and cannons, sand cladding of highwalls and stockpiles, removal of burning coal by dragline, tipping into water ponds and the treatment of sinkhole areas. A three month full scale trial of sprayed fly ash as an antioxidant is reported.

No surface geophysical method can map individual bords and pillars at the depths typical of the Witbank coalfield, a limit the review attributed to physics rather than to technology, since the targets are small relative to their depth and conductive layers often lie above the seam. Borehole laser scanning remains the workable option, with sonar suited to flooded workings.

Conveyance legislation promulgated in 2008 and enforced soon after left the coal industry without a lawful way to clean near and under running conveyors. The first phase defined the problem, recorded the cleaning practices mines already use successfully, and built a structured database of mechanised platform options worth pursuing. High risk areas remain drives, take ups, snub and tail pulleys and transfer points.

A single float sink test destroys the sample and gives one deterministic answer, so it cannot show how washability changes with particle size distribution. Simulating washability from petrographic images and tomography allows many size distributions to be tested statistically from one sample. Running simulation alongside float sink work during exploration lets the prediction error of each be compared.

Existing thermal imagery of the Witbank coalfield was traced to its holders and assessed for format, quality, resolution and coverage, then brought into one geographic information system with supporting metadata. Satellite thermal bands give a regional picture only; detailed mapping of coal fires or acid drainage discharge needs high resolution aerial surveys.

Magnetite and pyrrhotite each gave the most uniform and stable fluidised bed densities, with bed density variation under 0.7 per cent. A pyrrhotite and magnetite blend at a weight ratio of 40:60 beat magnetite alone, producing a product of 14.50% ash and 27.30 MJ/kg from a feed of 39.27% ash and 18.76 MJ/kg.

A three dimensional model of the northern Witbank and Highveld coalfield was built from more than 1100 borehole logs, with strata sorted into 13 major groupings and surface topography taken from satellite elevation data. It runs on open source visualisation software rather than a commercial package. Delays limited coverage to about a quarter of the coalfield.