Publications

Market prices are set out for sodium sulphate, sodium chloride, sodium nitrate, potassium nitrate and potassium chloride, in South Africa and abroad, as at early 2011, with Chinese supplier quotes alongside United States averages. The work was done to test whether salts recovered from mine water brine could be sold at a worthwhile price.

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.

The financial benefit of bees to a rehabilitating site could not be modelled with confidence, and a field trial to show direct benefit is hard to configure because so many variables affect rehabilitation. Apiaries suit sites where bee friendly plants are established, the return coming through honey yield rather than measured gains in biodiversity or ground cover, at low establishment cost.

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.

Compaction on rehabilitated opencast land restricts effective rooting depth so severely that only a small proportion of arable and grazing areas reach their stated capability. The review sets out the causes and symptoms, argues that symptoms are usually treated without addressing the cause, and recommends site specific, resource based management, mechanisation choices weighed against compaction, and land capability standards aligned with international codes.

Aircraft and ground based measurements at Kleinkopje Colliery showed spontaneous combustion to be a significant source of fine particles, with PM2.5 concentrations 91 per cent higher inside a combustion plume than outside it. Sulphur dioxide, nitrogen dioxide and carbon dioxide were also raised in plume, and benzene and toluene were detected. Average particle size was below one micron.

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 modified alkaline barium calcium process was tested on coal mine acid drainage, using calcium hydroxide neutralisation, hydrogen sulphide metal removal and barium carbonate sulphate removal. Gypsum formation during water treatment fell by 80 per cent, cutting the sludge sent to costly downstream processing to a fifth. Temperature, reaction time, reagent ratios and feed particle size affected thermal treatment of the sludge.

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.