Surface Environment

Level of acid mine drainage disturbance explained more of the variation in diatom communities than any other factor, with pan type second and season not significant. Sulphate and calcium concentrations and sulphate to chloride ratios were higher in disturbed pans of every type. Pan type specific indices were tested against established riverine indices.

Sets out the authorisation route for leaving a pitlake as a closure landform, covering water use licensing, environmental authorisation and the wider legislative process. There is no single application that grants approval, and the route is long and partly duplicated, so several applications are required.

Conventional rehabilitation relies on lime, fertiliser and compost to build fertility and select adaptive species, which produces short term cover but rarely a self sustaining ecosystem. The work argues for treating soil microbes as part of the system, since bacteria drive nutrient cycling, organic matter breakdown and soil aggregation, and proposes conditioning plants with adapted rhizosphere bacteria on coal waste substrates.

Rehabilitated opencast soils carried pastures and cash crops, but compaction and cover soil depth set the ceiling on what they could produce. Only land with deep cover soils suited maize and sunflower, and deep ripping with regular tillage was needed. Bulk density standards were not met at the trial sites, which the review judged enough to have changed the results.

A regional monitoring programme was found to be viable and is proposed as a public private partnership covering air emissions, air quality and energy efficiency on the Mpumalanga Highveld. The assessment concluded that the worst health impacts fall on residential areas, driven by inefficient coal burning for heating and by housing sited close to large industry.

Ion exchange converted reverse osmosis brine from a power station treating colliery water and cooling tower blowdown into fertiliser and explosives salts, with no liquid effluent left to dispose of. Part of the water rejected by the reverse osmosis stage was also recovered as potable water. Brine is currently used for dust suppression and stored underground.

Ion exchange treatment of acid mine drainage from a closed KwaZulu-Natal colliery was piloted and shown to give effluent free processing, converting the salts into saleable products rather than sludge and brine. Reverse osmosis had previously produced water of discharge standard but left both. Combined flow from the two mine compartments averaged 4.6 megalitres a day.

Ion exchange applied to brine from a three stage reverse osmosis plant at eMalahleni converted the brine entirely into saleable fertiliser and explosives feedstock, and recovered close to half of the water the reverse osmosis stage leaves behind. On this basis the existing brine pond and the two planned for the plant expansion would not be needed.

Watercourses on post mined land near Kriel showed deterioration in manganese, calcium, magnesium, sodium, total dissolved salts and sulphate, while other parameters stayed within drinking water standards. Aquatic invertebrate communities had suffered significant losses and two sites were classified as eutrophic. The water is not fit for human consumption or recreation, and a minimum 32 m buffer from wetland boundaries is recommended after earthworks.

Prices for calcium and magnesium sulphate are recorded for South Africa and for world markets as at mid 2012, together with price trends and the groundwater chemistry that governs which salts a mine water stream will yield. The figures were assembled to support feasibility studies on a eutectic freeze crystallisation plant and an ion exchange plant.

Eutectic freeze crystallisation was compared with evaporative crystallisation as a route for treating hypersaline mine brine. Optimised commercial evaporative crystallisers use 40 to 50 kWh per cubic metre of feed. Laboratory work measured a eutectic temperature of -21.1 degrees Celsius for pure sodium chloride solution, and found that a large difference between coolant and solution caused scaling on the heat exchanger wall.

Ion exchange was assessed as a treatment route for brine arising from mine water cleaning, from a market rather than a plant performance standpoint. World demand for ion exchange resins was expected to pass 535 million dollars by 2015, driven by urbanisation, pollution and shortages of clean water in developing regions.

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.

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.

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.

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.