Water

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.

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.

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.

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.

Monitoring and geochemical modelling at five pilot sites, on undisturbed soils and on opencast spoils, showed that most soils held a large share of the applied salt in the upper unsaturated zone and that salinity built up slowly. Leachate volumes, leachate quality and aquifer mixing ratios were quantified. Irrigation is recommended on alternating pivots and for no longer than ten years in one area.

A pilot brine concentrator treated Stage 3 reject effluent from a mine water reclamation plant, raising total dissolved solids from 24 g/L to 154 g/L at 88 per cent water recovery. The condensate met the national potable water specification. A separate run concentrated brine from 76 g/L to 145 g/L, solid salts were precipitated, and no scaling or fouling was seen.

A regional scheme to collect, treat and re-use mine water in the Upper Olifants River Catchment has merit, with the mines best placed to start it through a dedicated mine water company that brings in the water services authorities. Water legislation supports the scheme provided the regulator allocates mine water as a resource. Viability rests on the tariffs mines and water users pay.

Irrigation with calcium and sulphate rich mine water proved feasible and sustainable over eight years at a Mpumalanga colliery, with no significant impact on soil, surface water or groundwater. Sugarbeans, wheat, maize, potatoes and pastures were grown on a commercial scale. High calcium and magnesium suppressed potassium uptake, and waterlogging from poor site selection was the main problem.

Recharge factors of 23.5 per cent and 12.9 per cent were calculated at the two rehabilitated pits with complete data. The higher value reflected surface drainage towards the pit centre and eroded topsoil; the lower one, a deep pit floor with well compacted spoil and intact cover. The rates are site specific and no generic formula could be derived.

Grazing trials on tall fescue pasture irrigated with gypsiferous mine water on rehabilitated mined land, run over several seasons. The work covers steer stocking rates, dry matter intake by cattle, and the factors that control pasture quality and intake, among them nitrogen fertilisation, stage of growth, sward structure and grazing intensity. Findings are reported study by study.