Tackling Acid Mine Drainage in a big way

Written by  Sunday, 16 February 2014 18:09
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A mammoth new plant is nearly ready to treat toxic water.  A hundred tons of lime a day and a " hell of a lot" of electricity. This is some of what it will take to power the biggest acid mine drainage (AMD) plant of its kind in South Africa and the continent.


As early as next month, authorities plan to switch on this mammoth plant, located on a lonely stretch of road in Germiston, and begin to pump and treat 70 million litres of toxic mine water a day.
Built by Group Five and its subcontractors at a price of more than R600 million, the Central Basin pump station and treatment plant is a sophisticated network of concrete structures, AMD-proof piping and electrical systems.
It will draw the polluted mine water that is flooding abandoned, underground gold mine workings of the Central Basic, preventing it from decanting on the surface, poisoning groundwater and surface water, destroying ecosystems.
With its switch-on set tentatively for next month or April, it is the impressive face of the government's short term AMD intervention, which is being led by the Trans-Caledon Tunnel Authority, to pump and neutralise the corrosive cocktail of heavy metals and potentially radioactive water seeping from the Witwatersrand's mining basins.
John Otto, the chief resident engineer of Aecom, the design engineers of the project, says it has been a race against time to build the plant since the work started last January. Otto feels like a bit of a pioneer.
"It hasn't been easy because the programme had been tight. But it's the first time this has been done in the country. The gold mining companies have treated effluent gold mining water in the past, but in a very amateur fashion."
His colleague, John Botha, the resident engineer at Aecom, interjects: "Ja, there is a small plant on the West Rand cobbled together out of bits and pieces ofmine infrastructure (to treat decanting AMD).
"But it's what we call a skoro skore plant. It's nothing like this," he says, surveying the plant, which towers over a similar one at eMalahleni.
But it's what the plant does that matters. Right now, the pH of the AMD is 2.5 or "like sukphuric acid", explain Otto. After treatment, this climbs to a pH of around eight or nin. It is then discharged into the Elsbergspruit, flowing ultimately into the Vaal Barrage.
Environmentalists are worried that the neutralisation process does not remove the high salt content of the AMD, meaning 800 tons of these salts will flow into the Vaal from the Central and Eastern Basins every day when both treatment plants are running.
There is concern that there won't be enough water to dilute the high salinity of the Vaal.
Richard Holden, business analyst for TCTA, says it is in "concurrence with the Department of Water Affairs' Vaal River reconciliation strategy, which shows the need to desalinate the AMD from the Witwatersrand gold fields as a point source of pollution in the Vaal River system".


To do nothing is not an option.

"No AMD plant means Yellow Boy (AMD ) flows into the Elsbergspruit and into the Klip river; high salt loads (pass) into the Vaal Barrage, and then the release from the Vaal Dam of clean water (being transferred in from Lesotho and will require transfers from the Tugela as well), which threatens water security in the Upper Vaal Catchment," says Holden.
"The alternative is not to release the water and to let extremely poor quality water affect consumers in the Middle and Lower Vaal Catchments."
The mine water in the Central Basin is rising 0.28m a day. It will be 180 days before it reaches the environmentally critical level, he says.
But pumping and treatment will be well under way.
"At that point there is the potential to impact on any boreholes connected to the mine void," says Holden. "From a water supply point of view the impact would be limited as ZRand Water supplies all the potable water in the area."
Rising AMD from the Central Basin has reached the old operational level at Gold Reef City, the Department of Water Affairs says.
Department spokesman Themba Khumalo says" "Gold Reef City is busy with the development of another old level closer to surface.
"Further announcements on the reopening of the underground mining displays at Gold Reef City will be made as soon as all activities have been moved from level 5 to level 2."
One thing is certain - pumping the underground voids will need to continue indefinitely.
"How long is forever?" Botha shrugs. "We may need to build another treatment plant one day."