AEL Takes on AMD Problem with Eco-friendly Products

The Research and Development (R&D) Department at AEL Mining Services, an international leader and innovator in blasting solutions, has proactively taken the Safety, Health and Environment (SHE) concept further to add value down the supply chain to provide a potential  solution for the Acid Mine Draining (AMD) problem through its Eco-friendly products. 

By supplying environmental solutions developer Earth Metallurgical Solutions (EMS) with nitric acid, AEL has unlocked a source of Mixed Metal Nitrates (MMN), which includes magnesium, sodium and calcium.  

According to Larry Wilson, AEL Explosives’ Group Technical Manager, when the MMN solution is included in the oxidiser solution of AEL’s bulk explosives formulation, a number of key benefits are gained. The explosive product’s shelf life stability is improved, the re-pumpability of the emulsion explosive is enhanced and additional recycled waste oil can be incorporated into the formulations.

“From the work AEL’s R&D group has done, we have successfully demonstrated that we can incorporate up to 30% of the MMN solution into our formulation. Trials have proved successful,” comments Wilson. AEL is currently negotiating sufficient volumes from EMS to make field trials in the near future possible. “We look forward to enhancing our relationship with EMS and incorporating the MMN into all our explosive formulations in the future,” says Wilson.

What is AMD?

AMD is highly acidic water, usually containing high concentrations of metals, sulphides and salts as a consequence of mining activity.  AMD may result from drainage of underground mine shafts, run-off and discharge from open pits and mine waste dumps; tailings and ore stockpiles which make up almost 88% of all waste produced in South Africa.

Drainage from abandoned underground mine shafts into surface water systems (decant) may occur as the mine shafts fill with water.  The chemistry of AMD generation is straightforward, but the final product is a function of the geology of the mining region, presence of micro-organisms, temperature, as well as of the availability of water and oxygen.  These factors are highly variable from one region to another, making it critical to carefully consider the prediction, prevention, containment and treatment of AMD.

AMD’s impact in South Africa

Johannesburg is positioned on top of what is referred to as the Central Basin – an area with a legacy of over 100 years of mining.  Due to the absence of pumping of mine water from this basin for over a year now, the acidic mine water below Johannesburg is rising at between 600mm and 900mm a day, with its current level at 600m below the surface. “At this rate overflow could be in the Johannesburg CBD by early 2012 compromising the integrity of buildings and causing incalculable damage.  The window of opportunity in which to formalise a suitable response to this impending disaster is now only a few weeks away, as the lead time for the required engineering will take between 7 and 8 months thereafter,” says Larry Wilson.

According to Wilson, the warnings of acid mine drainage overflow have existed on the West Rand for almost 15 years. Civil society has played an active role in alerting government to the imminent threats.

“In 2008 and 2010, we witnessed overflow in this area,” said Wilson. “Earlier this year R6.9m was committed to a short-term solution by involving the purchase of lime to partially treat overflow of mine water in the West Rand. Unfortunately this treatment option has caused further problems.

“While helping to reduce the acidity of water, it has left sludge of heavy minerals in downstream dams, which can be reactivated by subsequent overflows. We saw first-hand the Hippo Dam in Krugersdorp, which has been turned into a reactor dam, something which should never exist outside of a mining property.”

On 14 July 2010, members of the mining sector presented a proposal to the government after four years of hard work and research.  “The West Rand basin is currently full and the Central Basin is rising.  The proposed solution, which involves pumping of acid mine drainage from the Western Basin into the Central Basin through a new pipeline, with subsequent pumping out of the Central Basin where the water will be partially treated before pumping, is as far as we know the only real option on the table. This option is ready to be implemented if approved quickly,” adds Andre Pienaar, AEL’s Chief Technologist

“It is not a perfect solution, but the immediate risks are tremendous!  If we wait for the perfect solution, Johannesburg will be in trouble.  By responding now we will buy some time, and in the meantime, a more permanent solution can be worked out, which would, amongst other things, need to include a higher degree of treatment of the water that will be discharged,” says Pienaar.

Further Studies to Address the AMD Problem

Various Universities in South Africa are currently conducting research on the treatment of this waste water. Possible solutions, including electrical evaporation, eutectic freeze crystallisation, reverse osmosis and ion exchange have been proposed.  These technologies focus on concentrating the salt and therefore minimising the problem, however, in all of the proposed methods, the problem of the mineral salt concentration still persists.

EMS has completed trials proving that Acid Mine Drainage (AMD) and AMD brines could be converted to potable water and saleable by-products, including fertiliser, explosives and the thermal salts for concentrated solar power plants by making use of ion exchange to clean the water. Regeneration of the filters is then tailored to ensure that value added products are being produced and could potentially be used in the current market.

EMS's initial AMD pilot programme was conducted at a Randfontein gold mine during 2009, followed by an extensive Coaltech-funded trial programme on coal AMD and brines at four of South Africa's largest coal-mining companies in 2010. The EMS technology does away with the need for waste storage, and can, in fact, remediate existing waste pools, such as brine ponds, which hold the waste from other processes, such as reverse osmosis and others currently used to treat some acidic mine waters in the coal sector.

ISSUED ON BEHALF OF AEL MINING SERVICES LIMITED

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