Acid mine drainage (AMD) 
 is one of the most serious 
 and potentially enduring environmental problems for the mining industry and, if left unchecked, could result in long-term water-quality 
impacts that could well be this industry’s most harmful legacy, says Environmental & Remedial Technology Holdings (Earth) 
director Richard Doyle.

He says that government should consider the different technologies on the market to effectively deal with this challenge.

“Government is a significant stakeholder in this and, perhaps, it should consider creating a 
formal process to analyse the 
different approaches and devise some intervention to assist in 
deciding on the selection of companies best positioned to solve this problem.

“AMD is a massive problem and it is doubtful that a single company will be able to solve this problem.”

Recently, Western Utilities Corporation (WUC) reviewed several treatment options developed in South Africa, after which it 
selected the Council for Scientific and Industrial Research’s ABC process.

WUC is now at a fairly advanced stage of planning the construction of a 75-million-litre plant in the Central Basin, south of Johannesburg. If approved, the plant would derive water from, besides others, Harmony Gold, DRDGold, Mintails, Pamodzi and Central Rand Gold.

An environmental-impact 
assessment (EIA) has been sent out for public review and the company is raising funds for the 
detailed feasibility study through a rights issue on the London Stock Exchange’s Aim. WUC says that it has secured capital, in prin-
ciple, for the eventual plant, which should be commissioned at the end of 2010.

Doyle says that, even if the WUC plant goes ahead, it will meet less that 10% of the total need in South Africa during the first phase and less than 20% in the second phase, which means that government still needs to consider additional ways of solving the AMD problem.

He explains that there are three  ways to manage acidic water. “The so-called Rolls-Royce of these methods is reverse osmosis, 
whereby the water is pushed through a very fine membrane, which holds back the gunk and grime. However, this residue has to be stored indefinitely, which means that this is not a sustainable solution, and it is also very expensive.”

The historical way to clean mine water is through precipitation. With this method, mines add chemicals to the water, ending up with relatively clean water, but also a sludge residue.

“After evaluation, Earth 
decided on a third approach, the ion-exchange method, to clean acidic water from the mines.”

He explains that ion exchange is the reversible exchange of similarly charged ions between a solution and an insoluble ion exchanger in contact with the solution.

Doyle says that the ion-
exchange technology has three major advantages. Firstly, it 
extracts all the ‘dirty’ components of the polluted water effectively and produces ultraclean water. Secondly, the process can 
‘sort’ the pollutants into their 
individual components (ions) and then reassemble them into different combinations, or with other chemicals, to produce useful and valuable materials that can be sold. Thirdly, it is possible to develop a residue-free system, sustainable in the long term after mine closure.

The Earth technology has previously been successfully demonstrated for sewage streams and is widely used for water softening. The current invention has been developed by Dr Robbie Robinson, former head of Mintek.

The initial set of by-products that Earth intends to produce from the treatment of mine water is ammonium sulphate and a mixed-metal nitrate. “They are both commodity products that can respectively be sold to the 
explosives industry and the fertiliser industry. The revenues gener-
ated from that make the economics of this process competitive.

“Also, because one is able to produce potable water and fertiliser, employment opportunities are created for the local communities after mine closure or even during the mining operations,” Doyle says.

Current Operations

Gold- and uranium-miner Rand Uranium intends to build a 
uranium plant which would use a fraction of its water in three to four years.

“In essence, Rand Uranium needs to anticipate the possibility that there would be an excess of water, which is why the company is exploring solutions that would reduce metals and sulphates in the water so that the water can be discharged or used,” says Doyle.

The mine is considering the dif-
ferent economic solutions that would ideally also work post mine-
closure and be completely effluent free.

Doyle says that Earth is currently running pilot trials at Rand Uranium’s Cooke plant at its own cost, adding that the clean water that is being produced in Earth’s trials is ten times purer than the standards set for human consumption, that is, it contains less than 100 parts per million total dissolved solids, which is about 10% of the impurity levels recommended for potable water.

“We are currently in discussions with various government and private-sector parties in firming up the details relating to input costs, product offtake agreements and water licences,” he says.

Mining and engineering consultancy TWP is providing engineering support and independent verification of the calculated economics.

“We intend to finalise the 
results of our trials and the economics of a proposed commercial plant in the coming weeks,” Doyle 
concludes.

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