Environmental solutions developer Earth Metallurgical Solutions (EMS) said it had 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.
“The trials have been a complete success and show effluent-free processes are possible and commercially attractive,” said EMS CEO Richard Doyle.
EMS’s initial AMD pilot programme was conducted at a Randfontein gold mine during 2009. This was followed in 2010 by an extensive Coaltech-funded trial programme on coal AMD and brines at four of South Africa’s largest coal-mining companies.
AMD was seen as one of the most serious environmental issues facing water-scarce South Africa.
Doyle explained that the EMS approach focused on the economic value of the AMD contaminants by using ion-exchange – likened to running a soup factory in reverse – to disassemble the AMD into its constituent elements.
Once isolated, these were recombined into useful and valuable products, which were sold to offset treatment costs and even generate profits in some cases.
The clean water produced at the end of the process, could be discharged into the environment or re-used either as drinking or industrial water.
Doyle said that a key feature of the EMS process was that it did not generate solid or liquid waste.
“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.”
EMS was currently completing laboratory trials that it believed would show that the salts from AMD could be converted into the thermal exchange medium used in concentrated solar plants, which South Africa was planning to demonstrate in the next three to five years.
This could be an import replacement opportunity and establish South Africa on the renewable energy map.
“It is also a sublime example of a virtuous circle where a toxic effluent from mining is converted to the basis of a renewable energy technology and creates value rather than requiring subsidies,” emphasised Doyle.
Doyle further stated that the EMS process was feasible for all mine waters tested, while reverse osmosis (RO) could only offer a competitive treatment option on a small fraction of ‘clean’ mine effluents.
RO is also expected to become less competitive, as the cost of electricity in South Africa increased.
“The EMS objective is profitable remediation of the AMD and the current technical developments are fast closing this gap. The technology in the current form is already close to cost-neutral in most instances and the pilot work demonstrated the potential for small operating profits at some mines,” said EMS director Chris Grobler.
The company said that a large engineering house recently submitted a water treatment tender using the EMS process , aimed at addressing an AMD problem at operating gold mines in the Western basin.
EMS is also working on proposals to a number of mines for commercial plants and is currently in discussions with Coaltech to supply and operate a demonstration-scale AMD plant.