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:: Maelgwyn Minerals’ Leachox Refractory Gold Process hits the Gold Standard
It’s now over 10 years since the European Patent Office advised its decision to grant Maelgwyn Mineral Services Ltd (MMS) a European Patent for its Leachox process for the treatment of refractory gold ores. Since that time the process route has become the industry leader in the low-cost recovery of gold from refractory and sulphide orebodies. There is now world-wide installed capacity of Leachox to recover over 3 million ounces per annum of gold contained in sulphides.
To compare process routes and recoveries, pressure oxidation can completely breakdown the sulphides and then achieve high gold recoveries, maybe greater than 95%. Where as with the Leachox process and the partial oxidation, depending on the nature of the mineralogy, recoveries in the range 80% to 90% can be expected.
However, the Leachox process has an order of magnitude lower capital cost than pressure oxidation and much lower operating cost. The Aachen Reactor, which is central to the Leachox process has been shown to be extremely versatile and can also be used to advantage to treat oxide and then transition ores that normally are processed before the deeper sulphide ore bodies are reached.
The use of the Reactor accelerates the leach kinetics allowing for higher throughputs through the CIL/CIP plant and reduces cyanide consumption by initiating efficient oxidation of cyanicides in the pulp that react with cyanide in preference to gold and reduces the leaching effect. Whilst in parallel the Aachen Reactor removes passivating layers on the mineral surface that can otherwise impair the leach reaction.
The relatively fast acceptance of the Leachox process is in no small part down to the collaboration the MMS associate company, Maelgwyn Mineral Services Africa Pty Ltd (MMSA), has had with Randgold Resources since 2010. MMSA is an independently operated company (48% owned by MMS) who has expertise in gold processing and has top of the range metallurgical laboratory and pilot plant facilities.
Randgold utilised MMSA’s expertise when developing a number of mines across Africa where the majority of the gold in the ore deposits was in the sulphides and refractory by nature. These reserves were not large enough to justify pressure oxidation or bacterial leaching and the deposits were all situated in remote areas of Africa. Randgold undertook a due diligence on the Leachox process and installed some trial Aachen Reactors at its Loulo mine in Mali. The trial proved successful (the Aachen Reactors are still currently in operation at Loulo) and so Randgold used the Leachox process as its basis of design for the Tongon operation in the Cote d’Ivoire.
Today all the Randgold Resources operations utilise Leachox or Aachen Assisted Leach in their process plants and there are currently 49 Aachen Reactors installed across all their operations. The nature of the agreement between MMSA and Randgold means than MMSA maintain all the Reactors on site with replacement wear parts and keep them in good working order.
The uses of the Aachen Reactor as a high shear mass transfer device are not limited to gold leaching. The technology has undertaken various roles in a number of processes including cyanide destruction, silver and copper leaching, ferric ion generation and pyrite suppression. It is also envisaged that the reactor has applications in uranium leaching and lithium production. The majority of applications of the Aachen Reactor have been in gold operations. However, MMS’s first silver application is at the Gumustas silver mine in Turkey where retrofitting an Aachen Reactor is already yielding excellent results with an immediate recovery increase of 8% and a 30% reduction in cyanide consumption.
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