Leachox™ Refractory and Sulphide Gold Process

The Leachox™ Refractory Gold Process – The Testing, Design, Installation and Commissioning of a large Scale Plant at the VASGOLD Gold Mine, Kazakhstan. Presented at the MEI Precious Metals ‘10 Conference, Falmouth, Cornwall, UK, June 2010.

A 3D model showing a proposed MMS Leachox™ Plant with four columns and four Aachen Reactors
(Click to here to view a large image)

MMS has successfully developed the Leachox™ Process for the treatment of sulphide gold ores. The Leachox process flowsheet can be designed to treat refractory or double refractory ores that contain “preg robbers”. It can also be used to treat standard, non refractory, flotation and gravity concentrates in a more cost effective manner than alternative methods. The Leachox process is covered by patent protection, as is much of the key technology that makes up the process. Evaluation and metallurgical testing of a project are undertaken by MMS under suitable confidentiality conditions. The process is offered to clients under a licence agreement arrangement.Leachox has been successfully applied to two refractory gold operations in South Africa. MMS are currently (2009) installing a Leachox plant into a refractory gold operation in Kazakhstan that will become one of the largest refractory gold treatment plants in the world.

Treating refactory gold ores

leachox_4_smLeachox™ Refactory Gold Recovery and Cyanide Destruction Flowsheet
(Download the LoxCN-DFlowsheet PDF)

Refractory gold ores are generally defined as those ores that do not give economical recoveries in conventional cyanide circuits where the ore has been ground to around 53 to 75 microns. The gold is normally present in refractory gold sulphide ores containing mainly pyrite, arsenopyrite or pyrrhotite and occurs in both the chemically bonded state and as micro or nano-size grains of metallic gold.

There have been a number of commercially successful processes developed over the years to treat such refractory gold ores – roasting, pressure oxidation and bacterial oxidation process are all aimed at destroying the sulphide matrix. The liberated gold is then easily dissolved in cyanide and recovered by conventional methods such as carbon-in-leach or carbon-in-pulp. All these processes can achieve very high gold recoveries with possibly greater than 95% gold recovery.

The above processes, while resulting in high gold recoveries, do have issues. Roasting is an environmentally unfriendly process and is not permitted in many countries. Pressure oxidation requires a fairly high degree of operator skill and control, and the bacteria used in bacterial leaching, in tanks or on a heap, are susceptible to changes in environmental conditions and require careful control. However the biggest issue is that all these processes have, in various degrees, very high capital and operating costs. This means that they are economic only on a high grade deposit or one that has generated enough reserves to justify the return on capital. There are not many occurrences of these “world class” gold deposits that will sustain such processes. The vast majority of refractory gold deposits are of lower grade and whilst many could contain enough reserves to sustain a high cost extraction process, invariably extensive drilling to determine this does not justify the risk/reward scenario.

Leachox™ is a low cost refractory gold process developed by Maelgwyn Mineral Services (MMS) based in Wales, UK and Johannesburg, South Africa. It is a process that whilst not claiming to achieve the high recoveries obtained by roasting or pressure oxidation can achieve gold recoveries over 90 percent that are similar to bacterial leaching and significantly high enough with low capital and operating cost to make treatment of lower grade deposits economically justifiable.