The Albion Process Technology (Albion Process) is a sulphide oxidation process developed in Australia by Mount Isa Mines, now Xstrata Plc, to oxidise refractory ores so that the recovery of precious and base metals can be achieved using conventional extraction technology, such as cyanide leaching in the case of gold.
A refractory gold ore is one in which the gold is usually present as finely disseminated particles in sulphide minerals such as pyrite. Conventional cyanide leaching relies on the cyanide lixivant making contact with the gold particle, dissolving the gold into a gold cyanide complex in order that recovery can then be achieved. In refractory ores, the cyanide is unable to penetrate the sulphide particle and make contact with the gold, resulting in poor metal recovery and significantly impacting on the ability to economically treat the ore.
The Albion Process is a combination of two technologies, ultra fine grinding and oxidative leaching at atmospheric pressure, which results in the sulphide particles being oxidised, facilitating metal recovery using conventional extraction processes such as cyanide leaching.
Ultra fine grinding is essential to the Albion Process, as it increases the surface area of the sulphide particles enhancing the rate of downstream chemical reactions as well as distorting the minerals crystal lattice, lowering the required activation energy for the chemical reaction to follow.
Ultra fine grinding is achieved through the use of an IsaMill, a patented horizontally stirred mill that uses a series of rotating disks inside a stationary shell to stir small ceramic beads. The ceramic beads impart energy to the sulphide particles resulting in an ultra fine grind. The ceramic beads are inert and have no impact on the chemistry of the slurry as they break down over time in the IsaMill.
There are in excess of 70 IsaMills installed worldwide at present, with more installed power (+200MW) than all other commercial ultrafine grinding mills combined. Laboratory scale IsaMills are able to determine grind characteristics and power draws for concentrates with high levels of accuracy resulting in minimal scale up risk to the commercial IsaMills.
Following ultra fine grinding stage of the Albion Process, the sulphide slurry is passed to a series of covered agitated tanks, where oxygen is introduced at the base feeding a chemical reaction that results in acid and heat generation as the sulphides oxidise. The acid and heat, along with the oxygen, drive the reaction until the sulphide particle passivates with a layer of gypsum. Due to the ultra fine nature of the sulphide feed, up to 94% of the sulphide particle can be oxidised before the reaction ceases.
Acid generated during the oxidisation of the sulphide ores is neutralised during the process, eliminating the potential for acid mine drainage from the final tailings slurry. The Albion Process is able to oxidise ores that are high in toxic elements such as arsenic and antimony, leaving elements in a stable form with the resulting tailings stream.
Operating and design parameters for the Albion Process are established at HRL Testing’s Laboratory facilities in Albion, Brisbane. The facility has a laboratory scale IsaMill and a number of Albion reactors as well as access to an Albion pilot plant, first developed for Xstrata Plc’s feasibility study into the Pueblo Viejo Gold Mine in the Dominican Republic, which is the source orebody for the Las Lagunas tailings.
The Albion Process, whilst using proprietary technology for ultra fine grinding, is a relatively simple process that can be utilised in developing countries. The capital requirements for the Albion Process are significantly lower than alternate oxidizing technologies such as pressure oxidisation, whilst the chemical complexity of the Albion Process is less than bacterial oxidation which requires the maintenance of living bacteria which can be sensitive to changes in ore chemistry and temperature.