The BIOX process for the treatment of refractory gold ores and concentrates has been commercially in operation for 18 years. A total of six BIOX operations have been successfully commissioned since the commercialisation of the process. Four of these BIOX plants are still in operation today. There has been a renewed interest in the process the past few years with two BIOX plants, the Suzdal plant in Kazakhstan and the Fosterville plant in Australia, scheduled for commissioning during 2004. Four new projects are also in various stages of development and are currently scheduled to be commissioned during 2005 and 2006._x000D_
Research into the process are currently focussed on the two highest operating cost items for the commercial operations, namely power for agitation and air dispersion and cyanide consumption during leaching. Laboratory aeration and agitation testwork using the A340 up-pumping agitation system has shown that similar mass transfer rates can be achieved at slightly higher agitator power. The up-pumping system, however, eliminates the need for a separate blower and sparger system as air is introduced into the slurry from the slurry surface. The use of the thermophile bacteria as the final oxidation step during biooxidation has shown great promise. Reductions in cyanide consumption of up to 50 per cent were achieved when using the combination mesophile and thermophile process compared to standard BIOX product solids. The combined process takes advantage of the milder oxidising conditions of the well known BIOX process for the bulk of the oxidation and then uses the high temperature thermophile bacteria to complete the oxidation._x000D_
The ASTER process for the biological degradation of cyanide and thiocyanate containing effluent solutions has been proven to be efficient and stable. The process uses an activated sludge system with a residence time of approximately six hours in the sludge reactor. Heavy metals and metal cyanide species have also been shown to be removed successfully from solution.