Tolerance to temperature and water quality for bacterial oxidation: The benefits of BacTech's moderately thermophilic culture

The use of bacterial oxidation as a pretreatment for gold recovery from refractory gold ores and concentrates is well documented. As more details are revealed concerning the operation and economics, it has become apparent that the operating temperature and the associated need for cooling are important in determining the viability of bacterial oxidation technology in some major gold mining regions. A bacterial culture which is suited to the mine environment is essential in order to achieve the best economics for the process. Thiobacillus-based cultures are generally restricted to temperatures less than 40°C and, in some regions, cooling must be provided to maintain the correct temperature range. Water cooling is the most obvious solution but the water available on mine sites in some regions is either very hard or saline and the quantities can be limited. Conventional cooling towers and heat exchangers suffer from scaling and corrosion under these conditions unless water treatment is used. Insufficient water may make cooling impractical and prevent the consideration of bacterial oxidation technology as a process option. Any additional temperature tolerance by a culture will reduce capital and operating costs associated with maintaining the optimum temperature range for the bacterial culture. The salinity of the plant water can also affect the performance of the bacterial culture and, in some cases, may cause a complete loss of activity. It is important that any culture applied in a mine site plant is able to perform the oxidation of the refractory sulphides using the local water, regardless of its salinity or hardness. BacTech (Australia) Pty. Ltd. has applied its moderately thermophilic culture in mine site-based tests for independent clients not associated with this company. The bacterial culture has been openly proven under a wide range of conditions ranging from arid desert to temperate mountain conditions in both summer and winter. The culture has operated up to 55°C without the need for cooling, thus removing the concern of scaling and limited water resources for cooling towers. The pilot plant trials have used saline, hard bore water and better quality dam water. The oxidation performance of the bacterial culture remained unaffected if basic nutrients were adjusted for the local water and gangue minerals. Gold recoveries greater than 90% were achieved after cyanide leaching of the oxidized sulphide flotation concentrate.