Bacterial Leaching

2 Pages 519 Words

Description:
Process which uses microorganisms for the recovery of precious metals from metal-containing processes and streams. This technology is targeted at using naturally-occurring, sulfate-reducing bacteria for the recovery of gold and silver from ores, instead of the more traditional -- and more toxic -- cyanidation process.
How it works:
Step 1: Aerobic bacteria catalyze bio-oxidation of low-grade, hard to treat (refractory), sulfidic gold ore. This step is currently being adopted by gold producers for freeing gold from base-metal sulfides (e.g., pyrite). A waste stream from the bio-oxidation step is used in a second step.
Step 2: Naturally-occurring, sulfate-reducing bacteria are used to convert the dissolved sulfate in acid mine drainage into a dissolved bisulfide leaching agent and to neutralize the acid mine drainage. These bacteria can use wood alcohol, grain alcohol or vinegar as food, and they are also capable of consuming hydrogen produced by the gold dissolution process. Gold dissolves in the bisulfide solution and is recovered with activated carbon or zinc dust. If needed, excess sulfur can be recovered as a byproduct. By using the natural sulfur cycle, the process provides a complete solution to the gold recovery problem.
Potential Competitive Advantages:
1. More environmentally friendly -- the bisulfide leaching agent used is about 200 times less toxic than cyanide. Since its invention in 1899, cyanidation and its variants have been the processes of choice for extraction of gold and silver from oxidized ores. Cyanide, however, is legendary in its toxic potency.
2. Improved economics -- with increasing awareness for the environment worldwide, containment, treatment costs and time spent on environment impact studies associated with cyanidation plants have skyrocketed. These factors have raised the economic hurdle necessary to justify a working mine. Environmentally acceptable alternatives could broaden the...