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Wednesday, December 28, 2011
Gold in Black Shale, Metal Extraction using Specially Cultivated Bacteria
A settling pond in front of a heap leaching pile. USGS
Gold and other metals are found in black shale usually in quantities too small to mine economically using the old methods, but that is all changed with the introduction of a process called bioextraction that is closely related to bioremediation. The author has actually use this technique in his environmental consulting business to remediate industrial sites that were contaminated with heavy metals. This particular method of metal extraction makes use of local bacteria that are already present in the soils around the area of black shale.
A cultivated bacteria used to heap leach black shale. NOAA
This method of using the natural bacteria is completelygreen allowing the extraction of metals without soil contamination. Of using a solution of bacteria for extracting metals from black shale was developed in the mid-2,000s in Finland on another poly metallic black shale. The process is extremely inexpensive to operate and can be fine-tuned to extract different metals from the shale. The process itself is based upon heap leaching the shale after it has been ground up and piled in its better then sprinkled with the bacteria bearing solution. The pregnant bacteria solution is then pumped into a central point where the metal is extracted then the solution is recycled back into the heap leaching process.
Black shales are noted for their poly metallic mineraldeposits all over the world. One such black shale is the Marcellus shale found in the eastern United States that is now being exploited for its natural gas content. In the process of extracting the gas in the shale is Hydro Fracked so that after the gas is recovered a solution of the metal extraction bacteria could be pumped down the hole and allowed to extract any metals that are left in the shale.
Besides allowing the extraction of gold this process allows the recovery of virtually any other metal found associated with Black shales including rare earth elements. For just gold mining this process would obviate the use of cyanide or mercury for the extraction of gold. By fine tuning the process any number of other metals can be extracted. Since the source of the bacteria is from the same area as the mine is causing this to be a completely green process.
This is only of a number of other processes that can be adapted from existing metal remediation used in the environmental remediation practice. Once the proper bacteria are extracted from the environment and cultured there is no limit to the different types of metals that can be extracted using this process.