Investigation of gold sorption by bacteria

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Publication Type thesis
School or College College of Mines & Earth Sciences
Department Metallurgical Engineering
Author Shitole, Shamita Anil
Title Investigation of gold sorption by bacteria
Date 2009-09-25
Description Gold cyanidation, also called the MacArthur-Forrest process, is the common metallurgical process used for gold extraction. Cyanide is the main lixiviant used for dissolving gold. Cyanide is commercially used for gold extraction because of its effectiveness in extraction. However, cyanide is extremely toxic. Several bacteria like Thiobacillus ferroxidans (Acidithiobacillus and thiobacillus ferrooxidans refer to the same microorganism); Thiobacillus thiooxidans are known for their ability to increase cyanide access to sulfide-trapped gold through sulfide mineral oxidation. Bacteria such as Bacillus subtilis and Bacillus megaterium and few others are capable of absorbing and possibly extracting gold, thereby offering the possibility of environmentally friendly extraction and recovery of gold. Microbiology processes contribute to the mineral wealth of the earth. Microbes excrete enzymes and utilize substrates from the environment for their metabolism. Bacteria have shown an amazing adaptability to scavenge electrons from any available source in the environment for cellular growth and maintenance. Initially six strains of bacteria were studied for their ability to load gold from standard solutions. Bacterial gold loading stability was assessed by washing gold-loaded bacteria in saline and mild detergent solution. Control tests with no bacteria confirmed the general testing procedures and that equipment such as plastic test tubes had no effect on gold concentration. Gold loading by activated carbon was greater than 99% in saline solution. In contrast, gold loading by carbon in Tripticase Soy Broth (growth medium for some bacteria) was only 10-15%, suggesting that TSB inhibits gold loading. The strains of bacteria evaluated include Bacillus subtilis, Pseudomonas stutzeri, Pseudomonas alcaligenes, Pseudomonas putida, Shewanella denitrificans, Pseudomonas pseudoalcaligenes, Thiobacillus ferrooxidans and Bacillus megaterium. The Shewanella denitrificans and Bacillus subtilis strains generally performed best. The initial gold • • 8 loading experiments performed show that 1.5 grams of bacteria per liter ( 5 x 1 0 cells/ml) loaded nearly as much gold as 10 grams of activated carbon per liter, though the activated carbon was not fully saturated with gold. Bacteria are less expensive to produce than activated carbon. Thus, bacteria may be a viable alternative to activated carbon for gold sorption. Results show excellent gold loading by bacteria, and washing tests indicate that the bacterially sorbed gold is relatively stable. Additional testing was done to repeat successful gold loading using effective bacteria {Shewanella denitrificans and Bacillus subtilis). Mixed cultures were also evaluated in the presence of ore samples provided by an industrial source using bottle roll tests. Experiments with pregnant leach solution from the mine site showed that bacteria do not selectively sorb gold when it is present along with other metals and ions, whereas activated carbon is able to absorb 98% of the gold from the pregnant leach solution. Some gold foil experiments were performed to test gold solubilization by bacteria with/without cyanide.
Type Text
Publisher University of Utah
Subject Bacterial leaching
Dissertation Institution University of Utah
Dissertation Name MS
Language eng
Relation is Version of Digital reproduction of “Investigation of gold sorption by bacteria” J. Willard Marriott Library Special Collections TN7.5 2010 .S45
Rights Management © Shamita Anil Shitole, To comply with copyright, the file for this work may be restricted to The University of Utah campus libraries pending author permission
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Identifier us-etd2,165663
Source Original: University of Utah J. Willard Marriott Library Special Collections
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