Electrochemistry of Thiobacillus ferrooxidans reactions with pyrite Page: 3 of 35
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EFFECT OF SILVER AND SOME OTHER HEAVY METALS
ON THE IRON OXIDIZING ABILITY OF
Gopal C. De and Batric M. Pesic
Department of Mining and Metallurgical Engineering
College of Mines and Earth Resources
University of Idaho
Moscow, Idaho 83843
The effect of silver and some other heavy metal ions on the iron
oxidizing ability of Thiobacillus ferrooxidans was studied using
electrochemical and some other physico-chemical techniques.
Electrochemical investigation was conducted using a method based on
redox potential change. Experiments were performed by adding an
aliquot of separately prepared concentrate of the bacteria into the
solution of ferrous ion and monitoring the redox potential for at
least one hour. Pyrite was used as the indicator electrode.
Parameters examined were pH, microbial cell density, ferrous and
ferric ion concentration, temperature, concentration of silver and
some other cations and anions, pre-conditioning period of the
bacteria with silver, etc.
Results obtained demonstrate that the reaction is pH dependent, the
optimum pH range being 1.5-2.0. The first order rate constant of
the reaction (standard value 0.06 m.in‘1) is largely influenced by
the substrate to cell concentration ratio and temperature. The
activation energy of this reaction has been observed to be 11.51
and 12.33 Kcal mole'1 in the absence and in the presence of 10 mg/L
silver, respectively. The presence of some heavy metal ions has
been observed to affect the rate of reaction, while the anions
studied (e.g. chloride and nitrate) have no effect on the reaction
being investigated. Mercuric and silver ions have been observed to
exert the most detrimental effects on the reaction rate. However,
the bacteria are found to maintain their ferrous iron oxidizing
ability in presence of a small concentration of silver depending on
pH. Under standard condition of pH 1.7, the bacteria can maintain
their iron oxidizing activity in a solution containing
approximately 0.7 mg/L of silver, whereas at pH 1.4, this limit
reduces to 0.25 mg/L of silver. Conditioning the bacteria with an
appreciable concentration of silver (e.g. 1 mg/L or over) has been
found to be adverse to the bacteria's iron oxidizing ability.
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Pesic, B. Electrochemistry of Thiobacillus ferrooxidans reactions with pyrite, report, January 1, 1992; United States. (digital.library.unt.edu/ark:/67531/metadc1093706/m1/3/: accessed January 22, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.