Bioleaching kinetics

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Bioleaching kinetics

• Lecture 5

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Biooxidation versus chemical oxidation

• The rate of bacterial oxidation is higher than
  that of chemical oxidation under the same
  conditions.

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Model of leaching kinetic

• The leaching of mineral particles by a reagent in
  solution can be represented by the reaction
• aA(s) bB(aq)? aqueous and solid products
• A the solid undergoing leaching
• B the reagent in solution
• a and b are stoichiometric coefficients

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Subprocesses in biooxidation

• Growth bacteria
• Ferrous to ferric oxidation Fe2 ?Fe3
• Disolved oxygen consumption O2?H2O
• Disolved carbon dioxide consumption CO2
• The rtes of oxygen and carbon dioxide
  utilization are measured by gas analyzers.

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Subprocess

• The bacterial oxidation of ferrous (Fe2) to
  ferric (Fe3) ions.
• The kinetic of bacterial growth was described by
  Monod equation
• ?max-maximum of specific growth rate 1/h
• KS Monods constant mol/L
• cS- substrate concentration mol/L

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Kinetic equations

• The rate of oxygen utilization is correlated to
  ferric to ferrous ratio
• The rate of ferrous iron utilization

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Kinetic parameters for Fe2 oxidation
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Logistic model

• The logistic equation is written for the rate of
  conversion of sulfide mineral X.
• where km rate constant.
• The fraction bioleached with time is given by
  integrating logistic equation.

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Kinetic of (bio-) leaching process

• The kinetic of leaching reaction are described
  by
• The shrinking core modeel
• The shrinking particle model

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Shrinking particle and core models
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Kinetic of bioleaching

• The rate of the heterogeneous reaction is
  controlled by
• 1. film diffusion
• 2. chemical reaction
• 3. product layer diffusion

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Shrinking core model
1-(2/3)a-(1-a)2/3kt a-is the fraction of
leached k-is the rate constant (1/day) t is time
(day)
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Shrinking particle and core models
1-(1-X)1/3 versus time
12(1-X)-3(1-X)2/3 versus time
where X is fractional conversion
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Bacteria oxidation

• According to the model proposed by
  Michaelis-Mentan the dissolution rate is given by
  following equation
• where V is the extraction rate of metal
• Vmax is the maximum metal extraction rate
• Ksis the Michaelis constant
• S is the pulp density
• Ks constant gives an idea aobout the efficiency
  of bacteria to the mineral surface.

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Plot of Michaelis-Menten for the copper and zinc
dissolution
Plot of 1/V versus 1/S for Cu and Zn The higher
rate KS for Cu then KS for Zn indicates a
preference of bacteria for copper.
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Indirect mechanism of bioleaching of galena
PbS(s) 2Fe3(aq)? Pb2(aq) S0(s) 2
Fe2(aq) Pb2(aq) SO42-(aq) ? PbSO4(s)
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Galena bioelaching
Effect of particle size on the
bioleaching of galena
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Microphotograph (magnification of 50x0 of a
partially oxidized galena particle

• unreacted galena
• b) lead sulfate/elemental sulfur product layer