Gold Liberation


The gold liberation in our project is an activity that is identified with the Acidithiobacillus ferroxidans. This process involves the bacterial oxidation of sulphide minerals; pyrite, arsenopyrite and pyrrhotite. Here the Acidithiobacillus ferroxidans employs a direct and indirect mechanism for the activity. The direct mechanism however involves the attachment of cells to the mineral releasing ferrous iron in the solution, resulting in the dissolution of the sulphide mineral. Oxidation of the ferrous iron to ferric is than by the bacteria in the solution. As a result of the presence of the ferric ion, the sulphide mineral is leached out through a chemical reaction. However, element sulphur produced in this reaction as a result of the indirect leaching can be converted to sulphuric acid by the Acidithiobacillus ferroxidans which helps maintain the pH of the media suitable for the growth of the bacteria and help in effective leaching of the oxide minerals.

Chemical Reactions Involved with the Process

  1. Reaction involved in the production of sulphuric acid in the Acidithiobacillus
    • 2S0 + 3O2+ 2H2O 2H2S04
  2. The oxidation reaction of the sulphide minerals for gold liberation could be summarized as
    • 4FeS2 + 15O2 + 2H2O 2Fe2 (SO4)3 + 2H2SO4
      2FeAsS + 7O2 + H2SO4 2H3AsO4 + Fe2 (SO4)3
      4FeS +9O2 + 2H2SO4 2Fe2 (SO4)3 + 2H2O

With a deep analysis of the gold liberation activity of the Acidithiobacillus, inferences were made to propose parts which would be instrumental in achieving a similar aim with the E.coli strain.
Three major parts designed to take on the gold liberation activity in Ecoli
  • High potential iron Sulphur protein (HiPiP)
  • pH resistance gene
  • Tetrathionate Hydrolase
  • Effective Role of Parts

    Figure 1. pH Resistance Gene This part served as a major component in our design to provide resistance to low pH levels that arise as a result of the gold liberation activity to enable the growth and metabolism of E.coli bacteria in the bio mining environment.

    High Potential Iron Sulphur Protein (HiPiP)This protein is a protein that is identified for its oxidation reactions and are effective in catalysing this reaction. With the gold liberation involving oxidation reactions, this part plays an important role in enhancing the E.coli bacteria gold liberation activity. This part fits in our design to undergo the oxidation reactions involved with the sulphide minerals.

    Tetrathionate Hydrolase This enzyme is one that plays an important role in the metabolism of the Acidithiobacillus ferroxidans by serving as an important intermediate in the dissimilatory of sulphur oxidation and in effect provides energy for the bacteria to undertake its activities. Hence in designing our parts for our E.coli activity we designed this part to suit the organism providing it with energy to undergo the gold liberation activity.