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
The oxidation reaction of the sulphide minerals for gold liberation could be summarized as
- Reaction involved in the production of sulphuric acid in the Acidithiobacillus
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