| Bioleaching of sulfide minerals using bacteria Thiobacillus
ferrooxidans has been identified as a promising method as it applies to
leaching of low grade mixed sulfide ore in a heap leaching or dump leaching
method. The mixed sulfide ore commonly contains sulfide minerals of iron,
copper and zinc. However, the problem with the bioleaching system is that
the rate is so low that it takes a long time (e.g., 1?2 years) to complete
the heap or dump leaching. Thus, the slow rate of the bioleaching reaction
renders limitations and restrictions for wider commercial utilization of
this biotechnology. The rate can be enhanced, however, by applying direct
current potentials to the bioleaching system. This proposal is based on
this electrobioleaching of sulfide minerals of pyrite (FeS2), chalcopyrite
(CuFeS2), and sphalerite (ZnS). The approaches are focused on the growth
of the bacteria under the influence of applied direct current potential.
The objectives of this project are to identify the optimum mode of application
for the bio? and the electro? leaching reactions and to optimize the conditions
of the mode. Also, the objective is to determine the technical and economical
feasibility of this technology as applied to a commercial process in which
low grade mixed sulfide ore is leached.
In an effort to search for the optimum mode of application, two approaches will be tested. In one approach, the apparatus will consist of an electrical cell and a bioleaching reactor. A solution will be circulated through the bioleaching reactor and the cathode compartment of the electrical cell. In this circulation, the catholyte containing mostly ferrous iron will then be fed to the bioleaching reactor. The idea of this setup is that the ferrous sulfate fed to the bioleaching reactor will grow the population of T. ferrooxidans which will catalyze the leaching of sulfide mineral. In another approach, an electrical cell having an anode compartment and a cathode compartment split with a diaphragm will be constructed and a potential will be applied. At the anode, a sample of sulfide mineral is leached in the presence of T. ferrooxidans; and at the cathode, ferric iron is reduced to ferrous iron like in the first approach. The anolyte and catholyte will be properly circulated to boost the bacteria growth.
In each approach, the concentration of dissolved metal values will be determined as a function of time under various parametric conditions including applied potential. The results of each approach will be analyzed as to which combination of parametric conditions yields the highest leaching rate of each sulfide mineral. Also, the results of both approaches will be compared to each other to decide which one is more beneficial as it applies to the leaching of low grade mixed sulfide ore in dump or heap leaching method.