Question

Give a detailed description of how bioleaching occurs for the mineral FeS2.

Answer 1

Bioleaching is the removal of metal from their ores by the use of living microbes. This method is commonly used in biohydrometallurgy.

Fes₂ is often called as iron pyrites

The element that is to be extracted here is the Iron and the following steps are usually followed for the extraction of iron.

1)Disulfide is spontaneously oxidized to thiosulfate by ferric ion (Fe³⁺), which in turn is reduced to give ferrous ion.

    ${\mathrm {FeS_{2}+6\ Fe^{{\,3+}}+3\ H_{2}O\longrightarrow 7\ Fe^{{\,2+}}+S_{2}O_{3}^{{\,2-}}+6\ H^{+}}}$

2) In the second step  ferrous ion is oxidized by bacteria using oxygen

${\mathrm {4\ Fe^{{\,2+}}+\ O_{2}+4\ H^{+}\longrightarrow 4\ Fe^{{\,3+}}+2\ H_{2}O}}$

3) Thiosulfate is also oxidized by bacteria to give sulfate:

   ${\mathrm {S_{2}O_{3}^{{\,2-}}+2\ O_{2}+H_{2}O\longrightarrow 2\ SO_{4}^{{\,2-}}+2\ H^{+}}}$

4) The ferric ion produced in reaction (2) oxidized more sulfide as in reaction (1), closing the cycle and given the net reaction:

${\mathrm {2\ FeS_{2}+7\ O_{2}+2\ H_{2}O\longrightarrow 2\ Fe^{{\,2+}}+4\ SO_{4}^{{\,2-}}+4\ H^{+}}}$

Thus the resulting iron is extracted from the iron pyrites.