1630 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
The absorption of light is caused by the excitation of
an electron from an occupied band to an unoccupied band.
In a leaching experiment, this means that an electron is
removed from a boning orbital, and if it is close to the sur-
face will result in dissolution because a bond at the surface
has been broken. Crundwell (1988a) dissolved a sample
of sphalerite with a low-iron content in the presence and
absence of UV-radiation. The results, which are shown in
Figure 5(b), demonstrate the acceleration of the leaching
kinetics by UV light, supporting the semiconductor model.
Pyrite
The band structure of pyrite is shown in Figure 6. A feature
of this is that the upper valence band, which is derived from
Fe 2tg orbitals, is of non-bonding characteristics. The sig-
nificance of this is that removal of electrons from this part
of the valence band will not result in bond-breaking, and
hence the kinetics of dissolution are inhibited. Therefore,
pyrite is not passivated, its rate of dissolution is intrinsically
slow because of its electronic structure.
Bryson and Crundwell (2014) studied the anodic dis-
solution of pyrite and concluded that surface states partici-
pated in the mechanism. Surface states are electronic energy
levels at the surface that exist between the valence and con-
duction bands and facilitate electron transfer between these
bands. In the case of dissolution, they facilitate the trans-
fer of electrons from the valence band to the oxidant in
solution. The detailed modelled provided by Bryson and
Crundwell (2014) describes both the current-voltage and
ac-impedance characteristics of pyrite.
An important result of the work of Bryson and
Crundwell (2014) is that the conduction type of the semi-
conductor (n- or p-type) does not affect the results in the
Figure 5. (a) Effect of iron on rate of dissolution with mechanism below. (b) Effect of UV radiation on the rate of dissolution,
with mechanism below
The absorption of light is caused by the excitation of
an electron from an occupied band to an unoccupied band.
In a leaching experiment, this means that an electron is
removed from a boning orbital, and if it is close to the sur-
face will result in dissolution because a bond at the surface
has been broken. Crundwell (1988a) dissolved a sample
of sphalerite with a low-iron content in the presence and
absence of UV-radiation. The results, which are shown in
Figure 5(b), demonstrate the acceleration of the leaching
kinetics by UV light, supporting the semiconductor model.
Pyrite
The band structure of pyrite is shown in Figure 6. A feature
of this is that the upper valence band, which is derived from
Fe 2tg orbitals, is of non-bonding characteristics. The sig-
nificance of this is that removal of electrons from this part
of the valence band will not result in bond-breaking, and
hence the kinetics of dissolution are inhibited. Therefore,
pyrite is not passivated, its rate of dissolution is intrinsically
slow because of its electronic structure.
Bryson and Crundwell (2014) studied the anodic dis-
solution of pyrite and concluded that surface states partici-
pated in the mechanism. Surface states are electronic energy
levels at the surface that exist between the valence and con-
duction bands and facilitate electron transfer between these
bands. In the case of dissolution, they facilitate the trans-
fer of electrons from the valence band to the oxidant in
solution. The detailed modelled provided by Bryson and
Crundwell (2014) describes both the current-voltage and
ac-impedance characteristics of pyrite.
An important result of the work of Bryson and
Crundwell (2014) is that the conduction type of the semi-
conductor (n- or p-type) does not affect the results in the
Figure 5. (a) Effect of iron on rate of dissolution with mechanism below. (b) Effect of UV radiation on the rate of dissolution,
with mechanism below