2162 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
controlling parameter of collector speciation. Such regions
were presented in the form of the well-known tool for elec-
trochemical speciation which is the Pourbaix Diagram.
This successful correlation between floatability of minerals
(in this case base metal sulphides), speciation of collectors
and operational Eh and pH values presents an important
guideline or control philosophy for flotation chemistry that
goes beyond ensuring oxidizing conditions within the plant
but defines lower and upper regions of control.
The simplest form of pulp potential control within
operational plants has been through sufficient aeration of
flotation pulps which results in oxidation of species that
preferentially undergo reduction and subsequently bring
the redox potential down. Such species include the ferrous
ion that is typically generated through grinding media or
the oxidation of iron rich minerals such as pyrite and pyr-
rhotite. Pulp potential has also been controlled through
the use of oxidizing agents. At least hydrogen peroxide has
been reported to have been a successful oxidizing agent on a
lead-copper ore that had highly reducing conditions before
the float (Uribe-Salas et al., 2000). The drawback with oxi-
dizing agents however is the potential for over oxidation
that results in hydrophilic species such as hydroxides being
formed on the value mineral surface. The paper from
Uribe-Salas et al., (2000) demonstrates the need for a criti-
cal mass of reducing species to consume the oxidizing agent
and allow the pulp potential to rise to less reducing levels
without compromising the surface of the valuable mineral.
The work of Chimonyo et al., (2017) demonstrates that
addition of oxidizing agents needs to be controlled through
concentration in order to avoid over oxidation of the min-
eral surface.
A significant body of work has been published to
demonstrate the redox potential dependence of base metal
sulfides. The work of Lotter et al., (2016) provides useful
handles for determining a control philosophy for optimiz-
ing flotation chemistry. Another commodity important
to the mining industry and that appears on the critical
minerals list is the platinum group minerals (PGMs) from
which the platinum group elements (PGEs) are sourced.
Although these are not all semi-conductors as discussed
above, they conduct electrons and therefore the mechanism
of collector adsorption follows that of base metal sulfides.
This paper reviews the reactivity of PGMs with specifically
X X e 2
2^adsh aq ?+--
^h
Reaction (1)
X X e
aq ads "+--
^h
Reaction (2)
M MX 2 4H 8 8e X S O SO H
2 2^s 4^aq
2-
aqh lh "+++++-+-
^^S ^^aqh h h h Reaction (3)
e 2 4 2 O H O OH
2 2 aqh ?++--
^^lh ^aqh Reaction (4)
Figure 1. Direct electron injection model for the electrochemical reaction representing
collector oxidation and subsequent adsorption on the mineral surface to achieve
hydrophobicity. Schematic drawn after Xu and Schoonen, (2000)
controlling parameter of collector speciation. Such regions
were presented in the form of the well-known tool for elec-
trochemical speciation which is the Pourbaix Diagram.
This successful correlation between floatability of minerals
(in this case base metal sulphides), speciation of collectors
and operational Eh and pH values presents an important
guideline or control philosophy for flotation chemistry that
goes beyond ensuring oxidizing conditions within the plant
but defines lower and upper regions of control.
The simplest form of pulp potential control within
operational plants has been through sufficient aeration of
flotation pulps which results in oxidation of species that
preferentially undergo reduction and subsequently bring
the redox potential down. Such species include the ferrous
ion that is typically generated through grinding media or
the oxidation of iron rich minerals such as pyrite and pyr-
rhotite. Pulp potential has also been controlled through
the use of oxidizing agents. At least hydrogen peroxide has
been reported to have been a successful oxidizing agent on a
lead-copper ore that had highly reducing conditions before
the float (Uribe-Salas et al., 2000). The drawback with oxi-
dizing agents however is the potential for over oxidation
that results in hydrophilic species such as hydroxides being
formed on the value mineral surface. The paper from
Uribe-Salas et al., (2000) demonstrates the need for a criti-
cal mass of reducing species to consume the oxidizing agent
and allow the pulp potential to rise to less reducing levels
without compromising the surface of the valuable mineral.
The work of Chimonyo et al., (2017) demonstrates that
addition of oxidizing agents needs to be controlled through
concentration in order to avoid over oxidation of the min-
eral surface.
A significant body of work has been published to
demonstrate the redox potential dependence of base metal
sulfides. The work of Lotter et al., (2016) provides useful
handles for determining a control philosophy for optimiz-
ing flotation chemistry. Another commodity important
to the mining industry and that appears on the critical
minerals list is the platinum group minerals (PGMs) from
which the platinum group elements (PGEs) are sourced.
Although these are not all semi-conductors as discussed
above, they conduct electrons and therefore the mechanism
of collector adsorption follows that of base metal sulfides.
This paper reviews the reactivity of PGMs with specifically
X X e 2
2^adsh aq ?+--
^h
Reaction (1)
X X e
aq ads "+--
^h
Reaction (2)
M MX 2 4H 8 8e X S O SO H
2 2^s 4^aq
2-
aqh lh "+++++-+-
^^S ^^aqh h h h Reaction (3)
e 2 4 2 O H O OH
2 2 aqh ?++--
^^lh ^aqh Reaction (4)
Figure 1. Direct electron injection model for the electrochemical reaction representing
collector oxidation and subsequent adsorption on the mineral surface to achieve
hydrophobicity. Schematic drawn after Xu and Schoonen, (2000)