2392 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Zeta Potential
Figure 3 revealed that zeta potential for serpentine was posi-
tive while that of pentlandite exhibited negative charge at
pH 10.1. Studies have also shown that serpentine maintains
a positive zeta potential over a wide pH range without or
little treatment (Alvarez-Silva et al. 2016). Brucite showed
a slightly positive charge while silica samples exhibited the
most negative charge at the same pH 10.1. In the aqueous
solution, the hydroxyl group of the brucite plane dissolves
easily and leaves behind magnesium cations on the surface
of serpentine, thereby creating a positive charge and deter-
mining the serpentine’s surface charge (Bo et al. 2013). Due
to the opposite charges, there is a heterogeneous agglom-
eration between pentlandite and serpentine meaning that
serpentine will slime coat pentlandite particles through its
brucite plane resulting in negative total interaction energy
for brucite with pentlandite i.e., attractive force or electro-
static attraction (Alvarez-Silva et al. 2016).
Upon introduction of STPP, the zeta potential of
serpentine decreased to about 1 mV at 5 mg/L of STPP
(Figure 4). Further increase in STPP’s concentration
resulted to a charge reversal of serpentine from a positive
zeta potential to a negative zeta potential of –21 mV at
10 mg/L which clearly continued to change until above a
concentration of 50 mg/L at which no significant difference
in the zeta potential was further observed. At 50 mg/L,
the zeta potential attained an optimum value of –54 mV
and even when the STPP concentration was doubled to
100 mg/L, only a minor difference of –2 mV was observed.
At this optimum concentration (50 mg/L) of STPP for
serpentine’s charge reversal, zeta potential of brucite also
reversed from a slightly positive potential of 8 mV to highly
negative potential of –51 mV (Figure 5). The zeta poten-
tial magnitude of pentlandite changed from –18 mV to
–53 mV, while that of silica remains unaffected at –77 mV
(Figure 5). STPP was able to complex Mg2+ on the surface
of serpentine through its phosphate groups (Equation 1),
forming a P-O-Mg bond and enhancing the positive charge
reversal on serpentine’s surface (Li et al. 2022).
3Mg 2PO Mg PO
2 4
3-
4
2
3 "++^h (1)
By reversing the charge of serpentine from a positive to a
negative zeta potential, STPP should suppress serpentine
and prevent slime coating of pentlandite in flotation tests.
The charge reversal is an indication that the attractive inter-
action or heterogeneous agglomeration between serpentine
and pentlandite samples are reversed or prevented. This
-80
-60
-40
-20
0
20
40
Serpentine Pentlandite Brucite Silica
Mineral
Figure 3. Zeta potential measurements of mineral suspensions serpentine, pentlandite,
brucite and silica
Zeta
potential
(mV)
Zeta Potential
Figure 3 revealed that zeta potential for serpentine was posi-
tive while that of pentlandite exhibited negative charge at
pH 10.1. Studies have also shown that serpentine maintains
a positive zeta potential over a wide pH range without or
little treatment (Alvarez-Silva et al. 2016). Brucite showed
a slightly positive charge while silica samples exhibited the
most negative charge at the same pH 10.1. In the aqueous
solution, the hydroxyl group of the brucite plane dissolves
easily and leaves behind magnesium cations on the surface
of serpentine, thereby creating a positive charge and deter-
mining the serpentine’s surface charge (Bo et al. 2013). Due
to the opposite charges, there is a heterogeneous agglom-
eration between pentlandite and serpentine meaning that
serpentine will slime coat pentlandite particles through its
brucite plane resulting in negative total interaction energy
for brucite with pentlandite i.e., attractive force or electro-
static attraction (Alvarez-Silva et al. 2016).
Upon introduction of STPP, the zeta potential of
serpentine decreased to about 1 mV at 5 mg/L of STPP
(Figure 4). Further increase in STPP’s concentration
resulted to a charge reversal of serpentine from a positive
zeta potential to a negative zeta potential of –21 mV at
10 mg/L which clearly continued to change until above a
concentration of 50 mg/L at which no significant difference
in the zeta potential was further observed. At 50 mg/L,
the zeta potential attained an optimum value of –54 mV
and even when the STPP concentration was doubled to
100 mg/L, only a minor difference of –2 mV was observed.
At this optimum concentration (50 mg/L) of STPP for
serpentine’s charge reversal, zeta potential of brucite also
reversed from a slightly positive potential of 8 mV to highly
negative potential of –51 mV (Figure 5). The zeta poten-
tial magnitude of pentlandite changed from –18 mV to
–53 mV, while that of silica remains unaffected at –77 mV
(Figure 5). STPP was able to complex Mg2+ on the surface
of serpentine through its phosphate groups (Equation 1),
forming a P-O-Mg bond and enhancing the positive charge
reversal on serpentine’s surface (Li et al. 2022).
3Mg 2PO Mg PO
2 4
3-
4
2
3 "++^h (1)
By reversing the charge of serpentine from a positive to a
negative zeta potential, STPP should suppress serpentine
and prevent slime coating of pentlandite in flotation tests.
The charge reversal is an indication that the attractive inter-
action or heterogeneous agglomeration between serpentine
and pentlandite samples are reversed or prevented. This
-80
-60
-40
-20
0
20
40
Serpentine Pentlandite Brucite Silica
Mineral
Figure 3. Zeta potential measurements of mineral suspensions serpentine, pentlandite,
brucite and silica
Zeta
potential
(mV)