XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2925
The Cleaner feed responded well to preconditioning, an average 4E recovery improvement of 5.8% being
attained over the baseline at 10 passes, and a 14 minute residence time. Despite the higher feed grades for the
cleaner tests with the Mach Reactor – an average of around 7.5 g/t vs the 6.9 g/t of the baseline – the upgrade
ratios were improved throughout due to the reduced mass pulls. The baseline figure of 2.2 was improved to 2.8
after 10 passes, and 2.9 and 2.8 after 20 and 30 passes respectively. Finally, preconditioning in the Mach man-
aged to lift the recovery-mass pull relationships for the Final Tailings feed when compared to the baseline. At
the 14 minute reference, a 4E recovery improvement of 6.0% and 9.5% respectively was achieved after 10 and
15 passes, accompanied by increased grades due to the reduced mass pulls. The 3.1 upgrade ratio of the baseline
increased to 3.5 after 10 passes.
The reason for the peak in kinetics with successive passes of the flotation feed through the Mach Reactor is still
a matter of further research investigation, but based on current understanding can most likely be ascribed to
the generation of slimes that passivate the valuable mineral surfaces, or excessive temperatures that impact on
reagent activity. This appears to be a function of several variables, including the type of ore and grade of the
particular feed (e.g., rougher, cleaner or tailings).
INTRODUCTION
The challenge for concentrator plants treating ore from the
Great Dyke orebody is the recovery of fine PGMs below
20 microns in size. This has been confirmed by the opera-
tions through mineralogical investigations of the plant tails.
Tests were carried out on the Mach Reactor cavitation tech-
nology on a testrig based on site in Zimbabwe to explore
potential benefits to recovery, grade and mass pull.
The Great Dyke mineralogy consists of silicate gangue
with pyroxene being dominant, and lesser amounts of
plagioclase, chlorite, tremolite and talc. About 50% of
platinum group elements (PGEs) are associated with base
metal sulphides (BMS), pyrrhotite being the major min-
eral followed by chalcopyrite, pentlandite and pyrite. The
remainder of the PGEs are associated with fine grained
bismuthotellurides and arsenides, which poses challenges
to recovery by flotation. Based on the considerable success
achieved in earlier work on improving the flotation perfor-
mance of PGMs by the application of the Mach Reactor on
feed streams (Singh 2016, Ross et al., 2019), a decision was
made to conduct a test programme at the SMC plant labo-
ratories on a mobile test rig to establish the likely impact
of this technology on the metallurgical performance. The
hydrodynamic cavitation within the venturis of the Mach
Reactor causes the nucleation of NBs on particle surfaces,
this being favoured on hydrophobic and rough particle
surfaces which could also have minute quantities of gas
trapped in crevices on the surface as they exit a milling cir-
cuit. These NBs on the particles are characterised by a high
stability and rapid attachment to hydrophobic surfaces
(Etchepare et al., 2017). Due to these properties, the NBs
thus also tend to function as a ‘secondary collector’ (Huang
et al., 2016) which can be stabilised by the addition of
frother to the slurry and can also lead to reduced consump-
tion of reagents (Sobhy and Tao, 2013). These NBs on their
own however cannot provide sufficient buoyancy to float
mineral particles and hence the presence of macro-bubbles
(MBs), typically in the range of 800 um to 2 mm, is still
required. It is therefore suggested that the NBs and MBs be
introduced into flotation cells to complement, rather than
replace, flotation size bubbles (Tao 2005 Tao et al., 2006).
Since ageing of the NBs as well as macro bubbles is detri-
mental to particle-bubble attachment, optimum flotation
conditions are obtained under conditions in which the two
are co-generated (Huang et al., 2016).
The mechanism of particle collection is understood to
involve the nucleation of NBs on the surfaces of fine and
ultrafine hydrophobic particles, where intensive mixing of
the slurry leads to the formation of aggregates of hydro-
phobic fines, as well as the fines binding with fast-floating
coarser particles, through a bubble bridging mechanism
(Tao et al., 2006 Singh, 2016). The final step in the so-called
Nucleation – Attachment – Levitation (NAL) sequence is
the presentation of an effectively larger and more homo-
geneously hydrophobic particle to an MB, resulting in an
increased collision and attachment efficiency, after which
the aggregate is levitated to the surface of the pulp and
transferred into the concentrate via the froth.
In addition to the NAL sequence of fine particle col-
lection, which is currently understood to predominantly
increase the kinetics of flotation of especially fine particles,
The Cleaner feed responded well to preconditioning, an average 4E recovery improvement of 5.8% being
attained over the baseline at 10 passes, and a 14 minute residence time. Despite the higher feed grades for the
cleaner tests with the Mach Reactor – an average of around 7.5 g/t vs the 6.9 g/t of the baseline – the upgrade
ratios were improved throughout due to the reduced mass pulls. The baseline figure of 2.2 was improved to 2.8
after 10 passes, and 2.9 and 2.8 after 20 and 30 passes respectively. Finally, preconditioning in the Mach man-
aged to lift the recovery-mass pull relationships for the Final Tailings feed when compared to the baseline. At
the 14 minute reference, a 4E recovery improvement of 6.0% and 9.5% respectively was achieved after 10 and
15 passes, accompanied by increased grades due to the reduced mass pulls. The 3.1 upgrade ratio of the baseline
increased to 3.5 after 10 passes.
The reason for the peak in kinetics with successive passes of the flotation feed through the Mach Reactor is still
a matter of further research investigation, but based on current understanding can most likely be ascribed to
the generation of slimes that passivate the valuable mineral surfaces, or excessive temperatures that impact on
reagent activity. This appears to be a function of several variables, including the type of ore and grade of the
particular feed (e.g., rougher, cleaner or tailings).
INTRODUCTION
The challenge for concentrator plants treating ore from the
Great Dyke orebody is the recovery of fine PGMs below
20 microns in size. This has been confirmed by the opera-
tions through mineralogical investigations of the plant tails.
Tests were carried out on the Mach Reactor cavitation tech-
nology on a testrig based on site in Zimbabwe to explore
potential benefits to recovery, grade and mass pull.
The Great Dyke mineralogy consists of silicate gangue
with pyroxene being dominant, and lesser amounts of
plagioclase, chlorite, tremolite and talc. About 50% of
platinum group elements (PGEs) are associated with base
metal sulphides (BMS), pyrrhotite being the major min-
eral followed by chalcopyrite, pentlandite and pyrite. The
remainder of the PGEs are associated with fine grained
bismuthotellurides and arsenides, which poses challenges
to recovery by flotation. Based on the considerable success
achieved in earlier work on improving the flotation perfor-
mance of PGMs by the application of the Mach Reactor on
feed streams (Singh 2016, Ross et al., 2019), a decision was
made to conduct a test programme at the SMC plant labo-
ratories on a mobile test rig to establish the likely impact
of this technology on the metallurgical performance. The
hydrodynamic cavitation within the venturis of the Mach
Reactor causes the nucleation of NBs on particle surfaces,
this being favoured on hydrophobic and rough particle
surfaces which could also have minute quantities of gas
trapped in crevices on the surface as they exit a milling cir-
cuit. These NBs on the particles are characterised by a high
stability and rapid attachment to hydrophobic surfaces
(Etchepare et al., 2017). Due to these properties, the NBs
thus also tend to function as a ‘secondary collector’ (Huang
et al., 2016) which can be stabilised by the addition of
frother to the slurry and can also lead to reduced consump-
tion of reagents (Sobhy and Tao, 2013). These NBs on their
own however cannot provide sufficient buoyancy to float
mineral particles and hence the presence of macro-bubbles
(MBs), typically in the range of 800 um to 2 mm, is still
required. It is therefore suggested that the NBs and MBs be
introduced into flotation cells to complement, rather than
replace, flotation size bubbles (Tao 2005 Tao et al., 2006).
Since ageing of the NBs as well as macro bubbles is detri-
mental to particle-bubble attachment, optimum flotation
conditions are obtained under conditions in which the two
are co-generated (Huang et al., 2016).
The mechanism of particle collection is understood to
involve the nucleation of NBs on the surfaces of fine and
ultrafine hydrophobic particles, where intensive mixing of
the slurry leads to the formation of aggregates of hydro-
phobic fines, as well as the fines binding with fast-floating
coarser particles, through a bubble bridging mechanism
(Tao et al., 2006 Singh, 2016). The final step in the so-called
Nucleation – Attachment – Levitation (NAL) sequence is
the presentation of an effectively larger and more homo-
geneously hydrophobic particle to an MB, resulting in an
increased collision and attachment efficiency, after which
the aggregate is levitated to the surface of the pulp and
transferred into the concentrate via the froth.
In addition to the NAL sequence of fine particle col-
lection, which is currently understood to predominantly
increase the kinetics of flotation of especially fine particles,