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147
World of Mining – Surface & Underground 72 (2020) No. 3 Mineral Processing
Overcoming breakage-inefficiency
by high-velocity impact comminution –
the VeRo Liberator® technology
GREGOR BORG, FELIX SCHARFE, CHRISTOF LEMPP, ANDREAS KAMRADT, Germany
Prof. Dr. GREGOR BORG,1,2
Felix SCHARFE, 1
Prof. (em.) Dr. CHRISTOF LEMPP,3
Dr. ANDREAS KAMRADT,2
1PMS, Abteistraße 1, Hamburg, Germany
2Economic Geology and Petrology Research Unit, Martin Luther
University Halle-Wittenberg, Germany
3Rock Mechanics and Engineering Geology Unit, Martin Luther
University Halle-Wittenberg, Germany
gregor.borg@geo.uni-halle.de
Mining and mineral processing industry are under pressure from
political and social stakeholders to deliver products more sus-
tainably with a much smaller environmental impact. Technical
innovations to achieve these goals include reduction in energy
consumption, waterless mineral processing, coarse particle
liberation, and safe dry stacking of tailings. Traditional, largely
abrasional comminution in robust ball and SAG mills is known for
its inefficiency with respect to breakage and energy consumption.
Earlier theoretical predictions and numerical modelling postulated
that more efficient impact breakage should occur at higher impact
energies from higher operational velocities. The VeRo Liberator
impact crusher operates in such a mechanical high-velocity
regime and achieves very high particle size reduction ratios and
degrees of particle liberation at very low energy consumption and
without using process water. These step-changing comminution
results are achieved from high frequency, high-velocity impacts
with an efficient momentum transfer that leads to the effective
disintegration of the feed material. The empirically tested results
have been experimentally simulated and confirmed in static and
dynamic uniaxial load tests and high-velocity impact gas cannon
tests. The VeRo Liberator technology has currently achieved TRL
7 and several units operate currently at mining operations and test
facilities in South Africa.
Keywords:
Impact comminution – Reduction ratio – Particle liberation –
Reduced energy consumption – High-velocity breakage
Effizienzsteigerung durch mechanische Hochgeschwindigkeitszerkleinerung
mittels VeRo Liberator® Technologie
1 Introduction – Setting the scene
Over the last decade, it has become increasingly obvious that
the future development of a growing global population must be
achieved in a sustainable manner to protect our global environ-
ment, climate, and overall well-being of our societies. These so-
cieties demand a growing supply of energy from renewable rather
than fossil sources and raw materials from recycling and primary
mineral resources. The renewable energy production from wind-,
water- and solar-power and the e-mobility by hybrid, full-electrical
and fuel-cell vehicles are the two most noticeable fields of technical
conversions that are already well underway and will continue to
develop and grow further, probably at even increasing rates. It is,
Die Bergbauindustrie steht unter großem Druck ihre Gewin-
nungs- und Aufbereitungsprozesse zu optimieren, um ökono-
misch, politisch und gesellschaftlich geforderte Einsparungen
und Nachhaltigskeitsziele zu erreichen und die verursachten
Umweltbelastungen substantiell zu reduzieren. Die Ziele sollen
durch Maßnahmen erreicht werden, die verschiedene Themen-
felder wie einen verringerten Energieverbrauch, wasserfreie
Mineralaufbereitung, Grobkornfreilegung sowie die effektive
Entwässerung von Absetzteichen und -dämmen umfassen. Die
bisher eingesetzte, äußerst robuste Kugelmühlentechnik inklusive
ihrer Weiterentwicklungen zerkleinert weitgehend mittels Abrasion
und nur untergeordnet durch substantielle Bruchbildung. Sie
zeichnet sich aber auch durch einen sehr ineffektiven Energie-
einsatz und hohen -verbrauch aus. Frühe theoretische Modelle
haben bereits um die Mitte des letzten Jahrhunderts postuliert,
dass sich die Effizienz der Zerkleinerung durch die Steigerung
der eingesetzten Impaktenergie deutlich verbessern könnte.
Der VeRo Liberator arbeitet und zerkleinert in genau diesem
mechanischen Hochgeschwindigkeitsregime und erreicht damit
sehr hohe Zerkleinerungsfaktoren sowie Freilegungsgrade und
dies zugleich bei drastisch geringerem Energieverbrauch und
völlig ohne Prozesswasser. Dieser grundlegende Wandel der
mechanischen Zerkleinerung basiert auf hoch-frequenten Hoch-
geschwindigkeitsimpakten bei denen eine effiziente Übertragung
der kinetischen Impakt-Energie in das zu zerkleinernde Material
stattfindet, was zur Zerbrechung und expandierenden Zerlegung
der Partikel entlang von Mineralgrenzen von innen heraus führt.
Unsere zunächst empirischen Zerkleinerungsergebnisse wurden
in ersten statischen wie auch dynamischen einaxialen Druckver-
suchen simuliert, die das Wirkprinzip bestätigt haben. Die mittels
Hochgeschwindigkeitsimpakten herbeigeführte Desintegration
von Erzbrocken konnte zudem experimentell in Videos dokumen-
tiert und illustriert werden. Die Produktreife des VeRo Liberator
entspricht derzeit dem „TRL 7-Niveau“ und mehrere Maschinen
sind derzeit in Bergwerksbetrieben und regionalen Testlabors in
Südafrika im Einsatz.
Schlüsselwörter:
Impakt-Zerkleinerung – Zerkleinerungsfaktor – Partikelfreilegung –
Energieeinsparung – Hochgeschwindigkeitsbruchbildung
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World of Mining – Surface & Underground 72 (2020) No. 3
Mineral Processing
however, far less perceived by political decision-makers and even
less by the wider public that these new technologies are far more
raw material intensive, especially in strategic and specialty metals,
than the conventional energy and mobility technologies up to now.
Hybrid vehicles require more than three times and full electrical
vehicles even four times more copper compared to vehicles with
combustion engines (Figure 1a).
The production of electrical energy by wind and solar power is
also far more copper intensive with wind energy requiring almost
twice and solar energy using more than five times the amount of
copper used in thermal energy production (Figure 1b). Copper is
not the only metal in increasingly high demand and battery met-
als (Li, Co, Ni), rare earth elements such as neodymium in high-
strength magnets of wind turbines, and platinum and palladium
for catalysts in fuel cells are all needed in far greater quantities
than ever before. The demand for and supply of copper for the
beginning technological conversions described above has already
increased drastically since 2010 as seen in the marked steepening
of the copper production curve of Figure 2.
The resulting additional demands cannot be met by charming
but insufficient concepts of a “circular economy” and “100 %
recycling”, which neglect the factual situation that recycling can
only contribute far smaller quantities that have entered the life
cycle of each metal at the beginning of its use, many years ago.
These quantities are totally insufficient to supply the present and
future demands as illustrated in Figure 2 for copper metal [2].
The average period of use for copper is approximately 30 years,
being longer in buildings and shorter in vehicles or electrical
equipment. Even when assuming a complete capture of all avail-
able copper, this mass is the copper produced and used some
30 years ago (Figure 2). The copper production and demand in
2010 (15 million tonnes), for example, was more than 8 million
tonnes higher than the recyclable quantity from 30 years before
(7 million tonnes) with the 8 million tonnes gap filled by mining of
primary ores. Assuming a realistically projected copper demand
of 32 million tonnes in 2025, the supply gap from recycling would
widen to 22.5 million tonnes (Figure 2). This supply gap needs
to be filled by the mining industry from existing and new copper
mines since there is no alternative to the mining of primary ores
to supplement the constantly widening supply gap. The mining
industry, which might be perceived as expendable in some poorly
informed public discussions, is under enormous pressure not only
to produce the mineral and metal commodities required by our
industry. The mining industry is also under pressure to achieve
public acceptance and its “social license to operate” through its
communication with local stakeholders. To achieve this license, it
is necessary to improve the efficiency of mining and subsequent
mineral processing and to minimise the environmental impact
along all steps of the mineral processing value chain. The two
most pressing demands for game-changing improvements in
mineral processing are the reduction of the carbon footprint by
significantly less energy consumption and the reduction or even
avoidance of the use of process water.
The unfavourably high level of energy consumption in conventional
comminution, i.e. crushing and milling, of mining and mineral pro-
cessing operations as well as in recycling of metallurgical slags
and waste incinerator slags is well known [3]. Cost and carbon
footprint reduction by improved efficiency are therefore ubiqui-
tous tasks for the extractive minerals industry. Consequently, all
Fig. 1:
Increased consumption of copper
metal [1]: (a) for hybrid and full
electric vehicles, compared to
vehicles with combustion engines;
(b) in renewable power generation,
compared to thermal, non-renew-
able energy sources
Fig. 2: Annual copper production/consumption from 1900 to 2018
[2] and linear forward projection. The steep rise since 2010
reflects partly the increased demands for renewable energy
production and e-mobility. Recycling can only contribute
the amount of copper produced some 30 years ago, which
leaves a significant gap to be filled by additional mining and
processing of primary copper ores.
b)
a)
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World of Mining – Surface & Underground 72 (2020) No. 3 Mineral Processing
stages of mining, mineral processing, and metallurgy need to be
reviewed carefully to identify substantial and suitable technical
innovations [4]. The efficiency improvement in the comminution of
ores has been on the international agenda of the mining industry
for some time but substantial advances are still relatively scarce.
It is generally agreed upon that major goals include a substantially
reduced energy consumption, systems that operate dry, markedly
enhanced particle size reduction, and improved particle libera-
tion. Ideally, comminution of competent materials must achieve
a sufficient particle size reduction and liberation of commodity
minerals, while consuming as little energy as possible to achieve
these goals. For a long time, energy consumption has not been
the biggest concern of the mineral industry and this has led to
the wide-spread use of ball mills and SAG mills, which can be
up-scaled relatively easily and are robust machines. However,
ball mills and SAG mills use excessive amounts of energy and are
inefficient regarding breakage [5, 6] (Figure 3a, 3b).
2 Earlier theoretical predictions for
high-velocity breakage
Detailed studies show that a major portion of the impact energy
at low velocity goes into abrasion and not into substantial particle
breakage [7] (Figure 4). It was therefore necessary, to develop and
apply a comminution technique that devotes most of the kinetic
impact energy to substantial impact breakage. Theoretical at-
tempts and predictions have been made to define physical and
specifically kinematic conditions (Figure 4), under which breakage
would be more efficient [5, 7, 8].
When taking this understanding into account, numerical model-
ling, in combination with animated visualisation allowed to predict
and show that improved breakage should occur at significantly
higher impact velocities (Figure 5) [8]. The still images from Paul
Fig. 3:
Depictions of breakage inef-
ficiency in conventional com-
minution systems: (a) number of
hits on ore particles that lead to
breakage in drop-weight tests
reflecting conventional ball mill
breakage. Breakage improves
with increased impact energy [5];
(b) the percentage of total energy
that causes breakage in conven-
Fig. 4:
Specific energy distributions per
particle size class versus number
of cumulative impacts in numeri-
cal models for SAG milling (after:
[7], modified by and courtesy of
Malcolm Powell). Higher specific
impact energy results in impact
breakage, which occurs relatively
rarely in conventional mill systems.
b)
a)
tional comminution is only an inefficient 1 %. The other part of the energy is lost as heat and electromechanical resistance [6].
b)
a)
Fig. 5: Numerical modelling illustration (by courtesy of Paul Cleary,
CSIRO): (a) of a high-velocity impact of a round (ore) particle
onto a solid tool (white bar at bottom) at the moment of con-
tact. Blue: no/least damage, red: maximum of damage/break-
age; (b) of the same round particle as in Figure 5a, showing
strong breakage and disintegration due to the high-velocity
impact.
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World of Mining – Surface & Underground 72 (2020) No. 3
Mineral Processing
Cleary’s (the provision of these videos and images is gratefully
acknowledged) numerical impact experiments show that at a
relatively high-velocity of 75 m/sec, the spherical particle is initially
impacted onto a solid tool with limited compressional abrasion at
the point of impact (Figure 5a). However, the transfer of impact
energy from the tool into the round particle leads to the break-
age from the inside to the outside of the particle with substantial
disintegration (Figure 5b). The VeRo Liberator achieves this kind
of efficient high-velocity impact breakage, as will be shown in the
following paragraphs.
3 Technical description of the
VeRo Liberator technique
The VeRo Liberator technique was invented in 2012 by PMS
GmbH, Germany (Figure 6a), and market entry was achieved in
late 2016 [9]. As the first global player in the mining world, Anglo
American plc, ordered four bespoke VeRo Liberator units so far,
all specially designed to be used in long-term industrial-scale pilot
tests at their operations. The integration of the VeRo Liberator is
part of the Anglo American FutureSmart MiningTM programme,
which aims to increase the efficiency in each step of the mineral
resource value chain. The technique has now achieved the Tech-
nical Readiness Level TRL 7 with wo machines in operation for
over two years in South Africa (Figure 6b), a third unit awaiting
shipment and the fourth machine currently being manufactured.
Anglo American and PMS are cooperating closely to bring the
VeRo Liberator technology to the next TRL.
The VeRo Liberator (Figure 6a, b) currently operates in the 100
to 130 t/h class, but up-scaling and down-scaling is currently
under way. Maximum feed size for the current VeRo Liberator
model is approximately 120 mm in diameter. Depending on the
input material from mining, this could be material from a primary
crusher or could even replace the primary crusher itself plus sub-
sequent crushing and milling stages. The comminution unit sensu
stricto has a relatively small physical footprint of 2.5 × 2.5 m only
(Figure 6a) and has been built in a modular fashion and is easy to
transport, assemble, modify or service according to customer’s
demands (Figure 6b). The relatively small unit size also allows
for semi-mobile use for in-pit crushing and conveying (IPCC)
operations. The main feature is a vertical, four-fold axle-in-axle
system. This axle-in-axle system can carry up to 144 hammer
tools that can be varied in size, weight, and steel composition.
These hammer tools are mounted individually on three separate
levels, which rotate clockwise and anticlockwise against each
other at high speeds, causing very high-velocity impacts due to
the counter-rotation. The material falls gravitationally through the
cylindrical armoured comminution chamber, where it is impacted
by the hammer tools and impacts onto the armoured housing with
specially designed and engineered inner liners, and with other
particles. The vertical, gravitationally driven material flow, without
lifting of material or machine parts, is one of the main reasons for
the low energy consumption of the VeRo Liberator compared to
conventional mills with horizontally rotating axles. It is also import-
ant to note that the VeRo Liberator works without process water
and is thus also suitable for operation in arid regions, where costs
and availability of water are a particularly serious issue.
4 Comminution results
Reduction ratios in classical dry crushing are generally small and
typically range between three and six in a single crushing stage
[10]. More innovative single-level impact crushers and hammer
mills reach reduction ratios that are rarely as high as 40 to 60. In
contrast, the particle size reduction ratio (PSRR) of the VeRo Lib-
erator is fundamentally larger (Table 1). The PSRR ranges from a
ratio of 144 (at 120 mm feed diameter) to a reduction ratio of 1000,
e.g. for Rio Tinto massive sulphide ore or even higher to 7500 for
diatomite [11]. It is important to note that the three tool levels of
the VeRo Liberator can rotate independently at variable speed,
typically in the range of 600 rpm to a maximum of 1400 rpm.
This variable setup allows to adjust the operating parameters of
the unit to the specific rock mechanical characteristics of each
feed material and to the required properties of the product. The
top level of rotating tools achieves predominantly the breakage
and particle liberation of the material, whereas the lower levels
achieve the required particle size reduction. Depending on the
requirements by the customer, this can either be an ultra-fine
product, e.g. for further chemical use, or particle liberation at
relatively coarse particles sizes. An example for the former is the
comminution of diatomite, e.g. for ultra-fine filtration of fluids,
whereas an example for the latter is the achievement of 85 % ore
mineral liberation at 835 µm for Pb-Zn-Ag-Au ore from Ciénega
Mine, Mexico. For the same degree of ore particle liberation,
the mine’s conventional comminution design currently needs a
reduction down to 113 µm, which requires far more energy and
is thus considerably less efficient.
Besides particle size reduction, one of the most important and
complex parameters in comminution is the particle liberation to
separate ore minerals from gangue efficiently to achieve a high
recovery of the commodity minerals [12]. Incomplete particle
liberation during size reduction poses a serious problem to effi-
cient recovery of commodity minerals with potential loss of value
minerals to the waste stream. A common countermeasure in
conventional comminution has been ultra-fine grinding, which not
only increases energy consumption but and causes also serious
b)
a)
Fig. 6:
VeRo Liberator comminution sys-
tem: (a) showing the casing cylin-
der that contains the vertical axle
with three levels of hammer tools.
Note the small physical footprint
of this 100 to 130 t/h throughput
unit; (b) as installed and operating
at a mine site in South Africa. The
core unit is the vertical cylinder in
the middle.
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World of Mining – Surface & Underground 72 (2020) No. 3 Mineral Processing
problems in the dewatering of the tailings dams. Based on some
early theoretical considerations, one author [12] stated vaguely that
“some systems exhibit a tendency to fracture at grain boundaries”,
which “would result in significantly better liberation than expect-
ed”. Surprisingly, little improvement of conventional comminution
systems materialised after this 50-year-old statement or at least
not until the VeRo Liberator was invented in 2012.
Initially observed from empirical particle liberation analyses of
test-comminuted bulk ore and slag samples (Figure 7a, 8a), the
degree of particle liberation as achieved by the VeRo Liberator
is significantly higher compared to conventional comminution
systems, with breakage occurring predominantly along particle
boundaries (Figure 7b, 8b), thus reducing or even largely avoid-
ing incomplete particle liberation. The “clean” liberation of the
commodity minerals from the gangue minerals is already visually
striking, even without statistical particle liberation analysis (Figure
7b, 8b).
The first example presented here shows a typical porphyry copper
ore from Los Bronces Mine in Chile (Figure 7a). The ore contains
typical finely disseminated, vein-, and breccia-hosted pyrite and
Table 1:
Selected range of particle size
reduction ratios (PSRR) from
test-comminution of various ores
and industrial minerals by VeRo
Liberator. Operational conditions
were continuous single pass
comminution, 20 to 30 s passage
time, rotor speeds were generally
900 rpm, unless stated otherwise.
Power consumption for all tests
was in the range between 12
and 4 kWh/t, which is between
50 % to 90 % less compared to
conventional comminution.
Mine/client Country Ore type F80 P80 PSRR
Imerys United Kingdom diatomite 120 mm 16 µm 7500
Rio Tinto Mine,
Atalaya Mining
Spain massive sulphide (Cu-Au) 120 mm 120 µm 1000
Aguas Tenidas Mine,
MATSA
Spain massive sulphide (Cu-Pb-Zn-Au) 120 mm 120 µm 428
Kropfmühl Mine,
AMG Mining
Germany disseminated ore (flaky graphite) 120 mm 280 µm 428
Nordic Mining Norway eclogite ore (garnet) 120 mm 380 µm 316
Clara Mine,
Sachtleben Bergbau
Germany vein-type (Ba-F-Ag) 120 mm 450 µm 267
Lünen Smelter, Aurubis
AG
Germany Cu anode, converter slag 120 mm 720 µm 167
Wolfram Camp Mine,
Almonty
Australia Greisen-type (W-Sn-Mo) 120 mm 750 µm 160
Cinéaga Mine,
Fresnillo plc
Mexico vein-/breccia-type (Pb-Zn-Ag-Au) 120 mm 835 µm 144
Olovo Mine (800 rpm) Bosnia cerussite Pb-ore 120 mm 1,8 mm 66
Olovo Mine (1400 rpm) Bosnia cerussite Pb-ore 120 mm 580 µm 207
Los Bronces Mine,
Anglo American
Chile porphyry copper ore 80 mm 520 µm 153
Fig. 8:
Copper process slag from a metal
recycling anode smelter of Aurubis
AG, Hamburg: (a) hand specimen of
slag with soft and malleable droplets
of metallic copper set in a matrix of
hard and brittle Fe- and Sn-oxides
(magnetite and cassiterite); (b) sieve
fraction of the comminuted VeRo
Liberator product of the slag from
Figure 8a. Note the extremely high
degree of liberation of non-flattened
copper droplets from the oxide
minerals. The high impact velocity
causes also a brittle behaviour of the viscose/ductile copper metal.
Fig. 7:
Porphyry copper ore from Los
Bronces Mine, Chile: (a) hand
specimen of typical ore; (b)
backscattered electron (BSE)
image with element mapping for
iron and copper of VeRo Liberator-
comminuted Los Bronces ore
(0.125-0.250 mm fraction); the ore
minerals chalcopyrite (orange) and
pyrite (yellow) show a remarkably
high degree of particle liberation
from the gangue minerals.
b)
a)
b)
a)
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World of Mining – Surface & Underground 72 (2020) No. 3
Mineral Processing
Cu-Fe-sulphide mineralisation (Figure 7a, b). Scanning electron
microscope images with mineral liberation analysis and element
mapping shows that the sulphide minerals are fully liberated and
that breakage has occurred along mineral boundaries (Figure 7b).
A second example is the comminution and particle liberation
of a copper anode smelter slag from a secondary metal scrap
smelter of Aurubis AG, in the town of Lünen, Germany (Figure
8a, b). This rapidly cooled process slag consists of solidified
spherical droplets to partly angular subhedral cubic crystals
of metallic copper, suspended in a matrix of the metal-oxide
minerals magnetite and cassiterite (Figure 8a). The matrix and
metal droplets are in stark rheological contrast in that the minerals
magnetite and cassiterite are hard and typically break by brittle
fracturing. The metallic copper, in contrast, is very soft and nor-
mally behaves viscous and ductile upon deformation. However,
the comminution product of this slag is rather surprising, not
only in that the particle liberation is virtually complete but also
that the metallic droplets have not been deformed or flattened
(Figure 8b) as might be expected.
The velocity of the impacts by the tools of the VeRo Liberator onto
the copper process slag is apparently so high that it prevents the
soft metallic copper to behave viscous and ductile, which it would
do in low velocity point load situations. The high-velocity thus
causes an embrittlement of the ductile material, which – together
with the breakage along mineral boundaries – results in the com-
plete liberation of the still droplet-shapes metallic copper particles.
The general and systematically higher degree of particle liberation
compared to conventional crushing and millings systems, e.g.
in ball mills, has been studied in comparative mineral liberation
analyses [13, 14]. Comparative test-comminution of complexly
intergrown and extremely fine-grained black-shale-hosted cop-
per ores from Rudna Mine, in the Polish KGHM Kupferschiefer
mining district, has documented that the degree of liberation
of the Cu-Fe sulphide ore minerals bornite, chalcopyrite, and
chalcocite is significantly higher in all liberation classes, when
comminuted by VeRo Liberator® compared to conventional
milling (Figure 9) [14].
5 The working principle of the
VeRo Liberator
Breakage by VeRo Liberator is only subordinately controlled by
fracture propagation between load points but is most probably the
consequence of several rock mechanical phenomena, all of which
are based on the differential deformation behaviour of the various
particles. The most obvious breakage feature of the VeRo Liberator
is fragmentation resulting from fracture nucleation and fracture
propagation predominantly on and along mineral boundaries. This
working principle of the VeRo Liberator accounts apparently for
the strongly reduced energy consumption. Fracture formation and
propagation along particle boundaries is highly energy-efficient
since the fractures must overcome less tensile strength compared
to cross-boundary fracturing. Interfacial strength is typically much
less than the strength within a homogenous particle or mineral
and the nucleation and propagation of fractures between particles
can be regarded as a “debonding” process with a high degree
of particle liberation as observed in VeRo Liberator comminution
(see Figures 7b, 8b, 9). This observation is relatively well known in
other types of rock breakage, e. g. in the almost effortless manual
splitting of roofing slate. The same roofing slate can be penetrated
by a nail that is hammered through the slate perpendicularly to
the schistosity without damage and breakage of the plate of slate.
However, the penetration by hammering of the nail through the
slate requires far more physical strength, i. e. breakage energy.
An additional aspect of comminution by the VeRo Liberator is
apparently the velocity- and thus time-dependence of the com-
minution processes. The induced stress difference between two
components must be high enough to exceed the critical stress
level for fracture formation and separation to take place at the
boundary of two minerals with a substantially different deforma-
tion state. We assume that stress accumulation in the oscillating
and vibrating components plays a significant role in inter-granular
fracture formation and thus in particle liberation. In normal im-
pact events, a release of stress takes place between the various
components due to a time-dependent stress relaxation process,
Fig. 9:
Comparison of liberation of cop-
per ore minerals from Kupfer-
schiefer ore from Rudna Mine,
Poland; the liberation in all classes
is higher in VeRo Liberator commi-
nution compared to conventional
ball mill results [13, 14]
Ore type Country Test type Mass
processed
Date
of test
speed
[rpm]
Size reduction
[Fw80 to P80]
kWh/t
[range]
kWh/t
[avg.]
Black shale
Cu ore
Poland/
Germany
Laboratory
scale
130 kg Mar.
2015
580-
660
120 mm-225 µm c. 5-8 c. 7
Basalt Germany Pilot scale 17.8 t April
2016
800-
1400
90 mm-220 µm 5.63-
6.89
6.3
Pyroxenite
Pt ore
South Africa Pilot scale 1.9 t Oct.
2016
800-
1200
125 mm- 4.8-10.6 7,9
Pyroxenite
Pt pebbles
South Africa Pilot scale 1.6 t Oct.
2016
800-
1000
125 mm- 5.5-7.3 6.4
Table 2:
Test results of different ores and
rock materials at different scales
of throughput quantities, showing
the very low specific energy con-
sumption of the VeRo Liberator
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World of Mining – Surface & Underground 72 (2020) No. 3 Mineral Processing
which commonly prevents breakage. This is the phenomenon
of needing numerous impacts before breakage as described for
conventional, tumbling (i.e. low-velocity) comminution systems [5]
(see Figure 3). In case of the VeRo Liberator the high frequency of
high-velocity impacts is far higher and faster than stress relaxation
within the components. Consequently, very high stress differences
build up between adjacent minerals, causing breakage at particle
boundaries, which is energetically more efficient.
The low energy consumption of VeRo Liberator comminution is
well established from extensive test work. As example, the fol-
lowing parameters (Table 2) document the efficiency of the VeRo
Liberator in test-comminution of various materials, e.g. black shale
hosted Cu sulphide ore from Poland (laboratory scale quantities)
and dense, hard, and tough magmatic platinum ores (industrial
pilot-scale quantities).
6 Comparative uniaxial load test
breakage experiments
In order to understand the empirical results and to test the pro-
posed high-velocity breakage model for the VeRo Liberator, we
have carried out rock mechanical experiments at the Rock Me-
chanics Laboratories of Martin Luther University Halle-Wittenberg.
Both static and dynamically steered uniaxial compression tests
have been conducted on drilled-out cylinders of copper smelter
slag as first experimental tests for the model (Figure 10). The slag
drill core samples had a diameter of 30 mm and a length of 80 mm.
In static load tests, the critical stress level was exceeded at ca.
70 MPa, leading to sample failure and breakage of the copper
slag (Figure 11a). In contrast, the dynamic load tests of similar drill
core samples of copper slag resulted in significantly reduced rock
strength under repeated high-frequency pulsating load events. In
these dynamic load tests, the sample cylinders have been stati-
cally stressed at a load of 35 MPa and additionally subjected to
several periods of dynamically pulsating dynamic loading (up to
65 MPa) and unloading (to a decreased minimum stress of 25 MPa)
(Figure 11b). The dynamic loading served as a first approximation
of the high-velocity impact forces (“shock waves”), which pass
through the material in VeRo Liberator comminution. As a result
of the pulsating dynamic loading and unloading, material failure
occurred already at 50 % of the uniaxial strength, compared to a
static loading test on a comparable sample of copper slag. This
significant reduction of the uniaxial strength during the dynamic
load test indicates significant changes in the rock mechanical
behaviour due to the dynamic, high-frequency loading. It has
already been pointed out that the high-frequency pulsating load
tests, which lead to mechanical fatigue failure of the rock sample
thus appear to come closest to the highly efficient comminution
effects achieved by the high-frequency, high-velocity impacts in-
flicted on heterogeneous solid material by the VeRo Liberator [15].
7 Comparative high-velocity impact
experiments
Additional experimental studies on impact breakage included high-
speed video footage of ore samples that were ballistically impacted
onto a steel tool by a gas cannon. These high-velocity impact
experiments have been commissioned by Anglo American jointly
with PMS GmbH and Anglo American granted permission to publish
selected results from this study [16]. Two sets of three consecutive
images each from two tests at different impact speeds, one at
sub-critical speed and one where major disintegration occurs, are
shown in Figures 12a, b. The material tested is from a dense, hard,
and tough magmatic platinum ore. The ores consist predominantly of
pyroxene and plagioclase with minor chromite and sulphide minerals.
The ore samples in these tests had a mass of approximately 12 to
15 g and the low-velocity ore sample was accelerated to a speed
of 50 m/sec (Figure 12a), whereas the high-velocity ore sample has
been accelerated to a speed of more than 150 m/sec (Figure 12b).
The images show the moment of impact onto a steel plate (the
surface of which is partly in the shadow; Figures 12a-a, 12a-b) and
subsequent images showing the developing impact phenomena
(Figures 12a-b to a-c, 12b-b to b-c). The low-velocity ore sample
becomes compressed and partly pulverised at the point of impact
(Figure 12a-b) but subsequently bounces back from the steel
plate, largely remaining intact (Figure 12a-c). This impact situation
without substantial breakage of the ore is the phenomenon typically
Fig. 10: Experimental uniaxial load test of drill core sample of copper
slag: (a) drill core sample prior to load test; (b) same drill core
sample of copper slag broken after exceeding the critical
stress level
b)
a)
Fig. 11:
Results of uniaxial dynamic load
tests on slag samples: (a) Increase
of loading stress in static uniaxial
static load test of copper slag
with breakage failure at 70 MPa;
(b) result of a uniaxial dynamic
load test, in which at the load of
35 MPa an additional stress is pul-
sated in several steps of increased
maximum stress of up to 65 MPa
and of decreased minimum stress
of 25 MPa. Breakage failure takes
place after a phase of dynamic
pulsing conditions at about half
the critical stress compared to the static load test (compare Figure 11a). This breakage under lower dynamically pulsed load conditions might resem-
ble the VeRo Liberator breakage most closely.
b)
a)
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World of Mining – Surface & Underground 72 (2020) No. 3
Mineral Processing
described from conventional ball mills or SAG mills, as shown in the
test results of Figure 3 and described in numerous publications [5].
At high velocities, above a critical velocity limit, which varies for
each specific ore and rock type, the breakage pattern changes
completely. The initial phase of impact onto the steel tool appears
similar to the moment of impact at low velocity, in that the tip of
the ore sample is also compressed and pulverised (Figure 12b-
a). However, the subsequent breakage pattern is totally different
with breakage occurring within and throughout the ore sample
(Figure 12b-b, b-c). This breakage pattern resembles very closely
the pattern predicted from numerical modelling of high-velocity
impacts of rocks as shown in Figures 5a, b and in other numerical
models [8]. This type of high-velocity impact breakage does not
continue with further compressive pulverisation as in the initial
phase but instead, breakage occurs from within the ore sample
(Figure 12b-b), spreading outwards in all directions and results in
disintegration-breakage of the entire ore particle (Figure 12b-c). It
is important to note that the predictions from numerical modelling
[8] were made well before the invention of the VeRo Liberator and
thus did not simply illustrate in hind site, what the VeRo Liberator
produced as an empirical comminution result.
The results from these ballistic high-velocity impact experiments
show several phenomena of breakage, fracture formation, disin-
tegration, and rock-tool interaction. The breakage phenomena at
such high impact velocities is totally different from static or dynamic
point load situations, which are typical for the compressive stress
situations created in conventional comminution, e.g. in ball mills
[5]. In such traditional mills, the rock is wedged between two steel
balls, a steel ball and the machine casing, or between rocks and
the above-mentioned items. In contrast, the high velocity impact
leads only to initial and visible compression of the frontal 20 % of
the rock sample from compressive forces between the steel tool
and the mass of the rock fragment itself. The remaining, much
larger portion of the rock sample does not only remain uncom-
pressed but disintegrates and expands by literally “exploding” and
“expanding” in all directions of space, away from the steel tool
(Figure 12b-b, b-c). It is important to note that this disintegration,
explosion, and expansion of the ore sample occurs without contact
to the steel tool and without outside compressive stress applied
to this major portion of the rock. It appears that the momentum
transfer of the kinetic energy from the steel tool into the ore particle
is so efficient that the transferred energy exceeds the tensional
stress limit of the rock, leading to the observed disintegration.
Different from the video recordings of the gas cannon experiments,
visual images from inside the VeRo Liberator during operation are
technically impossible. Anglo American, who are developing the
VeRo Liberator towards the next TRL jointly with PMS, has commis-
sioned a simplified but nonetheless realistic depiction of the commi-
nution process inside the comminution chamber, which is shown in
Figure 13 courtesy of Anglo American FutureSmart MiningTM.
Fig. 12:
Still images of high-speed video
coverage (shown here by courtesy
of Anglo American) of gas cannon
experiments with impacting ore
particles (5 × 4 cm in size) at: (a)
a low velocity impact (50 m/s),
similar to conventional ball mill im-
pacts a-a) ore particle approach-
ing steel tool, a-b) impact-com-
pression of a minor frontal part
of the particle, a-c) rotation and
rebound of predominantly intact
particle; (b) a high-velocity impact,
b-a) impact compression of the
frontal part of an ore particle, b-b,
b-c) disintegration and expansion
of the rest of the particle due to
efficient momentum transfer of
kinetic energy into the particle
Fig. 13: Artistic depiction of the high-velocity impact comminution
as happening inside the VeRo Liberator (courtesy of Anglo
American FutureSmart MiningTM)
b)
a)
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World of Mining – Surface & Underground 72 (2020) No. 3 Mineral Processing
The following summary of the high-velocity impact and breakage
phenomena of the VeRo Liberator has profited specifically from
discussions with Robert Morrison, who is gratefully acknowledged.
In detail, the impacting rock particle is apparently impinging in lay-
ers from the highest compressional forces (i.e. the direction of σ1)
between the hammer tool and the mass of the particle itself. When
the first layer hits the steel tool, it disintegrates when its elastic
limit is exceeded. The breakage front travels at very high velocity
further through the rock and a second layer disintegrates, again
when its elastic limit is exceeded. However, there is apparently a
limit to this layer-by-layer disintegration due to the absorption of
a critically high elastic load. When this happens and the specific
elastic limit of the rock type is exceeded the remaining portion of
the rock particle breaks and expands in all directions of space. The
same process will be repeated when the disintegrated fragments
of the initial rock particle are impacted by the subsequent collisions
with (counter-rotating) hammer tools, machine liners and other
rock fragments. However, the particle size and – consequently
– the particle mass will decrease rapidly downward from the top
level to the lower tool levels. Since only some 20 % of the rock is
comminuted by point load compression and the remaining part by
triggered disintegration and expansion, it becomes understand-
able that the energy consumption for this process is drastically
lower, compared to conventional comminution processes.
8 Conclusions
Growing global demands in metal and mineral resources are predi-
cable, not only due to a growing and increasingly resource-con-
scious world population, but also due to a widening recycling gap.
These demands, particularly for strategic metals for sustainable
technologies such as e-mobility and renewable energy production
necessitate mining and recovery of primary metal resources. In
order to gain public acceptance and to obtain a social license to
operate by all stakeholders, it is necessary to reduce the environ-
mental and carbon footprint of mining and mineral processing op-
erations. Comminution of ores and secondary resources appears
as a mature group of robust crushing and grinding technologies
with incremental degrees of innovation and improvements of ef-
ficiency in the past. Particularly the breakage and consequently
breakage inefficiency of low-velocity conventional ball mills and
similar systems is scientifically well documented but largely ac-
cepted. Over several decades, some scientists have predicted
step-changing breakage processes to occur at significantly higher
impact energies. These early concepts included also the prediction
that moving the position of breakage from within or across particles
to the boundaries for increased liberation results.
The invention, development, and successful marketing of a
high-velocity impact comminution system, the VeRo Liberator, now
offers such a step-changing technology. Within eight years, the
VeRo Liberator has been developed to TRL 7-8 with further im-
provements implemented constantly during industrial application
(Figure 14). Three levels of hammer tools, counter-rotating at high
speed around a vertical axle impact the feed material numerous
times at high velocities, resulting in highly turbulent particle flow.
The continuous gravitational material stream through the vertical
comminution chamber involves no lifting of material or equipment
and, consequently, is far more energy-efficient compared to
mills with horizontally rotating axles. Passage time through the
comminution chamber is in the order of 20 to 30 seconds only.
The VeRo Liberator operates without process water, which is an
additional advantage to minimise the environmental impact of
mineral processing.
The high-velocity impact comminution of the VeRo Liberator results
in unparalleled particle size reduction ratios and very high degrees
of particle liberation, in some cases already in coarse particle size
classes. Breakage at such high impact velocities results from the
highly efficient momentum transfer from the impactor to the ore
particle and the stimulation of the heterogeneous feed material.
Differential stimulation of the elasticity and compressibility mod-
uli of different minerals leads to stress accumulation on particle
boundaries with breakage nucleating and progressing on and
along mineral boundaries.
Empirical comminution results have been simulated by experi-
mental uniaxial load tests and high-velocity gas cannon impact
experiments. The former showed breakage at half the critical
stress in dynamically pulsed load tests, possibly simulating higher
velocity impact breakage processes, compared to stress-failure
in static load tests, being probably more similar to low velocity
abrasive impacts. High-velocity gas cannon impact experiments
revealed the efficient momentum transfer from impactor into the
particle, leading to a disintegration and expansion of the particle
along mineral boundaries. A major portion of the particle’s mass
Fig. 14:
Schematic diagram of technologi-
cal development of the VeRo Lib-
erator technology from invention
to the current technical readiness
level
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World of Mining – Surface & Underground 72 (2020) No. 3
Mineral Processing
disintegrates in this process without physical contact with the
impactor tool.
This combination of a gravitational free-falling material flow with
the contact-less high-velocity disintegration is the most probable
explanation for both the extremely low energy consumption and
unusually high degree of particle liberation of this new technology.
Acknowledgments
The development and improvement of the VeRo Liberator tech-
nology has profited greatly from test-comminution of bulk samples
from many mines and smelters, which are too numerous to list in
detail, but which are all gratefully acknowledged. We thank Shuji
Owada for pointing out early predictions of improved breakage
behaviour from higher energy impacts along particle boundaries.
We are grateful to the technical exchange with the staff of Anglo
American plc both in South Africa and London. The technical staff
at Anglo American’s test facility has provided valuable support
during test-comminution of various ores and is also gratefully
acknowledged. Flora Feitosa Menezes has helped with the perfor-
mance of the uniaxial load tests. Elisabeth Schramm has assisted
with retrieval and formatting of comminution data. Discussions with
the staff of Penoles and Fresnillo, Mexico, have also furthered our
technical understanding, particularly of the coarse particle liber-
ation. Fruitful discussions with Malcolm Powell, Robert Morrison,
Adrian Hinde, and Paul Cleary have helped greatly to understand
the working principle of the high-velocity impact breakage.
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