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Improved particle liberation of graphite and other complex ore minerals by high-velocity comminution - Introducing the new VeRo Liberator®

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The comminution of commodity particles such as ore minerals in mining and metals from recycling of slags, armored concrete, and incinerator slags by crushing, grinding, and milling makes up the biggest single cost factor in mineral processing. The comminution of graphite in various innovative applications is a particular challenge to the mineral processing industry. Ideally, the host rock containing the graphite without reducing the sixe of the graphite flakes and without leaving remnants of gangue minerals attached to the graphite flakes. Natural graphite is a high-tech commodity with a globally increasing demand for a growing number of highly innovative technical applications and products.
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World of Mining Surface & Underground 67 (2015) No. 3
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The comminution of commodity particles such as ore minerals in
mining and metals from recycling of slags, armoured concrete, and
incinerator slags by crushing, grinding, and milling makes up the
biggest single cost factor in mineral processing. In spite of a marked
lack in the development of new and significantly more efficient com-
minution equipment, an engineering start-up, PMS Hamburg, has
invented and produced an innovative high-velocity impact crusher,
the VeRo Liberator®. This new machine features highly improved
particle size reduction ratios and very high degrees of particle libera-
tion together with low levels of energy consumption and operational
noise and operates in a dry state, i.e. without using water.
The VeRo Liberator® is currently designed for a throughput of ap-
proximately 100 t/h and has been tested on a number of different
typical bulk ore and slag samples from mines and smelters around
the world. The comminution of graphite ore, with graphite currently
being a high-tech commodity in various innovative applications, is
a particular challenge to the mineral processing industry. Ideally, the
host rock containing the graphite flakes, needs to be disintegrated
and liberated from the graphite without reducing the size of the
graphite flakes and without leaving remnants of gangue minerals
attached to the graphite flakes. Graphite ore from AMG’s Graphite
Kropfmühl Mine has been subjected to comminution by the new
VeRo Liberator® and the comminution results of flaky graphite
hosted in quartz-feldspar-mica host rocks, are presented in this
Improved particle liberation of graphite and
other complex ore minerals by high-velocity com-
minution – introducing the new VeRo Liberator®
GREGOR BORG, FELIX SCHARFE, ANDREAS KAMRADT, CHRISTOF LEMPP,
Germany
publication. The graphite flakes have been liberated exceptionally
well from the gangue minerals with virtually no gangue minerals
left attached and no apparent breakage and thus size reduction
of the flakes themselves. Similar degrees of particle liberation have
already been achieved on various other materials, which are briefly
presented for comparison.
According to our current understanding, the unique working
principle of the VeRo Liberator® is based on high-frequency, high-
velocity and therefore high-kinetic-energy impacts inflicted on the
material by hammer tools. The hammer tools are mounted on
three separate levels of a vertical axle-in-axle system and rotate
at variably high speeds clockwise and counter-clockwise against
each other. The material and particle stream within the machine
is thus highly turbulent and each particle is certainly hammered
with high impact forces several times at a high frequency. These
high-frequency and high-velocity impacts occur apparently so
fast, that stress builds up along the particle boundaries due to
differential mechanical behaviour of the inhomogeneous materials.
The high frequency of the impacts prevents the various minerals
from relaxing sufficiently so that the stress between the different
particles is not released quickly enough. Eventually this results in
fracture formation along particle boundaries. This new comminu-
tion concept offered by the VeRo Liberator® allows the significantly
more efficient comminution of ores and recycling materials at far
lower energy costs and with far higher degrees of particle libera-
tion. Due to its enormous reduction ratio the VeRo Liberator® can
also replace two to three traditional crushing and milling stages,
saving substantially both in CAPEX and OPEX.
1 Introduction – current challenges
in mining and mineral processing
The processing of low-grade ore and the extraction of ore minerals
and metals, in general, pose an increasingly serious problem for
the international mining community. Although discoveries of new
high-grade ore bodies are still reported occasionally, the general
global trend to lower and lowest ore grades is well documented
[1]. It goes without saying that low mineral and metal commodity
prices increase the challenge even further to mine and process
ores and to extract and market metals profitably. Cost reduction
by improved efficiency is therefore a ubiquitous task for the ex-
tractive industry and all stages in mining, mineral processing, and
metallurgy need to be reviewed carefully to identify substantial and
suitable technical innovations. Comminution is a process right at
the beginning of the entire mineral processing chain, but – although
one of the biggest single cost factors – has received relatively little
attention in recent years [2].
Under these challenging circumstances, PMS GmbH, an engi-
neering start-up company, based in Hamburg, Germany, has
developed the innovative VeRo Liberator® (Figures 1 and 2), an
Prof. Dr. GREGOR BORG,
Economic Geology and Petrology Research Unit, Institute
of Geosciences, Martin Luther University Halle-Wittenberg,
Von-Seckendorff-Platz 3, 06120 Halle, Germany
Tel. +49 (0) 345-5526080
gregor.borg@geo.uni-halle.de
FELIX SCHARFE,
Managing Partner, PMS Handelskontor GmbH, Abteistrasse 1,
20149 Hamburg, Germany
Tel. +49 (0) 40-24426630
felix.scharfe@veroliberator.de
Dipl.-Geol. ANDREAS KAMRADT,
Economic Geology and Petrology Research Unit, Institute
of Geosciences, Martin Luther University Halle-Wittenberg,
Von-Seckendorff-Platz 3, 06120 Halle, Germany
Tel. +49 (0) 345-5528263
andreas.kamradt@geo.uni-halle.de
Prof. Dr. CHRISTOF LEMPP,
Engineering Geology and Rock Mechanics Unit, Institute
of Geosciences, Martin Luther University Halle-Wittenberg,
Von-Seckendorff-Platz 3, 06120 Halle, Germany
Tel. +49 (0) 345-5526090
christof.lempp@geo.uni-halle.de
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World of Mining Surface & Underground 67 (2015) No. 3 Technical Report
impact crushing machine with a high potential to solve several
comminution efficiency and cost issues simultaneously. The
VeRo Liberator® (patents pending) is a dry-crushing system with
very low energy consumption and achieves impressive reduction
ratios of 100 to 480 in a single pass. Thus the VeRo Liberator® is
capable to replace several comminution stages in some mineral
processing circuits. The VeRo Liberator® is suitable for primary ores
of sulphides, silicates, carbonates and oxides, slags from metal-
lurgical smelters, power plants, and waste incinerators as well as
for armored concrete and other heterogeneous solid materials.
First comminution results of various materials as well as technical
details on the VeRo Liberator® have been recently presented and
published at international mineral processing conferences [3, 4].
Natural graphite is a high-tech commodity with a globally increasing
demand for a growing number of highly innovative technical ap-
plications and products. Graphite is currently a much sought-after
mineral commodity with attractive market prices that is explored
for by a growing number of both junior and mid-size explorers and
specialised mining companies [5]. One particular challenge in mining
but particularly in subsequent mineral processing is to liberate and
separate the flaky graphite from gangue minerals without breaking
and thus reducing the size and value of the graphite flakes. An ad-
ditional challenge is the task to separate the graphite flakes with as
little gangue minerals as possible left attached, since these remnants
have to be removed chemically at significant costs.
Material from a three ton bulk sample of graphite ore from AMG
Mining AG – Graphit Kropfmühl, southeastern Germany, has been
comminuted in a single pass test run through the VeRo Libera-
tor®. The feed material as well as the output material has been
investigated and documented mineralogically, texturally, granulo-
metrically, and geochemically at the Economic Geology and Pe-
trology Research Unit, Martin Luther University Halle-Wittenberg,
Germany. The test work formed part of a 13 month research
project to independently document the comminution results of
a total of nine ores and slags from various mines and one base
metal smelter from different parts of the world. Comprehensive fact
sheets of the various results of this test work are available upon
request from PMS Handelskontor GmbH, Hamburg.
Recently, another bulk sample of graphite ore has been provided
from Woxna Graphite Mine, northwest of Stockholm, Central
Sweden, by Flinders Resources Ltd. for comparative comminution
testing. Test work and subsequent scientific documentation have
just started and first results are expected by mid-2015.
2 The new VeRo Liberator®
an innovative answer to typical
comminution problems
Besides featuring the impressive reduction ratios mentioned
above, the VeRo Liberator® achieves also a particularly high degree
of particle liberation. This is caused by high velocity impacts of the
hammer tools inflicted onto the ore particles. Apparently this leads
to preferential inter-particle breakage by the VeRo Liberator® rather
than cross-particle fractures, the latter causing both incomplete
particle liberation and high percentages of middlings, commonly
encountered in more traditional comminution systems [6, 7].
3 Technical specifications of the
VeRo Liberator®
The new VeRo Liberator® is a comminution machine in the 100 t/h
throughput class. The machine has been built in a modular fashion
and is thus easy to transport, assemble, or modify according to
customer’s demands. The main feature is a vertical axle-in-axle
system, which carries a total of up to 144 hammer tools, which
can be varied in size and weight. These hammer tools are mounted
individually on three separate levels, which rotate clockwise and
anticlockwise against each other at high speeds; causing high-
velocity impacts. The material falls gravitationally through the
cylindrical armored comminution chamber (see Figures 1 and 2),
where it is impacted by the hammer tools and impacts onto the
armored housing with specially designed and engineered inner
liners, and other particles. The maximum size of the feed for
the VeRo Liberator® is 120 mm in diameter. Depending on the
input material and the process in mining, mineral processing, or
recycling, this could be material from a primary crusher or could
replace the primary crusher itself plus subsequent milling stages.
Reduction ratios in classical dry crushing are generally small and
typically range between three and six in a single crushing stage
[7]. More innovative single-level impact crushers and hammer mills
reach reduction ratios as high as 40 to 60 (pers. comm. Holger
Lieberwirth, Institute of Mineral Processing Machines, TUBA
Freiberg, Germany). The reduction ratio of the VeRo Liberator® is
fundamentally larger and ranges from a ratio of 100 to ratios that
can exceed even the value of 450. This extreme size reduction ratio
has been achieved on a bulk ore sample of massive sulphide ore
from Rio Tinto, Spain, where an ore feed of 120 mm diameter has
been reduced in a single pass to 94 % with a diameter of less than
250 µm, thus representing an impressive reduction ratio of 480 [3].
Technically, the equipment is easy to maintain since the housing
can be lifted hydraulically and the entire drive shaft and tool unit
can be lifted from the main frame easily. This allows the quick
exchange with another drive shaft and tool unit or alternatively the
replacement of individual tools. The precise determination of the
energy consumption (Bond Work Index) of the VeRo Liberator® is
currently being prepared, but from the maximum material through-
put of 100 t/h and the maximum energy consumption of all four
electrical motors; the maximum consumption is in the range of
230 kWh and thus highly energy efficient. It goes without saying
Fig. 1: The VeRo Liberator® with feeding funnel and conveyor belt
fitted in the foreground
Fig. 2:
VeRo Liberator®
with sorting system
and ultra-clean filter
system fitted ac-
cording to customer
specifications
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that various feed solutions, e.g. conveyor belts etc. and output
solutions, e.g. sorting and filter systems can be added easily, due
to the modular construction concept (see Figure 2).
4 A case study of the comminution
of graphite ore
The VeRo Liberator® is also highly suitable for specialty miner-
als such as flaky graphite, which needs to be liberated without
reducing the size of the value mineral, as well as a great variety
of other materials. These other materials include sulphide, oxide
and carbonate ores as well as armored concrete, incinerator slags
as well as smelter slags. Several of the tested ores are charac-
terized by intricately intergrown ore and gangue minerals, which
require excessive milling and grinding in traditional comminution
processes to avoid incomplete particle liberation. Some of the
other materials tested, such as a variety of ores and one anode
smelter slag, are also briefly shown below.
The crude graphite ore from Kropfmühl mine (Figure 3) is hosted
by banded quartz-feldspar-gneiss, which contains the graphite
in lenses, thin layers as well as disseminated graphite flakes. The
gneissic host rock is generally medium- to coarse-crystalline and
commonly contains quartz- and feldspar-phenocrysts with diam-
eters of approximately 3 to 4 mm. Optical and scanning electron
microscope studies have shown, that the graphite occurs typically
in the form of flakes or laths in bands that are orientated sub-parallel
to the banding-parallel cleavage of the gneiss, but also orientated
randomly or as star-shaped flakes (Figure 4). The gneiss consists
predominantly of quartz and feldspar but contains accessory min-
erals such as biotite, subordinately muscovite, phlogopite, rarely
augite and some sulphide minerals. Locally the graphite flakes are
partly or completely enclosed in gangue minerals such as feldspar
and quartz (see Figure 4). Even more rarely the graphite flakes are
encapsuled in sulphide minerals such as pyrite, pyrrhotite, and
chalcopyrite. The graphite flakes can reach up to 1 cm in length and
are typically lath-shaped and commonly straight or slightly curved.
The two most striking features of graphite comminution by the
VeRo Liberator® are the drastically improved reduction ratio and
the very high degree of particle liberation when compared with
classical comminution systems. In a single pass crushing process
of graphite ore from Kropfmühl mine, the VeRo Liberator achieves
impressive reduction ratios between 120 and 240. This stems
from a size reduction of 120 mm feed material to 95 % of the
particles <1 mm in diameter and 90 % of the particles <0,5 mm
in diameter, respectively.
Fig. 6: SEM-image (same scale as Figure 5) of comminuted
but undeformed graphite (dark grey laths) ore and gangue
minerals (white to grey, quartz, feldspar, and mica)
Fig. 5: Scanning electron microscope (SEM) image of graphite
flakes (dark grey) and minor gangue minerals (light grey)
after comminution by VeRo Liberator®. The graphite flakes
are perfectly liberated and virtually undeformed.
Fig. 3: Underground tipping wagon at Kropfmühl mine, Germany,
filled with graphite ore and gneissic wall rocks (gangue)
Fig. 4: Optical microscopy image of a thin section (crossed pola-
rised light) of graphite ore showing opaque (black) laths of
graphite in a matrix of quartz-feldspar-gneiss
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World of Mining Surface & Underground 67 (2015) No. 3 Technical Report
After single pass comminution by the VeRo Liberator®, the
graphite flakes and laths and the gangue minerals have been
almost totally separated from each other (Figures 5 and 6). The
separation has occurred along the particle boundaries of the
graphite flakes without any quartz, feldspar or other gangue
minerals left attached to the surface of the graphite flakes (see
Figures 5 and 6). One might thus argue that the VeRo Liberator®
has produced a “clean” chemical product (flaky) graphite, prob-
ably with >98 % carbon, through a purely physical comminution
process. Additionally, the graphite flakes have not been disin-
tegrated into smaller particles but have remained largely intact
with little bending and feathering-out on the ends of the flakes
or laths (see Figures 5 and 6).
Although the particle size reduction and particularly the particle
liberation achieved for the graphite ore by comminution through the
VeRo Liberator® are significant, this effect is by no means limited
to graphite ore only. Similarly impressive results in both reduction
ratio and particle liberation have been demonstrated and partly
already published for other materials [3, 4]. Four other examples of
highly improved particle liberation results through application of the
VeRo Liberator® are briefly summarized in the form of four scan-
ning electron microscope images of different ore types (Figure 7).
These examples include massive Cu-Zn-Pb sulphide ore from First
Quantum’s Pyhäsalmi Mine, Finland (Figure 7a), low-grade W-Mo-
REE ore from Almonty Industries’ Wolfram Camp Mine, Australia
(Figure 7b), vein-type fluorite ore from Sachtleben Bergbau AG’s
Clara Mine, Germany (Figure 7c), and Aurubis AG’s, Lünen Smelter,
Germany, with anode smelter copper slag (Figure 7d). Compared
to our results of test work on graphite ore, the marked separation
of the commodity particles from gangue or waste along particle
boundaries shows impressively that the commodity minerals’
particle shape does not play a significant role in particle liberation.
Flaky and lath-shaped graphite is separated and liberated equally
well, compared to quasi-spherical metallic copper droplets and
polygonal to irregular sulphide or fluorite ore minerals.
5 Theoretical constraints
So far, the VeRo Liberator®s full working principle, which is respon-
sible for the high degree of particle liberation and high reduction ratio
in a quick single pass comminution, cannot be fully explained by
us yet. However, some of our other comminution results of various
other test materials as well as our current and constantly evolving
understanding of the VeRo Liberator®s working principle have
been presented recently at mineral processing conferences [3, 4].
To date, the obvious comminution success of the VeRo Liberator®
contrasts with a lack of theoretical explanation. This will require
further research in the form of both rock mechanical testing and
theoretical modelling. Thus, our preliminary ideas presented here
summarize our current understanding of the working principle.
The effects of a traditional ball mill, on the one hand, can be
experimentally simulated and explained in standardized rock
mechanical testing procedures either by tensile strength tests
(Brazilian test recommendation No. 8 of ISRM, 1977 [8]) or by point
load tests [9]. The spherical steel balls or load points in a ball mill
generate a compressive force that induce an orientated tensile
force perpendicular to the ball point load on an irregularly shaped
piece of rock, placed between two such load points (Figure 8a).
Generally, the tensile strength is only approximately 10 to 20 %
of the compressive strength. To generate such a tensile fracture,
the input of sufficient energy is necessary during the rotation of
the ball mill and the resulting collisions of the steel balls with rock
fragments. Fractures can thus develop as a consequence of the
tensile force between loading points at the balls’ contacts with
the rock. In this fracturing process, the tensile fracture propagates
through all mineral components, situated between the ball-to-rock
contact points. Particle boundaries, in this process, will be utilized
if the propagating fracture is orientated at a sufficiently shallow
angle to the particle boundary. If this critical angle is exceeded, the
fracture will cross-cut the mineral boundary, potentially resulting
in incomplete particle liberation (Figure 8b).
Fig. 7:
Typical examples of three different
ores and one slag, comminuted
by the VeRo Liberator® all showing
a very high degree of particle
liberation; a) comminuted massive
sulphide (Cu-Zn-Pb) ore from
First Quantum’s Pyhäsalmi mine,
Finland; b) comminuted low-grade
W-Mo ore from Almonty Indus-
tries’ Wolfram Camp mine, Austra-
lia; c) comminuted fluorite ore from
Sachtleben Bergbau AG’s Clara
mine, Germany; d) comminuted
anode smelter slag with metallic
copper “droplets” from Aurubis
AG’s base metal smelter in Lünen,
Germany
a) b)
c) d)
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In contrast, the working principle of the VeRo Liberator®, is
apparently less characterized by fracture propagation between
load points, but is probably the consequence of differential me-
chanical behavior of the various mineral components. The most
obvious phenomenon of the VeRo Liberator® is that separation
occurs predominantly along particle or mineral boundaries. The
theoretical explanation for such a separation of minerals due to
different moduli of deformation (deformation modulus or Young‘s
modulus) is still insufficient. One might argue that for this style of
liberation the different moduli of deformation of adjacent mineral
components are critical, but we have also to take into considera-
tion, that during static loading processes (as is similar to what
is happening in a ball mill) this different deformation behavior of
the various components does not display a dominant role in the
process of fracture formation and particle liberation.
Additionally, possibly significant aspects such as the velocity-
dependence and thus time-dependence of such high-velocity
comminution processes, need to be investigated in more detail.
This is necessary, since the induced stress difference between two
components must be high enough to lead to fracture formation
or separation at the boundary of two minerals with a substantially
different deformation state. We thus assume that some sort of
stress accumulation in the oscillating and vibrating components
plays an important role in inter-granular fracture formation and
thus in particle liberation. Normally, stress release would occur
in and between various components due to a time-dependent
stress relaxation process. However, in case of the VeRo Libera-
tor® the extremely high frequency of high-velocity impacts must
be assumed to be far higher and occur much faster than stress
relaxation within the individual mineral components. As a result,
accumulation of very high differential stress levels between ad-
jacent minerals may cause fracturing along particle boundaries.
These processes are possibly comparable to other, technically
well-known, supersonic frequency-dependent processes as ap-
plied e.g. in ultrasonic cleaning devices.
However, we are currently investigating, whether high-frequency
vibration processes occur inside the VeRo Liberator® in a sufficient
intensity to cause the observed particle liberation. Resonance
phenomena may additionally cause the accumulation of stress
and energy, comparable to the effects in resonant columns [10-
12]. Finally, the shape of the casing of the VeRo Liberator® is most
likely to have an additionally positive effect on successful particle
liberation due to specific resonance frequencies, which is being
investigated further.
Currently, we cannot offer a simple explanation for the highly
efficient comminution processes achieved by the VeRo Libera-
tor®. However, it is possible to numerically calculate the resulting
stress differences due to varying deformation behavior between
different particle boundaries [13]. Mineral separation should take
place at mineral boundaries between particles with different
deformation moduli, if the stress relaxation is not as fast as the
load event frequency. As an experimental first test for our model,
we have conducted a dynamically steered uniaxial compression
test, resulting in significantly reduced rock mechanical strength
under repeated high-frequency pulsating load events. A drilled-
out cylindrical copper slag sample (30 mm diameter, 80 mm
height) has been additionally stressed by increased loading steps
in three subsequent periods of dynamic loading and unloading.
This dynamic loading served as a first approximation of the high
velocity impact forces that are inflicted on the material by the VeRo
Liberator®. During the third dynamic loading and unloading phase,
the failure occurred already at approximately 50 % of the uniaxial
strength, compared to a static loading test on a similar cylindrical
sample of the same copper slag. This highly significant reduction
of the uniaxial strength during the dynamic load test is a clear
indication of significant changes in rock mechanical behavior due
to dynamic loading. Generally, this strength reduction is contrary
to standard static load experimental results, in which increased
velocities normally result in a higher strength of the rocks tested.
Our high-frequency pulsating load tests, which lead to mechani-
cal rock failure thus appear to come closest to the highly efficient
comminution effects achieved by the multiple high-velocity impacts
inflicted on heterogeneous solid material by the VeRo Liberator®.
A more detailed study of these breakage phenomena during static
versus dynamic uniaxial stress tests is currently conducted and
will be published soon.
Further research to explain the impressive comminution results of
the VeRo Liberator® is still being conducted to explain the work-
ing principle of this machine in both a more comprehensive and
more detailed way. For obvious reasons, practical engineering
and particularly performance success in test work on various ore
types has taken first place so far, but research will hopefully fill the
gap in our understanding soon.
6 Key features of operation and
conclusions
The new VeRo Liberator® offers a number of innovative and highly
efficient features, which are due to its innovative technical layout
and unusual working principle. The energy consumption is very
low, mainly due to the facts that i) the comminution material falls
gravitationally through the VeRo Liberator®, ii) the kinetic energy of
the impacts is multiplied due to the anticyclical rotation of the three
tool levels, and iii) the stress level required for rock breakage is ap-
parently lowered due to high-velocity and high-frequency impacts,
as discussed before. The combination of such a large number
of hammer tools, the special inner liners, and the high rotational
Fig. 8:
Mechanism and geometry of frac-
ture formation in classical com-
minuten systems such as ball mills
or jaw crushers; a) compressive
fracture formation in classical (ball)
mill systems; b) fracture orientation
across particle boundaries, leading
to incomplete particle liberation
a) b)
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World of Mining Surface & Underground 67 (2015) No. 3 Technical Report
speeds of the counter-rotating axles and tools all make sure that
no material can pass the VeRo Liberator® without being impacted
repeatedly. The system operates in a dry state, i.e. without added
process water and, as a consequence, water consumption is not
an issue and can thus save valuable resources. Another special
feature of the VeRo Liberator® is the extremely low operational
noise level, although detailed decibel measurements still need to
be carried out.
The most innovative achievements of the VeRo Liberator® are the
extreme reduction ratios (up to >480 as of now) and the high de-
gree of particle liberation. As shown by the various test materials,
the fracture separation of different particles occurs predominantly
along particle boundaries. This avoids that fractures cross-cut
particle boundaries of various materials at high angles, which is
a major cause for incomplete particle liberation [6] in classical
comminution systems such as ball mills (see Figure 8). Incom-
plete particle liberation, in turn, is a major cause for subsequent
inefficient separation and extraction by processes such as froth
flotation and solvent extraction.
It is certainly easier to describe the improved communition results
achieved by the VeRo Liberator® than to explain the working prin-
ciple of how this is achieved in detail. According to our preliminary
model (Figure 9) the high-velocity impacts that are inflicted by the
rotating hammer tools onto the inhomogeneous solid material (ore
or slag) sends numerous high-velocity and probably high-frequen-
cy shock waves through the material (Figure 9a).
The various components (particles or minerals) that are stimulated
by the seismic shock waves react differently to this stimulation
according to their individual petrophysical properties (Figure 9b).
These are primarily the compressibility modulus (“K”) and the
elasticity modulus (“E” or “Young’s modulus”) of heterogeneous
solid materials. The different particles thus react in their individual
“manner” and orientation within the heterogeneous material. This
differential behavior results in inter-granular stress, particularly
along the particle boundaries [13], which eventually leads to break-
age and formation of fractures, preferentially along these particle
or mineral boundaries. The breakage, separation, and liberation,
preferentially along particle boundaries are due to either extension
(Figure 9c) or inter-granular shearing. Thus, the material separates
virtually in all spatial directions (Figure 9d), which is rather differ-
ent from the typical mechanisms of predominantly compressive
deformation, e.g. in classical ball mills, that leads to extensional
fracture development parallel to the direction of σ1.
Engineering skills have apparently come up with a substantially
more efficient comminution system, the VeRo Liberator®. It is
now up to the users in mineral processing and recycling to utilize
this offer by applying individualized test work and by integrating
such machines in current and future mineral processing circuits.
Acknowledgements
Bulk samples of graphite ore and massive sulphide ore have been
generously provided by AMG Mining AG – Graphit Kropfmühl in
Germany. AMG Mining AG and its Mining Manager, Erich Hoff-
mann, are particularly acknowledged for granting permission to
publish these first results of the comminution of graphite ore. Nick
Wilshaw, Grinding Solutions, Truro, UK, and Christian Cymorek,
H.C. Starck, Goslar, Germany, are acknowledged for valuable
discussions on the working principle of the VeRo Liberator®.
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Schematic illustration of the pro-
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Die Zusammensetzung von Gesteinsfluiden und ihr Einfluß
auf das Festigkeitsverhalten von Gesteinen bei erhöhten
Drücken und Temperaturen. (The composition of rock fluids
and their influence on the strength behaviour of rocks under
increased pressures and temperatures.) – Sonderforschun-
gsbereich 108 Spannung und Spannungsumwandlung in
der Lithosphäre, Berichtsband 1990-1992 Teil B, Projekt
D5, 823-898, Universität Karlsruhe.
... Accompanying scientific research on the characterisation of feeds and products continued but was extended to research, trying to understand the functional principle of the VeRo Liberator® that delivers such innovative and drastically more efficient unintended comminution results. The university research team was enlarged by including the rock mechanics group, to test the initially proposed comminution mechanism (Borg et al. 2015a) and to refine it to our current understanding (Borg et al. 2015b(Borg et al. , 2015c(Borg et al. , 2016. Market entry has been achieved in late 2016, when Anglo American, after a series of comminution tests on different ores, ordered a bespoke VeRo Liberator®, specially designed to be used in a large-scale pilot test at one of their operations. ...
... The following examples of test-comminuted materials are thus not intended as presentation of full investigation results, some of which have been published elsewhere already (Borg et al. 2015a(Borg et al. , 2015b(Borg et al. , 2015c(Borg et al. and 2016. Additional comprehensive fact sheets, covering the test-comminution results of most bulk samples tested so far, are also available -unless confidential -upon e-mail request from PMS. ...
... These processes are possibly comparable to well-known, supersonic frequency-dependent processes such as the ones applied in ultrasonic cleaning and medical kidney stone disintegration devices (Cleveland and Tello 2004). This model explanation has first been published by Borg et al. (2015a) and has been subsequently refined (Borg et al. 2015b(Borg et al. , 2015c(Borg et al. , 2016 although still based on the same fundamental mechanisms, which has not been fundamentally questioned in any of the many discussions with colleagues. ...
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Full-text available
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 liberation. The VeRo Liberator® has been invented some five years ago and applies a completely new, mechanical comminution principle, which applies high‐velocity and high‐frequency impact comminution. The industrial scale 100 t/h VeRo Liberator® prototype features a vertical four‐fold axle‐in‐axle system, equipped with a large number of hammer tools, which rotate on three levels clockwise and anticlockwise against each other. The resulting high‐frequency, high‐velocity impacts cause a highly turbulent particle flow and trigger fracture nucleation and fracture propagation preferentially at and along phase boundaries. Breakage occurs from the high‐velocity stimulation of particles, where the elasticity and compressibility modules control differential particle behaviour. This differential behaviour results in the build‐up of stress along particle boundaries and eventual failure and breakage nucleation on mineral phase boundaries. Fracture nucleation and fracture propagation on particle boundaries rather than cross‐ boundary breakage explains the high degree of liberation and low energy consumption, compared to traditional comminution systems that feature breakage development parallel to 1 between point‐loads. Current research and high‐velocity impact experiments support our postulated breakage principle and further our understanding of this new and unconventional comminution process. The improved breakage behaviour results in a drastically reduced energy consumption of between 3 and 13 kWh/t, very high degrees of particle liberation, and particle size reduction ratios of up to 6.250 in single pass comminution. The VeRo Liberator® can either replace several conventional comminution steps or can reduce the application of less (energy) efficient technique to a minimum. The invention and production of the first industrial‐scale prototype (2011‐2012) was followed by extensive test comminution of bulk samples of a wide range of typical ores from various mines around the world (2012‐1014). This test work was accompanied by independent geometallurgical and mineralogical documentation and research (2013‐2015). In‐house presentations to mining houses and at international comminution conferences drew strong industrial interest and resulted in even more extensive test comminution of various types of industry‐supplied ores and smelter‐slags (2015‐2016). Presently, the first industrial‐scale pilot test phase is being launched jointly by PMS and Anglo American to test the VeRo Liberator® at one of their operations beginning in 2017.
... The VeRo Liberator ® is suitable for primary ores of sulphides, silicates, carbonates and oxides, slags from metallurgical smelters, power plants, and waste incinerators as well as for armored concrete and other heterogeneous solid materials. First comminution results of various materials as well as technical details on the VeRo Liberator ® have been recently presented and published at international mineral processing conferences by Borg et al. [2][3][4][5]. ...
... The physical mechanisms at work inside the VeRo Liberator ® cannot be observed directly but are currently described best by explanations that are in agreement with all empirical results obtained so far. Simplified illustrations and descriptions of the fundamental differences of communition and breakage between traditional ball mills and the VeRo Liberator ® have been published earlier already by Borg et al. [2][3][4][5]. ...
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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, improved particle liberation, and the move from ultra-fine grinding to coarse particle liberation and flotation. The innovative VeRo Liberator® applies a mechanical high-velocity comminution principle, where numerous hammer tools rotate clockwise and anticlockwise on three levels around a vertical shaft-in-shaft (hollow shaft) system. The resulting high-frequency, high-velocity impacts cause a highly turbulent particle flow and trigger fracture nucleation and fracture propagation preferentially at and along mineral boundaries. Breakage of coarser particles occurs from the high-velocity stimulation of bulk ore particles, where the elasticity and compressibility modules control differential particle behaviour. The improved breakage behaviour results in a drastically reduced energy consumption of only 3 to 13 kWh/t and very high degrees of particle liberation in the relatively coarse fraction of the product. On an industrial scale, Anglo American applies already two VeRo Liberators® in their South African operations and Penoles and Fresnillo, Mexico, have carried out advanced test-comminution of ores from several of their gold-silver-zinc-lead mines in Mexico. The current paper describes results from test-comminution by VeRo Liberator® of ores from Cienega Mine, Durango Province, Mexico, in comparison to Cienega's conventional comminution by SAG milling and ball milling. The results show that the VeRo Liberator® achieves a similarly high degree of particle liberation compared to the SAG mill, but at a drastically coarser particle size. This is achieved at significantly lower energy consumption and thus energy costs and allows for more efficient dewatering of comminuted waste material and, consequently, for potentially more stable slimes dams. The mechanical high-velocity impact comminution by VeRo Liberator® hence overcomes the notorious problems of inefficient breakage in conventional ball and SAG mills.
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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 liberation. The VeRo Liberator ® was invented some five years ago and applies a completely new, mechanical comminution principle, which applies high-velocity, high-frequency impact comminution. www.at-minerals.com Zusammenfassung: Die Effizienzsteigerung bei der Zerkleinerung von Erzen ist seit langem ein wichtiges Thema für die Bergbauindustrie, aber wesentliche Fortschritte sind immer noch verhältnismäßig rar. Einigkeit besteht darüber, dass die Hauptziele u. a. ein deutlich reduzierter Energieaufwand, trocken betriebene Anlagen, eine deutlich verbesserte Korngrößenreduzierung und die effektivere Freilegung von Wertpartikeln sind. Der VeRo Liberator ® ist vor etwa fünf Jahren erfunden worden und basiert auf einem vollkommen neuen, mechanischen Zerkleinerungsprinzip, das mechanische Hochgeschwindigkeits- und Hochfrequenzprallzerkleinerung anwendet. www.at-minerals.com
Chapter
Full-text available
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Book
This book is a collection of ISRM suggested methods for testing or measuring properties of rocks and rock masses both in the laboratory and in situ, as well as for monitoring the performance of rock engineering structures. The first collection (Yellow Book) has been published in 1981. In order to provide access to all the Suggested Methods in one volume, the ISRM Blue Book was published in 2007 (by the ISRM via the Turkish National Group) and contains the complete set of Suggested Methods from 1974 to 2006 inclusive. The papers in this most recent volume have been published during the last seven years in international journals, mainly in Rock Mechanics and Rock Engineering. They offer guidance for rock characterization procedures and laboratory and field testing and monitoring in rock engineering. These methods provide a definitive procedure for the identification, measurement and evaluation of one or more qualities, characteristics, or properties of rocks or rock systems that produces a test result.
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Comminution is known to be an inefficient user of energy. This makes it the largest energy consumer in many mine sites and therefore a large component of cost. One would therefore have thought that improving comminution energy efficiency would be receiving the undivided attention of the mining industry, but this is not the case. This paper considers why this is so and what the future might hold, by posing and attempting to answer three questions: • Is this really an important issue for the mining industry? • If so, can comminution energy be substantially reduced in a reasonable time frame? • What are the drivers that will motivate change, and what should now be done? The conclusions of the paper are pessimistic in the sense that forces may be gathering that will demand that the issue be addressed across the industry in the relatively near future, but optimistic in the sense that there is a clear development path. There is much that can be done with what is already known, and considerable promise exists in new developments which can be realised through sustained and focused R&D, building on new knowledge acquired in the last 20 years. These are outlined in the paper. It is concluded that there is a case for a global initiative to significantly reduce comminution consumption over say the next 10 years through a partnership between all parts of industry and the research community, covering short, medium and long-term innovation.
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A 152.4 mm (6 in) diameter resonant column device was modified to enable the direct measurement of torsional acceleration transfer functions of samples subjected to random excitation in the small-strain regime. Samples were tested over a wide range of confining pressures. By measuring the rotational acceleration of the end platens, the need to estimate the applied torque using a torque-current calibration factor for data reduction was eliminated, and issues such as back-emf, base fixity and eddy currents were bypassed. Preliminary calibration results illustrate that the first four peak frequencies and amplitudes can be readily employed for a calibration of modulus and damping characteristics over a wide frequency band, utilizing the continuous nature of the system rather than only the fundamental frequency of the specimen configuration.
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Comminution is one of the most intensively researched areas of the minerals industry. Much effort has been spent in attempting to reduce the high operating costs, but relatively little in developing practical methods to promote enhanced liberation of the minerals from each other. This paper considers the need to research more deeply the mechanisms of the breakage processes in current comminution machines, particularly the promotion of intergranular fracture. In order to do this control of crack propagation, and the nature and role of grain boundaries, are areas deserving most attention.
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The base metal mining sector, including copper, lead–zinc–silver and nickel, has been a prominent and critical feature of the Australian minerals industry. The various mines and fields have been producers of world significance, including Broken Hill, Mt Isa, Mt Lyell, Olympic Dam, Cobar and Kambalda. The long-term production trends in the base metal sector governing these historic fields remain relatively undocumented. This includes trends in ore grades, mining technique (open cut versus underground), solid wastes produced (tailings and waste rock), technology (e.g., milling) and known economic resources. This paper presents these results for the Australian base metals sector — arguably the first such systematic compilation undertaken. A historical overview is discussed for each major commodity to outline the principal developments and changes for that commodity, followed by the presentation of mining and milling trends. Overall, the key trends are declining ore grades versus increasing metal production and ore milled, and increased open cut mining and associated waste rock (though this latter aspect remains significantly under-reported). The extent of known economic resources has steadily increased for all commodities analysed, principally due to the inclusion of lower grade ores and/or difficult to treat ores (such as nickel laterites) or new deposit discoveries. Based on present mine plans and proposals, future metal production will increasingly shift towards lower ore grades and larger open cut mines to maintain production levels. There are sufficient known economic resources for about three decades or more, providing a basis to sustain the existing base metal industry but beyond this timeframe is difficult to predict. These trends point to the need to accurately report complete data on base metal mining and milling as key inputs into quantifying mineral resource trends as well as the environmental aspects of “sustainable mining”.
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A new model is proposed that allows for more general boundary conditions at both the active and passive ends of resonant column apparatus, especially those incorporated within the resonant column/quasi-static torsional shear devices. Analysis confirmed that use of the model is particularly important if the natural frequency of the soil-apparatus system is close to that of the passive end or reactin system, and that the calculated modulus and damping values can be highly inaccurate if simplified boundary conditions are assumed. Such situations occur when very soft soils, very stiff soils, or rock specimens are tested. Comparison of existing models and theb new solution to be observed response for a rubber testing specimen showed that the three-degrees-of-freedom assumption is more accurate in modeling the apparatus boundary conditions.
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For resonant column tests conducted in the flexure mode of excitation, a new methodology has been proposed to find the elastic modulus and associated axial strain of a cylindrical sample. The proposed method is an improvement over the existing one, and it does not require the assumption of either the mode shape or zero bending moment condition at the top of the sample. A stepwise procedure is given to perform the necessary calculations. From a number of resonant column experiments on aluminum bars and dry sand samples, it has been observed that the present method as compared with the one available in literature provides approximately (i) 5.9%–7.3% higher values of the elastic modulus and (ii) 6.5%–7.3% higher values of the associated axial strains.
The composition of rock fluids and their influence on the strength behaviour of rocks under increased pressures and temperatures.) – Sonderforschungsbereich 108 Spannung und Spannungsumwandlung in der Lithosphäre
  • Die Zusammensetzung Von Gesteinsfluiden Und Ihr Einfluß Auf Das Festigkeitsverhalten Von Gesteinen Bei Erhöhten Drücken Und Temperaturen
Die Zusammensetzung von Gesteinsfluiden und ihr Einfluß auf das Festigkeitsverhalten von Gesteinen bei erhöhten Drücken und Temperaturen. (The composition of rock fluids and their influence on the strength behaviour of rocks under increased pressures and temperatures.) – Sonderforschungsbereich 108 Spannung und Spannungsumwandlung in der Lithosphäre, Berichtsband 1990-1992 Teil B, Projekt D5, 823-898, Universität Karlsruhe.