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Breaking down comminution barriers -new dimensions of particle size reduction and liberation by VeRo Liberator®

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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 comminution equipment, an engineering start-up, PMS Hamburg, has invented and produced an innovative high-velocity impact crusher, the VeRo Liberator®, featuring highly improved particle size reduction ratios and very high degrees of particle liberation together with low levels of energy consumption and operational noise and operates dry, i.e. without using any water. The VeRo Liberator® is currently designed for a throughput of approximately 100 t per hour and has been tested on a number of different typical bulk ore and slag samples from mines and smelters around the world. Massive sulphide ore from the classic Rio Tinto Mine of the Iberian Pyrite Belt in Spain has been test-comminuted by the VeRo Liberator®. The ore and rare gangue minerals have been reduced in size by an amazing reduction ratio of 480 and have been liberated to a very high degree. According to our current understanding, these results are due to the unique working principle of the VeRo Liberator®, which 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 counterclockwise 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 comminution 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 13-15 August, 2015 San Luis Potosí, México 278 degrees of particle liberation. 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.
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Breaking down comminution barriers - new dimensions of
particle size reduction and liberation by VeRo Liberator®
Gregor Borg1, 2, Oscar Scharfe1, and Andreas Kamradt²
1 PMS, Abteistrasse 1, Hamburg, Germany
² Economic Geology and Petrology Research Unit, Martin Luther University Halle-
Wittenberg, Germany
Keywords: VeRo Liberator®, comminution, high-velocity impacts, reduction ratio,
particle liberation
Abstract
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 comminution equipment, an
engineering start-up, PMS Hamburg, has invented and produced an innovative high-
velocity impact crusher, the VeRo Liberator®, featuring highly improved particle size
reduction ratios and very high degrees of particle liberation together with low levels of
energy consumption and operational noise and operates dry, i.e. without using any water.
The VeRo Liberator® is currently designed for a throughput of approximately 100 t per
hour and has been tested on a number of different typical bulk ore and slag samples from
mines and smelters around the world. Massive sulphide ore from the classic Rio Tinto
Mine of the Iberian Pyrite Belt in Spain has been test-comminuted by the VeRo Liberator®.
The ore and rare gangue minerals have been reduced in size by an amazing reduction
ratio of 480 and have been liberated to a very high degree.
According to our current understanding, these results are due to the unique working
principle of the VeRo Liberator®, which 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
comminution 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
13-15 August, 2015San Luis Potosí, México 278
degrees of particle liberation. 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.
Parts of the following text has been presented at various conferences, in conference
proceedings volumes and various aspects of the comminution results and on the working
principle have been published by Borg et al. (2015 a, b, c).
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 (Mudd, 2007). 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 extractive 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 (Napier-Munn, 2014).
Under these challenging circumstances, PMS GmbH, an engineering start-up company,
based in Hamburg, Germany, has developed the innovative VeRo Liberator® (Figs. 1 and
2), an impact crushing machine with a high potential to solve several comminution
efficiency and cost issues simultaneously. The VeRo Liberator® (patents pending) is a
new comminution system, which operates completely dry 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 mineral
processing circuits. 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 Borg et al. (2015 a, b, c).
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 (Wills &
Atkinson, 1993; Wills & Napier-Munn, 2007).
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Technical Specifications of the VeRo Liberator®
The new VeRo Liberator® is a comminution machine in the 100 t per hour 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 (Figs. 1, 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.
Fig. 1: The VeRo Liberator® with feeding
funnel and conveyor belt fitted in the
foreground.
Fig. 2: VeRo Liberator®, front left, with
sorting system (middle) and ultra-clean
filter system (back right) fitted according to
customer specifications.
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 (Wills & Napier-Munn,
2007). 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 Borg et al. (2015 a).
The VeRo Liberator® works without any process water and is thus most suitable for
operation in arid regions where costs and availability of water are an even bigger issue
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than in wetter regions. However, the machine works not only in a dry process but is
additionally capable of actively warming/heating and thus drying the comminuted material
by converting the high velocity impact energy into thermal energy. This phenomenon has
been documented on test-comminuted silicate ore of industrial minerals for an undisclosed
client in the glass industry. The -120 mm ore had natural moisture levels from forest
outcrop, and some water had even collected at the bottom of the transport barrels. It has
been dried to a moisture content of 0.1 % by the comminution process in the VeRo
Liberator®. The comminuted product was suitably dry to be sieved with high throughput
down to size fractions of 0.18 mm, the finest screen applied (personal communication
Martin Oczlon).
Technically, the equipment is very easy to maintain. 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
throughput of 100 t per hour 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 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 (Fig. 2).
In a first and still very rough and estimated comparison of comminution costs of traditional
equipment with the VeRo Liberator®, it can be reasonably assumed that the VeRo
Liberator® can comminute brittle material at approximately 25% of the costs of traditional
comminution systems. This is based on the assumption by international comminution
experts that it costs currently approximately 8 US$/t to reduce material from 120 mm
diameter in size to less than 250 μm. Due to the fact that several classical comminution
steps (e.g. a primary crusher, secondary crusher and a first ball mill) can be replaced by a
single VeRo Liberator®, the same experts estimate that the cost are only in the order of
approximately 2,50 US$/t.
A Case Study of the Comminution of Massive Sulphide ore from Rio Tinto, Spain
The sample material provided for this study was taken from the ground level of the Cerro
Colorado East pit and represents blasted massive sulphide ore from the mining activities
prior to the year 2000. Subhedral cubic crystal faces of pyrite are notable on the surface of
the massive ore pieces. They can reach a size up to 2 cm edge width. Chalcopyrite occurs
in irregular blotchy fillings within the pyritic matrix.
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Fig. 3: Hand specimen of Rio Tinto
massive sulphide ore are composed mainly
of pyrite transected by thin veins and
fissures occupied by dark sphalerite and
iridescent chalcopyrite.
Fig. 4: Reflected light optical microscopy
photograph. Ore assemblage of primary
anhedral pyrite (Py) and replacement of
secondary sub- to euhedral pyrite and
anhedral interlocked chalcopyrite (Ccp)
and Sphalerite (Sph) in cracks and
interstices.
For the mineralogical investigation, polished sections of individual hand specimen have
been prepared by the in-house grinding laboratory of the Institute of Geoscience and
Geography of Martin-Luther University, Halle-Wittenberg, Germany.
The microscopic analyses have shown that the ore assemblage of metal sulphides is not
very complex. Pyrite represents the main mineral in the massive sulphide ore and built up
xenomorphic masses of pyrite that have been fractured intensively and appear with mostly
straight-lined, slightly bent fissures in mosaic patterns (Figure 5). The fractures have been
caused, assumedly, by brittle deformation and were replaced subsequently by anhedral
intergrown aggregates of chalcopyrite and sphalerite that enclose euhedral to subhedral
secondary cubic pyrite crystals with edge lengths up to 0.5 mm. In direct association to the
vein fillings, primary pyrite shows partially embayed crystal surfaces caused by resorption
by the emplacement of the hydrothermal Cu- and Zn-rich fluids. Thus, chalcopyrite and
sphalerite has been found as fillings of cracks and interstices. Some portions of the cracks
have been replaced by iron oxihydroxides, which could have been caused by weathering
of the ore.
Investigations of the comminuted sample have yielded that low contents of galena as well
as gangue minerals like phlogopite and quartz are also constituents of the primary ore.
Sieve Analysis (after German Industrial Standard DIN 66165)
The sieve analysis was performed on 7.9 kg of comminuted massive sulphide ore from the
Cerro Colorado pit of the Rio Tinto Mine. The grain size distribution curve of Figure 5
represents a narrow grain size range in which 99 % of the sample is crushed to particles of
< 0.5 mm diameter. Moreover, nearly 80 % of the sample has been comminuted to a grain
13-15 August, 2015San Luis Potosí, México 282
size < 125 microns and the half of this, nearly 40 % of the total weight, is constituted by
particles < 63 microns.
Fig. 5: Grain size distribution curve of the massive sulphide ore from the Cerro Colorado
pit of the Rio Tinto Copper Mine, Spain, treated by the VeRo Liberator.
Based on the grain size distribution curve, it can be stated that over 90 % of the sample
has been comminuted to particles of the grain size class of fine sand, which correspond to
grains with a size of < 200 microns.
Liberation and Morphology of the Comminuted Material
For the investigations of the liberation of the specific sulphide ore particles and their
morphological properties, polished sections of particles of the grain sizes < 250, < 125 and
< 63 microns, and additionally from the unsieved sample, were analyzed by Scanning
Electron Microscope.
The examinations of the polished sections by Scanning Electron Microscope (SEM)
equipped with an EDX-detector unit have shown that the individual sulphides of the
massive sulphide ore can be liberated and separated to an exceptionally high degree by
the VeRo Liberator. Generally, the comminution product is characterized by the ubiquitous
occurrence of pyrite clasts. Chalcopyrite and sphalerite particles appear commonly, but
represent a much lower portion on the total comminution product. The shape of the
particles is commonly angular, but grain tips can be often subrounded. Pyrite clasts are
more angular than sphalerite and chalcopyrite clasts, both in many cases comminuted to
smaller grains compared to pyrite.
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Gangue minerals found in the comminution product are phlogopite, forming round particles
with strongly subdivided grain surface or lath-like shreds. Accessory minerals, as barite,
cassiterite or arsenopyrite have been detected mostly intergrown with pyrite as minute to
few micrometer sized inclusions.
Comminuted Material in the grain size Fraction 125 – 250 Microns
The fraction of the 125 microns mesh represents about 15 % of the total comminution
product. The analysis of this fraction shows that a complete liberation of chalcopyrite,
sphalerite and galena can be found occasionally, but intergrowths of the base metal
sulphides with pyrite are quite common. In many cases pyrite encloses minute galena
droplets or sphalerite as well as chalcopyrite, which occurs irregularly intergrown with
pyrite. A part of the particles that consists mainly of pyrite are occupied by sphalerite or
chalcopyrite along grain margins. The clasts are angular to subrounded, concave break
lines of the individual grains are common. Pyrite grains show occasionally straight edges
and host commonly internal fissures (Figs. 6 - 9).
Comminuted Material in the grain size Fraction 63 – 125 Microns
The examination of the 63 – 125 microns fraction shows that the degree of liberation of
chalcopyrite, sphalerite and galena changes fundamental with decreasing grain size. The
comminution particles of this grain size range consist of almost completely liberated pure
sulphide mineral clasts; only in rare cases intergrowth, mostly of minute galena,
cassiterite, barite or arsenopyrite have been found enclosed in pyrite particles. Intergrowth
of pyrite and chalcopyrite or sphalerite have been observed very rarely (Fig. 6-9). The
shape of the particles ranges from angular to rounded grains or elongated forms.
Fig. 6: SEM-view to the unsieved
comminuted massive sulphide ore of the Rio
Tinto Mine shows abundant pyrite (Py) clasts
as well as less chalcopyrite (Ccp) particles
and gangue (Phl-phlogopite).
Fig. 7: SEM-image depicting completely
liberated pure phases of pyrite (Py),
chalcopyrite (Ccp), sphalerite (Sph) as well
as phlogopite (Phl) with an average size of
60 microns and angular to subrounded
shapes.
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Comparative test work of other Materials
Numerous other materials, including ores and smelter slags have been test-comminuted
with similarly impressive results (Figs. 10-13). Results of these test have been published
by Borg et al. 2015 a, b and are available as fact sheets under www.veroliberator.de.
Fig. 10: Scanning electron microscope
(SEM) image of graphite flakes (dark grey)
and minor gangue minerals (light grey)
from AMG Mining’s Kropfmühl Mine,
Germany, after comminution by VeRo
Liberator®. The graphite flakes are
perfectly liberated and virtually
undeformed.
Fig. 11: Comminuted low-grade W-Mo ore
from Almonty Industries’ Wolfram Camp
Mine, Australia. The ore minerals
scheelite, wolframite and molybdenite are
fully liberated from the gangue minerals
(quartz and mica).
Fig. 8: Amongst primarily liberated particles
some particles showing intergrowth of pyrite
(Py) with barite (Brt) or chalcopyrite (Ccp).
Gangue minerals (Phl-phlogopite, Qz-quartz)
have also been separated within the grain size
fraction.
Fig. 9: Exposed intergrowth of pyrite (Py)
with sphalerite (Sph) or quartz (Qz) occur
rarely. Most of the particles are
completely liberated by the VeRo
Liberator®.
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Fig. 12: Comminuted fluorite ore from
Sachtleben Bergbau AG’s Clara Mine,
Germany.
Fig. 13: Comminuted anode smelter slag
with metallic copper “droplets” from
AURUBIS AG’s base metal smelter in
Lünen, Germany.
The Comminution Mechanism of the VeRo Liberator®
The most striking and unique comminution effects of the VeRo Liberator® are the extreme
reduction ratios, achieved in single-pass comminution within approx. 10-20 seconds, and
the very high degrees of particle liberation along the particle boundaries. These new
features contrast starkly with the reduction ratio and degree of particle liberation achieved
by traditional comminution equipment such as jaw and cone crushers and classical ball
mills. In order to understand the particular working principle of the VeRo Liberator®, it is
worth to envisage the fragmentation process in these traditional pieces of equipment. More
detailed considerations on these comminution processes can be found in Borg et al. (2015
b).
Fig. 14: Compressive fracture formation in
standard ball mill systems.
Fig. 15: Fracture orientation across
particle boundaries, leading to incomplete
particle liberation.
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
13-15 August, 2015San Luis Potosí, México 286
of rock placed between two such load points (Fig. 14). Generally, the tensile strength is
only approximately 10-20 % of the compressive strength. To generate 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 will 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. Existing particle boundaries
will be utilized, in this process, if the propagating fracture is orientated at a sufficiently
shallow angle to the particle boundary. If this critical angle is exceeded, the facture will
trans-sect the mineral boundary, typically causing incomplete particle liberation (Fig. 15)
with all negative effects on subsequent steps of mineral processing.
Fig. 16: High-velocity impacts inflicted on
inhomogeneous material (e.g. ore, slag,
armored concrete) by rotating hammer tools
send shock waves through the material.
Fig. 17: The various particles react differently
according to their specific compressibility and
elasticity moduli under high-frequency
stimulation.
In contrast, the working principle of the VeRo Liberator®, is apparently less characterized
by fracture propagation between load points, but is apparently the consequence of
differential mechanical behavior of the various mineral components. The most obvious
phenomenon of the VeRo Liberator® is that separation occurs predominantly along
particle or mineral boundaries. According to our current understanding the inter-particle
separation of minerals occurs due to the different moduli of deformation of the different
particles (deformation modulus or Young´s modulus). Inside the VeRo Liberator®, the feed
material experiences an enormous number of high-frequency, high-velocity impacts by the
large number of steel hammer tools, by impacts into the casing and by impacts of particles
crashing into other particles (Fig. 16). These impacts send high-velocity shock waves
through the brittle material and stimulate the mineral specific rock mechanic moduli (Figs.
16 and 17). If the difference and orientation of the moduli is sufficient, the stress will build
up specifically along particle boundaries, which are the preferred sites of fragmentation
due to extension or shearing (Figs. 17 and 18).
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Fig. 18: The high frequency of impacts is
faster than the relaxation period of the
particles and results in tensional and/or
shear stress accumulation between
different particles and eventually leads to
inter-particle breakage along particle
boundaries from either extensional
separation or shearing.
Fig. 19: The result is a predominance of
inter-granular, rather than intra- or cross-
granular fracturing, which leads to the
observed high degree of particle liberation.
Additionally, the velocity-dependence and thus time-dependence of such high-velocity
comminution processes, appear to of significance for the unusually good results. 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 (Borg et al. 2015 b). Normally, stress release
would occur in and between various components due to a time-dependent stress
relaxation process. However, in case of the VeRo Liberator® 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 adjacent minerals may cause fracturing along
particle boundaries (Lempp et al. 1992). These processes are possibly comparable to
other, technically well-known, supersonic frequency-dependent processes as applied e.g.
in ultrasonic cleaning devices.
However, we assume that high-frequency vibration processes occur inside the VeRo
Liberator® in a sufficient intensity to cause the observed particle liberation. Resonance
phenomena probably cause further accumulation of stress and energy, comparable to the
effects in resonant columns (Ashlock & Pak, 2010; Ashmawy & Drnevich, 1994; Kumar &
Madhusudhan, 2009). Additionally, the shape of the casing of the VeRo Liberator® is most
13-15 August, 2015San Luis Potosí, México 288
likely to have also a positive effect on successful particle liberation due to specific
resonance frequencies, which will be investigated more detail in future.
Further research to explain the impressive comminution results of the VeRo Liberator® is
still being conducted to explain the working 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 additional ore types is taking first place so
far.
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 apparently 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 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.
Additionally, the impact energy of the VeRo Liberator® is at least partly converted into
thermal energy, i.e. heat, which has an additional drying effect on the comminuted product,
which can be improve subsequent dry sieving of the comminuted size fractions. The mill
operator reported a temperature increase of 20 K for a ground product versus the feed.
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 degree 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
(Wills & Atkinson, 1993) in classical comminution systems such as ball mills (Figs. 14, 15).
Incomplete particle liberation, in turn, is a major cause for subsequent inefficient
separation and extraction by processes such as froth flotation and solvent extraction.
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
The bulk sample of massive sulphide ore from the famous Rio Tinto Mine has been
generously provided by EMED Tartessus Mining, Huelva, Spain. Discussions with Christof
Lempp, Rock Mechanics and Engineering Geology Unit, Martin Luther University Halle-
13-15 August, 2015San Luis Potosí, México 289
Wittenberg, Germany have helped to explain the fragmentation processes of the VeRo
Liberator®. Fruitful discussions with Martin Oczlon, Senior Advisor Minerals Exploration
and Processing, Heidelberg, Germany are gratefully acknowledged and have deepened
our understanding of the working principle of the VeRo Liberator® and of its innovative
potentials.
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Advances in Comminution
and Classification
ISBN: 978-1-329-01332-2
13-15 August, 2015San Luis Potosí, México
Preface
In this book, the papers accepted for the International Comminution and Classification
Congress 2015 (ICCC 2015) held in San Luis Potosi, Mexico from 11th to 15th August
2015 are presented. Well recognized experts from all over the world showed the state of
the art in Comminution and Classification fields.
ICCC 2015 gathered professionals from industry, academics and government sectors.
This technical congress was an ideal occasion for the research community to approach the
Comminution and Classification industry. The new and emerging technologies were
presented in 39 different oral presentations and 5 novel training courses.
It remains for me to thank all the members of the technical advisory committee for their
time and affords to review each of the papers presented. Also, a special thanks to our
sponsors who have shown a great financial support to make this congress possible. I hope
to see everyone again at the next ICCC 2017.
Jose A. Delgadillo
Congress Manager ICCC 2015
www.iccongress.org
13-15 August, 2015San Luis Potosí, México i
Table of Content
Parameter studies on the production of submicron mineral particles.......................................1
Noise Analysis System and Intensity of Impact in the Mills Applicable to the Grinding
Circuit Optimization........................................................................................................................10
Using DEM to investigate how shell liner and end-liner profile can induce ball segregation
in a ball mill......................................................................................................................................22
Simulations of the Mineração Serra Grande industrial grinding circuit...................................33
Getting High Grade Barite by Gravimetric Concentration ........................................................44
Screening Evaluation of Industrial Aggregates for Construction Efficiency of Screening
Industrial and Aggregates Evaluation for Construction.............................................................51
De-Sliming of penalty U-Bearing particles in the recleaner feed of a copper Concentrator:
Investigating the effect of density on de-sliming using a cyclone rig......................................60
Application of air classification for upgrading of residues from dry off-gas de-dusting ........68
Mechanical Characterization and Study of the Brittle Fracture of The Rocks Of The XX
Century Mine Clearing...................................................................................................................78
Utilization of high frequency screens and classifier equipment in grinding circuit................89
Modelling and simulation of batch grinding with vertical screw stirred mill using
MATLAB/Simulink...........................................................................................................................97
Effect of grinding aid on through put rate of wet grinding ball mill in low grade limestone
........................................................................................................................................................ 113
Innovation and Increased Production in SAG-HPGR Circuit at Minera Peñasquito………
........................................................................................................................................................ 121
Sustainable Development in Cone Crushing Design and Implementation - CH860 &
CH865: Sandvik‘s New Reliable and Productive Crushers....................................................129
Productivity and Recovery Improvements by Closing Grinding Circuits with Derrick® Stack
Sizer® Screens.............................................................................................................................144
Numerical simulation of particle flow within a spiral concentrator operation using SPH
.................................................................................................................................................... …..154
What happens when hydrocyclone operates at inclined positions? Detail flow field and
performance analysis by CFD and Experiments .....................................................................161
Comminution in small-scale mining in Ecuador.......................................................................177
Exploration of hydrocylone designs for improved ultra-fines classification using multiphase
CFD model ....................................................................................................................................183
Multicomponent particles classification in a hydrocyclone.....................................................196
13-15 August, 2015San Luis Potosí, México ii
Developing DEM-CFD two-way coupled model for charge motion in a tumbling mill:
Validation against PEPT.............................................................................................................. 210
Mechanical Activation of Baddeleyite Concentrate.................................................................223
Recovery of vermiculite by elutriation.......................................................................................235
Simulation and Selection of a Crushing Circuit........................................................................245
Achieving SAG Mill Design Production at Start-Up Using Best Practices - Fact or Fiction ?
....................................................................................................................................................... 247.
An Experimental understanding of communition kinetics of overflow and grate discharge
ball mills…………………………………..……………………………………………….. ................................................256
Comparison of binary mix sampling techniques…………………………………..……………….……………..258
Optimization of LiFePO4 wet media milling …………………………………..……………….…………….. 267
Breaking down comminution barriers - new dimensions of particle size reduction and
liberation by VeRo Liberator®……………………………………………………..……………….…………….. 277
... 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. ...
... However, the machine works not only in a dry process but is additionally capable of actively warming/heating and thus drying the comminuted material by converting the impact energy into thermal energy. Another effect of the high velocity of the impacts is the embrittlement of viscous ("ductile") particles, such as spherical metallic copper droplets in smelter slags that remain spherical and are not flattened as in conventional comminution systems ( Fig. 13 in Borg et al. 2015c). Technically, the equipment is easy to maintain since the housing can be lifted hydraulically for single-tool replacement or the entire drive shaft and tool unit can be pulled from the main frame. ...
... 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. ...
Conference Paper
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]. ...
... However, the machine works not only in a dry process but is additionally capable of actively warming/heating and thus drying the comminuted material by converting the impact energy into thermal energy. Another effect of the high velocity of the impacts is the embrittlement of viscous ("ductile") particles, such as spherical metallic copper droplets in smelter slags that remain spherical and are not flattened as in conventional comminution systems ( Fig. 13 in [4]). Technically, the equipment is easy to maintain since the housing can be lifted hydraulically for single-tool replacement or the entire drive shaft and tool unit can be pulled from the main frame. ...
Article
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 ® 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
Conference Paper
Full-text available
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.
Article
Full-text available
The new VeRo Liberator® has been recently developed by PMS, Hamburg, Germany, and represents a highly efficient impact crushing system for dry comminution of ore, slag, armoured concrete, and aggregate in the 100 t per hour throughput class. The VeRo Liberator® operates with a vertical axle-in-axle system, which is equipped with a total of up to 144 hammer tools, each approximately 90 cm long. The hammer tools rotate on three levels clockwise and anticlockwise against each other at high rotation speeds. The gravitational flow of the material through the machine results in a very low energy consumption. The multiple high-velocity impacts of the tools inflicted on the material achieve unparalleled reduction ratios of up to more than 400 without clogging the system. The VeRo Liberator® achieves also an unusually high degree of particle liberation. Intergranular breakage is the predominant form of particle separation and is caused by the high velocity impacts, inflicted by the hammer tools, casing, and particles on each other. Apparently, the shock waves travelling through the impacted material stimulate the particles to react individually according to their elasticity “E” and compressibility “K” moduli. The specific “reaction” of the various shock-stimulated particles leads apparently to the pronounced intergranular breakage, separation, and thus particle liberation.
Article
Full-text available
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.
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.
Article
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.
Conference Paper
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.
Article
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.
Article
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”.
Article
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.
Article
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.