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High-velocity comminution of massive sulphide ores by the VeRo Liberator® technology for more energy efficient size reduction and particle liberation

Authors:
  • PMS Handelskontor GmbH
45
World of Mining Surface & Underground 68 (2016) No. 1 Technical Report
Massive sulphide ores are an important source of base and
precious metals and occur or are mined on all continents. The
comparatively high metal grades, when compared with other
deposit types such as porphyry copper ores or sediment-hosted
stratabound copper deposits, make the massive sulphide ores
especially attractive in times of depressed commodity prices. The
typical base metal sulphide ore minerals such as chalcopyrite,
bornite, chalcocite, sphalerite and galena tend to be intricately
intergrown with each other as well as with barren silicate or car-
bonate gangue. Comminution of these ores aims both at particle
size reduction and the liberation of the mineral phases from each
other to produce (ideally) separate ore mineral concentrates for
Cu, Pb, and Zn.
The newly developed VeRo Liberator® can contribute significantly
to a more efficient comminution of massive sulphide ores and
has been tested on various massive sulphide ores from three
characteristic ore deposits in Spain and Finland. Ores from the
mines at Rio Tinto and Aguas Tenidas in the Iberian Pyrite Belt,
Spain, as well as ore from Pyhäsalmi Mine in Finland have been
test-comminuted by single pass comminution. The VeRo Liber-
ator® is currently operating in the 100 t/h throughput class, has
a very low energy consumption of between 2.3 and 3.0 kWh/t,
and operates without process water. The fourfold vertical shaft-
in-shaft system has numerous hammer tools that rotate with
very high and variable speeds at three tool levels clockwise and
anticlockwise against each other, thus inflicting a multitude of high
velocity impacts onto the ore.
Particle size reduction of the massive sulphide ores during the
quick, single pass comminution has been between 444 and 1000,
which exceeds the results of traditional crushing systems by far.
High-velocity comminution of massive sulphide
ores by the VeRo Liberator® technology for more
energy efficient size reduction and particle
liberation
GREGOR BORG, FELIX SCHARFE, ANDREAS KAMRADT, Germany
The VeRo Liberator® can thus replace at least two or even three
comminution steps in conventional mineral processing setups.
The second most important effect of comminution by the VeRo
Liberator® is the high degree of particle liberation, which liberates
commodity minerals efficiently from waste particles. Apparently,
the fracture nucleation and fracture propagation occurs in the
VeRo Liberator® at and along particle boundaries, which is one
of the main reasons for the high efficiency and thus low energy
consumption. The abundance of high-velocity, high-frequency
impacts, the differential rock mechanical behaviour of the various
minerals, and interference phenomena of progressing and inverse
reflected shock waves lead to the mechanical fragmentation of
the ores, preferentially along particle boundaries.
The VeRo Liberator® thus offers a highly innovative comminution
technique that can increase energy efficiency and particle liberation
performance drastically. Besides the environmental advantage of
a reduced carbon footprint, increased comminution efficiency can
be a major factor in economically successful mining and mineral
processing operations, particularly in times of low commodity
prices as experienced in the present raw materials cycle.
1 Introduction
The unfavourably high level of energy consumption in conventional
comminution, i.e. crushing and milling, in mining and mineral pro-
cessing operations as well as in recycling of metallurgical slags and
waste incinerator slags is well known and documented (Figure 1,
http://www.visualcapitalist.com, [10]). Additionally, 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 [9]. Base/precious
metal-bearing massive sulphide ores are comparatively high grade
ores and are thus a welcome source of higher revenue in mining
and processing. Such ores are comparatively easy to explore for
by geophysical means and – as a consequence – have enjoyed
a high discovery rate but potentially undiscovered, remaining ore
bodies are more difficult to come by.
It goes without saying that the current period of depressed min-
eral and metal commodity prices increases the challenge even
further to mine and process ores and to extract and market metals
more efficiently and thus profitably. Cost reduction by improved
efficiency is therefore a ubiquitous task for the extractive industry.
As a consequence, all stages of mining, mineral processing, and
metallurgy need to be reviewed carefully to identify substantial and
suitable technical innovations [7]. In their conclusions, Cutifani &
Bryant ([7], p. 21) state that: “Miners must embrace this new mind-
set and apply it to the development of their internal strategies for
exploration, development, operations and closure. Also, all miners,
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
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World of Mining Surface & Underground 68 (2016) No. 1
Technical Report
regardless of their size, must significantly increase their innovation
efforts to develop new business models and methods for mining.
Without a step change in innovation investment, mining will not
be able to meet the expectations of society.” 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 [10].
In typical comminution designs for ores and secondary mineral
raw materials, the traditional set up includes initial crushing
stages, i.e. typically primary or secondary jaw or cone crushers,
followed by subsequent milling stages in ball mills, SAG mills or
HPGR mills. It is important to note that crushing processes, i.e.
the breakage or fracturing of rocks, is 10 to 20 times more energy
efficient compared to milling [8], which includes the time- and en-
ergy-consuming grinding and pulverisation to particle sizes suitable
for subsequent froth flotation. Moving comminution increasingly
from the grinding and milling side to the crushing side thus holds a
great potential for increasing the energy efficiency of comminution
significantly. The breakage sensu stricto, which results in particle
size reduction as well as particle liberation, consumes only 1 %
of energy in conventional mills with heat loss, electromechanical
loss using 87 % of the input energy (Figure 2, [8]).
Under these challenging circumstances, PMS GmbH, an engineer-
ing start-up company, based in Hamburg, Germany, has devel-
oped the innovative VeRo Liberator®, an impact crushing machine
with a high potential to solve several comminution efficiency and
cost issues simultaneously. The VeRo Liberator® is a new com-
minution system, which operates completely dry with very low
energy consumption and achieves impressive reduction ratios of
up to 1000 in a single pass. Thus the VeRo Liberator® is capable to
replace several comminution stages in mineral processing circuits.
Furthermore, the VeRo Liberator® achieves the comminution by
energy-efficient crushing instead of milling or grinding.
The VeRo Liberator® is suitable for primary ores of sulphides, sili-
cates, carbonates and oxides, slags from metallurgical smelters,
power plants, and waste incinerators as well as for armored con-
crete 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. [2-5].
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 de-
gree 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 mid-
dlings, commonly encountered in more traditional comminution
systems [11, 12].
2.1 Technical specifications of the VeRo Liberator®
The new VeRo Liberator® is a comminution machine in the 100 t/h
throughput class (Figures 3 and 4). 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. This can carry up to 144 hammer tools
that can be varied in size, weight, and steel composition. These
hammer tools are mounted individually on three separate levels,
which rotate clockwise and anticlockwise against each other at
high speeds, causing high-velocity impacts. The material falls grav-
itationally through the cylindrical armored comminution chamber
(Figures 3 and 4), where it is impacted by the hammer tools and
impacts onto the armored housing with specially designed and
engineered inner liners, and onto 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 [12]. 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
Fig. 1:
Distribution of energy consump-
tion at typical mine sites (modified
from http://www.visualcapitalist.
com); note that processes such as
electro-winning, refining, or smelt-
ing processes are not considered
here
Fig. 2: Schematic pie chart showing the utilisation of energy con-
sumed by conventional mills during operation [8]; please note
that only 1 % of the energy is used for the actual breakage
and thus size reduction of the material
47
World of Mining Surface & Underground 68 (2016) No. 1 Technical Report
Processing Machines, TUBA Freiberg, Germany). The reduction
ratio of the VeRo Liberator® is fundamentally larger and ranges
from a minimum ratio of 100 to a reduction ratio as high as 1000.
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 80 % with a diameter of less than 120 µm, thus representing
an impressive reduction ratio of 1000.
The VeRo Liberator® works without any process water and is thus
also suitable for operation in arid regions where costs and avail-
ability of water are an even bigger issue 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 docu-
mented 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 (pers. comm. 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 stand-by 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
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 4).
In a first and still very rough and estimated comparison of com-
minution 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 assump-
tion 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.
2.2 Comminution of massive sulphide ores
by VeRo Liberator®
Massive sulphide ores are a common source of base and precious
metals and occur on all continents. The sulphide ore minerals are
typically intricately intergrown with each other and – in many cases
– with silicate or carbonate gangue minerals. The present paper
illustrates the comminution results of massive sulphide ores from the
open pit of Rio Tinto Mine (Figure 5) and from Aguas Tenidas Mine
in the famous Iberian Pyrite Belt in Spain and from Pyhäsalmi Mine,
which is situated in a massive sulphide mining district in Finland.
Although massive sulphides can occur intergrown with relatively
little gangue material, they still pose a challenge in comminution.
Even where the sulphides occur as massive layers and enter
the processing plant as chunks of sulphide ore, the process-
ing is not only the straight forward particle size reduction. The
base metal massive sulphide ores consist typically of pyrite as
the predominant sulphide phase, which is commonly barren
waste unless the pyrite contains precious metals such as gold.
The commodity sulphides are typically chalcopyrite, bornite, or
chalcocite as Cu-carrying phases, sphalerite as Zn-sulphide, and
galena as Pb-sulphide. Mineral processing is most efficient if the
base metal sulphides are liberated and separated from the pyrite
(and the silicate gangue minerals) to produce (ideally) separate
base metal sulphide concentrates for further marketing or direct
hydro- or pyro-metallurgical processing.
Fig. 3: The VeRo Liberator® with feeding funnel and conveyor belt
fitted in the foreground (Photo: Christian Bendel)
Fig. 5: View of the old Rio Tinto open pit. Atalaya Mining plans to start
mining again in 2016; the steeply dipping lensoid massive sul-
phide copper ore body (grey) is enclosed in altered (yellow-brown)
and unaltered (dark grey) wall rocks. (Photo: Gregor Borg)
Fig. 4: The VeRo Liberator® with sorting system (middle) and
ultra-clean filter system (back right) fitted according to
customer specifications (Photo: Christian Bendel)
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2.3 Macroscopic and microscopic characterisation
of tested massive sulphide ores
2.3.1 Massive sulphide ore from Rio Tinto Mine, Spain
Atalaya Mining plans to start mining and processing of massive
sulphide ore from the famous Rio Tinto Mine in 2016. The massive
sulphide bulk sample was taken from the ground level of the Cerro
Colorado East pit and represents blasted massive sulphide ore
(Figure 6) from the mining activities prior to the year 2000. Subhe-
dral cubic crystal faces of pyrite are notable on the surface of the
massive ore pieces. They can reach a size up to 2 cm in diameter.
Chalcopyrite occurs in irregular blotchy fillings within the pyritic
matrix. For the mineralogical investigation of all ores, polished
sections of individual hand specimen have been prepared by the
in-house polishing 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. Such frac-
tured areas are characterized by predominantly straight to slightly
curved fissures in mosaic patterns (Figure 7). 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 diameters of up to 0.5 mm. In direct association
to the vein fillings, primary pyrite shows partially embayed crystal
surfaces caused by resorption 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. Low contents of galena as well as gangue
minerals like phlogopite and quartz are also constituents of the
primary ore.
2.3.2 Massive sulphide ore from Aguas Tenidas Mine, Spain
The Aguas Tenidas Mine is excavating ore from one of the numer-
ous massive sulphide deposits in the east-west-trending Pyrite
Belt of the Iberian Peninsula and is located in the northern part
of Andalucia in the Huelva Province, Spain. The mine is situated
on the northernmost limb of the Iberian Pyrite Belt, some 10 km
west of the Rio Tinto mining district and represents a volcanogenic
massive sulphide deposit, comprising massive sulphide lenses
underlain by a stockwork feeder zone.
The main product is copper, which is, together with zinc, extracted
as sulphide concentrate, but additional revenues can be generated
Fig. 7: 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
Fig. 6: Hand specimen of Rio Tinto massive sulphide ore are com-
posed mainly of pyrite transected by thin veins and fissures
occupied by dark sphalerite and iridescent chalcopyrite
Fig. 9: Reflected light microscope image of a polished section of
massive sulphide ore from Aguas Tenidas, showing complexly
intergrown pyrite (Py), chalcopyrite (Ccp), sphalerite (Sph),
and galena (Gn)
Fig. 8: Massive sulphide hand specimen from Aguas Tenidas Mine,
Spain, consisting of macroscopically visible pyrite and chalco-
pyrite (yellow) and sphalerite (black) and galena (grey)
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World of Mining Surface & Underground 68 (2016) No. 1 Technical Report
from lead, and limited amounts of gold and silver. Small-scale
mining activities can be traced back to about 1886. A completely
new processing facility has started its operation in 2008. The ex-
pected “Life Of Mine” (LOM) is forecasted until 2020, whereas new
exploration work have confirmed an expansion of the LOM until
2035. Currently, the mine can produce 2.2 Mt of concentrates per
year, half copper concentrate and half polymetallic concentrates.
The massive sulphide ore (Figure 8) appears dense and shows
generally brownish to pale brass-yellow colors paired with a varying
metallic luster. Pyrite makes up the main component of the ore
and is traversed by brass-yellow chalcopyrite veins of varying
thickness, partly tarnished by iridescent fracture surfaces. The
veins run commonly curvilinear and nest-like fillings can be noticed
occasionally within the massive ore. Small thin and elongated dark
brownish spots of sphalerite can be observed rarely within the
massive pyrite. Chalcopyrite, as the main commodity ore mineral,
occurs intricately intergrown with pyrite and minor galena (Figure
9). However, most of the massive sulphide ore pieces are tarnished
by a grey-brownish patina.
2.3.3 Massive sulphide ore from Pyhäsalmi Mine, Finland
Pyhäsalmi Mine, situated in the Oulu Province of central Finland,
is the deepest underground mine in Europe operating since 1962.
Pyhäsalmi Mine, formerly operated by Canadian Inmet Mining
Company, was bought by Canadian First Quantum Minerals Ltd.
in March 2013. The copper- and zinc-rich massive sulphide ore
(Figure 10) is exploited in underground workings down to 1444 m
below surface. The average grade of the ore, as reported for 2013,
contains 1.0 % Cu and 1.7 % Zn, with Au and Ag extracted as
byproducts.
The ore is hosted by metavolcanic rocks that have been altered
hydrothermally and affected by at least four deformational and meta-
morphic events. The deposit is associated with felsic metavolcanic
rocks at the base of the deposit, which grade into more intermedi-
ate and mafic metavolcanic rocks towards the top of the deposit.
Microscopically, the pyrite-dominated ore looks fractured and
veins transect the ore assemblage (Figure 11). In particular pyrite
has been fractured intensively and fissures were filled and partly
replaced by chalcopyrite (Figure 11), sphalerite, and pyrrhotite. The
sulphides are accompanied by intergrown xenomorphic gangue
minerals such as anthophyllitic amphibole, calcite/dolomite, and
quartz. Galena has also been observed as minute anhedral grains
(20 µm) embedded in calcite gangue. Baryte appears occasionally
associated with the vein mineralization.
The chalcopyrite-sphalerite-pyrite ore is characterized by dissemi-
nated and intergrown anhedral to subhedral sulphide crystals. The
individual ore minerals are medium to very fine-grained, commonly
several tens of microns in diameter, but can reach diameters up to
1 mm. The sulphide grains are embedded in a holocrystalline matrix
composed of hypidiomorphic amphibole, intergrown with xenomor-
phic, interlocked calcite and dolomite as well as potassium feldspar.
Arsenopyrite and sphene have been found as accessory minerals.
The microscopic analysis of the massive copper-rich sulphide ore
shows intensely intergrown anhedral pyrite and chalcopyrite, the
latter commonly associated with anhedral inclusions of sphaler-
ite and galena building up a very complex network texture. The
network of pyrite and chalcopyrite is transected by wider veins
dominated by chalcopyrite. Subhedral pyrite can be found in
vugs and open fractures and is accompanied by euhedral quartz
phenocrysts that locally host minute chalcopyrite inclusions.
2.4 Microscopic documentation of the comminuted
massive sulphide ores
The three types of massive sulphide ores have been test-com-
minuted by the VeRo Liberator® and have been investigated ore
mineralogically and characterized by standardized sieve analysis.
The sieve analysis has been carried out after German Industrial
Standard Procedure DIN 66165. Detailed and standardized fact
sheets of these investigations and the results are available upon
request from PMS (contact@veroliberator.de).
The particle size reduction ratios of the three massive sulphide ore
samples in quick single pass comminution by the VeRo Liberator®
are all impressive (Table 1). Feed material size in all three cases
was <120 mm and resulting particle size reduction ratios (reduced
to P80) range from 444 (Aguas Tenidas) to 480 (Pyhäsalmi) and
even to 1000 (Rio Tinto).
The reduction ratios of a representative range of other ores from
all over the world, which have been test-comminuted by VeRo
Liberator® to date, range from a minimum of 171 (tungsten skarn
Fig. 11: Optical microscopy image of a polished section of Pyhäsalmi
ore; cracks in sulphide ore are occupied by gangue (amphi-
bole (Amp), calcite (Cal)) and chalcopyrite (Ccp) ore
Fig. 10: Hand specimen of chalcopyrite-sphalerite-pyrite ore from Py-
häsalmi Mine, Finland; the sulphide minerals and gangue are
intricately intergrown and show subhedral to anhedral crystals
Table 1: Comparison of size reduction of the various massive sulphide
ores by single pass comminution with the VeRo Liberator®
Massive sulphide mine Feed material P80 Reduction ratio
Rio Tinto <120 mm <120 µm 1000
Aguas Tenidas <120 mm <270 µm 444
Pyhäsalmi <120 mm <250 µm 480
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World of Mining Surface & Underground 68 (2016) No. 1
Technical Report
ore) to 240 (baryte and fluorite vein type ore) to 300 (graphite ore),
which are all results that are far higher than those of conventional
crushing systems [12].
The other most remarkable comminution effect of the VeRo Lib-
erator® is its capability to liberate particles to a very high degree,
previously not known from conventional comminution systems.
Different mineral particles become separated from each other
predominantly along the particle boundaries and thus interparticle
breakage dominates over fracturing across particle boundaries.
It goes without saying that this effect is most welcome in mineral
processing since it avoids incomplete particle liberation. The latter
is a major obstacle in subsequent froth flotation and to date is
compensated by longer milling to much smaller particle sizes. This
in turn is not only extremely energy-consuming, but it can also
produce unwanted quantities of middlings or slimes, which can
be too fine for recovery during flotation.
The comminuted massive sulphide ores have been investigated
by scanning electron microscopy (SEM) combined with ener-
gy-dispersive X-ray fluorescence analysis (EDX) and modern
element-mapping software. The results are shown in Figures 12
to 14 and document the high degree of particle liberation. Pyrite,
which is a mineral without economic value in many massive sul-
phide ore bodies, has been very efficiently separated both from
silicate gangue minerals and from the commodity base metal
sulphides chalcopyrite, bornite, chalcocite, sphalerite, and galena.
In case of the comminuted massive sulphide ore from Rio Tinto
Mine (Figure 12) one can clearly recognize four fractions: two ore
mineral fractions, a) chalcopyrite/bornite (orange), b) sphalerite
(green), as well as two waste fractions c) pyrite (yellow) and d)
silicate gangue minerals (grey and white). The massive sulphide
ore from Aguas Tenidas (Figure 13) displays a very high degree of
liberation of ore minerals from barren pyrite and silicate gangue.
The commodity mineral phases comprise a) chalcopyrite/bornite
(orange), b) sphalerite (green), c) galena (blue) with sphalerite and
galena still showing some degree of intergrowth. However, clearly
separated from the commodity minerals are the waste minerals
such as d) barren pyrite and e) silicate gangue minerals. In case of
the massive sulphide ore from Pyhäsalmi, the commodity minerals
have also been liberated from the pyrite and silicate waste minerals
very efficiently although the degree of liberation of the commodity
minerals from each other is slightly below that of the ores from
Spain. The comminuted product from Pyhäsalmi (Figure 14) features
more complexly intergrown Cu, Zn, and Pb sulphides comprising a)
chalcopyrite/bornite (orange), b) some chalcocite (red), c) sphalerite
(green), and d) galena (blue). Sphalerite and galena occur in some
particles still intergrown and rare particles can be found where pyrite
is enclosed in chalcocite. Liberation from e) barren pyrite (yellow) and
f) silicate gangue minerals (grey and white), however, is complete.
In case of all three massive sulphide ores, the VeRo Liberator® has
produced a highly advantageous product for subsequent mineral
processing. Combined with the drastic particle size reduction ratio
and very low energy consumption, the VeRo Liberator® offers a
significantly improved raw materials efficiency compared to tra-
ditional comminution systems.
2.4 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 with an input of approx. 30 kg per second, and
Fig. 13: SEM-EDX multi element map (for Fe, Cu, Zn, Pb) of commi-
nuted massive sulphide ore from Aguas Tenidas Mine; base
metal sulphides (orange: chalcopyrite and bornite, green:
sphalerite, blue: galena) have been liberated from base-
metal-free pyrite (yellow) and barren silicate gangue (grey
and white)
Fig. 14: SEM-EDX multi element map (for Fe, Cu, Zn, Pb) of com-
minuted massive sulphide ore from Pyhäsalmi Mine, Finland;
base metal sulphides (orange: chalcopyrite and bornite,
red: chalcocite, green: sphalerite, blue: galena) have been
liberated completely from base-metal-free pyrite (yellow) and
barren silicate gangue (grey and white)
Fig. 12: SEM-EDX multi element map (for Fe, Cu, Zn, Pb) of commi-
nuted massive sulphide ore from Rio Tinto Mine; base metal
sulphides (orange: chalcopyrite and bornite, green: sphalerite)
have been liberated from base-metal-free pyrite (yellow) and
barren silicate gangue (grey and white)
51
World of Mining Surface & Underground 68 (2016) No. 1 Technical Report
the very high degrees of particle liberation along the particle
boundaries. These new features contrast starkly with the reduc-
tion ratio and degree of particle liberation achieved by traditional
comminution equipment such as jaw and cone crushers and
classical ball mills.
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. [2-5].
The working principle of the VeRo Liberator® is apparently less
characterized by fracture propagation between load points, but is
probably the consequence of several rock mechanical phenomena,
all of which are based on the differential deformation behavior of the
various mineral components. The most striking phenomenon of the
VeRo Liberator® is that fragmentation takes place 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 apparently one of
the causes but probably not the only one. An additional significant
aspect is apparently the velocity-dependence and thus time-de-
pendence of comminution processes inside the VeRo Liberator®.
The induced stress difference between two components must be
high enough for fracture formation and separation to take place at
the boundary of two minerals with a substantially different defor-
mation state. It must therefore be assumed that a kind of stress
accumulation in the oscillating and vibrating components plays a
significant role in inter-granular fracture formation and thus in particle
liberation. In normal impact events, a release of stress takes place
between the 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 is apparently far
higher and faster than stress relaxation can occur within the indi-
vidual components. As a consequence, very high stress differences
build up between adjacent minerals and cause fracture formation at
the particle boundaries. These processes are possibly comparable
to well-known, supersonic frequency-dependent processes such
as the ones applied in ultrasonic cleaning devices.
It is thus important to note that fracture nucleation is caused in
the VeRo Liberator® preferably at particle boundaries. Besides
differential behaviour of the various components, this can also
be caused by interference of the different velocity of the shock
waves in heterogeneous materials. Here, peak negative pressure
or extreme tensional stress can occur in juxtaposed positions of
progressing and inverse reflected shock waves. Such behaviour
has been modelled with ultrasonic processes in inhomogeneous
material by [6]. These authors have shown that interfacial strength
is typically far less than the strength within the material of the
individual particles. Fracture propagation along particle boundar-
ies is also far easier than across particle boundaries [1], which is
another reason for the markedly lower energy consumption of the
VeRo Liberator® compared to traditional comminution systems.
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.
3 Conclusions
Base and precious massive sulphide ores are an important source
of metals in international mining operations. Mineral processing
of these relatively high grade ores involves the comminution and
subsequent mechanical separation of the commodity minerals
(typically chalcopyrite/bornite, sphalerite, and galena) from sili-
cate gangue and barren pyrite. The new VeRo Liberator® offers
a number of innovative and highly efficient features that improve
the comminution of massive sulphides, 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 count-
er-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 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 material. 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 for massive sulphides (up to >1000 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 (see Figures 12
to 14). This avoids that fractures cross-cut particle boundaries
of various materials at high angles, which is a major cause for
incomplete particle liberation [11, 12] in classical comminution
systems such as conventional ball mills. Incomplete particle libera-
tion, in turn, is a major cause for subsequent inefficient separation
and extraction by processes such as froth flotation and solvent
extraction. Fracture nucleation at and fracture propagation along
particle boundaries between different minerals, as achieved by
the VeRo Liberator® is also drastically more energy efficient com-
pared to cross-boundary fracturing and explains the low energy
consumption of the VeRo Liberator®.
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 companies that have generously provided bulk sample of
massive sulphide ore are gratefully acknowledged and these are i)
for Rio Tinto Mine, at the time of sampling EMED Tartessus Mining,
now Atalaya Mining, Huelva, Spain, ii) for Pyhäsalmi Mine, First
Quantum, Finland and Canada, iii) for Aguas Tenidas, Minas de
Aguas Tenidas SAU, Almonaster la Real, Huelva, Spain. Christof
Lempp is gratefully acknowledged for his contructive input to
explain the working principle of the VeRo Liberator®.
References
[1] Bloyer, D.R., Venkateswara rao, K.T. & ritChie, R.O.
(1999): Fatigue-crack propagation behaviour of ductile/
brittle laminated composites. – Metallurgical and Materials
Transactions A, 30A: 633-642.
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Technical Report
[2] Borg, G., sCharfe F. & kamradt, A., (2015): Improved
Particle Liberation by High-Velocity Comminution – the
new VeRo Liberator®. – ICNOP2015, 27.-29.05.2015,
Trzebieszowice, Poland, Conference Proceedings Volume.
[3] Borg, g., sCharfe, f., lempp, C., kamradt, a. (2015): Im-
proved particle liberation of graphite and other complex
ore minerals by high-velocity comminution – introducing
the new VeRo Liberator®. – World of Mining – Surface
and Underground, 67, 3: 207-212.
[4] Borg, g., sCharfe, f., lempp, C., kamradt, a. (2015):
Stretching the limits of comminution – improved size
reduction and particle liberation by the new VeRo Liber-
ator®. – Conference Volume, Physical Separation 2015,
Falmouth, Cornwall.
[5] Borg, G., sCharfe, O. & kamradt, A. (2015): Breaking down
comminution barriers – new dimensions of particle size
reduction and liberation by VeRo Liberator®. – ICCC2015,
St. Luis Potosi, Mexico, ISBN 9781329013322: 277-289.
[6] CleVeland, R.O. & tello, J.S. (2004): Effect of the diameter
and the sound speed of a kidney stone on the acoustic
field induced by shock waves. – ARLO, 5, 2: 37-43.
[7] Cutifani, M. & Bryant, P. (2015): Reinventing mining: Creat-
ing sustainable value. – Kellogg Innovation Network. Avail-
able at: http://www.kinglobal.org/catalyst.php. Accessed
25 July 2015.
[8] manouChehri, H.R. et al. (2015): Sustainable Development
in Cone Crushing Design and Implementation – CH860
& CH865: Sandvik‘s New Reliable and Productive
Crushers. – ICCC2015, St. Luis Potosi, Mexico, ISBN
9781329013322: 129-143.
[9] mudd, G.M. (2007): An Analysis of Historic Production
Trends in Australian Base Metal Mining. – Ore Geology
Reviews, 32, 1-2: 227-261.
[10] napier-munn, T. (2014): Is progress in energy-efficient
comminution doomed? – Minerals Engineering, 73: 1-6.
[11] wills, B.A. & atkinson, K., (1993): Some observations on
the fracture and mineral assemblies. Minerals Engineering,
6, 7: 697-706.
[12] wills, B.A. & napier-munn, T.J. (2007): Will’s Mineral Pro-
cessing Technology. – Butterworth-Heimann/Elsevier, 7th
Edition, 444 p.
... 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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Wills' Mineral Processing Technology provides practising engineers and students of mineral processing, metallurgy and mining with a review of all of the common ore-processing techniques utilized in modern processing installations. Now in its Seventh Edition, this renowned book is a standard reference for the mineral processing industry. Chapters deal with each of the major processing techniques, and coverage includes the latest technical developments in the processing of increasingly complex refractory ores, new equipment and process routes. This new edition has been prepared by the prestigious J K Minerals Research Centre of Australia, which contributes its world-class expertise and ensures that this will continue to be the book of choice for professionals and students in this field. This latest edition highlights the developments and the challenges facing the mineral processor, particularly with regard to the environmental problems posed in improving the efficiency of the existing processes and also in dealing with the waste created. The work is fully indexed and referenced. · The classic mineral processing text, revised and updated by a prestigious new team · Provides a clear exposition of the principles and practice of mineral processing, with examples taken from practice · Covers the latest technological developments and highlights the challenges facing the mineral processor · New sections on environmental problems, improving the efficiency of existing processes and dealing with waste.
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A study has been made of the fatigue-crack propagation properties of a series of laminated Nb-reinforced Nb3Al intermetallic-matrix composites with varying microstructural scale but nominally identical reinforcement volume fraction (20 pct Nb). It was found that resistance to fatigue-crack growth improved with increasing metallic layer thickness (in the range 50 to 250 µm) both in the crack-divider and crack-arrester orientations. For a given layer thickness, however, the properties in the crack-arrester orientation were superior to the crack-divider orientation. Indeed, the fatigue resistance of the crack arrester laminates was better than the fatigue properties of unreinforced Nb3Al and pure Nb; both laminate orientations had significantly better fatigue properties than Nb-particulate reinforced Nb3Al composites. Such enhanced fatigue performance was found to result from extrisic toughening in the form of bridging metal ligaments in the crack wake, which shielded the crack tip from the applied (far-field) driving force. Unlike particulate-reinforced composites, such bridging was quite resilient under cyclic loading conditions. The superior crack-growth resistance of the crack-arrester laminates was found to result from additional intrinsic toughening, specifically involving trapping of the entire crack front by the Nb layer, which necessitated crack renucleation across the layer.
Improved particle liberation of graphite and other complex ore minerals by high-velocity comminution – introducing the new VeRo Liberator ® . – World of Mining – Surface and Underground
  • G Borg
  • C Lempp
Borg, g., sCharfe, f., lempp, C., kamradt, a. (2015): Improved particle liberation of graphite and other complex ore minerals by high-velocity comminution – introducing the new VeRo Liberator ®. – World of Mining – Surface and Underground, 67, 3: 207-212. [4] Borg, g., sCharfe, f., lempp, C., kamradt, a. (2015): Stretching the limits of comminution – improved size reduction and particle liberation by the new VeRo Liberator ®. – Conference Volume, Physical Separation 2015, Falmouth, Cornwall. [5]