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Progress and Challenges in Electrical Comminution by High-Voltage Pulses


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The recent progress in electrical comminution using high-voltage pulses and the technical challenges in order to bring this technology to the mining industry are outlined. Pre-weakening ore particles and preferential liberation of minerals at coarse sizes are the two major research outcomes that may have potential benefits for the industry. A particle pre-weakening characterization method by single-particle/single-pulse test has been developed. The emerging challenges for the mining industry to realize the benefits of this novel comminution technology include scale-up for industrial application, hybrid circuit design, maximization of pulse-induced cracks, and study of the downstream processing effects.
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Progress and Challenges in Electrical
Comminution by High-Voltage Pulses
The recent progress in electrical comminution using high-voltage pulses and the
technical challenges in order to bring this technology to the mining industry are
outlined. Pre-weakening ore particles and preferential liberation of minerals at
coarse sizes are the two major research outcomes that may have potential benefits
for the industry. A particle pre-weakening characterization method by single-
particle/single-pulse test has been developed. The emerging challenges for the
mining industry to realize the benefits of this novel comminution technology
include scale-up for industrial application, hybrid circuit design, maximization of
pulse-induced cracks, and study of the downstream processing effects.
Keywords: Electrical comminution, Energy, High-voltage pulses, Mineral liberation
Received: September 27, 2013; revised: October 28, 2013; accepted: November 21, 2013
DOI: 10.1002/ceat.201300660
1 Introduction
In 2009–2010, the mining industry in Australia used 509 PJ
energy, 8.6% of the total energy consumed in Australia [1].
This corresponds to 136 million tons of CO
emission. Com-
minution, including crushing and grinding, consumes about
one third of the energy used by the mining industry. This is
equivalent to the output from five 1400-MW coal-fired power
stations, all energy being necessary to crush and grind rocks.
Improved methods for mineral comminution are continually
being sought, in order to achieve the size reduction and miner-
al liberation required for better recovery of valuable minerals
at lower energy consumption and lower emissions.
High-voltage pulses to break rocks have attracted the atten-
tion of researchers for the past half century [2–12]. Previous
research in the mineral industry mainly focused on mineral
liberation which consumed significantly high amounts of ener-
gy. In the past five years, the Julius Kruttschnitt Mineral
Research Centre (JKMRC), in collaboration with SELFRAG
AG, has made a significant effort towards developing an elec-
trical comminution technique for the mineral industry. The
major outcomes and emerging challenges to overcome for the
mineral industry to realize the benefits are reported.
2 Electrical Comminution
The high-voltage (HV) pulse power technology consists of an
HV power supply, an HV pulse generator, and the process area
(Fig. 1 a, [13]). Materials are immersed in a liquid in the pro-
cess area. Dielectric liquids, like water, have a high dielectric
strength when the voltage rising time is kept below 500 ns
(Fig. 1b). Consequently, the water acts as a special electrical in-
sulator to prevent electrical discharge occurring outside the
rocks [14, 15].
A number of technical names related to HV pulse technolo-
gy appear in the literature. Tab. 1 lists their characteristic fea-
tures based on the method of transferring energy and the HV
rising time. The term electrical comminution is used to cover
all those applying HV pulses.
Note that the voltage rising time in electrohydraulic disinte-
gration is larger than 500 ns. Compared with other pulse tech-
niques using shorter voltage rising times, the energy efficiency
of electrohydraulic disintegration may be lower, and the results
of rock pre-weakening and mineral liberation may be different.
At present, two brands of HV pulse equipment appear on the
market: selFrag manufactured by SELFRAG AG based in Swit-
zerland, and Spark by CNT-MC based in Canada. The JKMRC
has installed a selFrag Lab machine. The selFrag Lab is
designed to treat samples in the 1-kg range per batch. The
selectable process parameters are: number of pulses, discharge
voltage (91–200 kV) which controls the energy per pulse, elec-
trode gap (10–40 mm), and frequency of discharge (1–5 Hz).
Chem. Eng. Technol. 2014,37, No. 5, 1–6 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Fengnian Shi
Emmy Manlapig
Weiran Zuo
The University of Queensland,
Sustainable Minerals Institute,
Julius Kruttschnitt Mineral
Research Centre, Brisbane,
Correspondence: Dr. Fengnian Shi (, The University of
Queensland, Sustainable Minerals Institute, Julius Kruttschnitt Mineral
Research Centre, 40 Isles Road, Brisbane, 4068, Australia.
Table 1. Features of high-voltage pulse technology.
Technical name Electrode
Voltage rising
time [ns]
Electrohydraulic disintegration Water > 500
Electrical disintegration Rock < 500
Electrodynamic disintegration Water < 500
Electrical pulse disaggregation Water < 500
Review 1
To avoid overbreaking the target minerals, a process vessel with
interchangeable sieve bottoms is used. Sieve apertures from 4
to 0.3 mm are typically applied.
3 Recent Development
More than ten ore samples including copper, gold, lead/zinc,
platinum ores, and industrial minerals from various mine sites
around the world were treated by HV pulses equipment and
by conventional comminution facilities for comparison. In
total, over 5 t of ore samples in the size range of 10–45 mm
have been processed by the JKMC. Data cumulated from the
extensive experimental work were used to develop applications
of electrical comminution for the mineral industry and to gain
knowledge on the factors affecting the efficiency of electrical
3.1 Pre-Weakening Ore Particles
A new application of HV pulse power has been developed
which applies the specific energies of 1–3 kWh t
to pre-weak-
en ore particles. Evidence of cracks and microcracks measured
by X-ray tomography (Fig. 2) and mercury porosimetry sup-
ported the principle of HV pulse power-induced damage on
rocks, resulting in a reduction of particle strength and, conse-
quently, a reduction in the energy consumption in the down-
stream process [16].
A residual breakage resistance indicator, A*b, of the pulses’
breakage product and mechanical breakage product was mea-
sured by a rotary breakage tester (JKRBT [17]). The typical
A*b values in the JKMRC database which consists of more
than 2000 standard breakage testing data for ore particles, are
between 20 to 300, A*b values less than 40 indicating very high
resistance to breakage and larger than 100 indicating less resis-
tance to breakage. Changes in the A*b values from 9 % to 52 %
(using 700 g per batch test) were observed between the two
products fragmented with similar specific energy levels. Up to
24 % reduction in the Bond ball mill work index in the selFrag
product was observed. Large variations of the pre-weakening
effect were found with these ore samples.
3.2 Preferential Liberation
Investigation of preferential liberation by HV pulses was con-
ducted on three ore samples (one copper ore, one gold ore,
and one platinum group metal (PGM) ore), in comparison
with the mechanical breakage products with identical specific
energy levels [18]. Mineral liberation analysis was performed
using a mineral liberation analyzer (MLA). Close to 400 MLA
datasets were collected for statistical analysis of the compara-
tive results. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eng. Technol. 2014,37, No. 5, 1–6
~500 ns
a) b)
Figure 1. The high voltage pulse technology [2], a) three major components; b) breakdown strength in relation to voltage rising time.
Figure 2. X-Ray tomography image of a gold-copper ore particle
treated with one electrical pulse, dark lines showing cracks/
Distribution of the liberated minerals demon-
strates that in the electrical comminution product
a large percentage of the liberated minerals appear
in size fractions coarser than 53 lm, while in the
mechanical comminution product the liberated
minerals are accumulated in fine and very fine size
fractions (Fig. 3). Therefore, there may be potential
benefits in recovering the coarse liberated minerals
in the electrical comminution product, prior to
further grinding.
3.3 Factors Affecting Electrical
A number of factors associated with HV pulse
operations were investigated through experimental
work and numerical simulations of electrical field
distribution using the software COULOMB 3D. It
was found that particles having the following dis-
tinguishing features may enhance the electrical
comminution performance: coarse grained miner-
als of interest, large feed particle size, conductive
minerals embedded within gangues, angular parti-
cle shape, and large difference in the electrical
properties between the valuable mineral-hosting
and gangue phases [19].
Numerical simulation also indicates that high electrical field
intensity was created around the boundaries of two mineral
phases with large differences in their permittivity and conduc-
tivity. Fig. 4 demonstrates that the electrical field intensity in
silicate is 4 kV mm
under 100 kV loading. The electrical field
intensity in the boundaries between chalcopyrite and silicate
rises to 5.4 kV mm
. Similar intensity occurs along the bound-
aries between pyrite and silicate. The larger electrical filed
intensity will cause higher tensile stress, leading to breakage
taking place along boundaries between minerals of different
permittivity. This elucidates the mechanism of preferential
liberation in electrical comminution.
3.4 Characterization of Pre-Weakening Effect
Recent research found that HV pulse discharges develop in an
array around the electrode axis, and particles further from the
electrode axis do not receive the same level of pulse energy as
the ones directly under the electrode [20]. The pre-weakening
effect determined through the standard 700-g batch tests is an
averaged effect of treated and mistreated particles.
A single particle subjected to a single pulse discharge meth-
od has been developed which effectively eliminates the influ-
ence of machine-inefficiency factor. Tab. 2 compares the pre-
weakening results by the 700-g batch tests and the single-parti-
cle tests on the same gold/copper ore sample. The A*b values
are compared at a nominal size of 30 mm.
Chem. Eng. Technol. 2014,37, No. 5, 1–6 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Figure 3. Distribution of the > 95 % liberated chalcopyrite deportment in the products of a copper ore sample, comminuted mechanically
and electrically using 9 kWh t
and 22 kWh t
respectively, with the error bars indicating the 95 % confidence interval.
Applied Voltage 100 kV
Chalcopyrite Pyrite
5.4 kV/mm5.4 kV/mm
0 kV/mm
(4 kV/mm)
Figure 4. Electrical field distribution of chalcopyrite and pyrite spheres em-
bedded in the K-feldspar immersed in water, with an electrical potential differ-
ence of 100 kV.
Review 3
Tab. 2 indicates very different pre-weakening results deter-
mined by the two methods. Some of the ore samples tested pre-
viously, showing a poor response to electrical comminution,
may not be due to their poor amenability, but due to the ma-
chine-inefficiency factor associated with the testing method.
Fig. 5 displays the calculated A*b values in relation to parti-
cle size for pulse-treated and untreated SAG (semi-autogenous
grinding) mill feed of a gold-copper ore. For both pulse-treat-
ed and untreated samples it is obvious that the larger particles
are weaker (higher A*b values) than the smaller particles (both
showing an increased trend). This is known as particle size ef-
fect on breakage. The size effect is more pronounced in the
HV pulse-treated fragments than in the untreated material.
This confirms that the larger fragments would achieve a better
pre-weakening effect than the smaller fragments when sub-
jected to HV pulses. The characterization result suggests that
using HV pulses to pre-weaken AG/SAG mill feed may achieve
more significant benefits in terms of energy saving or increased
throughput than pre-weakening the ball mill feed.
4 Challenges and Current Research
A number of challenges have emerged in the application of
electrical comminution technology. These need to be ad-
dressed in the current research, in order to realize the full ben-
efits of such technology for the mineral industry.
4.1 Scale-up for Industrial Application
The majority of the JKMRC research outcomes were achieved
based on laboratory-scale selFrag systems. Scaling up to treat
large particle sizes with high throughput in a continuous
operation mode is a challenge, but not a problem. The pilot-
scale unit of a pre-weakening station with 1 t h
capacity is
available on the market [21], the engineering design of 10 t h
pilot pre-weakening station is complete, and 100–1000 t h
multiple modules can be developed.
One of the real challenges is to maximize the probability of
every particle presented in the feed receiving the energy in each
pulse discharge. The single-particle characterization test has
demonstrated significant improvement in the pre-weakening
result. In a large-scale continuous operation system, how to
maximize the efficiency in delivering the pulse energy to all
feed particles holds the key to achieving better electrical com-
minution results for the mineral industry.
4.2 Hybrid Circuit Design
The electrical comminution unit needs to be integrated in the
traditional mechanical comminution circuit to achieve opti-
mal technical and economic benefits. To design a hybrid com-
minution circuit, factors considered include the selection of
the SAG mill feed size fractions to be treated by HV pulses, the
treatment of SAG mill pebbles, the transfer size between SAG
mill and ball mill, and the energy distributions among HV
pulse pre-weakening, SAG milling and ball milling.
Currently, the JKMRC is developing an electrical comminu-
tion model to describe the breakage probability and pre-
weakening index (PWI). It is expected the electrical commi-
nution model be integrated in the existing JKSimMet, the
popular comminution software used in the mineral industry,
to design the hybrid comminution circuit and its optimization,
based on ore breakage characteristics.
4.3 Cracks/Microcracks Generation
The X-ray tomography technique gives evidence to support
that cracks/microcracks induced by HV pulses are the main
reason for the ore particle pre-weakening effect. Recent
research found that the pulse-induced cracks/microcracks may
be exhausted in the first stage mechanical breakage, e.g., SAG
milling, leading to the secondary grinding (ball mill) feed ore
retaining the original hardness. The challenge is how to
increase the microcracks’ density in a particle induced by HV
A research program utilizing numerical simulation tools,
e.g., DEM and FEM, to understand cracks/microcracks genera-
tion mechanisms from fundamental approach will be under-
taken. The recently installed and commissioned Versa 500 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eng. Technol. 2014,37, No. 5, 1–6
Table 2. Comparison of the pre-weakening results; PWI – pre-
weakening index.
Method 700-g batch Single particle
Particle size [mm] 26.5–45 26.5–45
Particle mass [kg] 21 5.0
selFrag Ecs [kWh t
] 4.6 1.6
A*b (untreated) 31 31
A*b (treated) 52 84
Change in A*b [%] 68 171
PWI [% change in A*b
per kWh t
]15 107
Figure 5. Comparison of A*b values in relation to fragment size
between the high voltage pulse treated and the untreated SAG
mill feed of a copper ore sample.
X-ray tomography device at the JKMRC, in addition to the
existing Sky scanner, will provide useful facilities to validate
and guide the numerical simulations.
In the previous experiment, large variations in the pre-weak-
ening results were observed for various ore samples. The devel-
opment of a single-particle/single-pulse test has largely re-
moved the machine inefficiency factor in the laboratory
characterization process, yet the variations still exist. For
example, one copper ore sample achieved 81 % of particles
fragmented with one pulse treatment, but another copper ore
sample only had 40 % particles fragmented under the identical
selFrag operational conditions and for the same feed particle
size. Further research in this area is undertaken at the JKMRC
through fundamental study to investigate how ore properties
and selFrag operational conditions affect particle pre-weaken-
ing and liberation results, upon which a model for electrical
comminution will be developed.
4.4 Downstream Effects
Previous research has reported the pre-weakening effect and
the preferential liberation effect associated with HV pulses.
However, whether or not the pre-weakening effect on ore par-
ticles can result in decreased comminution energy or increased
mill throughput, and whether or not the better liberation can
lead to better recovery of valuable minerals in the downstream
processes are yet to be confirmed in the real mineral processing
Another challenge is the adverse effects of HV pulses on sur-
face chemistry or mineral phase of particles which, if exhibited,
may affect grade or recovery of valuable minerals in the down-
stream processes.
Another research program is currently being undertaken at
the JKMRC to evaluate the effects of HV pulses on down-
stream processing and how to overcome the adverse effects, if
any, in order to maximize the benefits of electrical comminu-
tion in the mineral industry.
5 Conclusions
The recent progress on electrical comminution using HV
pulses to improve grinding circuit energy efficiency is re-
viewed. To bring this technology to the mineral industry, chal-
lenges on facilities scaling-up, circuit design, cracks/micro-
cracks generation, and downstream effects are discussed.
The authors would like to acknowledge financial support from
the Australian Research Council Linkage Scheme (AMSRI –
LP0667828) and the project sponsors. Support from Anglo
American, Newcrest, Newmont, Rio Tinto, Xstrata, and Vale
mining companies is gratefully acknowledged. The collabora-
tive research partnership with SELFRAG AG is enjoyable and
The authors have declared no conflict of interest.
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Chem. Eng. Technol. 2014,37, No. 5, 1–6 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Review 5
Review: Comminution consumes about
one third of the energy used by the
mining industry. Therefore, improved
methods for mineral comminution are
continually being sought. A particle pre-
weakening characterization method by
single-particle/single-pulse test has
been developed. Challenges in terms
of facilities scaling-up, circuit design,
generation of cracks, and downstream
effects are discussed.
Progress and Challenges in Electrical
Comminution by High-Voltage Pulses
F. Shi*, E. Manlapig, W. Zuo
Chem. Eng. Technol. 2014,37 (5),
DOI: 10.1002/ceat.201300660
Applied Voltage 100 kV
Chalcopyrite Pyrite
5.4 kV/mm5.4 kV/mm
0 kV/mm
(4 kV/mm) © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Eng. Technol. 2014,37, No. 5, 1–6
... The first is the SELFRAG company (since 2007, Switzerland). SELFRAG LAB instruments (short for the selective fragmentation) have been delivered to many laboratories around the world [27,28]. This instrument is based on a Marx generator and has the following parameters: the operating voltage is 90-200 kV, the frequency is 1-5 Hz (in a pulse train), and the pulse-front duration is 150 ns. ...
... An example of this type is the FRANKA series of generators (Institute for Pulsed Power and Microwave Technology, Karlsruhe, Germany) which includes the laboratory facility FRANKA 0, with an output voltage of up to 250 kV, energy storage of 750 J and a pulse repetition rate of up to 5 Hz and the prototype industrial facility FRANKA 2 (FRANKA-Stein), with an output voltage of up to 350 kV and performance of up to 280 kg/h [2]. Many laboratories around the world use SELFRAG LAB systems (SELFRAG AG, Switzerland) [9,[11][12][13][14][15], which are also based on the Marx generator. A SELFRAG LAB system has the following parameters: operating voltage 90-200 kV, frequency 1-5 Hz, pulse front 150 ns. ...
A linear pulse transformer with air insulation at atmospheric pressure was created and tested under both constant resistance and non linear loads. The maximum power of the transformer output pulse reached ∼500 MW at a matched load with a charge voltage 50 kV. The transformer transferred ∼60% of the stored energy to the load over a characteristic time of about 1 μs. The scalability the generator was studied by connecting two identical transformers in series which gave a power output of ∼850 MW with doubled output voltage and reduced current. The frequency mode of operation was studied using one and two transformers with a charge voltage of 50 kV and a load that was, close to matched. In both cases, the power maximum and jitter showed no significant changes at any of the frequencies tested (up to 5 Hz). These results mean that the use of this generator can be recommended for a wide field of applications due to its scalability and low internal impedance.
... One successful variety of this approach, called Electro Pulse Drilling, is based on the creation of the electric breakdown channel between electrodes placed on rock surface. [5][6][7] This method requires, however, very high voltages to reach the electric breakdown strength of rock (e.g. 100-150 kV/cm for granite). ...
Full-text available
This paper presents a numerical study on cracking of granitic rock by high frequency-high voltage-alternating current actuation (HF-HV-AC) of piezoelectric properties of Quartz mineral. For this end, a numerical method based on 3D embedded discontinuity finite elements for rock fracture and an explicit time stepping scheme to solve the coupled piezoelectro-mechanical problem is developed. Rock heterogeneity and anisotropy are accounted for at the mineral mesotructure level. Novel numerical simulations demonstrate that disc-shaped and cylindrical granitic rock specimens (with the tensile strength of about 8 MPa) can be cracked by a sinusoidal excitation with an amplitude of ∼10 kV at a frequency matching one of the resonance frequencies of the specimen (e.g. 125 kHz in the present case of 30 mm radius and 10 mm height). The effects of specimen shape and electrode locations are tested. Various Quartz grain alignment schemes are tested and even the worst case of having a 50%:50% mixture of right- and left-handed Quartz crystals without any preferred orientation show stresses of about 1 MPa at the resonance frequency. The simulation results suggest that HF-HV-AC piezoelectric excitation of Quartz bearing rocks could be a potential pre-treatment technique in comminution.
With the development of photovoltaic (PV) energy, the recycling technology of end-of-life PV panels has received much attention; the existing recycling methods have various limitations. In this study, high-voltage pulse energy was used to crush PV panels, and the microscopic morphology, particle size structure, and elemental composition of the crushed products were analyzed. The liberation process and element enrichment during the high-voltage pulse crushing of PV panels were studied, the effect of each parameter on the selective crushing degree of high-voltage pulse crushing PV panels was obtained. Furthermore, a collaborative optimization study was carried out on the degree of selective crushing of various operating parameters. The significance order of the effect of various factors and the mathematical correlation between them were obtained. The best combination of operating parameters was obtained. The test results indicate that the source of high-efficiency liberation and element enrichment during the high-voltage pulse crushing of PV panels is the interface crushing and sequential selective crushing characteristics of high-voltage pulses. With the increase in electrode gap, the degree of selective crushing shows a increasing trend. As the voltage and pulses number increases, the degree of selective crushing first increases and then decreases. The significance of influence of each factor decreases in the following order: voltage > electrode gap > pulse number. When the operating conditions are 170 kV, 50 pulses, and 25 mm, the degree of selective crushing of product reached the maximum.
تکهسازی پالس الکتریکی روشی نوآورانه است که از قدرت پالسهای الکتریکی ولتاژ باال برای خردسازی انتخابی مواد و یا تضعیفسازی آنها استفاده میکند. در تکهسازی الکتریکی، سنگ در مایعی دیالکتریک غوطهور شده، با عبور پالسهای الکتریکی ولتاژ باال از سنگ، شکست الکتریکی صورت میگیرد. این روش نوین، تا کنون در فاز آزمایشگاهی با موفقیت توسعه یافته و نتایج، نشاندهنده آزادسازی درشتتر مواد معدنی و کاهش تولید ذرات نامطلوب در مقایسه با روشهای خردسازی مکانیکی مرسوم میباشند. این نتایج، پتانسیل تکهسازی پالس الکتریکی برای بهبود خردسازی سنگها را تایید میکند
The recycling of light-emitting diode (LED) lamps and tubes is becoming increasingly important due to their growing market share as energy-efficient lighting technology. Here we report on the use of high voltage electric-pulse fragmentation to recover elementary components such as LED chips and printed circuit boards (drivers). E27 LED lamps with plastic bulbs, which represent 48% of deposits collected by a French company, are used as a case study. More than 150 lamps were tested on a laboratory reactor for electrodynamic fragmentation. The technological process in which highly energetic electrical pulses were applied to materials immersed in water was studied in order to separate the components of the LED lamps using a minimal specific energy. The estimated energy necessary to achieve total separation assessed at 64%, without grinding pretreatment, was 5.2 ± 0.6 kWh per ton, representing a mass recycling rate of 74%. Based on the disassembled material, the commercial value of the recovered materials was thus estimated. Gold, as the most representative material, was found to represent 0.03% of the mass fraction for 83.6% of the total commercial value. The process disassembling capacity is a key issue to increase the recycling rate of current LED lamps and tubes.
Mining companies are actively looking for new and innovative techniques which can significantly reduce operational costs and processing carbon footprint. The high voltage pulse (HVP) is a novel technology with the potential to be applied in the mineral processing industries which provides enhanced liberation, pre-weakening and pre-concentration benefits for raw material. This paper reviews in detail the HVP working principles and the work devoted to the aforementioned three applications. In addition, major challenges affecting the industrial uptake of the HVP technique are also discussed in the context of HVP fragmentation specific energy consumption, machine wear, cost of water processing and machine throughput limitations. HVP selectivity in between particles is accentuated in this review and believed to have good prospects for industrial uptake due to its capability to achieve selective fragmentation and selective weakening effects for the mineralised particles. Finally, the paper is enclosed with an outlook of HVP future development.
To investigate influence factors of hard rock fragmentation, numerical simulation and experimental research of hard rock breaking by high voltage pulse discharge are examined by two parameters: electrode gap and hard rock type. Using the three-dimensional electromagnetic simulation software Computer Simulation Technology, the electric field distribution of the electrode and variation of motion trajectory of discharge particles within the hard rock are simulated. Breaking hard rocks by high voltage pulse discharge experiments are carried out to observe the breakage effect of hard rock and the waveforms of output voltage and current. The results show that the fragmentation effect of hard rock is strongly dependent on the electrode gap and rock type, and experimental results are consistent with the simulations. The above conclusions provide appropriate conditions for the subsequent application of high voltage pulse discharge in hard rock fragmentation.
A method based on single-particle tests has been developed to characterise the pre-weakening effect of high voltage pulses on ores. A pre-weakening index, PWI, defined as the percentage change in ore breakage resistance indicator (A*b) per unit of specific energy, is used to evaluate the energy efficiency of an electrical comminution machine, and to assess an ore's amenability to pre-weakening by high voltage pulses. A reduced JKRBT (JK Rotary Breakage Tester) testing procedure using five tests (instead of the standard 12 tests per sample) to determine the ore breakage parameters, makes characterisation by high voltage pulse pre-weakening more practical. A gold-copper ore sample treated by high voltage pulses, based on single-particle tests with a specific energy of 1.6 kWh/t, achieved an A*b change from 31 to 84 at a nominal particle size of 30 mm, representing a 171% pre-weakening result. X-ray tomography images show the induced cracks/microcracks in the pulses-treated rocks. The pre-weakening effect was found more pronounced for larger fragments, suggesting that the use of high voltage pulses to pre-weaken AG/SAG mill feed may result in more significant benefits in terms of energy savings or increased throughput than pre-weakening ball mill feed.
Factors affecting electrical comminution performance were investigated through experimental work and numerical simulations. The effects of feed size, under-sieve classification, incremental breakage and energy input level on particle pre-weakening and mineral liberation were tested with six ore samples. Using commercial software, COULOMB 3D, simulation was used to explore the trends between the electrical field distribution/intensity, and the ore particle electrical/mechanical properties. These results were used to interpret the differences in breakage and liberation for various ores. The results showed that the induced electrical field is strongly dependent on the electrical properties of minerals, the grain size, the location of the conductive minerals in rocks, and the particle shape/orientation. Understanding how the machine-related factors and ore-related factors affect the electrical comminution performance will assist in the machine scale up development.
Comparative comminution between high voltage pulses and conventional grinding, at the same specific energy levels, shows that the electrical comminution generates a coarser product with significantly less fines than the mechanical breakage. However, minerals of interest in the electrical comminution product are better liberated than in the conventional comminution with an over 95% statistical significance. There is a potential to use less energy in the electrical comminution to generate the similar degree of mineral liberation as in the mechanical comminution. Distribution of the liberated minerals demonstrates that, in the electrical comminution product, a large percentage of the liberated minerals appear in size fractions coarser than 53 gm; while in the mechanical comminution product, the liberated minerals are accumulated in fine and very fine size fractions. Therefore there may be potential benefits in recovering the coarse liberated minerals in the electrical comminution product, prior to further grinding.
A new comminution method has been developed by applying high voltage pulses at specific energy 1–3kWh/t to pre-weaken mineral particles, leading to reduction in energy consumption in the downstream grinding process. Four ore samples were tested using high voltage pulses and conventional crushing in parallel for comparison. Evidence of cracks and microcracks measured with X-ray tomography and mercury porosimetry supported the principle of high voltage pulses induced damage on rocks in the electro-comminution process, which resulted in energy saving up to 24% found in this study. Ore surface texture and mineral properties affected the efficiency of high voltage pulse breakage. The feasibility of the electro-comminution and its benefits need to be investigated case by case.
The sequences of development of the contemporary mineral liberation technique are reviewed, and the emergence and development of contemporary mills as a main mineral liberation tool, is discussed. The origin of development of the technique and the working hypothesis of the mechanism of high voltage electrical pulse liberation of minerals are described, and the state of the contemporary design and construction of pulse generators are discussed. The types of pulse generators and working chambers, used in the reported liberation tests, are presented. The technological results of tests on the liberation of diamonds, emeralds, minerals, containing metals of platinum group, refractory gold and silver, iron, copper, magnesium ilmenite, and of metals of smelter slags, are reported. The account of the application of pulse liberation technique for the recovery of gold from old tailings by application of high frequency and low energy pulses, is given. The prospects and ways of introduction of the technology of mineral liberation by pulses into industry are discussed.
A comparative study of the comminution products of an apatite-nepheline ore was carried out in a specially designed pulse-discharge apparatus, with electrical parameters and a dielectric medium as variables. Mineralogical analysis of the products confirmed the high selectivity of the process in liberation of monofractions, especially those of nepheline.
The disintegration of brittle composite dielectrics—in particular, ores and smelting slags—by explosive electrical breakdown is discussed. Electrical pulses are used to produce intergranular fragmentation and can liberate the constituents of composite solids with higher efficiency than conventional mechanical comminution. The energy consumption of the process can be reduced by the choice of the electrode configuration and by adjustment of the waveform of the pulses according to the spark constant of the disintegrating dielectric. As an example, the liberation of platinum-group metals from a South African ore is analysed from metallurgical and energy consumption perspectives.
Mechanical compressive and impactive disintegration of rock by metallic devices or by water shock waves consumes a disproportionally high amount of energy and are of low efficiency for liberating mineral aggregates in ores. The tensile loading of the rock, which results in significant saving of energy and decreases the cost of maintenance of equipment and substantially improves the mineral liberation, cannot be achieved in mechanical crushers. Electrical disintegration by high voltage pulses results from the tensile failure of rock and can be carried out in inexpensive light weight non-metallic containers. The plasma explosion, generated by pulses inside the rock fragments, is induced by development of the treelike conductive capillaries which result from application of an electrical field which exceeds the dielectric strength of the rock. The explosion takes place on return of the streamers bridging the two electrodes. Tests on continuous comminution of complex apatite-nepheline ore, gold bearing quartzites, emerald bearing pegmatites, diamond bearing kimberlites and other ores show high liberation results from the electrical disintegration technique. Efficiency of electrical disintegration depends on the right match of voltage and energy of pulses with mechanical strength of rock and desirable size of fragments, and is directly proportional to the rate of build up of voltage across the rock. Electrical disintegration of rock consumes substantially less energy than compressive mechanical crushing and enhances effect of liberation of mineral constituents of rock aggregates.
Ore breakage characterisation plays an essential role in the design and optimization of comminution circuits. Recently, the JKMRC comminution research team has developed a Rotary Breakage Tester (JKRBT) for rapid particle breakage characterisation tests. The JKRBT uses a rotor–stator impacting system, in which particles gain a controlled kinetic energy while they are spun in the rotor and are then ejected and impacted against the stator, causing particle breakage. The first industrialised JKRBT was installed at Anglo Research in Johannesburg in March 2007, and six more JKRBTs were deployed in 2008 around the world. This paper discusses the major design and calibration issues encountered in the JKRBT development and findings from detailed experimental studies.