au highpower pulses
TRANSCRIPT
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APPLICATION OF HIGH-POWER ELECTROMAGNETIC PULSES TO
DESINTEGRATION OF GOLD-CONTAINING MINERAL COMPLEXES
V.A. Chanturiya, I.J. Bunin
, A.T. KovalevResearch Institute of Comprehensive Exploitation of Mineral Resources, Russian Academy of Sciences,
4 Kryukovsky Tupik, Moscow, 111020, Russia
Work supported in part by the President of the Russian Federation under contract number 472.2003.5.email: [email protected]
Abstract
The application of High-Power Electromagnetic Pulses(HPEMP) irradiation in dressing of resistant gold-
containing ores appears attractive as this techniqueprovides for a significant increase in precious metal
recovery (3080% for gold and 2050% for silver),
therewith helping reduce both energy consumption andthe cost of products.
This study deals with plausible mechanisms ofdisintegration of mineral particles under the action ofnanosecond HPEMP with high electric field strength
E107 V/m. Experimental data are presented to confirm
the formation of breakdown channels and selectivedisintegration of mineral complexes as a result of pulse
irradiation, which makes for efficient access of lixiviant
solutions to precious metal grains and enhanced preciousmetal recovery into lixivia during leaching.
We studied the influence of HPEMP on thetechnological properties of particles of refractory gold-
and silver-containing ores and beneficiation productsfrom Russian deposits. Preliminary processing of gravityconcentrate of one deposit ore with a series of HPEMP
resulted in significant increase of gold and silverextraction into lixivia during the cyanidation stage, with
gold recovery increased by 31% (from 51.2% in a blanktest to 82.3% after irradiation) and silver recovery
increased by 47% (from 21.8%to 68.8%). Gold recovery
from stale gold-containing dressing tailings of the two
integrated mining-and-dressing works increased after
pulses-irradiation from 812% to 8090%.
I. INTRODUCTION
In Russia, like elsewhere in the world, development of
primary gold deposits is considered a first-priority line of
development for gold mining industry. Most of the gold-containing ores characteristic of Russian gold deposits are
resistant ores with gold content varying between 3 and 5
ppm, usually showing quite low gold and silver recoveryby cyanidation. Processing resistance of gold-containingmineral complexes is related to the presence of gold
particles of submicrometric size (
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methods should be mentioned first. The essence of these
methods consists in the increase of defects concentrationand arising of a great number of microcracks under the
polarization processes of sulfide and oxide minerals with
semiconductor properties [1]. The defects concentration
raise and microcracks emergence are caused under theseconditions by the electrochemical reactions which take
place on the mineral grain boundaries. In practice, the
electrochemical action is performed in the process of
grinding by the application of direct current of 36 A/m2
density and of 612 V voltage inside the ball mill. Theelectric power consumption in this case amounts to
0.20.4 kWh/ton and the degree of disclosure increases by
2025%.
Considerably better results were obtained under the ores
exposure to the acceleratedelectron beamwith energy of
12 MeV and current density of 15 A/cm2
beforegrinding [2]. The physical background of the effect is the
electric charge of the natural media of weak conductivity.This causes the emergence of microcracks, which lead to
the softening of mineral components. The 2080%
increase of grinding efficiency, as well as the 1520%raise of technological characteristics is observed under
these conditions for all types of ores.One of the noteworthy attempts to solve the problem of
disintegration of resistant ores and beneficiation products
was the irradiation of the ore by the microwave generator
[3]. The microwave generator provided a continuousradiation of 0.9-2.5 GHz frequency. The roast of the
medium up to 360 C increased the yield of gold inseveral experiments but no convincing results were
obtained. In UHF treatment, heterogeneous (non-uniform)absorption of microwave energy by different componentsof the mineral complex results in embrittlement of the
mineral matrix and destruction of its skeleton along theintergrowth boundaries, which "unseals" the valuable
components, making them easier to extract. In addition,intense physicochemical processes occur on the surfaces
of the sulphide samples exposed to UHF treatment: pyrite
oxidizes to hematite and elemental sulphur, andarsenopyrite oxidizes to magnetite, arsenic sulphide and
(minor) SO2, which helps increase gold recovery up to95% [4]. However, excessive UHP heating results in
unwanted effects, such as fusion and sintering of the
material and closure of as-formed cracks. In addition, thisprocedure is energy-intensive, with energy consumption
of at least 35 kWh per ton required to provide for plant
capacity of 510 tons per day.Magnetic pulse treatment of gold-containing ores is
meant to reduce energy expenditure for milling and
increase gold recovery [5]. This technique is realized bypassing the ore (or pulp) through a dielectric pipelinesegment enclosed in a system of electromagnetic coils
which, constantly generates electromagnetic field pulseswith repetition frequency up to 50 Hz. It is worthwhile to
implement this technique in ore processing just beforemilling and to include it in the cyanidatlon procedure,
which proves to yield a 11.5% gain in gold recovery inall.
A group of researchers affiliated in the ElectrophysicalInstitute of the Uralian Branch of Russian Academy ofSciences (Yekaterinburgh) designed a plant for
electrohydraulic treatment of resistant materials bynanosecond pulses with a positive polarity, a magnitude
of up to 250 kV, and a repetition rate of up to 300 Hz [6].This device does perform the mechanism of nanosecond
breakdown of water (the electrohydraulic methodproposed by L.A.Yutkin) with suspended microparticles,
yet having significant limitations on efficiency, capacity
and energy consumption, and some other technologicalrestrictions. In essence, electrohydraulic treatment is
realized through exposing the test material immersed inliquid, to shock waves generated by electrical breakdown
of the liquid, with an aim to destruct the resistant
particles. The essential disadvantages of this method are
the necessity of performing the process in a liquidmedium with solid-to-liquid ratio S:L=1:1, whichdecreases plant capacity and increases energy
consumption, and non-controllable changes in ioniccomposition of the aqueous phase of the pulp. In
particular, experiments with samples of stale tailings fromthe Uchala concentration plant revealed a sizable increasein concentration of Cu, Zn and Fe ions in the aqueous
phase of the pulp after electrohydraulic pulse treatment,which may disturb further processing and have negativeenvironmental sequels.
All the above discussed high-energy treatment methods
have the following disadvantages in common: high energy
consumption, overheating of the material subject toprocessing, and certain intensification of sulphide
leaching with uncontrollable passage of metal ions intothe liquid pulp phase.
In this paper we present a treatment method developedby IPKON RAS and IRE RAN researchers, which appears
to be free of the above listed disadvantages. This non-
traditional, highly efficient and environmentally safemethod of breaking up mineral complexes with
disseminated fine gold is based en non-thermal action of
nanosecond High-Power Electromagnetic Pulses onresistant gold-containing ores and beneficiation products
[7,8].
III. THE EFFECT OF HPEMP ON
BREAKING-UP OF GOLD-
CONTAINING MINERAL COMPLEXES
We have studied three plausible mechanisms ofdisintegration of mineral particles under the action of
nanosecond HPEMP with high electric field strength Ep10
7V/m [9]. The first mechanism consists in loosening
of the mineral structure due to electrical breakdown
effects, which only occurs in cases where small, highly
conductive inclusions are hosted in dielectric media. The
second mechanism is related to development of
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thermomechanical stresses at the boundary (interface)
between the dielectric (or semiconductor) and conductivemineral components, being only realized in cases wherethese components are comparable in size. The third
mechanism, assuming essentially non-thermal action of
HPEMP on mineral complexes, is related toelectromagnetic energy absorption by thin metallic filmsor layers much thinner than the characteristic skin layer
(skin effect).Figure 1a presents an image of a fragment of spallation
surface of a pyrite specimen after irradiation with a series
of nanosecond pulses. Although the action of the pulses
on the specimen surface was initially uniform, electric
breakdown developed quite unevenly, predominantlyclose to rough edges of the specimen and along the
intergrowth boundaries (Figure 1b). These experimentaldata are presented to confirm the formation of breakdown
channels and selective disintegration of mineral
complexes as a result of pulse irradiation, which makesfor efficient access of lixiviant solutions to precious metal
grains and enhanced precious metal recovery into lixiviaduring leaching.
For practical realization the specialists affiliated in
IPKON RAS designed a plant with capacity of 50100 kg(of ore subject to processing) per hour using a conveyermode of conveying ore into the zone of electromagnetic
pulse treatment. The plant includes the following units:
voltage converter, master pulse generator, capacitiveenergy accumulator, transportation system and electrodeunit. The efficiency of disintegration of mineral
complexes and breaking-up (unsealing) of precious
metal particles is controlled by the development of astreamer discharge in the gap between the electrodesthrough proper selection of the magnitude, duration and
shape of pulses. The required "dose" of electromagneticpulse effect for the specified mass of the mineral material
to be processed is attained by varying the speed of
conveyer belt movement and repetition frequency of
pulses from the pulse shaper. The flow of the material
subject to processing is conveyed (with equalizedthickness and limited width) into the unit of high-energy
treatment with nanosecond high-voltage pulses with the
following characteristics: voltage amplitude 2050 kV,
pulse front duration 15 ns, pulse repetition frequency
501000 Hz, with total plant power consumption notgreater than 3 kW.The employment of HPEMP in dressing resistant gold-
containing ores and beneficiation products appearsattractive as it provides for maximum breaking-up
efficiency for the mineral complexes being processed and
a significant gain in valuable components recovery
(3080% for gold and 2050% for silver), therewithhelping reduce both energy consumption and the cost of
products. Experiments on HPEMP-induced effects were
performed with various materials, including samples of
resistant ores, beneficiation products (gravitational andflotation concentrates) and stale tailings from
concentration plants. A feature in common to all the
materials selected for study was the presence of finelydispersed gold and silver (hundredths and thousandths of
m), much of this gold being related to sulphide minerals,
predominantly pyrite and arsenopyrite.
a)
b)
Figure 1. SEM image of the microstructure of
destructive zones of pyrite after HPEMP irradiation:
a) partial breakdown of surface in the vicinity of
metallic inclusion, and b) opening of the intergrowthboundaries.
The experimental procedure included pre-treatment of
mineral particles with a series of HPEMP, followed bycyanidation to extract precious metals. The experimentsinvolved both dry samples and samples wetted with water
in amount not greater than enough to fill the pores inmineral particles, i.e., to attain the solid-to-liquid ratio
S:L=(510):1. The number of pulses in a series and theirradiation parameters (pulse shape and duration) varied
depending on particular experimental conditions. Theappropriate value of electric field strength magnitude of
the electromagnetic field (varying from 5 to 50 MV/m)exceeding the electrical strength of the material was
attained through adjusting the gap between the electrodes
and their insulation. Data on gain in gold recovery by
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cyanidation from gold-containing ores, concentrates and
other processing products from different deposits afterHPEMP treatment are given in Table 1.
Table 1.Effect of HPEMP irradiation on gold extraction
by cyanidation from resistant gold-containing ores andbeneficiation products.
Deposit;
gold content,
ppm
Size class,
m
Gain in gold
recovery
(fromto), %
Initial ore
Kyuchus;
24.21000
12,11
(66.67 78.78)
Nevskoye;
1.31.8500
4,4
(91.2 95.6)
Olimpiadinskoye;
2.4100
8,33
(60.0 68.33)
oncentrates
gravitational
506,4
(77 3.4)Nezhdaninskoye;
80500
31.08
(51.22 82.3)
flotation
205.7
(82 87.7)Kumtor(Kyrgyzstan);
45 1407,9
(63.1 71)
Tailing from concentration plants
Aleksandrinskoye;2.34 74 31.2(52.56 83.76)
Gai;
2315
80
(11 91)
Uchala;
2.174
30
(12,86 42,86)
Urup;
1.02315
71.1
(8.5 79.6)
Uzelga;
2.2474
36,61
(6,25 42,86)
A series of process experiments confirmed the
theoretical assumption that maximum breaking-up
efficiency after E treatment would be expectedfrom gold-containing sulphides not finer grained than
200100 m, and that the effect of formation of
breakdown channels and selective desintegration isenhanced predominantly for wet samples. In particular,for a gravitational concentrate of ore from the
Nezhdaninskoye deposit exposed to HPEMP rather high
gain in precious metal recovery was obtained with
minimum energy expenditure of just 2 kWh per ton ofconcentrate being processed, while energy consumption in
a process involving mechanical grinding of the 500 m
ore to 50 m were about 2025 kWh per ton of ore.
IV. SUMMARY
The treatment of gold-containing raw material by High-Power Electromagnetic Pulses allows one to achieve the
maximum completeness of the intergranular breakdown
of the mineral components with minimum expenditures ofthe electric energy (the efficiency coefficient of
transformation of the industrial frequency energy into thepulse energy amounts to more than 90%). This fact
predetermines the creation of a fundamentally new,
highly-efficient, energy-saving technology of the oretreatment. This will exclude the necessity to make
investments into the power-consuming and ecologicallyhazardous process of oxidative roasting, or into the
expensive autoclave technology of concentratebreakdown. Consequently, this will make it possible to
reduce the distance from raw material to final commodity.
V. REFERENCES
[1] V.A. Chanturiya and V.A. Vigdergauz,"Electrochemistry of Sulphides. Theory and Practice of
Flotation," Moscow: Nauka, (1993).
[2] V.A. Chanturiya and V.A. Vigdergauz, "Scientificbasis and prospects of commercial application of
accelerated electron energy in mineral benefication
processes," Mining Journal (Gorny Zhurnal), no 7, pp. 53-
57, Jul. 1995.[3] S.W. Kingman, "Recent developments in microwave-
assisted comminution," Int. J. Miner. Process., vol. 74, pp.71-83, Jan. 2004.
[4] A.V. Khvan, et. al., "Feasibility of using UHF fieldeffects for ore preparation in gold production," Mining
Bulletin of Uzbekistan (Gorny vestnik Uzbekistana), vol.2, no 9, pp. 56-60, Sep. 2002.[5] S.A. Goncharov, et. al., "Employment of
electromagnetic treatment of gold-containing ores in
grinding and cyanidation processes," Information andAnalytical Mining Bulletin, no 7, pp. 5-7, Jul. 2004.
[6] Yu.A. Kotov, et. al., "All-round treatment of pyrite
waste products from mining-and-dressing works with
nanosecond pulses," Repts. Rus. Acad. Sci. (DokladyRAN), vol 372, no 5, pp. 654-656, May, 2000.[7] V.A. Chanturiya, et. al., "The opening of the refractory
goldcontaining ores under high-power electromagneticpulses," Repts. Rus. Acad. Sci. (Doklady RAN), vol 366,no 5, pp. 680-683, May, 1999.
[8] I.J. Bunin, et al., "Experimental studies of non-thermal
action of high-power electromagnetic pulses on resistant
gold-containing mineral products," Proc. Rus. Acad. Sci.(Izvestiya RAN). Ser. Phys., vol. 65, no 12, pp. 1788-
1792, Dec. 2001.
[9] V.A. Chanturiya, I.J. Bunin, and A.T.Kovalev,"Mechanisms of disintegration of mineral media exposed
to high-power electromagnetic pulses," Proc. Rus. Acad.
Sci. (Izvestiya RAN). Ser. Phys., vol 68, no 5, pp. 630-632, May, 2004.
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