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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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