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Microwave Energy AidedMineral Comminution

Presented by:

Ashish Kumar, Bala P Kamath, V V Ramarao (Speaker), D B MohantyCentral Research & Development Laboratory,Hindustan Zinc Limited

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Comminution in Mineral Beneficiationis an energy hungry process.

About 50 % of the total energy isconsumed during Comminution.

Measures to improve grindability of ore & attain energy savings were ontrial since early 1900s;Thermally

Assisted Liberation (T.A.L.) based onconventional heating was explored.Conventional T.A.L. was un-economical on commercial scale.

Recent researches in MICROWAVE &RF pioneered Microwave energy asan EFFECTIVE solution for Heatingsource.

Others0.9 %

Tailing disposal10 %

Flotation &Filteration

32.3 %

Milling43.6 %

Crushing13.2 %

Introduction

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Percy Le Baron Spancer 1 st to provide the idea of Heating by Microwaves in 1946.

Microwave energy is a form of Electro Magnetic Radiation having frequency between3000 MHz to 3000 GHz. Common applications of microwaves: communication; heating; Frequency bands for microwave heating application in India is 2450 50MHz.

Ore constituents have different thermal & mechanical properties (thermal expansioncoefficients, microwave absorption coefficients);

Microwave irradiation Differential heating of ore minerals Developing stress

Increased ore grindabilty to create trans-granular & inter-granular cracks / micro-fractures

Absorption of microwave is Characteristic phenomenon of respective Mineral. For example, presence of sulphides, oxides and graphitic carbon enhances fractureformation.

Breakthrough concept for various industries that consume large amounts of energyincluding mineral processing, cement etc.

Microwaves & Mineral Processing

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MICROWAVES

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Variety of applications of microwave heat in several

industries are in practice like:

Drying of food items (Tea leaves, seeds, edible items) Hospital sanitation Sprouting Vulcanization of rubber Carbon reactivation Pressure leaching Roasting Sintering Rocks & Ore comminution

Applications of Microwave

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COPPER

SIILSIILKCMKCM

A L U M I N I U M

B A L C O /

B A L C O /

MA L C O MA L C O

Z I N C & L E A D H Z L H Z L R & D C

R D L

VEDANTAVEDANTA

Background for Present Work

Hindustan Zinc Limited is aVedanta Group company;

CRDL is for HZLs R&D;

Technology cell at CRDL has

decided to adopt microwaveenergy use as a step changetechnology in its road map.

Work on Microwave aidedcomminution project started during2005; benefits targeted are Increased mill throughput

Reduced grinding energy

through reduction in the ore work index.

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3 Rod Mills

1107 Lead Roughers OK-16

10 Lead Scavengers OK-16

140

153

139

8 Zinc Roughers OK-38

181

9 Zinc Scavengers OK-38

151148

Regrind Cyclones

D 15

178

Zn 4-Stage Cleaning

196

193

190

187 162

282

288

Sec.Cyc.D 15

177

To Reclaim Water

Zn Stock Tank Zn Conc. Stock Pile

Pb Conc. Stock Pile

Pb Stock Tank

Tailing Thickener

Pb Conc.Thickener

Pb 3-Stage Cleaning

TAILING DAM

Neutralization Tank

Fine Crush Plant

Pri.Cyc.D 20R.O.M.

PrimaryCrusher

Coarse Ore Stock PileActive less than 9,000T

Fine Ore BinActive 4,500T (Each)

To

Recla im

Water

145

To

Recla im

Water

Pb Conditioner2 Zn. Conditioners

Regrind Mill

1153 Ball Mills

EXISTING RAMPURA AGUCHAEXISTING RAMPURA AGUCHA 6100 T.P.D. LEAD/ZINC CONCENTRATOR FLOWSHEET6100 T.P.D. LEAD/ZINC CONCENTRATOR FLOWSHEET

249

252

247254

14 M Dia

16 M Dia

7 Zn Filter PressesPF25

Zn Conc. Thickener

55 M Dia

222224

1 Pb Filter Press

PF25

14 M Dia

2 Zinc Roughers

additional fine ore bin

Rampura Agucha Beneficiation Plant

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Preparation of sample: 3 kg r epresentative samples from plant rod millfeed were prepared mixing ore size fraction in the range 19 mm to + 2mm in the same size proportion as in plant rod mill feed. (minus 2 mmsize fraction discarded in accordance with previous observations)

Grindability studies: Laboratory ball mill was used for wet grinding with3 kg sample each time at a pulp density of 60% solids (by wt); groundmaterial size distribution is known through wet sieving; Observations are:

o Effect of microwave on particle size distribution under water quenched &unquenched conditions w.r.t. unexposed samples.

o Effect of microwave on work index of ore. The relative work index of the ore

was calculated using Berry & Bruce formula.

Wi : work index kW.h/t; r and t refer for reference and test samples;

P and F refer to 80% passing of theproduct and feed stream.

Microwave Experimental Work

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o Effect of microwave on the grinding time, which is directly proportionalto the saving in grinding energy of the ore.

Simulation studies Prediction of mill throughput increase for reduction in ore work index;

o JKSimMet comminution softwareo Microwave irradiation (with quenching) at different time/intensity

ranges for using different work index values.

o Simulations predicted Throughput changes for same P-80 size;

Experimental Work . contd.

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Trend line (semi log) for average particle size distribution of R A Mine samplesunder water quenched, unquenched & unexposed conditions

y = -0.9906Ln(x) + 92.559

y = -0.9646Ln(x) + 95.346

y = -0.8184Ln(x) + 91.935

84

86

88

90

92

94

0 50 100 150 200 250 300 350 400 450

Sieve size (in mesh)

A v e r a g e o f c u m u l a t

i v e w

t % p a s s i n g

Blank UQ AVG Q AVG Log. (UQ AVG) Log. (Q AVG) Log. (Blank)

(more finer size for same grinding)

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Effect of microwave exposure for different time intervals on work index of ore

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70

Exposure t ime (min)

% r

e d u c

t i o n

i n w o r

k i n d e x

% Reduction in work index

Unexposed

(more grindability with more exposure)

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Microwave &Grinding Time

Plot of % passing fraction at

different particle sizes in groundproduct for different grindingtimes Irradiated & quenched Non-irradiated

More finer fraction generated for irradiated & quenched fractionsthan non-irradiated (normal)fractions 100 #, 150 # & 200 #

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Time o f grinding (min)

% c

u m u l a t

i v e p a s s

b y 2 0 0 m e s

h

Unexposed Exposed

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Time o f grinding (min)

% c

u m u l a t

i v e p a s s

b y 2 0 0 m e s

h

Unexposed Exposed

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Time of grinding (min)

% c u m u l a t

i v e p a s s

b y 1 5 0 m e s

h

Unexposed Expos ed

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Time of grinding (min)

% c u m u l a t

i v e p a s s

b y 1 5 0 m e s

h

Unexposed Expos ed

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Time o f grinding (min)

% c

u m u

l a t i v e p a s s

b y

1 0 0 m e s

Unexposed Exposed

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Time o f grinding (min)

% c

u m u

l a t i v e p a s s

b y

1 0 0 m e s

Unexposed Exposed

(for same grinding time morefiner product & for sameproduct size reduced residencetime)

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0

2

4

6

8

10

10 20 30 40 50

% reduction in work index

% i n c

r e a s e

i n p l a n

t t h r o u g

h p u t

Percent increase in plant throughput

Simulation studies to estimate the increased plant throughput ratewith percent reduction in work index

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Lead-Zinc sulphide ore of R A Mine is responsive tomicrowave radiation.

Water quenching immediately after microwave exposurecauses substantial reduction in work index of the ore.

Reduced work index results in reduction in grindingresidence time that reflects grinding energy reduction.

Increased grindability of ore causes increased plantthroughput rate (predicted by simulation studies).

Microwave energy has a potential role in commercial scalecomminution and other mineral / metallurgical operations;

Strong need for developing appropriate technology.

Conclusion

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Crusher

R.O.M.

Pri. Crusher Coarse OreStock Pile

Fine Crush PlantFOB

FOB

ApplicatorCavity

Microwave

Rod Mill

Ball Mill

Pri. Cyclone

Sec. Cyclone

To Flotation

Typical Flow Sheet For Microwave Aided Ore Milling(Proposed )

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Thank You !