DIRECT SMELTING – AN ALTERNATIVE METHOD TO RECOVERING GOLD USING MERCURY BY ASSM

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MENART GEOVENTURES ENT. LTDP. O. BOX 237

TARKWAGHANA

MARCH , 2013

PROF S. AL-HASSAN & PROF J. S. Y. KUMA

OUTLINE OF PRESENTATION• Objective

• Available alternatives

• Direct smelting – the technique

• Laboratory and field trials

• Challenges

• Conclusions

OBJECTIVE• Identify and introduce techniques or

processes to eliminate the use of mercury by Artisanal and Small-Scale Miners (ASSM) of gold in Ghana

SLUICING

PANNING

GOLD CONCENTRATE IN A PAN

AMALGAMATION

SQUEEZING EXCESS MERCURY FROM AMALGAM

FIRE PLACE FOR BURNING AMALGAM

SPONGE GOLD

WEIGHING: GATHER AND SELL

OPEN HEATH FOR SMELTING GOLD

MERCURY LOSS

• Spillage during amalgamation

• Poor amalgam distillation

• Disposal of amalgamation tailings

• Further processing of sponge gold

ALTERNATIVE PROCESSES TO AMALGAMATION

• Physical methodsShaking tables , special sluices,Centrifugal concentrators,

amalgamation

• Chemical methodsCoal gold agglomerationIGoliHaber processCyanide leachingDirect Smelting

SLUICING

Method Equipment/

Process

Principle Applicability

Physical Sluice Gravity

concentration

leading to

production of a

rough concentrate

that has to be

cleaned further

Used in virtually all small

scale mining centres as a

conventional rough

concentration unit.

COAL-GOLD AGGLOMERATION

Method Equipment/

Process

Principle Applicability

Physico-

chemical

Coal-Gold

Agglomeration

Agglomeration of

the gold particles

and coal, followed

by flotation with

diesel, kerosene and

other oils. The float

concentrate has to

be processed and

smelted

The process has been

tested in Australia, South

Africa, Brazil and

Tanzania. It appears that

despite its apparent

attractions, it was never

actually put into operation

and more research is

required.

IGOLI PROCESS

Method Equipment/

Process

Principle Applicability

Chemical Igoli process Leaching with HCl

and NaOCl followed

by filtration and

precipitation with

sodium

metabisulphite. The

slimes precipitated are

calcined and smelted

The process has been applied in

South Africa and Tanzania.

Due to the safety hazards

involved in working with acids

and the miners lack of training

in chemistry. Mintek insists on

miners attending a training

course. It is currently more

suited to organised medium

scale rather than ASSM

operations.

CYNIDATIONMethod Equipment/

Process

Principle Applicability

Chemical Cyanidation Leaching with sodium

Cyanide and oxygen

followed by adsorption

onto activated carbon,

elution, electrowinning and

smelting. Concentrated

solution that requires

further processing.

Cyanidation has been

applied by small scale

miners in Colombia,

Bolivia, Brazil and

Zimbabwe. The method is

not fast enough for

processing concentrates. It

is poisonous and illegal in

some countries like Ghana

HABER PROCESSMethod Equipment/

Process

Principle Applicability

Chemical Haber Leaching with a

concentrated

solution that

requires further

processing

The leaching reagent is proprietary. For this

process artisanal miners have to take their ore to

processing centres where it is processed. This is not

applicable to the artisanal mining environment as:

too costly and too complex for individuals or small

groups.

uses a proprietary chemical thus locking the

miners into a foreign third party supplier.

has major issues of trust and keeping track of an

individual’s ore.

DIRECT SMELTING

Method Equipment/

Process

Principle Applicability

Chemical Direct Smelting Melting black

sand

concentrates to

produce pure

gold

Smelting is applied in most small

scale centres and miners are familiar

with the method as it is being used

for purifying sponge gold. It has been

developed, tested and commercialised

in Ghana. It can be use for all types

of ores and comparatively cheaper

than amalgamation.

CRITERIA FOR SUITABLE ALTERNATIVE FOR ASSM MINERS

• Effective

• Easy - requires no special equipment

• Quick

• Cheap

• Suitable for processing small batches of concentrate

• Visible - the miners can see their products throughout the whole process

• Locally available

CHOICE OF DIRECT SMELTING

• Fulfils all the main criteria

• Uses non-toxic, cheap chemicals: borax, sodium carbonate, silica

sand

SMELTING

• Smelting is a high-temperature melting process used to recover metals from ores and concentrates

• Fluxes are added to the concentrate to assist melting and react with impurities so that the metal separates out

• The final products are pure metal and a glassy slag containing the unwanted components

• It can be used for all types of ores

SMELTING VS AMALGAMATION

• Smelting gave 99.9% recovery

• In the lab amalgamation gave around 97% recovery

• In the field amalgamation gave around 88% recovery

MIXING CHARGE AND FEEDING CRUCIBLE

ALTERNATIVE FUELSLPG

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FURNACES

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GAS FURNACE

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GAS FURNACE

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DIMENSIONS OF GAS FURNACES

ITEMDIMENSIONS

Small Size Large Size

Height 280 mm 280 mm

External Diameter 240 mm 405 mm

Internal diameter 170 mm 275 mm

Thickness of insulation 30 mm 60 mm

Thickness of metal shell 50 m 50 mm

Length of LPG inlet pipe 190 mm 190 mm

Air slot length 95 mm 95 mm

Air slot width 10 mm 10 mm

Number of air slots 3 3

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COST OF KIT WITH LARGE SIZE GAS FURNACESN Item Quantity Unit Cost (GH¢)

Total Cost (GH¢)

1 Gas furnace (L/S) 1 630.00 630.00

2 Gas cylinder (15 kg) 1 91.70 91.70

3 Gas (15 kg) 1 19.65 19.65

4 Fire extinguisher (4 kg) 1 72.00 72.00

5 Tongs 2 9.20 18.40

6 Cupels 2 19.65 39.30

7 Hammer 1 3.90 3.90

8 Gloves 2 2.60 5.20

9 Goggles 1 5.25 5.25

10 Spoons 2 0.20 0.40

11 Weighing scale 1 100.00 100.00

12 Crucibles 100 0.55 55.00

13 Flux reagents 1 260.00 260.00

14 Mixing bowl 2 2.60 5.20

  Total    1300.80

(680US$) 31

COST OF KIT WITH SMALL SIZE GAS FURNACESN Item Quantity Unit Cost (GH¢)

Total Cost (GH¢)

1 Gas furnace (S/S) 1 500.00 500.00

2 Gas cylinder (15 kg) 1 92.00 92.00

3 Gas (15 kg) 1 20.00 20.00

4 Fire extinguisher (4 kg) 1 65.50 65.50

5 Tongs 2 9.20 18.40

6 Cupels 2 19.65 39.30

7 Hammer 1 3.90 3.90

8 Gloves 2 2.60 5.20

9 Goggles 1 5.25 5.25

10 Spoons 2 0.25 0.50

11 Weighing scale 1 100.00 100.00

12 Crucibles 100 0.55 55.00

13 Flux reagents 1 260.00 260.00

14 Mixing bowl 2 2.60 5.20

  Total    1,170.25

(610US$)

DEMONSTRATION AND TRAINING

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DEMONSTRATION IN THE FIELD

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POURING OF MOLTEN MATERIAL

COOLING OF MELT IN A MOULD

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SEPARATION OF GOLD FROM SLAG

SEPARATION OF GOLD FROM SLAG

Gold

GOLD BEAD

COST COMPARISONAMALGAMATION DIRECT SMELTING

SN Item Cost (GH¢) SN Item Cost (GH¢)

1 Half teaspoon of Hg (27 g)

5.25 1 4 Crucibles(2 operations)

2.10

2 Heating of amalgam (charcoal)

0.65 2 Flux (2 x 200 g)

1.60

3 Smelting 2.00 3 Gas (2 x 0.75 g)

1.60

Total 7.90 (US$4.14)

Total 5.30 (US$2.76)

COST ESTIMATES FOR GAS KITSN Item Quantity

Unit Cost (GH¢)

Total Cost (GH¢)

1 Gas furnace (S/S) 1 500.00 500.00

2 Gas cylinder (15 kg) 1 91.70 91.70

3 Gas (15 kg) 1 19.65 19.65

4 Fire extinguisher (4 kg) 1 72.00 72.00

5 Tongs 2 9.20 18.40

6 Cupels 2 19.65 39.30

7 Hammer 1 3.90 3.90

8 Gloves 2 2.60 5.20

9 Goggles 1 5.25 5.25

10 Spoons 2 0.25 0.50

11 Weighing scale 1 100.00 100.00

12 Crucibles 100 0.55 55.00

13 Flux reagents 1 260.00 260.00

14 Mixing bowl 2 2.60 5.20

  Total     1170.25* (US$610)

CHALLENGES1. Retrieval of loan balances2. How is the money accruing from the sale of the

kits to be used?3. Formation and sustenance of Small Scale Miners’

Associations4. Sustenance of the Mercury Abatement Programme

(accessibility & affordability)5. Further follow-up to sustain the momentum of the

use of the technology.

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THE WAY FORWARD - GHANA

1. Ensure that the kits are readily available and accessible virtually at the door steps of the ssm;

2. Monies accruing from the sale of the kits should serve as revolving fund;

3. Outstanding loan balances should be retrieved by the respective District Offices of the MC;

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THE WAY FORWARD - GHANA CONT’D

4. Encourage the formation and strengthening of the SSM Associations

5. Monitoring and follow-up should be continued for at least two (2) years;

6. Use of the direct smelting method should be made a condition for the acquisition of license where amalgamation is used

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THE WAY FORWARD - GLOBAL

To achieve this feat it is recommended that the:

1. Countries should provide a budget or secure donor funds to

launch the project possibly using the Ghana Project as model

(at least €200,000.00);

2. Countries should organise Management Units (Ministry of

Mines, University, NGOs, etc) to manage the projects;

3. Countries should recruit local consultants with experience in

artisanal and small scale mining of gold to undertake the

projects;

THE WAY FORWARD – GLOBAL CONT’D

4. Menart Geoventures Ltd, University of Mines and

Technology, Tarkwa – Ghana, be contracted to

provide fabrication plans and a complete kit; and,

5. Menart Geoventures Ltd, University of Mines and

Technology, Tarkwa - Ghana may be contacted to

provide high level consultants to supervise the

projects.

UNIVERSITY OF MINES & TECHNOLOGYTARKWA, GHANA

ACKNOWLEDGEMENT• MINISTRY OF FINANCE & ECONOMIC

PLANNING • EUROPEAN UNION• MINERALS COMMISSION• PROJECT MANAGEMENT UNIT• BRITISH GEOLOGICAL SURVEY• UNIVERSITY OF MINES & TECHNOLOGY,

TARKWA (UMaT)

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INVESTITUREOF

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