direct smelting method
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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
NEW VICE CHANCELLOR
THANK YOU
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