<ul><li>Direct Smelting of Gold Concentrates as an Alternative to Amalgamation in Small-scale Gold Mining Operations   </l...
Today’ s Presentation <ul><li>Objective </li></ul><ul><li>ASSM Mining methods in Ghana </li></ul><ul><li>Available alterna...
Objective <ul><li>Identify and introduce techniques or processes to eliminate the use of mercury by artisanal and small-sc...
Map of Africa showing position of Ghana <ul><li>Area is about 230 020 km 2 </li></ul><ul><li>Population is about 21 millio...
Geological map of Ghana showing rock formations that contain gold
Location of Small-scale Mining District Centres, Ghana Upper East Bolgatanga  Eastern Akim Oda Central Assin Fosu, & Dunkw...
ASSM  Gold & Diamond Production 1989 Gold  2% Diamonds 40% 2001 Gold 6% Diamonds 95% 2007 Gold 12% Diamonds 98% SSM Contri...
ASSM Mining Methods in Ghana <ul><li>Washing and Panning (alluvials along rivers) </li></ul><ul><li>Shallow pitting (near ...
Mining in Dry Area (Eluvial) 90% greater than 1 mm
Concentration (Dry Area) Winnowing Washing
Mining of Alluvial Deposits
Mining Hard Rock (Reefs)
SSM Dredging in Ghana (Suction)
Milling (Hard Rock)
Flow sheet for operations <ul><li>Ore (hard rock) </li></ul><ul><li> </li></ul><ul><li>crushing/grinding </li></ul><ul><l...
Sluicing
Panning
Gold concentrate in a pan
Amalgamation
Squeezing excess mercury from amalgam
Fireplace for burning amalgam
Spongy gold
Gather and sell
Open hearth for smelting gold
Mercury Loss <ul><li>Spillage during amalgamation </li></ul><ul><li>Poor amalgam distillation  </li></ul><ul><li>Disposal ...
Alternatives <ul><li>Physical methods Shaking tables , special sluices Centrifugal concentrators </li></ul><ul><li>Chemica...
Alternative suitable for galamseyers <ul><li>Effective </li></ul><ul><li>Easy - requires no special equipment </li></ul><u...
Choice of direct smelting <ul><li>Fulfils all main criteria </li></ul><ul><li>Uses non-toxic, cheap chemicals, borax, sodi...
Smelting <ul><li>Smelting is a high-temperature melting process used to recover metals from ores and concentrates </li></u...
Smelting vs amalgamation <ul><li>Smelting gave 99.9% recovery </li></ul><ul><li>In the lab amalgamation gave around 97% re...
Furnace (sika bukyia) Removable chimney Steel shell Refractory bricks Stabilizer bar Combustion chamber Pipe for exhaust fan
Direct Smelting
Mixing charge and feeding crucible
Feeding the furnace
Heating crucibles in furnace
Temperature control
Removing crucible after smelting
Pouring of molten material
Cooling of melt in a mould
Separation of gold from slag Gold
Gold beads
Field trials
Demonstration of Method
Cost of Direct Smelting 1.6 Total 0.8 12 kg Charcoal 0.4 2 Crucibles 0.4 200 g Flux Cost (GH¢) Weight/number Item
Cost comparism 3.20 5.50 Total 1.50 Smelting  0.50 Heating of amalgam 3.20 4 crucibles (2 operations) 4.00 Half teaspoonfu...
Challenges (alternative fuels) PALM KENNEL
Challenges (concentrate pretreatment) <ul><li>Sulphidic concentrates </li></ul><ul><li>Concentrates with high metal conten...
Challenges (alternative fuels) GAS   Crucibles Gas cylinder Furnace
Challenges (alternative fuels) GAS
Challenges (integrity of crucibles)
Conclusions <ul><li>Direct smelting can be used to replace amalgamation </li></ul><ul><li>It is cheaper on consumables </l...
Cost estimates for kit CHARCOAL
Cost estimates for kit GAS
Acknowledgements <ul><li>The on-going direct smelting studies is being sponsored by the EU. The great support given by GBS...
RIDE A CROCODILE AT PAGA GHANA THANK YOU OBRIGADO
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S. Al-Hassan & R. K. Amankwah & R. S. Nartey, University of Mines and Technology, Ghana, Direct Smelting of Gold Concentrates as an Alternative to Amalgamation in Small-scale Gold Mining Operations

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S. Al-Hassan & R. K. Amankwah & R. S. Nartey, University of Mines and Technology, Ghana, Direct Smelting of Gold Concentrates as an Alternative to Amalgamation in Small-scale Gold Mining Operations

  1. 1. <ul><li>Direct Smelting of Gold Concentrates as an Alternative to Amalgamation in Small-scale Gold Mining Operations </li></ul><ul><li>S. Al-Hassan & R. K. Amankwah & R. S. Nartey </li></ul><ul><li>UNIVERSITY OF MINES AND TECHNOLOGY, GHANA </li></ul><ul><li>presented at the workshop at </li></ul><ul><li>CASM CONFERENCE, BRASILIA, BRAZIL </li></ul><ul><li>October 6 – 12, 2008 </li></ul>
  2. 2. Today’ s Presentation <ul><li>Objective </li></ul><ul><li>ASSM Mining methods in Ghana </li></ul><ul><li>Available alternatives </li></ul><ul><li>Direct smelting – the technique </li></ul><ul><li>Laboratory and field trials </li></ul><ul><li>Challenges </li></ul><ul><li>Conclusions </li></ul>
  3. 3. Objective <ul><li>Identify and introduce techniques or processes to eliminate the use of mercury by artisanal and small-scale gold miners (ASM) in Ghana </li></ul>
  4. 4. Map of Africa showing position of Ghana <ul><li>Area is about 230 020 km 2 </li></ul><ul><li>Population is about 21 million </li></ul><ul><li>Climate is tropical </li></ul>
  5. 5. Geological map of Ghana showing rock formations that contain gold
  6. 6. Location of Small-scale Mining District Centres, Ghana Upper East Bolgatanga Eastern Akim Oda Central Assin Fosu, & Dunkwa-on-Offin Western Tarkwa, Bibiani, & Asankragua Region District Centres Location
  7. 7. ASSM Gold & Diamond Production 1989 Gold 2% Diamonds 40% 2001 Gold 6% Diamonds 95% 2007 Gold 12% Diamonds 98% SSM Contribution Total Ghana Production Source: Minerals Commission, Ghana 839,235 2,628,290 2007 972,991 2,342,722 2006 1,065,923 2,138,944 2005 905,344 2,031,971 2004 904,089 2,274,627 2003 963,493 2,236,833 2002 1,090,072 2,381,345 2001 878,011 2,457,152 2000 Diamond Prodn (carats) Gold Prodn (oz) Year
  8. 8. ASSM Mining Methods in Ghana <ul><li>Washing and Panning (alluvials along rivers) </li></ul><ul><li>Shallow pitting (near surface placers) </li></ul><ul><li>Underground mining (reefs) </li></ul><ul><li>Tailings and waste dumps (of old closed mines) </li></ul>
  9. 9. Mining in Dry Area (Eluvial) 90% greater than 1 mm
  10. 10. Concentration (Dry Area) Winnowing Washing
  11. 11. Mining of Alluvial Deposits
  12. 12. Mining Hard Rock (Reefs)
  13. 13. SSM Dredging in Ghana (Suction)
  14. 14. Milling (Hard Rock)
  15. 15. Flow sheet for operations <ul><li>Ore (hard rock) </li></ul><ul><li> </li></ul><ul><li>crushing/grinding </li></ul><ul><li> </li></ul><ul><li>gravity concentration </li></ul><ul><li> </li></ul><ul><li>mercury  amalgamation </li></ul><ul><li> </li></ul><ul><li>filtration of excess mercury  liquid mercury </li></ul><ul><li> </li></ul><ul><li>burning of amalgam  mercury vapor </li></ul><ul><li> </li></ul><ul><li>sponge gold </li></ul><ul><li> </li></ul><ul><li>smelting </li></ul><ul><li> </li></ul><ul><li>bullion </li></ul>
  16. 16. Sluicing
  17. 17. Panning
  18. 18. Gold concentrate in a pan
  19. 19. Amalgamation
  20. 20. Squeezing excess mercury from amalgam
  21. 21. Fireplace for burning amalgam
  22. 22. Spongy gold
  23. 23. Gather and sell
  24. 24. Open hearth for smelting gold
  25. 25. Mercury Loss <ul><li>Spillage during amalgamation </li></ul><ul><li>Poor amalgam distillation </li></ul><ul><li>Disposal of amalgamation tailings </li></ul><ul><li>Further processing of sponge gold </li></ul><ul><li>it is estimated that for every gram of gold recovered at least 0.43g of mercury is escapes </li></ul>
  26. 26. Alternatives <ul><li>Physical methods Shaking tables , special sluices Centrifugal concentrators </li></ul><ul><li>Chemical methods Coal gold agglomeration IGoli Haber process Cyanide leaching Smelting </li></ul>
  27. 27. Alternative suitable for galamseyers <ul><li>Effective </li></ul><ul><li>Easy - requires no special equipment </li></ul><ul><li>Quick </li></ul><ul><li>Cheap </li></ul><ul><li>Suitable for processing small batches of concentrate </li></ul><ul><li>Visible - the miners can see their products throughout the whole process </li></ul><ul><li>Locally available </li></ul>
  28. 28. Choice of direct smelting <ul><li>Fulfils all main criteria </li></ul><ul><li>Uses non-toxic, cheap chemicals, borax, sodium carbonate, silica sand </li></ul><ul><li>Technology not developed for artisanal use </li></ul>
  29. 29. Smelting <ul><li>Smelting is a high-temperature melting process used to recover metals from ores and concentrates </li></ul><ul><li>Fluxes are added to the concentrate to assist melting and react with impurities so that the metal separates out </li></ul><ul><li>The final products are pure metal and a glassy slag containing the unwanted components </li></ul>
  30. 30. Smelting vs amalgamation <ul><li>Smelting gave 99.9% recovery </li></ul><ul><li>In the lab amalgamation gave around 97% recovery </li></ul><ul><li>In the field amalgamation gave around 88% recovery </li></ul>
  31. 31. Furnace (sika bukyia) Removable chimney Steel shell Refractory bricks Stabilizer bar Combustion chamber Pipe for exhaust fan
  32. 32. Direct Smelting
  33. 33. Mixing charge and feeding crucible
  34. 34. Feeding the furnace
  35. 35. Heating crucibles in furnace
  36. 36. Temperature control
  37. 37. Removing crucible after smelting
  38. 38. Pouring of molten material
  39. 39. Cooling of melt in a mould
  40. 40. Separation of gold from slag Gold
  41. 41. Gold beads
  42. 42. Field trials
  43. 43. Demonstration of Method
  44. 44. Cost of Direct Smelting 1.6 Total 0.8 12 kg Charcoal 0.4 2 Crucibles 0.4 200 g Flux Cost (GH¢) Weight/number Item
  45. 45. Cost comparism 3.20 5.50 Total 1.50 Smelting 0.50 Heating of amalgam 3.20 4 crucibles (2 operations) 4.00 Half teaspoonful of mercury (27 g) Cost, GHC Direct smelting Cost, GHC Amalgamation
  46. 46. Challenges (alternative fuels) PALM KENNEL
  47. 47. Challenges (concentrate pretreatment) <ul><li>Sulphidic concentrates </li></ul><ul><li>Concentrates with high metal content </li></ul>
  48. 48. Challenges (alternative fuels) GAS Crucibles Gas cylinder Furnace
  49. 49. Challenges (alternative fuels) GAS
  50. 50. Challenges (integrity of crucibles)
  51. 51. Conclusions <ul><li>Direct smelting can be used to replace amalgamation </li></ul><ul><li>It is cheaper on consumables </li></ul><ul><li>It takes a similar length of time </li></ul><ul><li>It uses no hazardous reagents </li></ul><ul><li>It is suitable for small batches </li></ul><ul><li>It is visible </li></ul>
  52. 52. Cost estimates for kit CHARCOAL
  53. 53. Cost estimates for kit GAS
  54. 54. Acknowledgements <ul><li>The on-going direct smelting studies is being sponsored by the EU. The great support given by GBS and Wardell Armstrong is worth commending. I am grateful to the organizers of this CASM Conference for sponsoring me for this presentation. </li></ul>
  55. 55. RIDE A CROCODILE AT PAGA GHANA THANK YOU OBRIGADO

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