Direct smelting method
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This document describes direct smelting as an alternative to mercury amalgamation for artisanal and small-scale gold mining in Ghana. Direct smelting involves melting gold-bearing concentrates using borax, sodium carbonate and silica sand as fluxes to separate pure gold. The technique was tested in the lab and field and found to recover over 99% of gold, compared to 88-97% for amalgamation. It is presented as an effective, simple, quick and affordable non-toxic alternative suitable for small-scale operations. Challenges to adoption include ensuring continued availability and affordability of equipment kits for miners.
Direct smelting method
- 1. DIRECT SMELTING – AN ALTERNATIVE METHOD TO RECOVERING GOLD USING MERCURY BY ASSM MENART GEOVENTURES ENT. LTD P. O. BOX 237 TARKWA GHANA PROF S. AL-HASSAN & PROF J. S. Y. KUMA MARCH , 2013 1
- 2. OUTLINE OF PRESENTATION • Objective • Available alternatives • Direct smelting – the technique • Laboratory and field trials • Challenges • Conclusions
- 3. OBJECTIVE • Identify and introduce techniques or processes to eliminate the use of mercury by Artisanal and Small-Scale Miners (ASSM) of gold in Ghana
- 4. SLUICING
- 5. PANNING
- 6. GOLD CONCENTRATE IN A PAN
- 7. AMALGAMATION
- 8. SQUEEZING EXCESS MERCURY FROM AMALGAM
- 9. FIRE PLACE FOR BURNING AMALGAM
- 10. SPONGE GOLD
- 11. WEIGHING: GATHER AND SELL
- 12. OPEN HEATH FOR SMELTING GOLD
- 13. MERCURY LOSS • Spillage during amalgamation • Poor amalgam distillation • Disposal of amalgamation tailings • Further processing of sponge gold
- 14. ALTERNATIVE PROCESSES TO AMALGAMATION • Physical methods Shaking tables , special sluices, Centrifugal concentrators, amalgamation • Chemical methods Coal gold agglomeration IGoli Haber process Cyanide leaching Direct Smelting
- 15. SLUICING Method Equipment/ Principle Applicability Process Physical Sluice Gravity Used in virtually all small concentration scale mining centres as a leading to conventional rough production of a concentration unit. rough concentrate that has to be cleaned further
- 16. COAL-GOLD AGGLOMERATION Method Equipment/ Principle Applicability Process Physico- Coal-Gold Agglomeration of The process has been chemical Agglomeration the gold particles tested in Australia, South and coal, followed Africa, Brazil and by flotation with Tanzania. It appears that diesel, kerosene and despite its apparent other oils. The float attractions, it was never concentrate has to actually put into operation be processed and and more research is smelted required.
- 17. IGOLI PROCESS Method Equipment/ Principle Applicability Process Chemical Igoli process Leaching with HCl The process has been applied in and NaOCl followed South Africa and Tanzania. by filtration and Due to the safety hazards precipitation with involved in working with acids sodium and the miners lack of training metabisulphite. The in chemistry. Mintek insists on slimes precipitated are miners attending a training calcined and smelted course. It is currently more suited to organised medium scale rather than ASSM operations.
- 18. CYNIDATION Method Equipment/ Principle Applicability Process Chemical Cyanidation Leaching with sodium Cyanidation has been Cyanide and oxygen applied by small scale followed by adsorption miners in Colombia, onto activated carbon, Bolivia, Brazil and elution, electrowinning and Zimbabwe. The method is smelting. Concentrated not fast enough for solution that requires processing concentrates. It further processing. is poisonous and illegal in some countries like Ghana
- 19. HABER PROCESS Method Equipment/ Principle Applicability Process Chemical Haber Leaching with a The leaching reagent is proprietary. For this concentrated process artisanal miners have to take their ore to solution that processing centres where it is processed. This is not requires further applicable to the artisanal mining environment as: processing •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.
- 20. DIRECT SMELTING Method Equipment/ Principle Applicability Process Chemical Direct Smelting Melting black Smelting is applied in most small sand scale centres and miners are familiar concentrates to with the method as it is being used produce pure for purifying sponge gold. It has been gold developed, tested and commercialised in Ghana. It can be use for all types of ores and comparatively cheaper than amalgamation.
- 21. 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
- 22. CHOICE OF DIRECT SMELTING • Fulfils all the main criteria • Uses non-toxic, cheap chemicals: borax, sodium carbonate, silica sand
- 23. 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
- 24. SMELTING VS AMALGAMATION • Smelting gave 99.9% recovery • In the lab amalgamation gave around 97% recovery • In the field amalgamation gave around 88% recovery
- 25. MIXING CHARGE AND FEEDING CRUCIBLE
- 26. ALTERNATIVE FUELS LPG 26
- 27. FURNACES 27
- 28. GAS FURNACE 28
- 29. GAS FURNACE 29
- 30. DIMENSIONS OF GAS FURNACES DIMENSIONS ITEM 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 30
- 31. COST OF KIT WITH LARGE SIZE GAS FURNACE Total Cost (GH SN Item Quantity Unit 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 1300.80 Total (680US$) 31
- 32. COST OF KIT WITH SMALL SIZE GAS FURNACE Total Cost (GH SN Item Quantity Unit Cost (GH¢) ¢) 1 Gas furnace (S/S) 1 500.00 500.00 2 Gas cylinder (15 kg) 1 92.00 92.00 3 Gas (15 kg) 1 20.00 20.00 4 Fire extinguisher (4 kg) 1 65.50 65.50 5 Tongs 2 9.20 18.40 6 Cupels 2 19.65 39.30 7 Hammer 1 3.90 3.90 8 Gloves 2 2.60 5.20 9 Goggles 1 5.25 5.25 10 Spoons 2 0.25 0.50 11 Weighing scale 1 100.00 100.00 12 Crucibles 100 0.55 55.00 13 Flux reagents 1 260.00 260.00 14 Mixing bowl 2 2.60 5.20 1,170.25 Total (610US$)
- 33. DEMONSTRATION AND TRAINING 33
- 34. DEMONSTRATION IN THE FIELD 34
- 35. POURING OF MOLTEN MATERIAL
- 36. COOLING OF MELT IN A MOULD
- 37. SEPARATION OF GOLD FROM SLAG 37
- 38. SEPARATION OF GOLD FROM SLAG Gold
- 39. GOLD BEAD
- 40. COST COMPARISON AMALGAMATION DIRECT SMELTING SN Item Cost (GH¢) SN Item Cost (GH¢) 1 Half teaspoon 5.25 1 4 Crucibles 2.10 of Hg (27 g) (2 operations) 2 Heating of 0.65 2 Flux 1.60 amalgam (2 x 200 g) (charcoal) 3 Smelting 2.00 3 Gas 1.60 (2 x 0.75 g) Total 7.90 Total 5.30 (US$4.14) (US$2.76)
- 41. COST ESTIMATES FOR GAS KIT Unit Cost SN Item Quantity Total Cost (GH¢) (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)
- 42. CHALLENGES 1. Retrieval of loan balances 2. How is the money accruing from the sale of the kits to be used? 3. Formation and sustenance of Small Scale Miners’ Associations 4. Sustenance of the Mercury Abatement Programme (accessibility & affordability) 5. Further follow-up to sustain the momentum of the use of the technology. 42
- 43. 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; 43
- 44. 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 44
- 45. 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;
- 46. 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.
- 47. UNIVERSITY OF MINES & TECHNOLOGY TARKWA, GHANA
- 48. ACKNOWLEDGEMENT • MINISTRY OF FINANCE & ECONOMIC PLANNING • EUROPEAN UNION • MINERALS COMMISSION • PROJECT MANAGEMENT UNIT • BRITISH GEOLOGICAL SURVEY • UNIVERSITY OF MINES & TECHNOLOGY, TARKWA (UMaT) 48
- 51. INVESTITURE OF NEW VICE CHANCELLOR
- 59. THANK YOU