The document summarizes alternative processes and technical solutions to reduce or replace mercury use in artisanal and small-scale mining operations. It discusses problems with whole ore amalgamation and provides examples of improved amalgamation techniques from various countries that reduce mercury emissions such as using barrels, centrifuges, and additives. It also explores alternative processes like cyanidation, flotation, direct smelting, and electrolysis but notes challenges for artisanal miners. Mill-leaching of gold ore with cyanide during grinding is presented as a potential mercury-free alternative.

1. Marcello M. Veiga Associate Professor of University of British Columbia Vancouver, Canada Reducing/Replacing Hg in ASM Operations Suriname, 2008 Presented at the 8 th CASM – Community and Small-scale Mining Annual Conference Brasilia October 6-12, 2008

2. Control Hg Bioavailability Technical Solutions for Hg Pollution Alternative Processes to Replace Hg Reduce Hg Use and Emissions Long-term Short-term Medium-term Replace amalgamation with other process Avoid methylation covering or dredging Hg-contaminated tailings Avoid exposure to Hg and eliminate bad practices

3. Technical Solutions Alternative Processes Cyanidation Electrolytic Control Hg Bioavailability Polluted Sites Mercury Dispersed Re-suspension of Sediments Covering Dredging & Treatment Bioaccumulation Occurring ? Monitoring N Y Y Change of Food Habits Fish Hair Process Reduction of Hg Emissions Systemic Solutions Individual Solutions Processing Centers Organization of Associations Law Enforcement Permanent Biological Monitoring Education Retorts & special Fume hoods Activated Hg Use Hg far from people & Technical Assistance Bioaccumulation Occurring ? Amalgamate concentrates Other Lixiviants Direct Smelting

4. Amalgamation of the Whole Ore Huge Hg losses, large environmental problem Burning Amalgams in Pans Health problem for miners, family and neighbors Hg o CH 3 Hg in fish Cyanidation of Hg-contaminated tailings Hg o vapor lungs and/or Reduction of Hg Emissions Depends on the Amalgamation Procedure

6. Hg is retained in the riffles giving the impression that amalgamation occurred in the pool Hg is spread in the pool and pumped to the sluice box Venezuela, 1995 Amalgamation of the Whole Ore (Mercury Spread on the Ground)

7. Hg goes with tailings Brazil, 1999 Amalgamation of the Whole Ore (Mercury in the Sluice Box) Hg is added here

9. Plates: attrition remove Hg from plates = Hg is lost Amalgamation of the Whole Ore (Cu-Plates with Hg) Brazil, 2008 Venezuela, 2003

10. Venezuela, 2003 Amalgamation of the Whole Ore (Cu-Plates with Hg)

11. Venezuela, 2003 Amalgamation of the Whole Ore (Cu-Plates with Hg)

12. Zimbabwe, 2005 Use of Copper Amalgamation Plates generates tailings highly contaminated with Hg (usually 50-200 ppm Hg) Amalgamation of the Whole Ore (Cu-Plates with Hg)

13. Amalgamation of the Whole Ore (Grinding with Hg) Indonesia, Talawaan, 2001 Adding Hg into the Grinding Circuit 25 to 30% of the Hg added is lost with tailings (“flouring”)

16. Brown Sugar in the Ball Mills with Hg Ecuador, 2004

17. Amalgamation in Antioquia, Colombia “ coco”” elutriator “ coco” (with balls) elutriator cyanidation 70kg ore 30L water 120g Hg 50kg balls (1/2 volume) 200g Ca(OH) 2 4 hours Excess Hg + amalgam 90g Hg 10mL molasse 10L lime juice NaHCO 3 pH 5 pH 11 3 hours Excess Hg + amalgam

19. Using Urine to Amalgamate Chile, 2008

20. Forming Sodium-amalgam (increase coalescence = reduces Hg flouring = less Hg loss with tailing) sodium-amalgam is more consistent than pure Hg Also called “ Hg Activation” Battery 12 V wire Mercury Water with NaCl (10%) + - Graphite rod Dr Pantoja’s Method

21. Brazil, 2006 Zimbabwe, 2006 3800 miners in the GMP site in the Amazon adopted this technique

23. Tanzania, 2005 Manual Amalgamation Must Be Avoided

26. Reducing %Hg in amalgam from 40% (manual squeeze) to 20% (centrifuge) filtered mercury PVC cups amalgam clamps piece of cloth Indonesia, 2001

27. Manual Centrifuge Brazil, 2006 Filtering Amalgam

29. Gold Not Liberated Liberated Gold Assuming that the dark particles are gold Gold Concentration is Fundamental Gold Recovery is Low when Gold is not Liberated Gravity Separation 0.07 mm

31. Good Grinding Does not Need Sophisticated Equipment Mozambique, 2005 Indonesia, 2004 NO Hg ADDED in the ball mills 10 kg of ore ground with 14 steel balls for 45 min.

32. Panning in a closed pool (away from rivers) Some Hg-free gold can be obtained but in most cases Hg is introduced at the end of the panning step to capture fine Au Mozambique, 2005 Gold Concentration by Panning

33. Zig-zag Sluice Indonesia, 2006 Zig-zag sluices increase chances of capturing gold Suriname, 2007

34. Concentrating Gold in Sluice Box Indonesia, 2006

37. Why Are Centrifuges More Efficient? When the particles are subjected to G = 60, the difference in fall velocity is much higher than with G = 1 0 1 2 3 4 5 6 0 20 40 60 Gravity (G) Difference in Fall Velocity (mmec)

40. Sudan, 2004 Using Small Cleangold Panning Tailings with Cleangold

41. Concentrating Gold Using Fridge Magnets Mozambique, 2005

42. Gravity Concentration of a Gold Ore from Talaawan, Indonesia HMMS = Homemade magnetic sluice P80 = 0.25 m m Conclusion: gold is not liberated and it’s very fine 5% 8% 7% Au Recov ery (%) 11.31 11.40 11.95 Tailings 16.00 117.00 64.00 Concentrate 11.50 12.30 12.60 Feed Knelson ® HMMS Cleangold ® Au (ppm or g/t)

49. Electrolytic Process - + Cl 2 ClO - AuCl 4 - NaCl solution Pulp of gold ore

55. Ecuador, 2007 Amalgamation of a Pre-concentrate Followed by Cyanidation - Ecuador A pre-concentrate is obtained in sluice boxes (discharge every hour)… … and amalgamated in barrels

56. Ecuador, 2007 Some operations use pH = 7 in Cyanidation Amalgamation of a Pre-concentrate Followed by Cyanidation - Ecuador Tailings (with or without Hg) are leached with NaCN

59. Cyanidation Gold Ore from Talaawan, Indonesia HMMS = Homemade magnetic sluice Au (ppm or g/t) P80 = 0.25 mm 6 hours of leaching in agitated tank 84% 5% 8% 7% Au Recov ery (%) 1.96 11.31] 11.40 11.95 Tailings 32.00 16.00 117.00 64.00 Concentrate 12.20 11.50 12.30 12.60 Feed Cyanidation Knelson ® HMMS Cleangold ®

61. Mill-leaching (Cyanide in Ball Mill) Gold Ore from Talaawan, Indonesia Grinding with NaCN for 2h + Leaching Time 14.8 93.6 0.86 10.7 10.7 24 15.0 93.3 0.88 11.1 11.4 8 17.5 93.1 0.78 11.9 12.1 6 16.2 85.5 0.88 12.2 12.3 4 14.7 77.9 0.88 12.2 12.3 2 Au in the sample, g/tonne %Au Recovered Final Na CN g/L pH Initial Final Leaching Time, h

65. Cyanidation in Agitated Tank Ecuador, 2007

69. Other Reagents Adapted from Trindade & Barbosa Filho. Reagentes Alternativos ao Cianeto. Chapter 9, p. 211-252. In: Extração de Ouro - Princípios, Tecnologia e Meio Ambiente . CETEM/CNPq, Rio de Janeiro, Brazil AuCl 4 - 1-4 Cl - , OCl - , Cl 2 ClO 3 - Chlorine [Au(S 2 O 3 ) 2 ] 3- 8-11 S 2 O 3 2- Thiosulfate [Au(SCN) 4 ] - 1-3 SCN - Thiocyanate AuI 2 - 1-5 I - Iodine AuBr 4 - 1-7 Br - Bromine [Au(NH 2 CSNH 2 ) 2 ] + 1-4 NH 2 CSNH 2 Thiourea Complex formed with Au pH Reagent Name

71. iGoli Photo: Mintek, South Africa 2001