Outokumpu HydroCopper  Process

1. Outokumpu HydroCopper Process O. Hyvärinen, M. Hämäläinen, R. Leimala Outokumpu Research Oy, Pori, Finland Chloride Metallurgy, 2002 Montreal, Quebec, Canada October 21, 2002

2. Gold Silver By-Products Leach Residue Outokumpu HydroCopper Process Block Diagram Copper Concentrate • Leaching of Concentrate • Leaching • Purification • Precipitation NaCl Solution • Regeneration of • Chemicals • Chlor-alkali Electrolysis Cl2 (g) NaOH Cu2O • Metal Production • Reduction • Melting • Casting Copper Product H2 (g)

3. Air Leach Residue Concentrate Counter Current Leaching Au Cu2+ Cu+ Oxidation of Cu+ CaCO3 NaOH Cu2+ Precipitation Hg Cl2 Cu Silver Removal Ag (Zn,Pb)CO3 Na2CO3 Metal Precipitation HCl Ion Exchange NaOH Cu2O Precipitation Chlor-alkali Electrolysis NaCl H2 Reduction Melting Casting Copper Product

4. Leaching Conditions Three-stage counter current atmospheric leaching of concentrate in agitated reactors • lixiviant 250 - 300 g/l NaCl • oxidants are cupric ions and oxygen (air) • solids content 150 – 300 g/l • temperature 85 - 95 oC • pH 1.0 – 2.5 • total leaching time typically 10 – 20 h

5. Leaching Reactions • Dissolution of chalcopyrite CuFeS2 + 3 Cu2+ = 4 Cu+ + Fe2+ + 2 S • Sulfide minerals MeS + 2 Cu2+ = Me2+ + 2 Cu+ + S where Me = Cu, Zn, Pb, Ni, Co, Ag, etc.

6. Gold Recovery • Gold is leached in the third stage where the redox potential is at its highest Au + 3 Cu2+ + 6 Cl- = AuCl4- + 3Cu+ + 2 Cl- • Gold ions are adsorbed on activated carbon

7. Iron Oxidation • Removal of iron is carried out by oxidation 3 Cu+ + ¾ O2 + 3 H+ = 3 Cu2+ + 1½ H2O Cu2+ + Fe2+ = Cu+ + Fe3+ Fe3+ + 2 H2O = FeOOH + 3 H+ • The overall reaction of chalcopyrite leaching is CuFeS2 + Cu2+ + ¾ O2 + ½ H2O = 2 Cu+ + FeOOH +2 S

8. Leaching Yields • Base metals 98 % • Gold and silver >92 % • About 10 % of sulfur is oxidized to sulfate • Pyrite is refractory

9. Leach Residue Small grain size, but filterable, consisting of: • Elemental sulfur • Goethite or hematite • Gypsum, silica, etc.

10. Solution Purification • Sulfate is controlled by adding limestone • Cu2+ is removed as hydroxy-chloride, pH = 3 –5, 4 CuCl2 + 6 NaOH = 3 Cu(OH)2* CuCl2 + 6 NaCl or by reduction with copper powder Cu2+ + Cu = 2 Cu+ • Silver is cemented out with Cu powder and mercury as amalgam • Multivalent metals are precipitated as hydroxides or carbonates, pH = 6 – 7 • Traces of these metals are removed by ion exchange

11. Precipitation of Cuprous Oxide • Cuprous oxide is precipitated with sodium hydroxide, pH = 9 - 10 2 CuCl + 2 NaOH = Cu2O + 2 NaCl + H2O • Impurities in the purified cuprous chloride solution have to be well below 0.1 mg/l

12. Reduction, Melting and Casting • Cuprous oxide is reduced by hydrogen gas at T = 400 – 550 oC in a rotary kiln (Outokumpu Demo Plant) Cu2O(s) + H2(g) = 2 Cu(s) + H2O(g) • Copper powder is melted in an induction furnace and cast into wire rod using the renowned Outokumpu Upcast® Technology

13. Lixiviant Regeneration • NaCl solution from the Cu2O-precipitation is fed into a membrane Chloralkali Electrolyzer 2 NaCl + 2 H2O = 2 NaOH + Cl2 + H2 • Products of the electrolyzer are recirculated • NaOH to Cu2O precipitation • H2 to Cu2O reduction • Cl2 to oxidize cuprous to cupric before leaching ½ Cl2 + Cu+ = Cu2+ + Cl-

14. Chlor-alkali Electrolyzer • Chlor-alkali cell in HydroCopperTM Processreplaces copper EW cell • Compared with the EW cell the highly advanced Chlor-alkali cell is • proven technology • operates at a higher current density • copper is not in contact with the cell and is not harvested from it • the cell is compact and needs less maintenance