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

Outokumpu HydroCopper Process Block Diagram Copper Concentrate Gold Silver By-Products Leach Residue NaCl Solution Leaching of Concentrate Leaching Purification Precipitation Regeneration of Chemicals Chlor-alkali Electrolysis Cl2 (g) NaOH Cu2O Metal Production Reduction Melting Casting Copper Product H2 (g) 10 November 2018

Counter Current Leaching 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 10 November 2018

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 10 November 2018

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. 10 November 2018

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 10 November 2018

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 10 November 2018

Leaching Yields Base metals 98 % Gold and silver >92 % About 10 % of sulfur is oxidized to sulfate Pyrite is refractory 10 November 2018

Leach Residue Small grain size, but filterable, consisting of: Elemental sulfur Goethite or hematite Gypsum, silica, etc. 10 November 2018

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 10 November 2018

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 10 November 2018

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 10 November 2018

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- 10 November 2018

Chlor-alkali Electrolyzer Chlor-alkali cell in HydroCopperTM Process replaces 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 10 November 2018