Outotec HydroCopper® Process consists of copper concentrate leaching, solution purification, and metal recovery by hydrogen reduction. The product is high-quality copper wire rod.
Leaching of copper concentrate
Chalcopyrite can be leached efficiently in a chloride environment, with the help of Cu²+. Leaching takes place in an atmospheric counter-current operation at a temperature of 80–100°C, using stirred tank reactors and thickeners. Divalent copper leaches the copper of chalcopyrite and other sulfides. Ferrous iron is further oxidized by air or oxygen into ferric, which precipitates as goethite or hematite. The other sulfides present in the concentrate are also dissolved. Once all the copper has been leached, gold begins to dissolve as chloro- and bromo-complex. Gold is recovered in the last leaching stage.
Fast oxidation of cuprous solution
Half the solution from the concentrate leaching is fed into the oxidation reactors, and copper is oxidized into cupric, using chlorine gas.
Solution purification
A solution of very high purity is needed before copper (I) oxide can be precipitated. This is achieved using the HydroCopper® process solution purification system: removal of Cu²+, cementation of silver, precipitation of zinc, lead etc. and polishing the solution using ion exchange.
Precipitation of cuprous oxide
Copper is precipitated as copper (I) oxide, using sodium hydroxide. After precipitation, the slurry is filtrated on a vacuum belt filter. The filtrate, pure NaCl solution, is directed to CAE (chlor-alkali electrolysis).
Chlor-alkali electrolysis (CAE)
In the CAE, NaCl solution is used to produce caustic soda, chlorine and hydrogen.
Hydrogen reduction of copper oxide
Wet cuprous oxide (Cu2O) from the belt filter is fed into a reduction furnace. In the furnace the Cu2O is dried and reduced to metallic copper with hydrogen. Copper is discharged and fed into the melting furnace.
Melting and casting of copper
The copper is melted in an induction furnace and the molten copper is de-oxidized with a protective graphite cover. The molten copper is cast into copper products like copper wire rod, and optimum added value can be achieved by casting into sizes of 8–16 mm.
