Post by fathihabashi1928 on Apr 2, 2008 10:45:14 GMT
CHALCOPYRITE: BIOLEACHING VERSUS PRESSURE LEACHING
Bacterial leaching has been successfully applied for heap leaching of copper ores. In the past few years there has been interest to apply bacterial leaching to treat chalcopyrite concentrates. Three demonstration plants went into operation between 1998 and 2002 - - all of them were shut down.
1) The first plant was constructed in 1998 at Mt. Lyell in Tasmania and was integrated with downstream solvent extraction and electrowinning for copper recovery.
2) The second plant was constructed in 2001 at Peñoles in Monterrey in Mexico. It operated for a year with a capacity of 200 tpa copper cathode production. However, due to the low price of copper at that time plans for a larger demonstration plant did not go forward.
3) The third plant was built in 2002 near Chuquicamata in Chile for $ 50 million. The plant was composed of six large reactors, mechanically agitated, and lined with acid-resisting brick. Since a thermophilic bacteria is used in this system it was possible to operate at a temperature of about 90oC.
The enthusiasm for bioleaching technology, was based on two possible advantages:
1) It was believed that acid generated during leaching can be used effectively for leaching oxide ores since the leaching reaction is supposedly being the following:
2CuFeS2 + 17/2 O2 + 5 H2O → 2Cu2+ + 2Fe(OH)3 + 4SO42- + 4H+
2) Any arsenic present in the concentrate would co-precipitate with the ferric hydroxide.
The reaction, however, is slow - - it is complete in 4 – 5 days and in addition, some nutrients must be supplied to the reaction mixture. Also in the recovery step by electrolysis, acid will be generated and must be disposed of, possibly for leaching oxide ore in the plant. Some lime however may be needed to dispose of the surplus sulfates.
When this technology is compared with pressure leaching, the reaction takes place in one autoclave at 150oC and 4000 kPa oxygen partial pressure:
2 CuFeS2 + 4 H+ + 5/2 O2 2 Cu2+ + Fe2O3 + 4 S + 2 H2O
The advantages of this route are the following:
The reaction is fast - - complete in 20 – 30 minutes
Oxygen consumption is less than one third of that required for bacterial leaching
One reactor is enough
Nearly all the sulfur in the concentrate can be obtained in the elemental form
Acid generated in the recovery step is equal to that required for leaching the concentrate
Any arsenic present in the concentrate will also remain in the residue as ferric arsenate
In summary, bacterial leaching in heaps of low grade copper ores is well accepted, but it is believed that bioleaching of chalcopyrite concentrates in agitated tanks cannot be economical. A more detailed analysis of this technology by the present writer can be found in “Chalcopyrite — Atmospheric versus Pressure Leaching,” Metall 61(5) 303–307 (2007). Comments are welcome.
Fathi Habashi
Laval University, Quebec City, Canada
Fathi.Habashi@arul.ulaval.ca
Bacterial leaching has been successfully applied for heap leaching of copper ores. In the past few years there has been interest to apply bacterial leaching to treat chalcopyrite concentrates. Three demonstration plants went into operation between 1998 and 2002 - - all of them were shut down.
1) The first plant was constructed in 1998 at Mt. Lyell in Tasmania and was integrated with downstream solvent extraction and electrowinning for copper recovery.
2) The second plant was constructed in 2001 at Peñoles in Monterrey in Mexico. It operated for a year with a capacity of 200 tpa copper cathode production. However, due to the low price of copper at that time plans for a larger demonstration plant did not go forward.
3) The third plant was built in 2002 near Chuquicamata in Chile for $ 50 million. The plant was composed of six large reactors, mechanically agitated, and lined with acid-resisting brick. Since a thermophilic bacteria is used in this system it was possible to operate at a temperature of about 90oC.
The enthusiasm for bioleaching technology, was based on two possible advantages:
1) It was believed that acid generated during leaching can be used effectively for leaching oxide ores since the leaching reaction is supposedly being the following:
2CuFeS2 + 17/2 O2 + 5 H2O → 2Cu2+ + 2Fe(OH)3 + 4SO42- + 4H+
2) Any arsenic present in the concentrate would co-precipitate with the ferric hydroxide.
The reaction, however, is slow - - it is complete in 4 – 5 days and in addition, some nutrients must be supplied to the reaction mixture. Also in the recovery step by electrolysis, acid will be generated and must be disposed of, possibly for leaching oxide ore in the plant. Some lime however may be needed to dispose of the surplus sulfates.
When this technology is compared with pressure leaching, the reaction takes place in one autoclave at 150oC and 4000 kPa oxygen partial pressure:
2 CuFeS2 + 4 H+ + 5/2 O2 2 Cu2+ + Fe2O3 + 4 S + 2 H2O
The advantages of this route are the following:
The reaction is fast - - complete in 20 – 30 minutes
Oxygen consumption is less than one third of that required for bacterial leaching
One reactor is enough
Nearly all the sulfur in the concentrate can be obtained in the elemental form
Acid generated in the recovery step is equal to that required for leaching the concentrate
Any arsenic present in the concentrate will also remain in the residue as ferric arsenate
In summary, bacterial leaching in heaps of low grade copper ores is well accepted, but it is believed that bioleaching of chalcopyrite concentrates in agitated tanks cannot be economical. A more detailed analysis of this technology by the present writer can be found in “Chalcopyrite — Atmospheric versus Pressure Leaching,” Metall 61(5) 303–307 (2007). Comments are welcome.
Fathi Habashi
Laval University, Quebec City, Canada
Fathi.Habashi@arul.ulaval.ca