Two 2205 duplex stainless steel elution columns over 12 metres long have been installed in a replacement project at Kalgoorlie Consolidated Gold Mines in Western Australia.
Elution columns are used in the mettalurgical process of extracting gold from carbon.
Carbon impregnated with gold is hot washed with caustic cyanide in the elution columns to dissolve the gold out of the carbon. The gold solution is pumped away while the barren carbon remains in the columns and then is removed for reuse.
The columns hold temperatures of 140°C and operate under pressures of 550 kilopascals (KPa).
he previous columns, constructed from grade 304 stainless steel, were beginning to fail due to pitting corrosion caused by chlorides carried over in the process water, combined with erosion corrosion on the internal surface. The tanks were in service for a total of five years.
Stainless steel supplier, ASSDA member Sandvik Australia, worked with a consultant to find a more suitable grade of stainless steel for the job.
2205 was chosen for its ability to provide a higher resistance to chloride attack. The grade also has improved hardness over grade 304, thereby offering better resistance to the erosion effect of the activated carbon.
Kalgoorlie Consolidated Gold Mines Mechanical Engineer Adrian Rowell, said the grade change was made to try to ensure the columns lasted the life of the mine.
"The plant is planned to operate for another 15 to 20 years," Mr Rowell said . "By shifting to 2205 we anticipate that the columns will last that long."
Fabricated by ASSDA member Specialised Engineering Services (WA) Pty Ltd, the columns were constructed from 2205 duplex stainless steel
8 millimetre plate, which offered a significant weight saving over the original 10 millimetre grade 304 vessel. The columns were fabricated to AS 1210 class 28 Pressure Vessels with a maximum design temperature of 150°C.
Each elution column is 12.4 metres long, 1.7 metres in diameter and positioned vertically.
This article featured in Australian Stainless magazine - Issue 18, May 2001.