Comparison of methods of concentrating and recovering fine gold particles
By Charles Kubach, Mine-Engineer.Com
The data for this article comes from the British Geological Survey Technical Report WC/97/14.
Then the old mercury amalgamators were tested, using mercury to form a chemical bond with gold. These were effective in the particle
size range of 1.5 mm down to 70 microns, yielding efficiencies of 98% for gold in the range of 1.5 mm to 500 microns (35 mesh).
The efficiency dropped off dramatically as the particle size decreased , yielding only 65% recovery for -75 micron gold.
Illustration of small mercury amalgamator
Finally good old cyanide was tested. Due to the time required to dissolve gold in cyanide, only -200 micron gold was used and the efficiency was 80% to 90%, It can take 24 hours or longer to dissolve gold particles in cyanide in a agitated tank, with proper aeration. Up to 2-3 months on a heap leach operation.
So, based on the results of their testing program, it would look like centrifugal concentrators and gravity tables, along with spirals would be the best equipment to use for gravity separation of gold in a oxide placer operation, where the particle sizes were below 50 mesh and especially if much were fine, from 200 to 400 mesh. Of these three items of equipment, the centrifugal concentrators would be the easiest to use for a small scale miner, since little technical knowledge is required to operate it, once it is set up, sized material is fed to it, along with adequate water supplies.
No dry concentrating devices were tested in this study, but if they were the results would not be very good, since efficiencies would most likely be below 50%.
Again, CJ Mitchell, EJ Evans and MT Styles of the British Geological Survey conducted the testing program, prepared the report from which the basic data were used for this article.
Illustration of small mercury amalgamator
Finally good old cyanide was tested. Due to the time required to dissolve gold in cyanide, only -200 micron gold was used and the efficiency was 80% to 90%, It can take 24 hours or longer to dissolve gold particles in cyanide in a agitated tank, with proper aeration. Up to 2-3 months on a heap leach operation.
So, based on the results of their testing program, it would look like centrifugal concentrators and gravity tables, along with spirals would be the best equipment to use for gravity separation of gold in a oxide placer operation, where the particle sizes were below 50 mesh and especially if much were fine, from 200 to 400 mesh. Of these three items of equipment, the centrifugal concentrators would be the easiest to use for a small scale miner, since little technical knowledge is required to operate it, once it is set up, sized material is fed to it, along with adequate water supplies.
No dry concentrating devices were tested in this study, but if they were the results would not be very good, since efficiencies would most likely be below 50%.
Again, CJ Mitchell, EJ Evans and MT Styles of the British Geological Survey conducted the testing program, prepared the report from which the basic data were used for this article.
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