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Recovering Gold from Water
Field Tested in Alaska
The purpose was to evaluate, under actual field conditions, the ability to remove free and float gold from fast-running streams with high turbidity. I have been assaying water for some time and felt it was time to design and construct equipment capable of recovering micro-fine gold and be able to withstand the rigors of field operations.
Alaska was chosen as the test-site. The last frontier, just about the most rugged conditions there are. Not the beautiful summer, but rather the last half of November, generally way below freezing and lots of snow. Extremely fast moving glacial runoff loaded with silt would be the most difficult to collect the gold because it would continually foul the membranes. This would be the same conditions as the muddy water from a sluice carrying "float" gold!!
Prior testing to be conducive to the evaluation process identified two sites. One site has been tested on a monthly basis revealing a high of $5.30 per gallon and a low of $1.40 per gallon. These values were arrived at by cementation with zinc, which would not be a commercially viable process but is definitely a good indicator.
I wanted to ascertain the recoverable values with a proven process and decided that membrane technology would be a good indicator of the free and float gold present on a continuous float basis.
Design and construction parameters:
- Portable equipment
- Be able to work with sluice wash water or in rivers and streams
- Be able to function in extremely dirty or silty wate
- Recover gold to 0.02 micron (smaller than a bacteria)
Test site parameters:
- Receding glacie
- Gold-bearing area
- High and fast water flow
- Silty, very turbid wate
- Downstream from rapids
- Close to the tidal break
The gold recovered in the membranes during the tests by the Micron Gold Recovery Machine was digested from the membranes with CDE 2 leach and then refined by solvent exchange technology. My experience with this methodology is approximately 950 fine on the first pass and then approximately 999 fine on the second digestion/solvent exchange processing.
We got all of the "free and float" gold. The difference between available and recovered gold is due to the large volume of gold in colloidal and ionic form. I have completed the equipment needed to strip the colloidal and ionic gold from aqueous solution in the lab, but I just didnt have the field model ready. Now that the first part of the recovery method is field-verified within a financially acceptable parameter it is a lot easier to justify the expenditure to construct a portable colloidal and ionic gold recovery unit to tie-in to the Micron-Gold Recovery Machine.
There were no surprises with the machine. It is small enough to carry as check-in luggage on an airplane, strong enough to endure the rigors of the plane trip and the pounding of travel and operation at remote sites. There were no breakdowns, no leaks, and no failures. The spare parts kit I packed was excess baggage. This equipment can be supplied to run at 35 gallons per minute flow rate.