Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

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remove oxygen in leach samples (4 replies and 3 comments)

J
oro
6 years ago
oro 6 years ago

I am learning / testing a torch assay method for ores and leaches developed a couple decades ago by Charles Butler.  He developed the system for small - medium scale hard rock miners so they can perform initial tests on ores in the field and leaches in the lab in a simple and low cost manner to determine with relative accuracy the values or worthiness of further testing by more professional means.  What’s most interesting is that the methods are simple and results are fast, the cupeled bead measured or weighed.  My point here isn’t to open a discussion on this method but rather ask a simple question which is how to remove the oxygen from a small sample of pregnant solution so as to precipitate the dissolved metals (Au/Ag) with a pinch of zinc powder.  I read where heating the solution near boiling point for several hours will remove the oxygen but I was wondering if there was a faster / better method, for samples from a few hundred ml up to 2 liters.  Or maybe removing the oxygen might not matter for small samples.  Charles Butler doesn’t mention removing the oxygen in sample solutions but does recommend using zinc powder to drop the dissolved metals.  I’ve read elsewhere about precipitation with zinc for leach samples and no mention of removing the oxygen.  So, how to remove oxygen or not remove at all?

d
Cyanide
6 years ago
Cyanide 6 years ago
Like

In the Merrill Crowe process https://www.911metallurgist.com/blog/merrill-crowe-zinc-precipitation-circuit-operation

The oxygen is removed by subjecting the solutions to high vacuum.

The need for doing this really depends on how much oxygen you have to begin with.

Did you measure the dissolved oxygen? under 0.5 ppm best for zinc precipitation.

T
Todd H
6 years ago
Todd H 6 years ago
Like

There are a couple of methods you could use for small samples:

  1. Yes boiling will work as the solubility of oxygen decreases with temp but it wont reduce it all the way to zero but close.
  2. Sparging the sample with nitrogen or other gas to strip the oxygen can work - just bubbling the gas through the sample.  Again you have to be careful not to allow the sample to contact the air after sparging
  3. Oxygen scavenging chemicals can be added - sodium bisulfite as an example - used in boiler water to scavenge oxygen
  4. Vacuum applied to the sample - small vacuum pump

Regards

 

Todd Harvey - Global Resource Engineering http://www.global-resource-eng.com

J
Joeram
6 years ago

Hello Todd, I am getting ready to use cyanide and it keeps coming up de-aerate solution. I have never done this or any mining. Assay yes gold arsenic and sulfur. If I boil solution first then add SMB then zinc, Will this work? Thanks

T
TonyE
6 years ago
TonyE 6 years ago
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Build a chamber out of perspex, or polycarb. Add two stopcock valves. One at the top, one at the bottom. Place the magnetic stirrer inside the chamber with the sample. Purge the chamber with an inert  non flammable gas through the valves From the bottom to the top) while performing the precipitation under a hood. Oxygen will be displaced, out of the system including the sample with time. Add the zinc through a small tube at the top of the chamber.

T
TonyE
6 years ago

100% air saturation is the equilibrium point for gases in water. This is because gas molecules diffuse between the atmosphere and the water's surface. According to Henry's Law, the dissolved oxygen content of water is proportional to the percent of oxygen (partial pressure) in the air above it 13.

J
oro
6 years ago
oro 6 years ago
Like

thanks for the suggestions -

Currently I don't have a method to measure dissolved oxygen so that is one handicap. 

Sparging a gas is an interesting idea.  I have a small ozone generator from a water purification system. O3 will oxidize the O2 along with other (unwanted) effects maybe. O3 will oxidize any residual cyanide. Is that good or bad? 

T
TonyE
6 years ago

Don't use ozone. You should use an inert gas.


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