# Leach Gold Ore with Chlorination



## meatheadmerlin (Sep 25, 2015)

I found this process for leaching ore.
http://www.ehow.com/how_10075085_leach-gold-ore-chlorination.html

I'm not sure this is a sound process to begin with, but
I noticed 2 errors in it off the top.
It says to make additions of HCl instead of Bleach to sustain the reaction,
and It says to use sodium metabisulfATE for precipitation.

Also, I don't see the citric acid wash listed in items needed employed in the process outlined.
And, I don't think I agree with the waste disposal process advocated.
Beyond that, it takes no account of there being other base metals present or ore compounds that may require roasting first.

But, I thought I would share other information I've found online with the people here.
I am even more glad now to have a resource like GRF to consult.
I would appreciate any other feedback on the process detailed,
and if anyone has pointers to a post on how the intended process really should be done.


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## Deano (Sep 26, 2015)

If you are wanting to carry out an actual chlorine leach on an ore the procedure is as follows.

Mill the ore down to around 100# or 150 microns top particle size. You will probably wear out a concrete mixer before you get rock pieces down to this size.

If you are just wanting to carry out a small scale leach then do your milling by hitting the rocks with a heavy sledge hammer to about 3mm size. The heavier the hammer the slower you can swing it and still get the rock to break. The slower the hammer is swung the less rock chips spray around, use eye protection.

Take the rock chips from the hammering and put them in a small coffee grinder, you can get around 100 grams of chips milled before the grinder falls apart, depends on brand.

You can substitute a hand operated mincer for the grinder, it will last longer but involves a lot more work.

Make up a leach solution of HCl at pH 3 to 4, this is your operating range. The pH will always rise during the process so you need to add very small amounts of HCl to keep the pH in the range.

Add straight common salt to the leach to reach 4% salt in solution. The salt speeds up the leach reaction, it is not necessary to have it but is a good idea.

Use a stirrer to keep the ore agitated in the leach solution, a magnetic stirrer or a plastic overhead stirrer are good.

Understand that chlorine gas will be evolved in the leaching process, do the leaching in a fume cupboard or standing upwind outdoors.

Also understand that chlorine is nasty enough to be declared as a banned agent in war.

Moving on, add a small quantity of hypochlorite to the leach solution, checking with the ORP meter to see that you are reading 1000mv.

If the reading is less than 1000mv you need to add hypochlorite to get it up to 1000mv.

When you add hypochlorite you will raise the pH so you will need to add HCl to get the pH back into range.

If the redox is less than 1000mv you will start preferentially leaching base metals and will also precipitate out some of the already leached gold.

Any sulfides present will be digested by the chlorine and the gold will all be leached from them.

If there was no free gold visible at the start of the leach then you are looking at a leach time of around a half an hour or until any sulfides are completely digested.

At the end of the leach the pulp is filtered through filter paper, usually a double thickness.

The liquid is allowed to sit long enough for the chlorine to volatilise, the hotter the faster. Check that this has happened with your ORP meter, you want to be below 400mv.

Gold can then be precipitated from the solution with metabisulfite.

If you are working with small ore samples you will most likely not have enough gold in solution to precipitate, use the stannous test as a check on gold presence.

The article is a typical research job where any actual knowledge was absent.

Deano


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## meatheadmerlin (Sep 26, 2015)

Thank you for the detailed reply!
That definitely covers the process with enough detail to be properly armed.

While searching here, I found a link to an Australian newspaper article from 1891.
I found it very insightful and copied the text to a post here:
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=44&t=18828&p=240284#p240284
It talks about the chlorination process and when it may be best to apply/avoid it for leaching.


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## Finn from Ecuador (Oct 5, 2015)

Dear Sirs

Well, this is my first post, i thought that i may me able to add a detail that might be interesting what comes to this subject.



Deano said:


> Mill the ore down to around 100# or 150 microns top particle size. You will probably wear out a concrete mixer before you get rock pieces down to this size.
> 
> If you are just wanting to carry out a small scale leach then do your milling by hitting the rocks with a heavy sledge hammer to about 3mm size. The heavier the hammer the slower you can swing it and still get the rock to break. The slower the hammer is swung the less rock chips spray around, use eye protection.
> 
> ...



Under the following link is mining engineer Randy Clarkson's report about his study about improving gold recovery from fine black sand concentrates for placer miners. It includes also instructions how to make a small rod mill.

http://kpma.ca/news/article/124

Salud

Finn


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## FrugalRefiner (Oct 5, 2015)

Welcome to the forum Finn!

Dave


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