# Iodine/Iodide Leaching of Gold from Black Sand



## Traveller11 (Sep 3, 2012)

From what I have read, Iodine/Iodide leaching seems to be a straight forward and effective method of recovering gold. What I am having truble finding out is whether or not it is a selective leach. In other words, will it prefer the iron in the black sand to the free gold present with the black sand?


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## butcher (Sep 3, 2012)

I have not used the iodine leach, I also do not see how it would be selective, as it is a halide, my guess is it would form other metal halides in solution, and would react as the other halides do, just my guess here.


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## jeneje (Sep 4, 2012)

Traveller11 said:


> From what I have read, Iodine/Iodide leaching seems to be a straight forward and effective method of recovering gold. What I am having truble finding out is whether or not it is a selective leach. In other words, will it prefer the iron in the black sand to the free gold present with the black sand?


The only leach i have heard of using Iodine is the SSN leach you can read about it here http://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=15277 Irons said it is another version of poormans AR hope this helps
Ken


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## butcher (Sep 7, 2012)

The SSN saturated salt and nitric acid, is not the iodine leach, these are two completely different halide leaches.


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## Labman (Sep 18, 2012)

The iodine leach is iodine dissolved into a solution of potassium iodide and will dissolve gold preferentially from the platinum group which isn't very soluble in potassium salts. 8)


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## butcher (Sep 18, 2012)

Iodine Iodide 
Just a little stuff on this Halide:

Iodine (I2) is much more expensive from chlorine, as iodine comes from seaweed kelp being a main source.

It is my belief it would be harder to dissolve and precipitate gold from this solution as easily as we do with the chlorine halogens, iodide solutions can be used to leach ore, but I really do not know it is that popular in the mining industry, expense of the leach, and other related factors.

Iodine in its elemental state is oxidized, it is in this state that it is needed to react with gold to dissolve it, problem is in this state it is a blue black solid which will not dissolve in water (only very slightly soluble), potassium iodide (KI) is the reduced state of iodine which is a liquid, the iodine will dissolve in this potassium iodide solution forming (KI3) triiodide (Lugol's solution) basically three iodide atoms, so now we can dissolve gold with this solution.
KI + I2 -->KI3

After gold is leached into the iodide solution (red brown solution), Sodium Hydroxide (NaOH) can be use to reduce the iodine in solution to iodide and precipitate the gold, at this point the solution will go more colorless as the sodium iodide (NaI) is colorless, gold being impure is a black powder.
I2 + NaOH -->NaI

Iodide (I) can be oxidized to iodine (I2) with chlorine (or with sodium hypochlorite also called bleach).
2KI + Cl2 --> 2KCl + I2
If excess chlorine a solid iodine would form.

Silver nitrate (AgNO3) and potassium iodide would form silver iodide (yellow silver precipitant) and potassium nitrate solution.
AgNO3 + KI --> AgNO3 + KNO3
This silver salt, like the silver chloride salt is light sensitive, and can be used in photography; the light can reduce the silver to elemental silver metal and iodine.
2AgI--light--> 2Ag + I2

Unlike silver chloride, silver iodide is not soluble in ammonia solutions.


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## Traveller11 (Sep 29, 2012)

I have been investigating the recycling of the iodine/iodide leach and have come across some interesting info.

This solution, as butcher points out , can be oxidised to elemental iodine by the addition of an oxidiser such as sodium hypochlorite or hydrogen peroxide. While some sites recommend reducing elemental iodine to sodium iodide by adding sodium hydroxide to iodine, it turns out this will only transform about 60% of the iodine to sodium iodide. The remainder will be sodium iodate (NaIO3). This can be converted to sodium iodide by heating the mixture to 425° Celsius and driving off the oxygen from the iodate. It is said a fairly pure sodium iodide can be obtained this way.

However, another fellow has posted that mixing sodium thiosulphate with elemental iodine will produce sodium metabisulphite and sodium iodide with no iodate present. This interests me greatly, since the less I have to handle sodium hydroxide, the happier I am. 

It was a fairly old post on a rather obscure science forum but, luckily, the poster is still a regular on this site. I have PM'ed him to see how difficult it is to separate the sodium thiosulphate from the sodium iodide and to see if there are any dangers in this process.

I'll pass information along as it comes in.


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## donnybrook (Nov 9, 2012)

With the iodine leach keep your pH at 4.5. Iron is not a problem if kept at that.
donnybrook


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## herbbartley (Nov 22, 2012)

I have some povidone iodine 10%. It says that equates to 1% titratable. Do you think that will work Donnie?


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## donnybrook (Dec 2, 2012)

Yes thats what I use 10% providene. From memory you then break it down with five parts water. Don't forget to roast to remove sulphides (if there) then rinse with 10% hydrochloric. Drop it in a calico bag (pillow case size) and hang it over a bucket to let it filter. Rinse at least three times. I usually give it another roast so I know I have a fairly neutral or close to that sample to work with. Butcher on the forum has also been a great help as I wanted to recover it for re use. The cost in Australia is about $40 a litre or about $200 a gallon over your way but the material I have been working with has been rich enough to warrant the cost. So I am lucky. I will be tabling it down to about 5% per ton in the future which would be about 60 pounds.


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