# Need help with Iodine leaching black sand



## oldtimeminer (Oct 11, 2011)

:lol: 

Looking for anybody with experience leaching gold out of black sand. 

My black sand agua regia assays at 3oz per ton. Mostly extremely small, 520 mesh free gold balls, some small visible flake, and gold bond to black sand. Too fine for any mechanical separation. Tryed them all.

Practiced potassium iodide/iodine leaching on small gold flake and circuit brds. On clean gold can repeatedly get 90+% of gold recovery after leaching.

However same procedures and chemistry are not working on black sands.

After leaching black sand and raising PH to around 9, alot of purple residue starts to come out of solution. Looks like it could be gold at first, however there is too much of it and drying it turns light tan. Treatment with acids and even aqua regia will not dissolve residue. Also aqua regia will not extract any gold or any other metal out of residue. After separating residue, continue raising leach to 12.5 PH does not percipate gold, or anything else out of solution, like it does leaching clean gold.

Can conclude residue is: non-metal, binds easy with iodine, eats up free iodine in leach, and is stopping free iodine from binding with gold or other metals in black sand.

Anybody have any idea what this residue is and how I can pretreat black sand so it does not eat up my iodine leach?

Whatever the residue is, it both makess and breaks it's iodine bond easily. 

Current plan is to:

1. Lower PH to 9, drop residue, centrifuge off.
2. Increase PH back to 3, which should reactivate free iodine.
3. Leach 2 liter test sample of black sand again.
4. Repeat steps 1-3 until no more unkown residue is leached out of sample black sand.
5. When leach is free of unknow residue, increase PH to 12.5 to drop any dissolved gold.
Think will throw in some gold circuit brd fingers to monitor what, if any, gold leaching is happening.

Multiple leaching is alot of time and work. If anybody has already run into this issue, would appreciate any info or short cuts.

Note: Please do not recommend mercury. Have used it, it does work. However has also discovered by running mercury processed black sands through blue bowl...there is ALWAYS mercury flouring no matter how careful the process, no matter how freshly retorted the mercury, no matter how freshly charged the mercury is.

Later
8) 

Thanks


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## shaftsinkerawc (Oct 12, 2011)

I can't help with the Iodine ? but have a couple of my own for you.
1) Have you had your black sands assayed?
2) Are you running raw black sands or have you tried crushing them?

A few years ago I was running placer recovery in my house and threw some chlorox in my recycle tank to keep the scum down and ended up with purple water that a professor said was the chlorox attacking the sulfides in my concentrate.


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## oldtimeminer (Oct 12, 2011)

Thanks for replying shaftsinkerawc :lol: 

Assay question: Yes..my own aqua regia assay came up 3oz gold/ton on a 5lb sample of concentrate. 

Also send in 20 lb sample for professional fire assay. Fire assay came back 3.4 oz/ton Au, 8.7 oz/ton Ag.

Orginal sand is from dry desert wash with huge amount, around 30% heavy black sands. So my concentrate is 30% volume of raw sand.

Samples for assays and leach were screened down to 50 mesh. There is gold in 50-10 mesh screenings, however my aqua regia assay of rougher mesh sample only gave 0.6 au/ton, so I do not bother with rougher screenings. 1/2 of black sands are naturally under 50 mesh.

Blue bowl is only mechanical separation that can further refine concentrate. However even it can not separate out 520 mesh spherical gold. Do do that, I have to hand pan finished blue bowl material.

Most people that would see thin stream of fine gold in my pan would dismiss it as too little bit of color and move on.

It is only because of aqua regia assay, fire assay, and mercury tests that I know there is a huge amount of 520 mesh free gold in black sand.

Do have a dico pulverizer. Future plans do include grinding down +50 mesh material to -50 to see if that frees up more gold. However most gold is already free around 520 mesh, so my main concern for now is getting iodine leaching to work.

The amount of rough sand available is enough for last a few live times.

If I can get the iodine leaching to work, can make a good living without a huge amount of work or expense.

As a single independant prospector, can not afford $50k, $100k, or $more bonds to run a small operation with dangerous chemicals.

Iodine leaching does work. Iodine is more expensive than other leaches, however is it completely recyclable, re-useable, and with care and careful chose of other chemicals, all by products and waste can be human and environmentally safe.

Am quessing the main reason it is not used more is because of problems I am running into now.

Later
8)


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## shaftsinkerawc (Oct 13, 2011)

Did you have a multi element assay done on the 20lb sample? If so what else showed up?
Can you describe how you ran your +50/-10 mesh material? Do you do a pre-soak in anything to get rid of unwanted's. Is it possible other elements used up your chemicals and didn't have much chance to work on the Au or Ag. Or with it being larger size that you didn't give it enough time to work? 

(Orginal sand is from dry desert wash with huge amount, around 30% heavy black sands. So my concentrate is 30% volume of raw sand.)
So this means you are trying to leach unconcentrated raw sand?

How much material was in your +10 mesh fraction, and did you look at it with a loupe or microscope?

I would think that a disc pulveriser would smear your Au flatter and finer but for leaching that would be alright. I use a impact crusher (keene buchet crusher) and like the way it balls the fine Au up some making it easier for mechanical seperation.

Keep trying and keep us informed.


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## manorman (Oct 13, 2011)

What is the PH when you leaching?
iodine is selective to gold and silver if you can keep the PH low but you will leach Iron and silica (i think i remember that right)if the PH to high.
you might try roasting that tan powder at a red hot heat then try the acids.
Mike


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## Traveller11 (Sep 4, 2012)

Hello Oldtimeminer

How are things going with the Iodine/Iodide leaching? I, too, am seeking info on this leach as I am attempting to recover ultrafine gold from a beach placer here. Unfortunately, there is a lot of data on the net regarding this leach and much of it contradicts other data. For instance, one guy says to use Lugol's Iodine and NOT tincture of iodine, the next guy says tincture of iodine is the best to use. Precipitants range from carbon to sodium hydroxide to ascorbic acid (vitamin C).

You seem to be actually doing real experiments with Iodine so I will listen intently to any advice or instruction you wish to pass my way.

I did read in a few places that, although Iodine/Iodide will work over a broad spectrum of ph, a ph of less than 5 will stop the leach from working. Several sites advised adding small amounts of hydrochloric acid to keep the ph between 3-5.

One question. As my deposit is on an ocean beach and contains salt, do you think NaCl will have any effect on this leach?


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## Traveller11 (Sep 4, 2012)

Oldtimeminer

I was going over your original post again and a question occurred to me. Did you use tap water or distilled water to mix with your iodine/iodide solution? If you used tap water, is the water where you live very hard? I think you may have given me enough clues to solve this problem.

The purple colour could be what is called "sublimated iodine". This site explains it better than I can:

http://www.infoplease.com/ce6/sci/A0847062.html

The tan coloured residue sounds like calcium. If your water is hard, it likely has a great deal of calcium in solution. Raising the ph of the water, as you did when attempting to precipitate gold, will cause calcium to come out of solution and deposit as scale. 

In the drinking water industry, this is called "lime softening" and the process has been around since the 1800's. Very hard water has a base, such as sodium hydroxide, added to it to raise ph to roughly 11-12, or whatever is necessary. Calcium and magnesium fall out as scale. In the next step, an acid is added to bring the ph back to just over 7. It is an effective method of softening water but requires close monitoring.

I'm not sure if this is related to the sublimation of your iodine but it is a possibility. The articles I have read all say to used distilled water for mixing with your ore instead of tap water.

I live in a remote place and distilled water is not only difficult to get, its price is inflated. However, I have a dehumidifier at home and find I can produce four litres/day of distilled water with no problem. Unless you live in an area subject to acid rain, rainwater probably works well, too.


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