Sciencemadness Discussion Board - Leaching Gold with Lugol's Soultion and Recycling Lugol's Solution

Leaching Gold with Lugol's Soultion and Recycling Lugol's Solution

Traveller - 12-10-2012 at 19:33

Hello

I am fairly new to this forum and possess a limited knowledge of chemistry; hence, my appeal to you for advice.

I am attempting to recover ultra-fine gold particles from the top surface of a deposit of clay. It is a fairly rich deposit of gold a few millimeters thick on the upper surface of the clay.

The method I am attempting is leaching with Lugol's Solution. Reputedly, it is a selective leach and will only dissolve gold, leaving the base metals.

Lugol's Solution (iodine, sodium iodide, water) is not the most popular method of leaching, due to the high cost of iodine, but it has been well known as a leach since the late 1800's. Many prospectors carried a bottle of Lugol's with them to assay samples in the field.

As the process has been described to me, one takes finely ground ore, places it in a container and covers it with Lugol's Solution. A tight fitting lid is placed on the container and the container shaken regularly for 4-6 hours, at which time any free gold should be in solution. Maximum particle size should be about 80 mesh. The solution is filtered and the ph raised by the addition of sodium hydroxide. Raising the ph should cause the gold to come out of solution as a fine powder. The solution is again filtered to separate gold and solution. The iodine is recovered as elemental iodine by the addition of hydrochloric acid and an oxidizer such as hydrogen peroxide or sodium hypochlorite. Lugol's Solution is re-made by adding sodium hydroxide to the iodine to make sodium iodide, then adding iodine and distilled water to this mix.

Two questions I have:

If all I am attempting to do is raise the ph to precipitate gold, can I use something besides sodium hydroxide, such as sodium carbonate? NaOH is a little dangerous to use.

Once I have raised the ph and dropped the gold from solution, do I not still have Lugol's Solution, just at a higher ph? Using a ph meter, could I not just slowly add HCl until I brought it back to the original ph of Lugol's Solution? Would this not be normal Lugol's Solution again? What is the normal ph of Lugol's Solution?

Oops, that was more than two questions. Hope someone can help me.

weiming1998 - 12-10-2012 at 20:03

Quote: Originally posted by Traveller

Hello

I am fairly new to this forum and possess a limited knowledge of chemistry; hence, my appeal to you for advice.

I am attempting to recover ultra-fine gold particles from the top surface of a deposit of clay. It is a fairly rich deposit of gold a few millimeters thick on the upper surface of the clay.

The method I am attempting is leaching with Lugol's Solution. Reputedly, it is a selective leach and will only dissolve gold, leaving the base metals.

Lugol's Solution (iodine, sodium iodide, water) is not the most popular method of leaching, due to the high cost of iodine, but it has been well known as a leach since the late 1800's. Many prospectors carried a bottle of Lugol's with them to assay samples in the field.

As the process has been described to me, one takes finely ground ore, places it in a container and covers it with Lugol's Solution. A tight fitting lid is placed on the container and the container shaken regularly for 4-6 hours, at which time any free gold should be in solution. Maximum particle size should be about 80 mesh. The solution is filtered and the ph raised by the addition of sodium hydroxide. Raising the ph should cause the gold to come out of solution as a fine powder. The solution is again filtered to separate gold and solution. The iodine is recovered as elemental iodine by the addition of hydrochloric acid and an oxidizer such as hydrogen peroxide or sodium hypochlorite. Lugol's Solution is re-made by adding sodium hydroxide to the iodine to make sodium iodide, then adding iodine and distilled water to this mix.

Two questions I have:

If all I am attempting to do is raise the ph to precipitate gold, can I use something besides sodium hydroxide, such as sodium carbonate? NaOH is a little dangerous to use.

Once I have raised the ph and dropped the gold from solution, do I not still have Lugol's Solution, just at a higher ph? Using a ph meter, could I not just slowly add HCl until I brought it back to the original ph of Lugol's Solution? Would this not be normal Lugol's Solution again? What is the normal ph of Lugol's Solution?

Oops, that was more than two questions. Hope someone can help me.

1, I'm not sure about that. It depends on whether the gold exists in solution as gold (III)/(I) iodide/triiodide or as a complex. It also depends on what pH the gold "un-complexes" and precipitates out. I have not found a mechanism on the action of Lugol's Solution on gold. It's best to use NaOH. You don't even have to use concentrated solutions of it. A 1 molar solution can bring the pH up very quickly. Just put on a pair of gloves and eye protection and you're pretty much safe.

2, Once you raised the pH, you don't have Lugol's solution any more, but a mix of IO3- and I- ions. That's because Lugol's solution is a solution of triiodide and sodium/potassium ions. The I3-, (probably) disproportionates like I2 to I- and IO3- ions when basic, since it is I2 dissolved in I-. Look at your solution afterwards. If it is colourless, the I3- ions are gone. Thus, it is not Lugol's Solution anymore. Adding HCl will simply result in an acidified iodide/iodate mix.

Traveller - 12-10-2012 at 20:29

Weiming

Thank you for your reply.

Uh, not quite sure what IO3- is. Is this iodate?

Any ideas on regenerating the solution, following the addition of NaOH and the precipitation of gold, back to the original mixture of I2 and NaI found in Lugol's Solution? I imagine the elevated ph has to be dealt with at some point.

Perhaps the only way of recycling is taking everything back to elemental iodine and starting over, as I read.

weiming1998 - 12-10-2012 at 21:15

Quote: Originally posted by Traveller

Weiming

Thank you for your reply.

Uh, not quite sure what IO3- is. Is this iodate?

Any ideas on regenerating the solution, following the addition of NaOH and the precipitation of gold, back to the original mixture of I2 and NaI found in Lugol's Solution? I imagine the elevated ph has to be dealt with at some point.

Perhaps the only way of recycling is taking everything back to elemental iodine and starting over, as I read.

Take the solution and heat/evaporate until the water is gone. Then take the solid and heat in a crucible. This will decompose the iodate to iodide. After that, dissolve some iodide in water (not all of it) and react with H2SO4 or acidified H2O2. This will produce iodine. Dissolve your remaining iodide in water and start adding iodine until no more can dissolve, or until all of it is used up. This will regenerate your Lugol's solution, although I would just buy a new bottle.

Traveller - 12-10-2012 at 21:42

Weimer

Thanks again for the reply. You have an ability for making a complicated matter simple which, for the simple minded like me, is a blessing.

In the method I read about, they reduced the solution to elemental iodine by adding HCl and an oxidizer. They then made sodium iodide by adding NaOH. However, I have read, on this forum, that this will give you sodium iodide AND sodium iodate.

For my purpose of making Lugol's solution for leaching gold, will the presence of sodium iodate interfere with the process or would it need to be driven off by heat?

weiming1998 - 12-10-2012 at 23:41

Quote: Originally posted by Traveller

Weimer

Thanks again for the reply. You have an ability for making a complicated matter simple which, for the simple minded like me, is a blessing.

According to Wikipedia, iodates will react with iodides under acidic conditions,(http://en.wikipedia.org/wiki/Iodine_clock_reaction) to form iodine, so you might be right in acidifying the spent solution to regenerate the Lugol's Solution, but I'm not sure if that's true or if HCl can provide the H+ needed.

I'm also not sure if the iodate will interfere with the leaching. A precipitate of gold (III)/(I) iodate might form and thus interfere with leaching. I would get rid of the iodate, just in case, by heating or adding a reducing agent (like sulfite).

hissingnoise - 13-10-2012 at 02:00

If the clay particles are small could you not use the physical method of weight-separation?

AJKOER - 13-10-2012 at 10:12

Alternately, here is a description of the less expensive commercial cyanide-process for Gold extraction being essentially the use of air and a dilute potassium-cyanide solution followed by treatment with a large excess of Zinc. To quote (source: http://gold.atomistry.com/extraction.html ):

"Access of air is essential to solution of gold in potassium cyanide, the process being attended by evolution of hydrogen. Lead, bismuth, antimony, cadmium, silver, and mercury also dissolve in presence of air; but copper, iron, aluminium, nickel, cobalt, and zinc dissolve in absence of air. Gold and silver are distinguished by the fact that their maximum solubility corresponds with a very low concentration of the potassium-cyanide solution, a phenomenon probably due to the slight solubility of air in concentrated solutions of this salt. The solution of gold in the cyanide solution is accompanied by the intermediate formation of hydrogen peroxide, and the process is accelerated by addition of this substance:

2Au+4KCN+2H2O+O2 = 2KAu(CN)2+2KOH+H2O2;

2Au+4KCN+H2O2 = 2KAu(CN)2+2KOH.

A similar accelerating effect is exerted by other substances, such as potassium ferricyanide, potassium permanganate, potassium chromate, sodium peroxide, barium peroxide, cyanogen bromide, cyanogen chloride, persulphates, and certain organic compounds. The best method of reducing the proportion of the other metals is to maintain the cyanide solution dilute.

In precipitating the gold by zinc, the proportion required is about seven times that indicated by the equation

Zn+2Au•=2Au + Zn••,

the discrepancy being due to solution of part of the zinc in the cyanide solution, with evolution of hydrogen. Purity of the zinc is an important factor in counteracting this loss."

Other Gold extraction processes are discussed, but in less detail.

[Edited on 13-10-2012 by AJKOER]

Traveller - 13-10-2012 at 13:22

Quote: Originally posted by hissingnoise

If the clay particles are small could you not use the physical method of weight-separation?

No, the particle size of the gold involved makes it impractical for removal with gravity methods.

Traveller - 13-10-2012 at 13:30

Quote: Originally posted by AJKOER

Alternately, here is a description of the less expensive commercial cyanide-process for Gold extraction being essentially the use of air and a dilute potassium-cyanide solution followed by treatment with a large excess of Zinc. To quote (source: http://gold.atomistry.com/extraction.html ):

"Access of air is essential to solution of gold in potassium cyanide, the process being attended by evolution of hydrogen. Lead, bismuth, antimony, cadmium, silver, and mercury also dissolve in presence of air; but copper, iron, aluminium, nickel, cobalt, and zinc dissolve in absence of air. Gold and silver are distinguished by the fact that their maximum solubility corresponds with a very low concentration of the potassium-cyanide solution, a phenomenon probably due to the slight solubility of air in concentrated solutions of this salt. The solution of gold in the cyanide solution is accompanied by the intermediate formation of hydrogen peroxide, and the process is accelerated by addition of this substance:

2Au+4KCN+2H2O+O2 = 2KAu(CN)2+2KOH+H2O2;

2Au+4KCN+H2O2 = 2KAu(CN)2+2KOH.

A similar accelerating effect is exerted by other substances, such as potassium ferricyanide, potassium permanganate, potassium chromate, sodium peroxide, barium peroxide, cyanogen bromide, cyanogen chloride, persulphates, and certain organic compounds. The best method of reducing the proportion of the other metals is to maintain the cyanide solution dilute.

In precipitating the gold by zinc, the proportion required is about seven times that indicated by the equation

Zn+2Au•=2Au + Zn••,

the discrepancy being due to solution of part of the zinc in the cyanide solution, with evolution of hydrogen. Purity of the zinc is an important factor in counteracting this loss."

Other Gold extraction processes are discussed, but in less detail.

[Edited on 13-10-2012 by AJKOER]

Hello AKJOER

I have read extensively about the use of potassium or sodium cyanide for dissolving gold and wish that I could use it, mostly because it can be prepared to only dissolve gold and ignore base metals. It is an effective and economical method of gold extraction; evidenced by the fact that upwards of 90% of gold extracted annually is extracted with cyanide.

The down side of cyanide is its tendency to form toxic gases at lower ph's, its environmentally detrimental byproducts and the fact that an individual, such as myself, cannot legally purchase it in Canada.I know it is possible to take the necessary safety precautions and it is possible to neutralize cyanide solutions with sodium thiosulphate but, is it possible to purchase cyanide on the open market?

Eddygp - 13-10-2012 at 13:37

If you plan to take a piece of clay to your lab, I would suggest mercury, because it is quite efficient. However, it is very toxic and difficult to find these days.

zed - 13-10-2012 at 14:13

Seems to me Oxone plus a Halide salt may be used for some metal leaching processes.

[Edited on 13-10-2012 by zed]

hissingnoise - 13-10-2012 at 15:10

Quote:

I would suggest mercury, because it is quite efficient. However, it is very toxic and difficult to find these days.

I used this this seller fairly recently and cost and delivery was reasonable . . .
He specifies collection, now, but that may change!

[Edited on 13-10-2012 by hissingnoise]

Traveller - 13-10-2012 at 17:58

I don't mean to be critical but, I did not ask for advice on mercury, gravity separation or cyanide. I have looked into all of these methods and can find no way to apply them to my situation.

I am, however, eager to learn anything you have to offer about iodine/iodide leaching of gold and recycling of this leach.

hissingnoise - 14-10-2012 at 04:11

I see! Your entire focus is on acquisition of I2?

Traveller - 14-10-2012 at 08:12

No, my focus is on recovering fine gold using Lugol's Solution and being able to recycle that solution, due to its high cost.

hissingnoise - 14-10-2012 at 11:42

You already have the required Lugol's Solution then, I take it?

Traveller - 14-10-2012 at 11:47

I have a small supply I am using to experiment with. There is a chemical supply house in Vancouver that tells me they will supply me with iodine and sodium iodide once I am ready to scale up to an operational volume.

Traveller - 14-10-2012 at 11:51

I have been informed that a second thread I began about Lugol's Solution should have been part of this thread. I will transfer it's contents here plus the one reply to it thus far.

Thread content:
Is this guy making Lugol's Solution in a kind of backwards way?

http://www.youtube.com/watch?v=CLhwkFKLdPA

Reply from Vargouille:
Short answer, no.

Lugol's solution is a mixture of iodine and an iodide salt. This process is a simple oxidation of iodide by acidified hydrogen peroxide, which converts almost all of the iodide into iodine, with little to no production of triiodide. One could argue that because of the lack of precise measurements on the amount of reagents used, some triiodide may be produced if the amount of iodide salt is in excess, however, the main product is free iodine, which precipitates and is removed. The dark color of the solution remaining is, I believe, from the small amount of iodine that is soluble in water, rather than a concentrated solution of potassium triiodide.

Traveller - 14-10-2012 at 11:53

So, if the solution he ended up with is free iodine in water, what would happen if he added more potassium iodide powder to this solution?

hissingnoise - 14-10-2012 at 12:18

Quote:

Now the ore is in the jar. Pour in the Iodine solution so that the ore is well covered. Shake it occasionally for some time, maybe ½ to 1 hour. Now you must remove the ore. You can let it settle and pour off the Iodine containing the gold or you can filter it with a small funnel and some coffee filter paper. The idea is to get the solution as clear as possible. Now you add a small glob of mercury and shake. At some point the solution will lose it's red-brown Iodine color and become a (usually) clear yellowish liquid with sediment of heavy "floured mercury" in the bottom of the jar/test tube. Allow this to settle for a few minutes and then carefully pour off the liquid. Add some water to the mercury, shake, allow it to settle, and pour off. Don’t throw the liquids away. Now you have your precious metals amalgamated in the "floured mercury". Now you simply add some nitric acid (not more than 50/50 with water) and dissolve the mercury. When the mercury is all dissolved you will be left with a black or brown material that you cannot dissolve. This is your precious metal. Don’t throw the nitric solution away. Now take a good look at the black sediment. Try to get a feel for how much there is so that you will have a comparative idea of how much you have. You can buy, from chemical supply companies, a graduated, conical test tube. If you run the assay in this you can simply read off the quantity of precious metals on the scale engraved on the tube. It’s a nicety that the old timers didn’t have but it is convenient.
The reason to save all the liquids is simple, we are going to recover all your Iodine and mercury. The solution that contained Iodine is treated with a few drops of chlorox. The Iodine will settle to the bottom. The liquid is poured off and then you add a little lye water until the solution becomes clear and colorless. Your iodine is in solution ready to use again . . .

"Floured mercury" is the metal in the form of small globules which do not agglomerate to the liquid form!
It must be carefully handled due to its toxicity . . .

Traveller - 14-10-2012 at 12:55

Thank you for this information. However, I am really not interested in using mercury. One of the reasons I became interested in the iodine leaching process is that I do not wish to introduce toxic compounds into the environment I live in.

Remember this guy?

[Edited on 14-10-2012 by Traveller]

Vargouille - 14-10-2012 at 12:57

Quote: Originally posted by Traveller

So, if the solution he ended up with is free iodine in water, what would happen if he added more potassium iodide powder to this solution?

In that case, I believe that it would form a yellowish solution of dilute potassium triiodide.

CRC states that iodine has a solubility of 0.03 g/100 g H2O at 20C. This lab from the University of Delaware states that dilute solutions of triiodide are yellowish, while more concentrated ones are brown. That, incidentally, is why starch is used during titrations of iodine, because it forms an intensely blue-black solution even at very low concentrations of triiodide. It was probably warmer than 20C when the video was taken, but let's assume that the solubility wasn't altered too drastically. That corresponds to a 0.001 M solution of iodine. Now, the concentration of triiodide that constitutes a dilute solution isn't defined, but it's safe to say that 0.001 M is dilute enough.

I would not, mind you, call this "Lugol's Solution". Lugol's solution is significantly more concentrated based on iodine, either about 0.2 M (for 5%) or 0.08 M (for 2%).

[Edited on 14-10-2012 by Vargouille]

hissingnoise - 14-10-2012 at 13:09

Quote:

Remember this guy?

Milliner's disease resulted from prolonged exposure to mercury vapour!

Traveller - 14-10-2012 at 13:19

There were lots of prospectors in Canada that went crazy or died from inhaling mercury fumes while retorting gold/mercury amalgam. As I said, I am not interested in using it.

hissingnoise - 14-10-2012 at 13:34

If you send me the top layer of clay, I'll be only too glad to do the separation!

watson.fawkes - 14-10-2012 at 15:58

Quote: Originally posted by Traveller

I am attempting to recover ultra-fine gold particles from the top surface of a deposit of clay. It is a fairly rich deposit of gold a few millimeters thick on the upper surface of the clay.

How much clay is it, exactly. What's the percentage of gold by mass?

Traveller - 14-10-2012 at 16:41

There is a few miles of this clay. The assay results are on a need to know basis only. Suffice it to say it is worth putting considerable effort into.

Traveller - 14-10-2012 at 18:07

http://www.freepatentsonline.com/3957505.html

watson.fawkes - 14-10-2012 at 21:46

Quote: Originally posted by Traveller

There is a few miles of this clay. The assay results are on a need to know basis only. Suffice it to say it is worth putting considerable effort into.

And you do know this is a forum for amateur science, right? Your secrecy is utterly characteristic of money-making mining operations.

Stripping a few miles of streambed (since you specified a linear length, rather than an area, I'll assume it's an alluvial deposit) is just not at the amateur scale. As an estimate, take 10 km of stream, 5 mm of surface thickness, 2 m of width, and 1% gold by mass. I'll take the density of wet excavated clay at 1.8 kg/m³. That's 100 m³ of clay. I don't know anyone with a garage large enough to hold the raw material. Gold content estimated at 1.8 kg, or about 58 troy ounces. At USD 1700 per ounce, that's just shy of USD 100,000.

Traveller - 15-10-2012 at 07:40

Well, I don't know of many people who mine gold just for the fresh air and exercise. At some point, the novelty of seeing the yellow metal wears off and one likes to see a slight return on one's efforts.

You assumed, when I stated there was a few miles of this clay, I had the means and authority to strip mine miles of clay at a time. Nothing could be further from the truth. I am limited to the tools I can pack in on my back to a very remote and isolated locale and it would take several lifetimes for me to successfully exploit this entire deposit. Also, it is not a stream. Beaches are measured in miles, as well, and this deposit sits atop a layer of marine clay a few feet below the surface of an ocean beach. The gold is deposited by waves during winter storms.

As you can see, I am not a large mining corporation. If I were, I likely wouldn't be asking for advice on this forum but would, instead, hire engineers and chemists to work out the leaching problems. I am just a person trying to supplement his income in these troubled times by trying to recover an ounce or two of gold when time permits.

watson.fawkes - 15-10-2012 at 08:47

Quote: Originally posted by Traveller

I am just a person trying to supplement his income in these troubled times by trying to recover an ounce or two of gold when time permits.

Are you planning to do leaching on site, then? Or to haul back clay and process in the lab? My guess is that you'll get better mass / unit-transportation efficiency by hauling clay rather than hauling a portable lab around.

I think you'll also find that iodine in any form is fairly expensive and recovery of spent iodine is difficult. Cyanide leaching is well understood, much less expensive, and importantly for your concerns, and be remediated before discharge. Oxidation to cyanate is quite common, but electrowinning of gold has the side effect of regenerating the cyanide in ionic form, where it can be reused. Search on "cyanide remediation" for lots of hits.

Traveller - 15-10-2012 at 09:37

Quote: Originally posted by watson.fawkes

Quote: Originally posted by Traveller

I am just a person trying to supplement his income in these troubled times by trying to recover an ounce or two of gold when time permits.

Correct. And as leaching takes time, a person would be tied to the site until the gold was dissolved and precipitated. My basic plan is to scrape off the minimal amount of clay I can, break it down to a liquid form in a bucket and screen it down to -30 mesh. At this point, it should be a manageable volume for packing out.

As for recovering and recycling iodine, I posted the patent by Richard Homick for everyone's perusal of his plan for recycling.

I know cyanide is very economical, straightforward to use and can be neutralized to prevent it harming the environment. However, when things go bad, they go bad in a big way. I'm not sure what country you are in but, in Canada, there does not appear to be a legal method for a small time operator, such as myself, to obtain cyanide.

Traveller - 18-10-2012 at 16:30

Another question about Lugol's Solution, is it particularly volatile? What I mean is, the patent requires the leaching process to be agitated. I was thinking of the smallest cement mixer I could find to keep the clay and Lugol's constantly mixed and moving. Would it be necessary to cover the top to prevent evapouration losses of iodine?

Vargouille - 18-10-2012 at 17:12

Well, there are a few points to be told to answer that. Lugol's solution, as a whole, is not particularly volatile at standard temperatures. The conversion of iodine to triiodide keeps it in solution unless something happens to separate the iodine (or the iodide) from the triiodide. For iodine, it can be either a reducing agent, or heat. A mixer of the type you describe will certainly produce at least some amount of heat, from friction, although I'm not certain whether or not that amount is enough to liberate iodine from triiodide. When in doubt, however, I find it best to err on the side of caution. So, unless you're a gambling man, you may want to consider keeping it covered during operation, or use something to keep the temperature down.

zed - 26-10-2012 at 15:11

Other Halogens will do. Beside liberating Halogens via the action of Oxone on Halide salts....More economical routes are available.

Herein, someone is suggesting Sodium Hypochlorite plus HCl....to produce Cl2.

http://www.ehow.com/how_10075085_leach-gold-ore-chlorination...

Traveller - 26-10-2012 at 16:27

Quote: Originally posted by zed

Other Halogens will do. Beside liberating Halogens via the action of Oxone on Halide salts....More economical routes are available.

Herein, someone is suggesting Sodium Hypochlorite plus HCl....to produce Cl2.

http://www.ehow.com/how_10075085_leach-gold-ore-chlorination...

The sodium hypochlorite/hydrochloric acid leach is very effective at dissolving gold. However, it is even more effective at dissolving iron (the HCl turns oxides such as haematite and magnetite into ferric chloride) and actually preferrs iron to gold. Because there are large amounts of magnetite and haematite found in the top layer of clay, it would be necessary to remove the iron from the clay before leaching; unless a way could be found to make the NaClO/HCl leach selective for gold. Perhaps by ph adjustment?

Traveller - 26-10-2012 at 16:27

Quote: Originally posted by zed

Traveller - 26-10-2012 at 16:28

Quote: Originally posted by zed

The sodium hypochlorite/hydrochloric acid leach is very effective at dissolving gold. However, it is even more effective at dissolving iron (the HCl turns oxides such as haematite and magnetite into ferric chloride) and it actually prefers iron to gold. Because there are large amounts of magnetite and haematite found in the top layer of clay, it would be necessary to remove the iron from the clay before leaching; unless a way could be found to make the NaClO/HCl leach selective for gold. Perhaps by ph adjustment?

[Edited on 27-10-2012 by Traveller]

zed - 30-10-2012 at 18:54

Ummm. The Iron bearing components of sand are often magnetic. To the best of my knowledge, Gold is not magnetic.

I would suggest removing as much Iron as possible via magnets, prior to Cl2 treatment.

Other salts of Iron, may be soluble via less extreme conditions. The idea of using Halogens to dissolve Gold... is due to few other things being able to.

Traveller - 30-10-2012 at 23:38

Quote: Originally posted by zed

Ummm. The Iron bearing components of sand are often magnetic. To the best of my knowledge, Gold is not magnetic.

I would suggest removing as much Iron as possible via magnets, prior to Cl2 treatment.

Other salts of Iron, may be soluble via less extreme conditions. The idea of using Halogens to dissolve Gold... is due to few other things being able to.

Sounds really simple, doesn't it? Yes, magnetite is quite magnetic (gee, I wonder if that's how it got its name?) and, with the new N42 and N52 neodymium magnets, even haematite can be removed magnetically.

The problem is this. When particles of iron or "black" sand, as we call it, are attracted to a magnet, they move towards that magnet in a tightly knit wave. Any particles of gold in the way of this "wave" get snowploughed by the black sand and end up being stuck to the magnet with the black sand.

AndersHoveland - 31-10-2012 at 00:45

The use of bromine in the extraction of gold was proposed by R. Wagner (Dingler's Journal, 218, p253)
Encyclopaedia Britannica, Volume 4 p633

Interestingly, the reaction of iodine upon gold is reversible:

Action of Iodine on Gold.
At ordinary temperatures pure dry iodine is without action on gold ; between 50° C. and the melting point of iodine combination takes place with the formation of amorphous iodide; above that temperature crystalline aurous iodide is formed. The direct reaction is always limited by the inverse decomposition of the iodide formed, but in the presence of excess of iodide pure aurous iodide may be obtained; this in excess is then best removed by subliming the mixture at a temperature of 30° ... In the presence of water, gold and iodine react in a closed vessel to form aurous iodide, but the reaction is limited, and, at normal temperatures, if the iodine can escape, the iodide is entirely decomposed. — F. Meyer (Comptes rend., 1904, 139, 733).
Pharmaceutical journal; A weekly record of pharmacy and allied sciences, Volume LXXIV, Great Britain, 1905

For more information about the chemistry of iodine and gold, see "Hand-book of chemistry", Leopold Gmelin, Volume 6, p211

One of the more obscure ways to reduce gold(III) chloride back to elemental gold is to use an alkaline solution of hydrogen peroxide. Although usually oxidizer, in some reactions H2O2 can act as a reducing agent.

(2)AuCl4[-] + (3)H2O2 + (6)OH[-] --> (2)Au + (8)Cl[-] + (6)H2O + (3)O2

The gold from this reaction usually separates out in a finely divided state, and appears brown by reflected light and greenish blue by transmitted light. If very dilute solutions are used, the gold sometimes separates out forming a yellowish film on the sides of the test tube.

zed - 31-10-2012 at 11:55

The process you are going to use to extract your Gold and remove other unwanted metals, needn't involve a total reinvention of the wheel. There will be a lot of literature on the subject. It's all been done before. Don't like magnets.....try something else. Or, try rinsing your magnetized iron ores to remove adherent Gold. It won't matter what you try; no method will be 100% effective in recovering ALL of the Gold that is actually present.

I'm merely suggesting Cl2, because it is inexpensive and it might scale up easily. Iodine is expensive. And, its purchase in quantity might attract unwanted attention. Nosy folks could show up...demanding permits, mining claim documentation, a cut of the take, and/or tax payments.

There is nothing more offensive to people in general, than seeing someone else make an buck. Makes 'em crazy.

I suggest the two famous Bogart films...."Treasure of The Sierra Madre" and "Beat the Devil".

leaching of gold with iodine

rustbucketguy - 7-10-2014 at 10:46

I realize this is an old thread, but I have not seen a whole lot of answers except outright, untested, negative responses. If you have (or suspect you have) material with micron gold, pm me or check www.blacksand2gold.com I do not intend to post details openly, but I welcome the opportunity to test your material for you. Most people have a very poor understanding of the iodine chemistry when used with gold. It is very simple, fast, and not nearly as expensive as people think.