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Dissolving mica flakes


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#1 THX-1138

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Posted 13 September 2007 - 08:39 PM

I have about 2cc of 0.1mm particles (and smaller), some of which are flakes of placer gold but most of which are common mica. I want to separate these.

A centrifuge would be useful -- if I had one, which I don't. The particles are small enough, as is my skill in the technique :rolleyes:, that panning is suboptimal. So I'll try falling back on straight chemistry to remove the mica threads from among the gold.

Short of HF, what would be good for dissolving the mica fragments? YT2095 says that heated solutions of some common hydroxides (NaOH, KOH, LiOH) will attack glass (and I'm extrapolating to hope they'll go after other silicates), but my first attempt -- glass in boiling NaOH solution -- yielded no discernible effect. Perhaps I didn't meet the necessary criteria, or perhaps the effect is too small to be useful in this case.

DrDNA suggested aqua regia or piranha, but aside from being things I want to avoid, they won't help -- both are safely stored in glass, and aqua regia would dissolve the gold and leave the dross.

So, any alternative ideas for something that will dissolve mica but leave gold and a nickel or carbon crucible untouched?

(Yes, I realise I'm not talking about putting the mica into solution, but 'dissolve' gets the idea across adequately, I think. :D )

TIA..
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#2 geoguy

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Posted 13 September 2007 - 11:25 PM

I'm not sure what you are trying to do. You have a residue containing gold and mica? Or, to the contrary, is this in a matrix rock such as quarzite? If it's a residue then simply dump the gold and mica into a tall clear glass of water and the gold will sink much quicker....the difference so obvious that you just have to tilt the glass after the gold sinks to separate them.

I have to question if you actually have flakes of gold and mica....they will be quite distinct if you look with a hand lens. There couldn't be an element and a mineral easier to separate just by vibrating them on a sheet of paper. No fancy solutions or equipment are necessary. Even blowing on the residue will separate them.
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#3 DrDNA

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Posted 14 September 2007 - 12:55 AM

Personally, I think HF is your best bet.....happens every day in the semiconductor industry.

But have you thought of putting them in a regular test tube with water and then trying to separate with a pasture pipette?
The "mica sand", since is less dense, should be pulled into the pipette much easier than the gold, much like a centrifuge....

Then I think you may be left with mercury, which is still used to purify gold from ore.....

If you don't want to mess with mercury...TOXIC!!...ignore the following....:eek:

If there is still some impurites left (I'm sure there are) cover the concentrates with water. Add one tablespoon of household lye to the concentrates and swirl it around for several minutes. This will remove surface impurities such as dirt and oils from the gold.

Pour off the lye laden water. Add fresh water and add one ounce of mercury.

*** WARNING!!! WHEN USING LYE YOU SHOULD WEAR SAFETY GOGGLES AND RUBBER GLOVES TO AVOID GETTING ANY IN YOUR EYES OR ON YOUR SKIN. WHEN USING MERCURY, USE THE SAME PRECAUTIONS. IN BOTH CASES DO NOT INHALE ANY OF THE FUMES!!! ALWAYS WORK OUTSIDE AND UPWIND.

Slowly swirl the contents with the mercury. As the mercury goes around the pan it will pick up all the finest gold in the pan. The more gold there is the stiffer the mercury becomes.

Once you have all the gold gathered, pan or suck off the sands (or use a magnet in a plastic baggie to retrieve black sands), leaving only the gold laden mercury and free mercury. The free mercury will roll around easily where the gold laden mercury is stiff and does not toll well. Place your mercury container INSIDE another gold pan and pour off the free mercury into the container. Using another pan keeps it from spilling out onto the floor or ground. If you spill mercury on the floor or God forbid, the living room carpet, you will be inhaling evaporating fumes for years!

Once you have a stiff ball of gold laden mercury in the plastic pan flush it out into a glass measuring cup. To this add a few drops of nitric acid Keep adding nitric acid until you get a bubbling or fizzing action from the mercury. !!! DO NOT BREATH THE FUMES !!! The acid will dissolve the mercury as well as any trace silver. After awhile the fizzing stops and at the bottom of your cup is a bronze colored metallic looking blob.... It's GOLD!

You can recover your mercury from the nitric acid by placing a flat copper bar or copper sheet into the acid and letting it set overnight. The next day the mercury will have come out of solution and attached itself to the copper now you can scrape the mercury from the copper and put it back into your storage container.

Carefully pour off the remaining liquid and neutralize the acid with baking soda, a little at a time until you get no reaction from the acid and soda. Gently rinse the gold in the cup with fresh water avoiding hard sprays that could rinse away your gold. Pour off the water and let dry. The remainder is your pure gold! (actually 95% - -98% pure)
http://www.learngold...oncentrates.htm
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#4 geoguy

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Posted 14 September 2007 - 01:11 AM

Personally, I think HF is your best bet.....happens every day in the semiconductor industry.

But have you thought of putting them in a regular test tube with water and then trying to separate with a pasture pipette?
The "mica sand", since is less dense, should be pulled into the pipette much easier than the gold, much like a centrifuge....

Then I think you may be left with mercury, which is still used to purify gold from ore.....

If you don't want to mess with mercury...TOXIC!!...ignore the following....:eek:

If there is still some impurites left (I'm sure there are) cover the concentrates with water. Add one tablespoon of household lye to the concentrates and swirl it around for several minutes. This will remove surface impurities such as dirt and oils from the gold.

Pour off the lye laden water. Add fresh water and add one ounce of mercury.

*** WARNING!!! WHEN USING LYE YOU SHOULD WEAR SAFETY GOGGLES AND RUBBER GLOVES TO AVOID GETTING ANY IN YOUR EYES OR ON YOUR SKIN. WHEN USING MERCURY, USE THE SAME PRECAUTIONS. IN BOTH CASES DO NOT INHALE ANY OF THE FUMES!!! ALWAYS WORK OUTSIDE AND UPWIND.

Slowly swirl the contents with the mercury. As the mercury goes around the pan it will pick up all the finest gold in the pan. The more gold there is the stiffer the mercury becomes.

Once you have all the gold gathered, pan or suck off the sands (or use a magnet in a plastic baggie to retrieve black sands), leaving only the gold laden mercury and free mercury. The free mercury will roll around easily where the gold laden mercury is stiff and does not toll well. Place your mercury container INSIDE another gold pan and pour off the free mercury into the container. Using another pan keeps it from spilling out onto the floor or ground. If you spill mercury on the floor or God forbid, the living room carpet, you will be inhaling evaporating fumes for years!

Once you have a stiff ball of gold laden mercury in the plastic pan flush it out into a glass measuring cup. To this add a few drops of nitric acid Keep adding nitric acid until you get a bubbling or fizzing action from the mercury. !!! DO NOT BREATH THE FUMES !!! The acid will dissolve the mercury as well as any trace silver. After awhile the fizzing stops and at the bottom of your cup is a bronze colored metallic looking blob.... It's GOLD!

You can recover your mercury from the nitric acid by placing a flat copper bar or copper sheet into the acid and letting it set overnight. The next day the mercury will have come out of solution and attached itself to the copper now you can scrape the mercury from the copper and put it back into your storage container.

Carefully pour off the remaining liquid and neutralize the acid with baking soda, a little at a time until you get no reaction from the acid and soda. Gently rinse the gold in the cup with fresh water avoiding hard sprays that could rinse away your gold. Pour off the water and let dry. The remainder is your pure gold! (actually 95% - -98% pure)
http://www.learngold...oncentrates.htm


what the heck? This is gold and mica. You are making a mountain out of a mole hill. Pour them in a glass of WATER and the gold and mica will separate. Odds are the mica silicate plates will float. No need for mercury :rolleyes: etc.
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#5 DrDNA

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Posted 14 September 2007 - 01:22 AM

what the heck? ........ You are making a mountain out of a mole hill. :rolleyes: etc.


Excuse me, but can't you see that we are trying to win a Rube Goldberg contest here!
:doh:
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#6 foodchain

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Posted 14 September 2007 - 01:41 AM

"In December 1997, a chemistry professor, Karen Wetterhahn, working at Dartmouth College in the United States spilled a drop of dimethyl mercury on her latex glove. She began experiencing the symptoms of mercury poisoning within 5 months of the exposure and, despite treatment, died a few months later."

This and more in the link. The post being overboard or not, I donít think its bad that maybe hobby chemists or such develop a more broad understanding of what they may play and or work with.

http://en.wikipedia....rcury_poisoning
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#7 DrDNA

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Posted 14 September 2007 - 02:00 AM

Point well taken.
However, not to minimize dangers associated with mercury poisoning, please note that methyl mercury is NOT elemental mercury.
Methyl merc is considered to be the form of mercury most easily bioaccumulated. Also, mercury (and methyl merc) is known to easily penetrate latex, so they should not have been used in the situation you mention. Latex gloves were never intended for chemical lab use and shouldn't even be there. One should NEVER use them as the only means of protection in a chem lab. They were developed for routine biological/clinical (ie, aqueous liquid only) work. Nitril gloves are known to be a better option for work with mercury (and many other chemicals).
I agree with you. The best protection is knowledge (and proper equipment).
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#8 foodchain

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Posted 14 September 2007 - 02:22 AM

Point well taken.
However, not to minimize dangers associated with mercury poisoning, please note that methyl mercury is NOT elemental mercury.
Methyl merc is considered to be the form of mercury most easily bioaccumulated. Also, mercury (and methyl merc) is known to easily penetrate latex, so they should not have been used in the situation you mention. Latex gloves were never intended for chemical lab use and shouldn't even be there. One should NEVER use them as the only means of protection in a chem lab. They were developed for routine biological/clinical (ie, aqueous liquid only) work. Nitril gloves are known to be a better option for work with mercury (and many other chemicals).
I agree with you. The best protection is knowledge (and proper equipment).


I concur. I had a friend back in high school, years ago of course, into the whole anarchist cook book deal, he managed to make some pretty impressive stuff along with basically getting both his hands and a good percent of his arms covered with serious burns. Reactions can be rather instant, like boom instant!

With that being said proper understanding and care should be taken with this stuff just for the reality that its rather real, the outcome of such, its not as if you made a mistake on you math homework or what not. The other idea is not just toxicity of elements to our particular chemistry but the reality that say having high velocity shards of glass to a multitude of other realties that can come about as a product of unknowing actions. Some poisons only become such through long periods of absorption also, so you would not even know you are harming yourself. Now that I have taken the thread off track I will make apologies and hope all is well as I go on my merry way:D
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#9 THX-1138

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Posted 3 October 2007 - 11:46 AM

I'm not sure what you are trying to do. You have a residue containing gold and mica? Or, to the contrary, is this in a matrix rock such as quarzite? If it's a residue then simply dump the gold and mica into a tall clear glass of water and the gold will sink much quicker....the difference so obvious that you just have to tilt the glass after the gold sinks to separate them.

I have to question if you actually have flakes of gold and mica....they will be quite distinct if you look with a hand lens. There couldn't be an element and a mineral easier to separate just by vibrating them on a sheet of paper. No fancy solutions or equipment are necessary. Even blowing on the residue will separate them.


It's a residue -- essentially dust. 0.1mm wide at the largest, most much smaller. And around m0.005mm maximum thickness at a guess. Small enough to be strongly affected by Brownian motion.

And actually, no, they aren't quite distinct. At 15X, which is rather stronger than a hand lens, I've manually separated most of the obvious bits -- but there are plenty of UNobvious ones.

Thanks for the suggestions for alternate procedures, but I'd also like to pursue my original idea of using chemistry rather than mechanics. :D
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#10 DrDNA

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Posted 4 October 2007 - 12:33 AM

Perhaps there is some type of affinity chromatography (or similar) system available, or you can make one.....thiols and disulfides stick to gold but not to glass (nor mica) and thiolated/disulfide silanes (silanes are used to derivatize affinity supports) are readily available, so the affinity supports are either available or they would certainly not be to difficult to make.
After the functionalized support is in hand, flow the mixture over the support and the gold should stick while the rest of the stuff flows right over it.....IF the gold particles are small enough to bind tightly to the support. Then the gold should come off the thiols with mild denaturing conditions.

It would be worth a quick google search....

On the other hand, it just occured to me.......mica is negatively charged (SiO- on the surface), so in an electrical field, the mica should be attracted to the postive electrode. But gold should not be attracted to either electrode.......Sort of like electrophoresis.......this might be easier
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#11 Mr Skeptic

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Posted 4 October 2007 - 01:59 AM

Since you have them in very small quantity and fine powder, there are lots of options. Depending on the variety of mica, it might float in water (might need a little salt). That would be your best bet if it works. If you want to be creative, maybe static electricity could do it but I don't know.
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#12 nitroglycol

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Posted 5 October 2007 - 01:45 AM

Personally, I think HF is your best bet.....happens every day in the semiconductor industry.

But have you thought of putting them in a regular test tube with water and then trying to separate with a pasture pipette?
The "mica sand", since is less dense, should be pulled into the pipette much easier than the gold, much like a centrifuge....

Then I think you may be left with mercury, which is still used to purify gold from ore.....

If you don't want to mess with mercury...TOXIC!!...ignore the following....:eek:

Mercury is indeed toxic, but I'd use metallic mercury over HF any day. HF is really toxic.
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#13 DrDNA

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Posted 5 October 2007 - 02:48 AM

Mercury is indeed toxic, but I'd use metallic mercury over HF any day. HF is really toxic.


You would?
I think it's all relative. They are both pretty nasty.
Mercury is banned from most places nowadays...but semiconductor sites use HF by the drumloads every day.
HF will attack the Ca in your bones and the Ca in rest of your body.....causing havoc.
Mercury is a potent neorotoxin.....
Pick your posion.......use caution.
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#14 nuclear1

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Posted 30 June 2012 - 06:12 PM

I am assuming the mica is the larger proportion of your mixture.
The easiest way to separate them is to dissolve the gold with an Aqua Regia acid mixture.
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#15 Enthalpy

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Posted 2 July 2012 - 07:17 PM

Mercury is banned from most places nowadays...but semiconductor sites use HF by the drumloads every day.


Because of RoHS law, we must use a **** solder that doesn't solder anything, despite nobody will churn an electronic card...
But mercury is used increasingly in power-saving lamps, and you'll inhale it if you break the lamp.

Semiconductor industry... uses really nasty chemicals, HF not being the worst! Not even hydrazine is the worst there.
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