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Stripping Gold

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LutzH

Tue Jan 05 2010, 08:04PM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
Location:
Posts: 136

Hello:

Simple chlorine, or bromine water, or the iodine suggested will dissolve thin gold. Chlorine water was used even for platinum extraction. This is safer than aqua regia. The benifit here also is that you do not have a large insoluable element load in the resulting solution. Good Luck :)

Sulaiman

Tue Jan 05 2010, 09:41PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Why are you trying to dissolve the gold?
Wouldn't it be easier to dissolve the pin leaving the gold behind.
Using a mild acid over a longer time with some agitation may do it.
I'd expect most of the non-gold metals will be dissolved away.
e.g. shear off the pins mechanically, put in a glass container with dilute acid
(sulphuric for copper etc.) and give a shake now and then.

wylie

Tue Feb 23 2010, 07:54PM

Registered Member #882 Joined: Sat Jul 07 2007, 04:32AM
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Posts: 103

Wouldn't it be easier to dissolve the pin leaving the gold behind.

Yeah, based on the replies here I'm not sure why that approach didn't occur to me 1st. I had really no idea what direction to take so i was just tossing up any-and-all ideas that popped into my head. Snipping the pins off and dissolving the base metal definitely seems the way to go.

Rather than having to go out and buy some acid and having to do a bunch of very careful pouring, making nitric at home is the current plan. Based on this thread, it shouldn't be too hard.

I'm thinking about a digestion chamber setup. Diagram:

1266950558 882 FT79798 No2 Digestion Chamber

I based the electrode arrangement on the wikipedia description of the Birkelandâ€“Eyde_process. I'm not sure if i have the magnets properly aligned though. Based on some scribbles i did with field lines to determine left-hand-rule direction, i think a DC arc should progress around the circumference of the outer electrode, achieving a sort of plasma disk as described in the article. (crazy idea: what if i used an AC arc, and arranged the magnets pole-to-pole around the electrode. At the right frequency to match the N-S reversals, would the arc be "accelerated" around the circle?)

I get the idea that spreading the arc around really helps with yield since there's more air volume coming in contact with the arc, compared to a static point-to-point arc. Using a jacobs ladder would have a similar effect. You could pump the air through faster, but at a point the flow would just extinguish the arc, right? I think convection will provide suitable flow.

Pop the pins in the water, put the lid-assembly on, and fire it up. Run till the chamber clouds with oxides, and let it sit for a while (days, weeks maybe?). When it seems all activity has stopped, i filter out the pins and start over with a fresh batch of water.

Questions:
1. I'd love to use copper tubing for the electrode assembly. Would it dissolve so fast from acid produced in water vapor in the chamber air that the apparatus would be ruined just as fast as the metal Iâ€™m trying to dissolve?

2. Will i get sufficient acid concentration to dissolve my base metal with just surface diffusion of the nitrogen oxides into the water? I understand it will take longer, but will it take so long that Iâ€™ll need to get married and have some descendants who can finish the task long after my death?

3. Filtering. If I understand the wiki article on HNO3, paper is totally not going to work. Steel wool maybe? What else is there for the cheapskate hobbyist?

4. Neutralization of used solvent. Is Sodium Bicarb ok with (probably VERY) dilute HNO3?

Bored Chemist

Tue Feb 23 2010, 08:55PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Any really good reason not to just use battery acid or (if you really want NOx fumes) battery acid with NaNO3 in it?

wylie

Tue Feb 23 2010, 09:07PM

Registered Member #882 Joined: Sat Jul 07 2007, 04:32AM
Location:
Posts: 103

Getting the acid out of the battery falls under the "very careful pouring" restriction. Plus, I'd cry if i made myself kill a usable car battery. I suppose i could look for dead cells...somewhere. They don't allow scavenging at my local hazwaste drop-off though.

I wasn't expecting escaping fumes. Are there sealing considerations with solder and epoxy of which I'm unaware? The wiki articles aren't clear to me as for the corrosive properties of NO and NO2.

Bored Chemist

Thu Feb 25 2010, 07:25PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

You would make nitric acid and it would eat the equipment.
You can buy sulphuric acid as drain cleaner (at least, you can in the UK).

plazmatron

Thu Feb 25 2010, 08:32PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

I tried this, just before my last major clean out. Before dumping my junk, any bits of PCB with "gold fingers" on, were snipped off and dissolved in HNO3. Any silver, lead and copper is dissolved fairly quickly leaving the plating in the form of thin "foils" to slip off the PCB, and into the bottom of the container.

From what I have sitting on the shelf, it looks like a lot of gold, but I suspect not.

The next step, would be to dissolve the foils in Aqua Regia, which is a little more economical that starting with AR at the beginning.

Gold can be VERY selectively precipitated from AR with Sodium Metabisulphite.

I haven`t gotten this far yet, since I have just spent a ton of vacuum equipment, however, when I get round to it, I will be completing the process, hopefully enough to make a suitable target with, maybe 0.5g or so.

Failing that I will have to go back up to Tyndrum, to pan for some

Les

badastronaut

Fri Feb 26 2010, 04:38AM

Registered Member #222 Joined: Mon Feb 20 2006, 05:49PM
Location:
Posts: 96

I can tell you from experience that you will need a lot of chips to produce a small amount of gold. It takes about a pound or so of those gold plated edge connectors to make one gram of gold.

The best source of gold is the ceramic pentium 1 and 486 processors. 20 such processors produces about 1 gram of gold. Pentium 1s have about a dollars worth of gold in them while 486s have 2-4 dollars.

ShawnLG

Fri Feb 26 2010, 07:23PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

Why not just sell your CPUs and other gold berring parts on ebay. There are people buying up these things for big money. Search "gold scrap recovery" on ebay.

Ocean Waves

Fri Nov 04 2011, 04:24PM

Registered Member #4181 Joined: Thu Nov 03 2011, 02:39PM
Location:
Posts: 42

THIS IS A TOPIC OF INTENCE INTREST TO ME.............

1.just use nitric acid and aqua regia, and dissolve everything, helps if you grind all the chips first, in a hammer mill, which exposes all that nice palladium silver alloy, and all of the traces. As most of the gold is hidden in the the ceramic and epoxy

first get the palladium and silver into solution, with plain old 40% nitric acid, this gets the copper, nickel and other base metals at the same time, no problem, filter the solution and wash a bit to get a reasonable amount of the palladium residue from the leach, then add sodium chloride slowly to the solution a light fluffy precipitate will form, with a slight pink color, what you looking at the silver chloride with some co-precipitated palladium, which gives it the slight pink color, you'll have to re-refine this a bit later with nitric, then filter, and add ammonium chloride, and the palladium (and platinum not present here) is thrown down as an oxblood precipitate, with about a 5 percent co-precipitation of nickel. ignite in a clean coors crucible at 1200 degrees to recover palladium sponge of 95 percent purity, to purify repeat the process, until no nickel is present.

next the gold:
at this point pretty much only gold and platinum should be left as well as iridium and rhodium which should not be there, though some times ruthenium is present and a reside from the palladium

add enough distilled water to cover the the leach, and the add just enough AR that you think you need to dissolve the remaining metal, you don't want a huge excess of acid at the end, as its rather bothersome to take care of, just do what you need to get is dissolved taking care and giving it plenty of time, time is the trick to a good leach, the other trick is heat to about 60C for dilute acid, once you have dissolved all the metals you have to get rid of nitric acid there can be no nitrium ions left unbound at the time of precipitation, 2 options, filter well, add urea until the solution is rendered neutral at the cost of 2-10% recovery, as urea binds PGM's from standard perception methods to some extent, or boil down the solution to a syrup then add HCL and repeat until all of the nitric has been distilled off, a process that yields better than neutralization. Now add a volume of distilled water, to bring the solution back to about 10 percent TDS , add the reduction reagent of your choice, I recommend sodium meta bi-sulfite sold pure as stump remover in home depot, but make sure you test if with conc H2SO4 first to make sure its not a chlorate or nitrate of the 3 possible meta bi-sulfite seems to be taking over now.

Acidify with HCL to ph 1 and Add 1 ounce of meta for every suspected ounce of gold, stir and do try to avoid breathing the SO2 evolved, now wait for hours and days for a very colloidal brown dust to fall out this is thought to be gold sulfide or gold oxide which is not clear, collect and fire under borax at 1000C, you have pure gold, if platinum I present the dust will take on more of a black color, and your gold will have an orange peel texture when fire polished or cast...................you can remove the platinum first with a small amount of ammonium chloride, but there is usually not enough to care in electronics scrap, usually more iridium

2. if you just want the gold and silver , use sodium cyanide doped with about 5% lead acetate and enough hydroxide to keep the ph above 10, the lead which coats copper and other base metals preventing there interference, this mixture is known to trade secret industry as â€œsuper stripâ€ and yes you can safely make technical sodium cyanide at home by several a dozen or so novel pyro-chem reactions happening at around 700C (charcoal barbeque and some metal food cans, though I prefers an electric kiln with a pid controller) , read Haber on the production cyanides Haber's novel process is listed in the poor mans James bond, but google books on the production of cyanogen and its compounds are better. I make the stuff all the time in quanity with reasonable quality for extractive metal uses, I obtain it about 60-80% pure from a reaction Im reluctant to share openly. When you find your method don't publish it openaly or you reagents may dissaper from the shelf!!!!!!! now go read google books on cyaniding gold for procadures and methiods, you can obtain zinc metal as castings and electrical condit fitttings, you will know whats its for after you read...............

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