Sciencemadness Discussion Board - Gold Recovery Computer Scrap Complete Process

posted on 8-10-2015 at 09:29

I think aga wants a 'show stopper' of sorts

Not at all !

I just don't fancy the idea of spending hours machining the gold down into a fine powder.

deltaH

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Though if it works, it would be one

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kadriver

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posted on 8-10-2015 at 10:11

posted on 8-10-2015 at 11:36

That's pretty kadriver and your yields are thoroughly consistent!

The way I see it, this process has three important sections:

Mineral acid-free 'fish and chips' gold refining process

(1) Base metal leaching: vinegar + salt + air bubbling + initial H2O2
(2) Gold foil dissolution: vinegar + salt + bleach
(3) Base metal recovery: ?

Comments:

* Step (1) has now been tried on small and larger scales thanks to the pioneering work of aga and kadriver. Step (2) has only been tried on a small scale by aga and Step (3) is largely completely open.

* Step (3) is vitally important though. Without it, the process doesn't deal with its waste and is incomplete.
Also, part of the copper containing solution from step (3) could be recycled into step (1) so that peroxide is no longer needed, then this thing would come full circle and you would have a reliable, low cost and safe complete process that could be used again and again.

Looking forward to someone continuing the research into this, i.e. scaling up of step (2) and development of step (3).

[Edited on 7-10-2015 by deltaH]

How about 2a; precipitating the pure gold powder?

There are several choices. I prefer sodium meta bisulfite. It is sold at the hardware store as "Stump Out" stump remover by BONIDE. Stump out by spectracide is NOT sodium meta bisulfite, it is potassium nitrate! So be sure it's stump out by BONIDE.

Another good one is copperas (ferrous sulfate) it is also sold at gardening shops and the hardware store. To use I pour about 200ml of the green powdered ferrous sulfate into a 600ml beaker, then fill with tap water to about 500ml and stir over low heat until dissolved.

It will look orange in color, I add about 10ml of hydrochloric acid to turn it green. I set up a filter station with a ring stand and filter the dissolved ferrous sulfate directly into the clean chloroauric acid solution. The gold precipitates quickly and cleanly.

Ferrous sulfate produces no noxious fumes, but SMB make lots of sulfur dioxide gas and must be done in a fume hood.

kadriver

Another good point, yes the reducing agent does indeed warrant some thought.

The whole idea with the fish and chips process is to use benign and also environmentally benign, cheap OTC reagents.

Nothing too wrong with the ferrous sulphate nor sodium metabisulfite, but... there's always a but

... I would favour an even more benign and environmentally friendly reducing agent.

In that sense, I am thinking a non-toxic organic agent is better. Something like ascorbic acid (vitamin C)? It's cheap, you can chuck it down the drain with no impact on the environment and it's completely non-toxic and benign to the user working with it.

Can you share your experience with us on this kadriver? Can it be used?

I've used SMB, copperas (ferrous sulfate), oxalic acid (wood bleach), SO2 gas, and cement the gold on copper. I've never even considered vitamin C. How would that work? That would be something!

kadriver

deltaH

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Ascorbic acid (Vitamin C) is a mild reducing agent that gets oxidized to dehydroascorbic acid by two electrons, so you need a minimum (an excess would be wise) of 3/2 moles ascorbic acid per mole of gold.

It can reduce most oxidizing metallic solutions with boiling. You're supposed to use 100% ascorbic acid, not lemon juice aga

Here's an example:

https://www.youtube.com/watch?v=J-rZXQNFauI

Note: with copper the yields are not very good, but then copper(II) is a weak oxidant, unlike silver and gold, which should be much faster and better yielding.

I was just wondering if anyone actually tried it with gold and how well that worked.

EDIT:

Here's a brief video of the reaction with silver nitrate... definately much faster as expected.

https://www.youtube.com/watch?v=V7r2gUA9gTM

Again, boiling it would probably be wise to help the nanoparticles coalesce and then settle out overnight.

EDIT: using sodium ascorbate might work better for chloroauric acid solutions.

[Edited on 8-10-2015 by deltaH]

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posted on 8-10-2015 at 18:27

Can I get ascorbic acid from a health store like GNC? I could do this experiment tomorrow if I had the vitamin C.

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posted on 8-10-2015 at 18:38

Most vit C tablets are high purity ascorbic acid. Capsules if you can find them are even better. you can always recrystallise if you think those impurities are likely to be problematic.
Or, you can buy it as a lab reagent fairly easily if you have the contacts. probably easily available on eBay too.

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posted on 10-10-2015 at 05:32

$9.50 US per lb. in bulk-

http://www.amazon.com/gp/aw/d/B00YO53APY/ref=mp_s_a_1_5?qid=...

It also makes a decent propellant when mixed with Potassium nitrate...

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posted on 10-10-2015 at 20:34

OK, here is part 1 of 2 of the video where I scale up the Vinegar - Salt - Hydrogen Peroxide recovery of gold foils from the trimmed circuit card fingers.

Now that I kind of know what to expect I should be able to complete the experiment on VIDEO.

Many thanks to deltaH and aga for the help they provided!

https://youtu.be/ouYW_7-Njbs

kadriver

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posted on 10-10-2015 at 21:23

Very nice indeed, well done and thank you for making the excellent videos! There's small things that you do that just makes it a cut above the rest, like the way you place the glass rod in line with the beaker lip when you pour ans the controlled movements throughout, it's chemical choreography :cool:

I can not tell you how disappointed I was to see the video end where it did... I know, patience

You should consider making this part of a series of 'Gold Recycling using Green Chemistry'. From all that has been discussed, there could be several videos in it already and I think once news gets out of a complete series of these videos, you will have excellent viewership.

Please try to cut out HCl completely throughout, then we would have really accomplished something here. For the gold dissolution step, I strongly suggest you raise the pH of the salted vinegar BEFORE adding bleach with 0.2M sodium hydroxide solution to 4.5 so that one avoids the copious production of chlorine gas (hopefully).

You could finish off everything with an ascorbic acid reduction to make the process really Green and interesting. Like Bert showed, it's cheap stuff in semi-bulk scale.

[Edited on 11-10-2015 by deltaH]

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posted on 10-10-2015 at 21:36

cool stuff you guys are doing here. I have been following in silence. the notion of green chem in a field that is so full of harsher verities is really awesome. this also gives more people access to a process that won't get the cops called by ordering multi gallon shipments of HNO₃, like LGA said. kudo's

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posted on 10-10-2015 at 21:40

I can't possibly be the only one who thought of this,but using Aqua Regia would have been less time-consuming in my opinion.

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posted on 10-10-2015 at 21:44

posted on 10-10-2015 at 21:56

I can not tell you how disappointed I was to see the video end where it did... I know, patience

Wow! These are great suggestions. The bubbling took about 4 or 5 days to get about 98% of the foils off the fingers. I'll shoot video of the bubbler at 12 hour intervals to give a good picture of what's happening.

Aga has already dissolved the foils in the salt vinegar solution just by adding heat and bleach, completely eliminating any HCl.

I'm embarrassed to say that I have no idea how to make and add 0.2M NaOH solution. And I only have paper test strips to read pH. Can you give me a little help there. Where can I get a good pH meter that will stand up to these chemicals? I don't mind paying a little extra for a good meter.

I'd like to dissolve some gold foils ahead of time, off camera, using the directions you've given above. That way when it comes time to actually dissolve on camera I know what to expect.

I'll get some of the chemical Bert referenced to do the precipitation. This will be unbelievable if it works as expected.

You guys really know your stuff. I am so grateful to everyone who has input to this chemistry/gold refining adventure!

kadriver

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posted on 10-10-2015 at 22:05

I can't possibly be the only one who thought of this,but using Aqua Regia would have been less time-consuming in my opinion.

Absolutely, but I think we are trying to find a process that completely eliminates those corrosive mineral acids.

So far we are only using;

01) white distilled vinegar
02) sea salt
03) hydrogen peroxide 3%
04) lye to raise pH
05) bleach to dissolve the gold foils
06) ascorbic acid for reduction - precipitation

So far no nitric, hydrochloric or sulfuric acids!

If we can eliminate the chlorine gas by raising the pH as deltaH proposes, then this would almost be suitable as an eight grade science project - but NOT recommended as such.

kadriver

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Developments have been thick and fast here and I will admit to not having read the whole thread or viewed all of the videos. But, in my view, this is really exciting. Please, when done, as well as the videos, do a write-up in prepublication. This great work deserves all the recognition it can get. And as for school projects, I can really see it working. I am going to put it on the list of suggestions for my students next year.

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posted on 10-10-2015 at 22:27

posted on 10-10-2015 at 22:42

no idea how to make and add 0.2M NaOH solution

Look up the molecular weights of each element (Na, O, H) on the periodic table http://ptable.org

The M.W. is the bottom left number in each box.

Na = 22.99
O = 15.99
H = 1.01

Add them up and the weight per Mol of NaOH = 39.99

So if you dissolve 39.99g of NaOH in 1 Litre of water, you'd have a 1 Molar concentration of NaOH in that solution.

You'd write that as '1.0M NaOH solution'.

That's 5 times too strong for the 0.2M required, so you can either add 5 times more water (5 litres + 40g) or 5 times less NaOH (1 Litre + 8g) to reach 0.2M concentration.

deltaH

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Quote:

Very nice indeed, that should look great!

Quote:

Aga has already dissolved the foils in the salt vinegar solution just by adding heat and bleach, completely eliminating any HCl.

Yes but aga added the bleach to neat vinegar and salt which evolved 'tons' of chlorine gas. The real benefit here is going to come from finding the sweet spot for pH, where chlorine gas is not evolved in copious amounts, but where the solution is still strong enough of an oxidant to dissolve the gold.

As a first guess, pH 4.5 according to those diagram I attached earlier looks close to being right. I'd go slightly higher if necessary, but not lower, unless higher or 4.5 doesn't work, in which case going lower is the last remaining choice, but then one will evolve some chlorine.

Quote:

I'm embarrassed to say that I have no idea how to make and add 0.2M NaOH solution.

Don't be embarrassed, we're all learning. The molar mass of sodium hydrogen is the sum of the atomic masses of the elements in its formula multiplied by the number of one element, in this case all 1: NaOH, read off a periodic table: 23 for sodium*1 + 16 for oxygen*1 + 1 for hydrogen*1 = 40g/mol. 40g is thus one mole of sodium hydroxide. 0.2M means a concentration of 0.2 moles dissolved in 1 litre of water. so 0.2 moles is 0.2*40g, or 8g NaOH which has to be dissolved in 1 litre of water to get a 0.2M solution.

Quote:

And I only have paper test strips to read pH. Can you give me a little help there. Where can I get a good pH meter that will stand up to these chemicals? I don't mind paying a little extra for a good meter.

pH strips can work here, you can target pH 4-5. You're adjusting pH before adding any oxidants so you should worry about bleaching the dye at this stage.

For a good pH meter, there are others and threads on SM that can advise better. Just don't forget to calibrate the meter before each use.

Quote:

I'd like to dissolve some gold foils ahead of time, off camera, using the directions you've given above. That way when it comes time to actually dissolve on camera I know what to expect.

A good idea. The pH 4.5 is an educated guess, but may require tweaking. If you still see fizzing after adding bleach, then it's too low and I would try pH 5 and so on until you have the lowest pH that doesn't release large amounts of chlorine.

If you see no fizzing at pH 4.5 as expected, then next time you might want to try pH 4 and see if that fizzes etc.

Optimal is the lowest pH at which you don't release lots of chlorine.

Quote:

I'll get some of the chemical Bert referenced to do the precipitation. This will be unbelievable if it works as expected.

I am 99.99% sure ascorbic acid will reduce gold. The only problems I anticipate is that you might have residual oxidant (bleach) in your gold dissolution solution which will require more ascorbic acid to neutralise than for the gold alone and also that the gold will initially be in a colloidal form (nano-gold). So the trick here will be to coalesce and merge those so they get large enough to settle. That means boiling it after adding the ascorbic acid.

As a procedure, I'd say in a fume cupboard, add 3% H2O2 drops to your dissolved gold until it doesn't fizz when the drop hits. This is to destroy excess bleach by making oxygen. The fast reaction is:

ClO^- + H2O2 => Cl^- + H2O + O2(g)

Then pre-dissolve 2g ascorbic acid in 8 ml water and add it the solution with stirring. Then boil the mixture in a fume cupboard and then set aside to cool and settle the gold (overnight if necessary) before filtering and washing at the filter with clean water.

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deltaH

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posted on 10-10-2015 at 22:46

posted on 11-10-2015 at 01:52

I can't possibly be the only one who thought of this,but using Aqua Regia would have been less time-consuming in my opinion.

He he, I see in the time it took for me to write my long response, there's been a 1000 responses already lol HOT TOPIC!

You can actually substitute the lye which is corrosive with sodium bicarbonate, then it can become a junior lab project

Kid's love adding bicarb to vinegar after all!!!

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Little_Ghost_again

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A couple more weeks and this process should be down to using vinegar and just a packer of aga'a special nitrogen!

I hope he has it in bulk

Dont ask me, I only know enough to be dangerous

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posted on 11-10-2015 at 15:33

Quote: Originally posted by aga

posted on 11-10-2015 at 16:11

no idea how to make and add 0.2M NaOH solution

So I could add 0.8 grams NaOH to 100ml distilled water to make a 0.2M NaOH solution, rather than dissolving 8grams in 1 liter.

Great explanation by the way, thank you.

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posted on 11-10-2015 at 16:20

You can actually substitute the lye which is corrosive with sodium bicarbonate, then it can become a junior lab project

Kid's love adding bicarb to vinegar after all!!!

Do you think that the bicarbonate would do? If you think it will work then I'll use it instead of lye.

I shot some more video at noon on Sunday, I'll get some more footage at midnight. There were just a few foils at noon today, Sunday.

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posted on 11-10-2015 at 16:33

So I could add 0.8 grams NaOH to 100ml distilled water to make a 0.2M NaOH solution, rather than dissolving 8grams in 1 liter.

Yep. You got it.

If you already made a 1.0M concentration solution of NaOH, you can use the formula

C1V1 = C2V2

to make a different LOWER concentration.

So, if you got 1000ml of a 1.0M concentration solution of NaOH (40g in 1 litre)

You need 0.2M concentration.

C1 = what you got = 1.0 M concentration
V1 = 1 litre = 1000ml of water containing that stuff.

C2 0.2M = the concentration you want

V2 = the Mystery Number.

rearrange the formula and you get V2= (C1 x V1) / C2

So V2 = ( 1.0 x 1000 ) / 0.2 = 5000ml, or 5 litres.

So just add an extra 4 litres of water and your 1.0M solution becomes a 0.2M solution.

The [M] thing is how many Moles there are.
A Mole is defined as 6.022 x 10<sup>23</sup>
Usually written as M, [M] or Mol to avoid embarassment, or confusion with moles.

So if you dissolve 39.99g of totally pure NaOH in 1 litre of totally pure water (to make a 1.0M solution) then there are about 602200000000000000000000 molecules of NaOH in that water.

The number is too big to handle easily, so we use the Mol as a measure instead.

Incredible that i'm explaining this to somebody else now, as two years ago i had absolutely no idea at all.

Knowledge is a wonderful thing, as is this forum.

[Edited on 12-10-2015 by aga]

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posted on 11-10-2015 at 16:47

I can't possibly be the only one who thought of this,but using Aqua Regia would have been less time-consuming in my opinion.

I would have used AR anyways since all you have to wait for is for it to dissolve the material(which happens much faster),use a reducing agent to precipitate the solute,then just separate the gold from plastic with a torch.Since gold and plastic have different melting points, it is possible to melt one of them and then separate the liquid, then keep doing it until the gold is surely separated.

aga

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Rethink or erase that Agari.

You clearly have not read this thread or understood the direction it is going in.

Is Agari another other persona of a well known SM member ?

It could just be my innate paranoia, but there seem to be a few similar personae emerginging recently, related to some not-so-recent.

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posted on 11-10-2015 at 17:02

Quote: Originally posted by aga

I actually did not read all of the above lol.

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posted on 11-10-2015 at 17:08