Gold Off PCB

How much is a function of the thickness.

Gold has very little chemistry. ttp://www.webelements.com/webelements/elements/text/Au/key.html gives an idea of the extraction of gold from ores.

Copper is above silver and gold in the same group of the periodic table, indicating similar chemistry, so the question becomes one of separating gold from copper with both metals in solution.

first see reply 11. that is by far the cheapest way to go if possible.

ammonia dissolves copper but not gold. It will take a lot of time for the copper to be dissolved and you will need to mechanically expose the copper. Check into getting rid of the copper ammonia mix before you start. It might be quite expensive in your local. Once there is an amount of copper dissolved the room temperature process speeds up for a while before the ammonia is depleted.

I have no idea of how the solder will affect this solution. I don't know what ammonia does to circuit boards and components.

there is a rather strong odor with ammonia. Your wife and neighbors will need to be kept happy

The cost of the retrieving the little bit of gold in small quantities seems to exceed the value.

Gold is however retrieved from mine dumps.

A road extensively use for the moving of mined rock over the last 20 years was recently excavated and loaded onto trucks. taken to the reduction plant. The value of the gold paid for the construction of the new road and a profit was made.

Thanks gentlemen, but I was realy loking more by the way of

"well you take the copper foil off the pcb, dissolve the copper in acid (what type), and because the gold dosnt dissolve it will be left"

More practical ideas please

Thanks

Gold is not on the PCB but is used as connectors inside Microchips between the chip and the external electrical connectors.

Since a lot of work has been done to protect the chip it will be very difficult.

Cheapest way would be:

1. Mechanically cut off tops of the chips
2. Use heat (forge) to melt off all the metal inside the chip
3. Since gold is denser and heavier then any other metal, use old fashioned methods of separating metals (settling tank, skim or drain off off lighter metals)

I thank you for your input, but I'm really not interested in the gold inside the chips, I use the chips to make earrings and broaches to sell at the local fair, i admit that getting the gold out from there is to difficult

I am really interested in getting the gold that is used to plate the edge connectors on the boards that plug into the motherboard. It is used there because it does not corrode, and keeps a good connection over time.

HP boards are known to be very liberal with the gold plating on their older boards, but even modern boards do have a reasonable amount on them, but getting it off and separating it out is the problem

Separating gold from anything is always the problem; that's why the metal in its refined form attracts much value. Any acid that dissolves gold will probably also dissolve the copper. At a wild guess, what about electrodeposition from gold/copper solutions under tightly-controlled electrode voltages - would that work?

One would need to check the legality of selling gold that hasn't got an assay mark, depending on national laws.

"Gold is not on the PCB but is used as connectors inside Microchips between the chip and the external electrical connectors." Very little gold here. Secondary to the considerably greater amount to be found on the board itself.

Gold is electroplated onto the copper traces, through holes, and edge connectors to ensure ease of soldering and good contact at edge connectors and chip sockets.

Military and NASA spec. boards are salvaged from used/obsolete equipment and processed, in large quantities to recover the gold.

yeah, I know what you are talking about. You are etching your own traces onto a blank pcb right? I have done this, making a circuit board from scratch. it was a long time ago, however, and I am sorry, I cannot remember the specific name for the type of acid bath used to make traces. But it should help to know that the reason the others were right in saying it isn't gold. The traces that are etched onto the circuit board (pcb) are not gold (none that I have ever seen, even really high end equipment); the traces on a pcb are always etched (acid bath burns in) to become copper.

I hope that helps. perhaps google or wiki "circuit board etching"

Quite often certain traces on PCBs are gold plated. For example, it the board has a number of fingers for a connector, regardless of how cheap the product, the fingers are always gold plated. It is the only way to definitely assure no corrosion in the connection.

If you get the copper pealed off the PCB material, you want to look to see if the copper is covered by any type of binding agent - epoxy, etc. If yes, soak it in methylene chloride to remove it (very eco-unfriendly, by the way). Next, you can use nitric acid to remove the copper from the gold. Or another possible chemical is ferric chloride, which will dissolve copper. There are other copper etchants, as well.

I'm guessing, though, when all is said and done you'll probably wind up with as much gold as in the bottom of a bottle of good Goldwasser.

You'll need to dissolve away the gold and copper in aqua regia, then precipitate the gold out, possibly with urea (I'm not too sure about this part). Finally, you need to heat it at high temperature in a furnace to burn of the contaminants.

Why use something that will dissolve both the gold and the copper when you can use a chemical (say, ferric chloride) to just dissolve the copper, leaving the gold intact. Woof!!!

Hi Facilitator,

A friend of mine used to recycle old PC boards and radiographic film. Remember that old photocopiers are also a source of selenium from the drum.

I have not really done any PCB recycling, but there are some basic principles.

We can't answer your question in only a paragraph or two and quite a bit of work is required to determine the economics of the process.

Firstly, it would be great to know how much gold and other potentially revenue earning metals there are in a typical sample of your PCB's. First, take a representative sample (how much is difficult as I don't know how much or what boards you have).

If you have an assay laboratory reasonably close by, you may be able to take the sample to them, they will mill it and split out a sample for analysis for you.

You would obviously like to know the gold content so you would ask them to analyse for gold specifically (ask for a fire assay). Other metals that would be of interest (and I'm sure I will miss some), are, silver, copper, selenium, cadmium, nickel, platimum group metals (PGM's).

You should repeat the exercise using several samples so that you have a range of values. From this you can do an exercise to evaluate if there is sufficient metal of value in what you intend to process to justify the expenditure. The volume of material that you process will also influence this decision (do you have access to kilograms, tone or hundreds of tone of PCB's per month?).

Size reduction (below) will be required no matter what subsequent treatment process is chosen. I will discuss this and then briefly touch on the subsequent extraction procedures.

1. Size reduction

First we would have to mill the PC boards. The finer we mill them the greater surface area we create. This is of benefit if we melt the PCB's or use a lixivant to dissolve the required metals.

The object of milling the PCB's is also to expose gold that is encapsulated in chips etc. The degree to which you have to mill will depend on the size of the smallest size of device, but my guess is that if you could reduce the size to all passing 3 mm, this would be adequate to expose the metals inside all but the smallest chips. You could go for broke and mill everything to less than 0.1 mm, but without some test work, we don't know what is the optimum economic comminution size.

There are several methods for breaking / milling boards. Ititially you would have to probably break them up into something like 150 mm pieces. For PCB's, a wood chipper may be ideal. To mill finer, we would either need to use a rotating cylinder filled with steel balls or rods or a hammer mill.

All the above processes may be conducted dry. Adequate dust collection must be provided & the dust will be an important by-product as well.

2. Extraction

At this point, we want to extract the valuable metals from the rest of the material. Two basic methods are available, basically lixivation (dissolving) and smelting (heating up to form a liquid).

If we go for the lixivant approach, the safest and most cost effective (believe it or not) would probably be cyanide. You would very lilely have to get a permit to purchase cyanide. Sodium cyanide (NaCN) is about the cheapest unless you can get calcium cyanide (CaCN2).

We then work in a alkaline environment, no special materials required, no corrosion etc.. We only require a very dilute solution of cyanide (depending on the copper content), this could range from 100 - 500 ppm (this would have to be determined from test work).

We make up a slurry of recycle material in a weak cyanide solution (dissolved in water) at a pH of no less than 10 (important). We need to keep the slurry adequately aerated (could use a cement mixer or tumbling drum or agitated tank). The dissolution may take as little as two hours or as long as 48 hours (test work required).

Once the gold & other metals are dissolved (PGM's, Cu & Ag), we can filter off or decant off the solution and adsorb the dissolved species onto activated carbon (granular) or precipitate with zinc dust.

Cyanide (like any dangerous chemical), is a highly toxic chemical and must be handled with the utmost care and respect. When used responsibly, it is quite safe to use, but if handled by cowboys...

The EPA and law will have all the guidelines for handing toxic chemicals. These should be adhered to at the very least.

Thiourea has also been used as an economic gold lixivant, but again we are in an acidic environment - corrosion, special materials, dangerous by way of contact, exposure etc.

Aqua Regia (a mixture of HNO3 & HCl) is nasty in the extreme to use in any quantity.

I will finish on dissolution here as we still don't know if the process is economical or not and briefly discuss the smelting option.

We could throw the material into a smelting pot with some flux (mainly borax and silica) at about 1 300 degrees C. The actual flux composition will also have to be determined.

This process would produce what may be referred to as a mixed metal matte, which is generally saleable to a metals refiner. Again, we have a flue from the smelting furnace and will require adequate dust and gas collection facilities as well as an environmental impact assessment & permit.

We must take into account how we are going to dispose of the waste products.

I'm afraid that it's not the sort of thing one can do in ones garage (legally), but if you work or have access to a laboratory or similar facility, a great deal of the

First thing is to establish what you have and how much you have in your PCB's. Then to do an economic assessment on the value of recoverable metals contained. Once we have this we know that we have (say), US$ 5 / ton of potential revenue, thus our total costs (capex & opex), must be less than this to make it worth while.

If we establish that there is sufficient value in the PCB's to justify further work, we need to do some process tests to determine the optimum process route/s.

Next we need to consider the legal & environmental remifications of our selected process route/s.

I'm sorry if I have made it all sound a lot more complex than you wanted it to be, but I'm afraid it is. Otherwise process engineers wouldn't have jobs.

I knew some one who brought and sold surplus military hardware, once he recieved several tonnes of circuit boards, which had gold plated connectors on them. He simply removed the connectors and sold them in an unstripped condition, I cant remeber how much he sold them for but he obviously made enough to employ 2 people to process them. To sell them he found a contact through a scrap yard.

Back more than several years ago, there was a company that extracted precious metals from PCB by incinerating the entire mess in a super hot cyclone incinerator and then fractionaly distiiling the metals out the bottom. I don't know how economic it was.

I thank you all for your comments and suggestions, I must admit that getting other metals out of pcb,s and chips sounds daunting. i think i,ll try for the nitric acid route, but will the acid dissolve the gold!!

I've been told that you could amalgamate the gold off of connectors using mercury (I have never tried this and have never seen or heard of someone actually doing this). After the gold has amalgamated let the mercury evaporate. Good luck finding that much mercury!...not to mention the hazards...and environmental impact...

OK, here it is,

there are 2 methods used to extract gold of PCB.s,

KCN is the most popular. The other uses urea.

But, the waste issue is grand.

This is what I suggest. Send the waste to recycling, a large number of companies do this. It is just a matter of volume.

If small then use the urea method. If you don't know this method at this time, I strongly suggest you do not proceed. But find a recycling company.

Facilitator,

To answer your last question... HNO3, or Nitric acid does not dissolve gold under normal circumstances.

Sounds like you have gotten a bit more information than you were looking.

Bottom line is if you just have a few pounds of this pcbd material than chemically stripping it may be alright for you but not economical for handling larger volumes of pcbd scrap. I personally, would take it a company which does this for a living. Depending on where you are located, there is most lkely a facility located fairly close to you. There are also brokers out there who will buy this material from you for a fraction of its real intrinsic value.

Value determination of pcbd is very important, but not easy. Even if the boards are all the same mfg.... their content will vary. For example, ball park ranges for loaded mother boards w/ processor, RAM and components attached may run b/w 0.35-0.75% Au or 10-20 troy oz of Au/ton. Compare this to the same boards w/o these devices & components attached... the Au value may very well drop in half.

Rule of thumb here is... the more material you have the better your terms and grearter your return. I have worked w/ a facility which may be of help... check out the website below www.norandarecycling.com

VERY IMPORTANT DISCLOSURE : The KCN & NaCN chemicals are the active ingredients in most stripping solutions and are extremely dangerous. Do not use if you are not fully aware of the safety & health risks.

I hope this has been helpful.

Safety First!!!

Partner Pat

Get a furnace and put broken PCB's into the crucible, and into the furnace. The metals on the PCB's will melt, and the rest of the PCB's is thrown away. Make thin plates with the metal alloy.

Take a copper plate and connect to the positive end of a battery, inside a tank of electrolyte solution, making it an anode. Connect the metal plate made with metals from the pcb, to the negative pole of the battery, making it a cathode. Now, the copper will move from the alloy to the copper plate. After a while, replace the copper plate with a plate made from stainless stell. This will attract silver. The rest of the anode, is mostly gold!

This is not a very simple metod, but you will get not only gold, but copper and silver too!

thanks alot for your input,

just one question. what type of electrolyte solution would you suggest.

The facilitator

check out our gold refining forum, we can teach you if you really want to spend the time to learn to do this safely, and yes you can get pure gold silver and platinum group metals, no its not cheap. but a great education. butcher

heres link http://www.goldrefiningforum.com/phpBB3/index.php

DEFINITIVE ANSWER

Just to note; gold is VERY MUCH on, or rather IN PCBs along with connectors, contacts, wires, filaments, and the like.

For the cheapest way I've found over the years (I'm a computer tech that 'moonlights' as a deconstruction recycler) is to buy a gold and precious metals testing kit., (read: a bunch of acids in bottles). They tend to be under 20 dollars and on amazon or eBay and you can often find them for under 10.

Pre-req

A gold/silver kit

A piece of ceramic or Pyrex tile -the bigger the better (really, trust me on this) but make sure it's REAL ceramic or authentic Pyrex or you'll wish you had listened.

LATEX gloves (sorry if you're allergic, but that's life)

One 1/8 or greater piece (strip) TRUE TIN 'Sn'. you can find this at any Home Depot, Lowes, Meijer, Wal-Mart or the like.

All these tests/recovery steps assume you're using proper listed acids from a proper kit (tubes or bottles of WELL marked acid in 2-6 oz containers or 55 gallon drums (for the excessive ones out there). You will be wearing the gloves, using the acid, and placing the acid and components to be melted on the tiles.

Step 1: Scrape, cut, break or what ever you can do to break down the components to the most % of gold and least amount of scrap/crap.

Step 2: Use the acid/ammonia concoction labelled 12K Gold. a. For various reasons this tend to be the best choice at melting remaining copper, silver, zinc, nickel, and plastic with the least amount of fumes.

b. most 'computer' gold ranges between 14k and 24k since 1987. For 1982-1985 use 14k acid

for 1984/5 back use 18k as most connectors were between 18-24k.

Step 3: dip/drop enough acid on the 'item' to cover it completely.

Wait 10-15 minutes

Step 4 Scrape ALL material from the tile into a baggie. You now have raw gold at the kt rating of the acid used.

To note for you penny-pushers out there. Using too high a rating of acid will leave you with less, or most likely NO gold at all. Be smart, stick to the years listings I have posted.

I have been in the tech industry from one stand-point or another since I started my own gaming tips and decompiling company when was 14 I have over 20 years experience but make no claim that everything I posted will work on every component at every attempt.

Side note on recovery. For those looking for an extra buck without being worried about every cent:!

Most of the sets of testing sets include AT LEAST one silver acid if not two or three.

Most often, the silver/grey wiring used in computers is silver or nickel. Sometimes highend wires such as Monster, ASUS, and Gigabyte and the like have platinum or palladium plating; and Monster, ASUS, iBuyPower, Falcon and others have been known to use .75 (Bell), .78 (Greek), .995 (Stirling) and .999 (Fine) silver in wires. For some extra Lincolns (or Euros) snip and strip a small piece and test it with the silver acids included in the acid kit. Also you can try the higher end platinum or palladium acids on stripped wires. You never know and I've come across a few over the years.

Hi There

thanks a lot for your input, I never expected this to go on this long, I started this thread in april 2007. I still have a tin full of edge connectors from PC cards that I'm wanting to harvest the gold from, I have yet to think of a way of crushing them or taking off the metal from the cards easily.

Then I hope to have a sludge, or grit that I can put into acid to disolve the copper nd leave the gold.

Have a great day

Bill

The Facilitator