# Gold dissolved in Nitric and salt.



## Ardibash (Jan 16, 2012)

OK, I have a strange thing going on.

I processed some keyboards for silver, with nitric and salt> It produced about 20 l of dilute (20-25%) nitric acid, which had lots of salt content from silver chloride precipitation.

I was just curios of what it will do if I put in a whole motherboard, will it eat the copper and leave the tin nitrate. BUT What I got the next morning is all pins and SMDs fallen of the boards. I was really happy as it did not touch any of the plastics or gold and copper, there where also no salts and seddemnts. So I had an excellent solder remover (that's what I thought). After about 100 motherboards where stripped the liquid was not working any more.

So I deiced to make a similar liquid, just took some Nitric acid added salt water and placed some boards in it. The next day (cold day, about -1) I checked and some SMDs where fallen but the thicker solder near the connectors was not fully digested. I thought it was cod day, and the solution could work better when warmed up. I place a water heater inside the bath, and set it to 35 C.

4 hours late NO FINGERS, NO METALS, NO GOLD, it even dissolved the gold foils.

What did I create ?


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## Anonymous (Jan 16, 2012)

Ardibash said:


> I processed some keyboards for silver, with nitric and salt..........I was just curios of what it will do if I put in a whole motherboard........After about 100 motherboards where stripped the liquid was not working any more.


You stripped 100 motherboards using nitric?! . :shock: .. :shock: .. :shock: .. :shock: .. :shock:
We have countless threads on here,that discuss the reasons you do not use acid,to dissolve excess amounts of base metals.


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## Ardibash (Jan 16, 2012)

Mic, I just used semi-spent nitric it to strip the SMDs and connectors of the motherboards (after all aluminium and iron is mechanically removed), but not to dissolve the copper. I used other acid combination to digest base metals.

My question is where is the gold? Did salt, somehow, aid the dissolving of the gold? Was the temperature a factor ...?


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## Anonymous (Jan 16, 2012)

Ardibash said:


> Mic, I just used semi-spent nitric it to strip the SMDs and connectors of the motherboards (after all aluminium and iron is mechanically removed), but not to dissolve the copper. I used other acid combination to digest base metals.
> 
> My question is where is the gold? Did salt, somehow, aid the dissolving of the gold? Was the temperature a factor ...?


 I understand the problem you are having Ardibash,unfortunately I do not know what happened.Some time back I used SSN(saturated salt/nitric) solution to dissolve values,but it doesn't sound like that is what you have created here.
I am highly concerned at the idea of any acid for base metal dissolution.There are many drawbacks for doing such a thing.And did you ever install a distillation setup? I am very worried to say the least.Please abandon this idea after you recover your gold.There is not enough values in mobo's to justify processing them in this manner.You are spending $100 in chemicals,to recover $10 in pm's.


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## butcher (Jan 17, 2012)

Salt NaCl and nitric acid HNO3, would make an HCl, HNO3 and sodium in solution, basically a form of aqua regia, since the gold was very thin it dissolved in this solution and plated back out on un-dissolved base metals, the only way to get it back would be to dissolve every bit of base metals, the problem with whole circuit boards is there can be base metals deep down under or inside of board or components, also the tin and lead (solder would give you other troubles).

We tell people not to use aqua regia until they eliminate the base metals.
We tell people to seperate the materials as much as possible mechanically, and process them seperately.
We tell people not to try and process whole circuit boards.
You are finding out why we say these things.

It would be very difficult to retrieve your values from this mess (could be done, but dangers involved time and trouble I do not think it would be worth it).

Maybe you can wash what is left of boards and sell them to a circuit board refiner, and count this as an learning experiment, then spend more time learning, study more and follow known working procedures.

This is why we say the wheel works well and it is already round, why try to invent one.


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## Ardibash (Jan 17, 2012)

mic said:


> I am highly concerned at the idea of any acid for base metal dissolution.There are many drawbacks for doing such a thing.And did you ever install a distillation setup? I am very worried to say the least.Please abandon this idea after you recover your gold.There is not enough values in mobo's to justify processing them in this manner.You are spending $100 in chemicals,to recover $10 in pm's.



MIC you lost me here  !

so what would you use o dissolve base metals other than acids ?
and what kind of distillation step are we talking about ? I have a distillation setup, but that's for something else, it's an apparatus to boil and recover HCl. (see attached)


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## Ardibash (Jan 17, 2012)

butcher said:


> We tell people not to use aqua regia until they eliminate the base metals.
> We tell people to seperate the materials as much as possible mechanically, and process them seperately.
> We tell people not to try and process whole circuit boards.
> You are finding out why we say these things.



Guys it seems you are not reading and understanding my post.

Butcher, thanks, Now I understand that I have created a sort of AR, the thing is, the acid from silver leach was still very active ... so did not want it to go to waste.
- When it's cold (below 12C) it some how only attacks the tin and lead and if left for 3-4 days it will attack the the copper very lightly.
- My problem was, that, when heated to 34.5C it acted as normal AR, and stripped the boards of everything.
- when processing boards, I'm stripping CMDs chemically, a HCl bath mostly, but it has drawbacks, some polymers get messy.
- I know that you should attack base metals first, I do that with combination of Sulphuric, nitric and water (after everything is removed from boards).

And most importantly, there is a immersion stripper for Sn/Pb alloy called "ALSTRIP 2000"which is based on stabilised nitric acid, and doesn't attack copper. SEE ATTACHED DATA SHEET


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## butcher (Jan 17, 2012)

I briefly looked at the All-strip data you posted, it does not really say what it is but seems to me like some stripping for lead solder, in what application I do not know, as depending it can dissolve other metals, unless it was a very weak solution, it says nothing of what it actually is except it may have some nitric in solution, and some hydrogen peroxide, no clue what else it may contain and what other metals it may attack, although I think it would dissolve many base metals including silver and maybe Palladium depending on percentages, but without more details of this product anybody’s guess would be as good as mine as to what it is or contains.

HCl alone will break down solder (will not attack copper, silver, gold. or PGM, unless you added an oxidizer), making lead chloride white powder and tin dissolved into solution (which by the way does not dissolve very well and makes solution very hard to filter, one reason you do not want your values dissolved in this solution),

HCl/3%H2O2 (small additions) also called acid peroxide will also break down solder, and dissolve copper, but will not dissolve silver, or gold or PGM (unless you made oxidizer stronger or major part of solution).

But until you remove components from circuit board (or know how to deal with tin and lead in solution), it is better just to use the Hcl to remove solder from you parts mechanically removed from the circuit board.

There are many ways to deal with removing components from circuit board that do not involve acids and these are preferred over acids, soldering Irons, heat guns, even torch's, hot solder, and sand baths, cutting off components and many others.

You have much to learn, try spending some time searching the forum for tips on the things your trying to do, you will find many way's that work well, and in doing so you will not be throwing away your gold and other values trying things that do not work.


Mic was just trying to tell you dissolving all your metals or whole circuit boards is not a good idea you end up with problems like your having now.


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## Ardibash (Jan 17, 2012)

Butcher, can you tell me a little bit more about hot solder and sand baths, all I could find on the forum was sand baths for boiling, noting about solder removing. Torch is not an option for me as I have 1-3 tons of motherboards coming in each month.


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## Anonymous (Jan 17, 2012)

Ardibash said:


> MIC you lost me here !
> 
> so what would you use o dissolve base metals other than acids ?


I wouldn't dissolve them.If there was a large amount of base metals,I would leach off the gold,either chemically,or electrically.Base metal refiners use melting and smelting to recover the metals.


Ardibash said:


> what kind of distillation step are we talking about ?



The distillation setup would be to recover the nitric.At that volume,I imagine that you are losing a significant amount of nitric through vapors.


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## Geo (Jan 17, 2012)

are you refluxing the nitric acid back to your reaction vessel? this is a simple operation that will extend the usefulness of your nitric acid making less acid do more work.or you can add acid resistant tubing from your reaction vessel into a receiving vessel containing hydrogen peroxide and capturing the NOx fumes thus creating more nitric acid.


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## butcher (Jan 17, 2012)

Flat pans with a thin layer of molten solder (pan just heated to the melting point of solder, the circuit board can be set on the solder (not enough solder to flow on to the top component side, the parts can then be pulled off from the top, some problems with this method are if reusing components, you may over heat them if in solder bath too long, also keeping the hot pan level and stable.

A version of this is an electric oven type toaster, if board parts are not to be reused, boards are heated, to melting point of solder, boards are removed and slapped against the lip side of a can, or other object, knocking off almost all of the components at once, that do not have wires bent overt on bottom of board (this type can be ground off beforehand), problems parts are cooked too high temperature so more temperature sensitive components cannot be reused, resins in circuit boards can sweat ooze liquids and smoke (very dangerous as fume's).

Other methods like charcoal under a steel plate boards are set on are similar to ones above.


A hot air blower (kind of like an industrial hair dryer is a nice tool, its controlled temperature can be directed at somewhat of one portion of board the remove wanted components (board in vise dryer hot air gun in one hand, and part grabbing tool in other hand pulling the part from board), this method has the advantage of you can remove part and not overheat it, also you do not have to get circuit board so hot as to produce the very dangerous fumes in these epoxy's and resins.

Propane torch can also be used in this manner although somewhat less control of overheating parts and possible getting board too hot and creating some fumes.

Do not breath fumes from circuit boards these are very damaging to your health.
(Like ole timers used to tell us, it’ll stunt yer growth), these can make you linger with cancer while your waiting to die.

De-soldering, can be done with soldering irons of several types, a person can even use de-soldering irons with several types of tips some larger and flat to remove chips heating all pins at once, or a soldering iron with an automatic vacuum source to suck out solder from each leg of component (so you do not have to use regular soldering iron and hand held solder sucker tool or solder absorbing copper braid).

A trick I use to remove components for reuse or for recovery with a regular soldering iron is to add a blob of solder (to the components solder side), heating this blob covering several legs at once this blob can be moved around with the iron so all of the components legs get the solder molten and part can be pulled from the board (you can remove integrated circuits, transformers relay's and many other multi-pin components using this method).
I can depopulate a large circuit board in less than an hour (without damaging components for reuse) using a regular soldering iron, with a propane torch or hot air blower in less than a few minutes, although this may damage some components for reuse.
Parts can be chiseled off or pried or twisted off, even power chisels or cutters can be used, fingers or boards can be cut in shears, 
Parts can even be sheared of with board placed in jig and hydraulic shear plate can shear off all of the components in one motion.


There are many ways to remove parts or components from circuit boards, many posts have been made on this subject, I believe Laser Steve even made a video or something to show a few methods.


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## qst42know (Jan 18, 2012)

Ardibash said:


> Butcher, can you tell me a little bit more about hot solder and sand baths, all I could find on the forum was sand baths for boiling, noting about solder removing. Torch is not an option for me as I have 1-3 tons of motherboards coming in each month.



As I understand it the big outfits incinerate. Have you investigated this as an option?


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## Ardibash (Jan 18, 2012)

Butcher, I have tried most of the methods you described, the best one for me is the propane torch under a fume hood connected to a wet scrubber. BUT, it's very very hard to process 2-3 tons of motherboards this way. I will give a try to solder bath and see if it's any faster. I was more interested in a sand bath, it the sand can absorb the solder then that's an option for me. I need to process at least 100kg a day to keep up with the supply.

qst42know

I have investigated incineration, but it requires High Temperature Pyrolysis Furnace.

Also boards can be put in a nitrogen atmosphere oven, cocked to 600-900 C and the vapours distilled, but this is a very expensive price of equipment ....

What other options are there to process 100 kg a day other then HCl bath?


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## etack (Jan 18, 2012)

It seems your best option would be to collect till you get a truckload and sell to a refiner. Additionally cherry pick first and refine in house the good stock.


Eric


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## Ardibash (Jan 18, 2012)

etack said:


> It seems your best option would be to collect till you get a truckload and sell to a refiner. Additionally cherry pick first and refine in house the good stock.
> Eric


 

 I'm trying to be a refiner ... not a scrap dealer.


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## etack (Jan 18, 2012)

I can understand that. however 100Kg a day is not a lot. its more than I can do or get. 

It will create a lot of waste that will be expensive to get rid of.

Start small and when you can buy the expensive equipment do it.

there are members that take in a lot of boards and they cherry pick and send out the rest.

Eric


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## butcher (Jan 18, 2012)

I agree cherry pick and sell the rest to a circuit board refiner, he will recover metals you cannot, he will pay you for these metals, if you try and refine the whole thing some of your values will be lost to these other metals (and lost in your waste), also these other metals are just waste to you that you may have to pay to dispose of, why not just get paid for them, the cherry picking the cream of the crop would keep you busy recovering the high dollar stuff, and you will be paid for your waste (metals you would be unable to recover).

The hot sand will melt solder into it, parts can be removed by picking off with tools or board can be slapped on bucket rim and parts knocked off, very similar to solder bath above. The sand will get loaded with solder, but can be separated from the lead.


Something to consider is lead when melted will dissolve some gold into it, so removing fingers before hand would be my advise, this way you do not loose some gold to the solder or contaminate your gold with the solder.

You may also find it more profitable to be a scrap dealer than a recovery and refiner, even with the higher value components (separating them from the rest of the scrap) you just may find more gold in your pocket.


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## nickvc (Jan 19, 2012)

There a post by 4metals I believe that describes how the big boys in board recovery operate. Basically it involves granulating, incineration, sorting and then smelting into dore bars. This is all high cost equipment especially with the necessary environmental controls and they don't refine but ship the bars to copper refiners to do the refining, and settlement from them can take months. 
As butcher and others have advised cherry pick the boards and sell on the balance, full recovery from boards is almost impossible for the small refiner, with the quantities you have it shouldn't be hard to find companies to buy the boards and it will save you chasing your tail for pennies.


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## patnor1011 (Jan 19, 2012)

Processing motherboards in acids will send you in red numbers. Another thing is that it cant be done in timely manner. Any attempt to speed up process will increase risk of losing more of values.


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## qst42know (Jan 19, 2012)

There are companies that incinerate powder coat paint hooks. They have the proper equipment and incinerate as a service. Having this step of the process done for you might be less trouble and expense than the chemical stripper you are using, or the labor of hand stripping.

Keep in mind this is just an idea and not from experience.


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## patnor1011 (Jan 19, 2012)

I do not want to discourage anybody but... 99% of forum members are hobbyists. 1% make living refining. Out of that 1% most of them refine karat gold. I have yet to see somebody who is making living processing just boards.
Some people can have comfortable and nice income from recycling or recovery operation. That mean they take whole electronics and separate. Bulk of their income comes from selling scrap metals. As I have said, I do not know anybody who can say he make enough for living just processing motherboards. It cant be done without proper and costly equipment and know-how.


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## Ardibash (Jan 22, 2012)

Hi, sorry I was busy building equipment.

I understand that big refiner use destructive pyrolysis to process broads. But one has to start from somewhere.
I built a disordering station with a catering grill (365C) and sand, works OK ... but some components, which have SMDs on both sides can not be done this way, so I put them in an HCl bath. I noticed that 25 L of HCl can depopulate about 300 boards. In average, a ton of mixed boards (with heat sinks) contain 1200 PCBs. Depopulation with HCl would cost me about £200. The gold (only gold) refined would be about 100 g according to a reliable source. (see attached data from Umicore group). So at the end depending on the price I pay for a ton of PCBs the chemical depopulation would be an option for me (for now). 




I'm thinking of building a pyrolysis furnace. If anyone knows any ting about it and can help me to make the drawings, please let me know. I will build it, and post detailed description in the forum.

I'm working on 7 machines 

20L vacuum filter, 
boiling station with condenser, 
titanium reactor, 
wet scrubber, 
semi-automated depopulating bath, 
neutralisation and base metal recovery apparatus 
and base metal leaching reactor which uses combination of acids to digest base metals apart from lead, tungsten

and will post the manufacturing process in in few weeks.


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## butcher (Jan 24, 2012)

For the scale and materials your talking about you would need a furnace with an after burner, and possibly ash collectors and fume scrubbers.

You should check with your local authority's DEQ, EPA. Or pollution control officials to find out the requirements, and follow their instructions.

Without following their advice you could find yourself with big problems costing you more than any gold you can dream of getting.


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## seawolf (Jan 24, 2012)

Somewhere in my searching I found te artical below:

An electro-dissolution method has been developed by Pozzo and coworkers (1991) to remove solder coatings from printed board scrap to facilitate the recovery of copper. Rotating trammel screen baskets, each 20 cm long, and made of stainless steel or mild steel are used as the anode and a semi-cylindrical shaped sheep of stainless steel as the cathode in the electrolyte cell. The anode is rotated with an electric motor at 40 RPM. The electrode setup and the electrolyte solution are placed in a rectangular container made of polypropylene of a capacity of about 22 liters. Sodium hydroxide is found to be the right electrolyte as it dissolves both lead and tin rapidly. Eleven liters of 1 mole solution is used. Samples of printed circuit board scrap with a bulk weight of 500 grams are charged into the basket anode. With a cell voltage of 2volts both tin and lead dissolve rapidly and selectively from copper. An increased rotation speed of the reactor basket improves the dissolution rate, while the percentage extraction of lead and tin remains nearly the same even when an increased amount of scrap is charged. Power consumption in the removal of the lead averaged 97 MJ (27kWh) per ton of the charge.

I have no idea if this might be a solution to cleaning the tons of boards or not. Some of the other members might know more and pass it along or show why it won't work. (nothing was said about recovering the metals before the solution was disposed of) Mark


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## Ardibash (Jan 28, 2012)

I will try that and post the results. Right now I'm experimenting with stabilised nitric looks promising, once I have results will post here.


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