Introduction

[Maurice]

Hello everyone,

My name is Maurice and I stumbled on this forum by accident. I was look over a marketplace type of website and was looking for a cheap CPU that would fit on an old motherboard that I had laying around. And while I was looking over the search results that I got I notice that someone was selling a Ceramic CPU for gold recovery. I knew that gold was used on electrical components because of it's excellent electrical proprieties, but I never have thought about getting the gold out of a CPU.

After seeing that I went to google and started looking for leads and information about gold recovery from CPU's and I found a lot of information that intrigued me. One of those links lead me to this forum and after reading a number of posts I have signed up for the forum.

I'm an electrical and computer engineer, 41 years old. And rather fond of playing games and fishing.

I have been collecting all kinds of components, PCB's, CPU's, pins and other electronic scrap that might contain precious metals.

For now most of this is just theory as I live in a rather crowded location. I did however buy 5 liter of HCL 30% to perform a couple of small tests.

For a small test I have used two plastic water bottles. One I filled with 2 cm gold plated pins from HDD's and one with 2 cm solder that I obtained when I was desoldering components from PCB's. To both bottles I added 4 cm HCL 30% and placed a wet piece of cloth as stopper. I let both bottles stand in the sun during the day and under a roof during the night.

When I first opened the HCL I saw fumes come out and was startled at that. I quickly closed the bottle and looked on the internet what that might be and if it would be normal for 30% HCL to do that. I found out that it was the acid that reacted to the moister in the air to form those fumes. Nasty stuff.

The two bottles have been standing there for a week now and I noticed that the color of the bottle with the solder was slowly turning purple while the bottle with the pins has a slight yellow tint to it. After a week both bottles are still bubbling. Besides the color change I also noticed that in both bottles there is a fine grey power on the bottom of the bottle. Seeing the both bottles are still bubbling that means that not all the tin and lead (and other base metals) have been totally dissolved yet, so I'll keep those bottles in the sun until everything is dissolved.

What I found particular is that when I poured the bottle with the solder in a new container and added water to the original container it turned all milky white. The same happened when I poured the contents of the other bottle in a new container. The original bottle also turned milky white when I was cleaning it. I let both original containers sit for a short while and saw that the milky white cleared up and I ended up with a white layer of material in both bottles. So while deluding the remaining HCL (changing the PH of the solution) I precipitated some white substance. My guess this *********** is lead and/or tin.

My questions:
- How do I precipitate the tin from the solution ?
- How do I precipitate the lead from the solution ?
- Why is one solution turning purple and the other slightly yellow ?
-> My guess would be that the bottle with the solder contains more then just solder. Perhaps some small electric components (resistors, ceramic capacitors or other small components) ended up in the solder or other contamination and those items produces the purple color.
- Is there a way to "clean" up the HCL so that it can be reused ?
- What might the gray power be that is on the bottom of both bottles ?

Kind regards Maurice.

 

[Claudie]

Glad to see you are wanting to learn something new and you have came to the right place. Here is a link to get you started: http://goldrefiningforum.com/phpBB3/viewtopic.php?p=6873#6873

 

[butcher]

My questions:
- How do I precipitate the tin from the solution?
Tin is a very reactive metal, there are few ways you can use to precipitate or cement it from solution, you can replace it in solution with a more reactive metal (see the reactivity series of metals), You can convert it to an insoluble substance like a carbonate, sulfide, hydroxide… (see the solubility rules). Tin is one metal that will oxidize fairly easily even when in solution, tin can be a complicated metal in its chemistry, you could write a book on its chemistry alone.
Stannous chloride is a clear solution, the cloudy solution when you added water to stannous chloride, you could have been seeing the tin hydrolysis occurring with the addition of water.
Tin dissolves slowly in dilute HCl to form stannous chloride replacing hydrogen from the acid as gas:
Sn + 2HCl à SnCl2 (aq) + H2 (g)
Diluted in water hydrolysis can occur:
SnCl2 + H2O à Sn(OH)Cl + HCl
- How do I precipitate the lead from the solution ?
See the solubility rules, all chloride salts are soluble, except silver (Ag+), lead II (Pb+) and mercury (Hg+) some others not mentioned like copper I chloride is fairly insoluble in water).

- Why is one solution turning purple and the other slightly yellow?
Some metals will color solution, many metals will not.
It is possible the purple was a reflection of light off of the invisible colloidal gold, when solder is melted with gold it can dissolve some of the gold into that solder, although there are other possibilities.
Iron could give a yellow color, as well as a few other metals.
Colors can sometimes be indicators to what may be in solution, but they will not tell you what you actually have in solution, unless that color is from a specific reaction with a test of the solution to determine the metal you have, and the chemical you are using to test is reactive to that metal giving you a specific color, and even then sometimes even these tests will react with more than one metal, which can give you a similar color, so then you may have to do further testing to determine which of these metals you actually have,

-> My guess would be that the bottle with the solder contains more then just solder. Perhaps some small electric components (resistors, ceramic capacitors or other small components) ended up in the solder or other contamination and those items produces the purple color.
YES
- Is there a way to "clean" up the HCL so that it can be reused ?
No and (kind of yes)
Sometimes we can recover some of the hydrogen chloride gas in a process like distilling, and bubbling this gas into water to form hydrochloric acid
This can depend on the metal you used with the acid, (see the reactivity series of metals) reactive metals above hydrogen will displace hydrogen as a gas that leaves the solution, when the metal is oxidized to form chloride salts, at the same time the acid is reduced to chlorides.

To be (or to become) an acid we need that hydrogen, without it we do not have HCl (hydrogen chloride) to distill off.
Metals below hydrogen do not dissolve in HCl without an added oxidizer (these oxidizers can be more volatile than the HCl (hydrogen chloride) and distill of before and with the HCl, depending on the oxidizer used.
This would take me too long to explain, and could fill several pages of my rambling ons.
Lets just say no, unless your doing it anyway and have a use or it.
HCl acid is cheap it does not make sense economically to try and reclaim it most of the time, although there are times I will when trying to keep it from polluting our environment, or I am distilling, or evaporating a substance and wish to use the byproduct with another reaction.

- What might the gray power be that is on the bottom of both bottles?

I’m lost now I do not remember what we were talking about.

My guess is maybe Lead chloride, and Copper I Chloride, (doubtful but there is a slight chance the white powder could be silver chloride, or even sodium chlorideif any source of sodium metal was involved).
Try to see if the white powder is lead chloride, add some cold water to the powder, lead chloride is very insoluble in cold water, now heat it to boiling, lead chloride becomes pretty soluble in boiling hot water, lower heat and let the insolubles settle, but keep it hot, decant the clear liquid solution to another vessel and cool it, you may see lead chloride crystals form these can look like powder or needles depending on how much lead and how the solution cools
(NaCl will dissolve in cool water just about as much as it will in hot water)
(Silver chloride is pretty much insoluble in cool water or hot water or HCl)
Copper I chloride is fairly insoluble in water cold or hot, but will dissolve in HCl to form the green Copper II Chloride solution (which can look blue if very dilute).

Silver chloride will dissolve in household ammonia
CAUTION if you try this make sure you add HCl acid to precipitate the silver back out o solution as silver chloride, after the test, Do not store this with silver in solution. Do not let it dry. Do not mix this or its waste with other solutions or with other waste products, which could cause an explosive compound.
Silver chloride dissolved in ammonia looks clear (unless colored by another metal like copper), when you add HCl acid back to it you will see a white cloudy substance form and then the cottage cheese looking silver chloride form (with enough silver in solution) which will slowly precipitate as a fluffy white powder.

Got Hoke’s?
Do the getting acquainted experiments in her book, you will love these, and you will learn many interesting things, that will become an extremely useful tool to help you understand recovery and refining of precious metals, and how different metals react with acids, and how some metals will become problems in solutions, her book also covers testing for several metals in solution including the precious metals, these are tools you will need and use and they help you with a better understanding of recovering and refining of precious metals …

 

[Maurice]

Thanks for the lengthy response. I have read it several times and each time it makes more sense

I was reading Hoke and have been reading it and the more I read it the more pieces are falling together. To bad I can't do most of the experiments that she mentions at the moment. I have no location in which I can do them without the possibility to harm myself or someone else. So I have to rely on the internet and other sources to answer Hoke's questions she places with the experiments.

You are right HCL is cheap. 14 Euro's per 5 liter. A little over $19 for 10% more then a gallon. I just wondered if it would make sense to reuse it instead of disposing of it the normal way.

I did read that you can make regular salt with the use of causic soda together with HCL. When the solution reaches a PH of 7 it should be NaCl + H2O. perhaps a good way to make it disposable.

For now all I can do is test and see how HCL reacts with all kinds of metals.

The two bottles that I created about 4 weeks now are still bubbling although at a rather slow rate. I have no way to heat it so I let them stand in the sun and use the sun's heat to speed up the process somewhat.

I'll post some pictures of the two for those people that like to see them. I can point out the different layers of material that has formed out of the solder that was put into it. The other bottle with the HDD connector pins is forming a light silvery colored substance on the bottom of the bottle. It is lighter in color then the layer in the solder bottle but I suspect it is the same material. The material settles quite quickly after it has been disturbed.

 

[Maurice]

Some further experimenting.

After a couple of months not much has changed. I've added 2 experiments to my current collection. See below for a small summery.

Bottle 1 (hcl 30% cold):
- IDE gold pins with and without solder

Bottle 2 (hcl 30% cold):
- Solder that I obtained with a soldering sucker that you use when desoldering components.

Bottle 3 (hcl 10% cold):
- Various metal connectors

Bottle 4 (hcl 5% cold):
- 2 small telecom PCB's
- 1 small WiFi board

What I have noticed is that the reaction starts (depeding on the concentration of the hcl that is used) but eventuely stops. This is not due to the fact that the acid is spend. When adding a very small piece of Al to the solution the acid quickly disolves it. In all my experiments I noticed that a small black layer is formed on top of the metal parts. This black layer seems to prevents the acid from doing it's job. It was quite easy to see this in action on the components in bottle 4. The PCB's had pieces of blank copper that is turned black now. When I use a pice of plastic to scrape some of this black layer off the acid was able to attack the material again. But only for a short period.

I have placed the bottles in the sun and did notice that the heat of the sun did result in a more active solution.

I was wondering what the black layer might be. I looks like something simular that happens with Al, which forms a small layer that protect the Al from further oxidation. I have searched on the internet, but I have not been able to find an anwser. But I bet someone here will be able to tell me what it might be or point me in the right direction.

Kind regards Maurice

 

[Geo]

It's called passivation. http://en.wikipedia.org/wiki/Passivation_(chemistry)

 

[Maurice]

Thank you for your reply Geo.

Seems like I was on the right track.

What's the usual way to break down this pacification layer ?

Heating up the solution and stirring it with a glass rod now and then ?
and or adding a little H2O2 to the solution while heating it up a little ?

My goal was to dissolve the tin to depopulate the boards in the 4th bottle. Leaving me with a handful of components that can be collected and sorted to be processed at a later stage.

My goal in the 3th bottle was to see how well base metals will be dissolved leaving me with a residue that should only contain a sludge with traces of gold and silver fron solder with other material that can't be dissolved in 10% hcl.

 

[Geo]

Well, personally, I find the best way is to take it out of solution and hit it with a hammer. It may not be that dramatic but is symbolic. The crust can be broken by impacting the material. If the piece is large enough, a stirrer or glass rod may not be enough to break the oxidation layer. Incineration of the material will break the layer off and that's the general recommendation. The first recommendation would have been to raise the target metal content to a high enough level that the leech will work properly. A better understanding of the processes wouldn't hurt much either.

Good luck. 8)

 

[Maurice]

Thanks again Geo.

I'm very patient and I take my time to read and learn. I learn the best by experimenting and looking at the results trying to explain what is happening and of-course look up information on the internet about similar experiments by other people. And when I can't find the information I'm looking for I'll as other people to give me a hint/pointer in the right direction. I'll not do anything dangerous unless I understand what's involved, take the proper precautions and make sure that I, nor my environment will be harmed in any way. If that means that I can't do an experiment I'll not do it. I love live a bit to much for that

I love smashing stuff.. a good way to get a workout and alleviate stress

Pacification layer:
A pacification layer is a layer that protects the metal under it from further attack by the acid that is is placed in. Like that silver will form such a layer when played in undiluted Nitric acid. But placed in 50% nitric and 50% distilled water + heat and the silver dissolves.

That was the basis that I used in the 5% hcl solution with the pcb's. Instead of 10%. As I got the black residue in an earlier experiment thinking the acid might still be to strong. The only thing that I have not tested yet was to heat up the acid solution. I have no proper heat source. I only have an open flame, so that is not the best way to go about it.. certainly when hydrogen gas is produced. I do like to have roof above me in the coming months

Impact:
So impacting is a way to break the layer another way to remove part of it would be to scrape the layer of with something sharp like a chisel (hope I've got the right word here). It will be labor intensive and it will not prevent the pacification layer from forming once more. I used a sharp object earlier to remove some of the pacification layer and the acid immediately started working again. And of-course it stopped after a couple of hours as the pacification layer was once again generated.

Incineration:
Another way you mentioned is incineration. You mean burning everything till only the material can be pulverised by hand or heated in such a way that the oxidation layer is burned away as I have read in various texts on the internet.

I have used incineration with as an experiment on a couple of ic's that I collected (my first experiment). After the incineration I crushed the material to a fine powder. I have not put the fine powder in HCL yet. I wasn't sure what reactions I might be getting and what fumes might be generated from that so I have not done that yet. The end product is a fine powder that I need to process. My goal was to obtain the separate components not a fine powder .

Raising the metal content:
You mention that I should raise the metal content. So I should use less acid and or more material for the acid to work on ?

You are suggesting that there is a threshold (a acid vs metal ratio) that I need to overcome in order for the acid to work as expected ?

Besides the 3 small pcb's in 5% hcl I also have a bottle with about 150grams of various metal connectors in a bottle with 10% hcl. The layer of metal is about two inch and the acid level is about an inch above the metal. In this experiment I also got a pacification layer that has formed after a couple of days.

So in 2 different set-ups that I have created I get the same results. The pacification layer takes a couple of days to develop in both situations. I also should note that I have not heated the hcl and the average temperature is between 14 - 19 degrees Celsius. So it is quite cold.

Processes involved:
Still learning . I spend a lot of time searching the internet for information about hcl and base metals. Read and watched video's about it. Looked at animations. Anything I can get my hands on. And I think I'am beginning to grasp some of the mechanics involved, but I'am still a newbie at chemistry.

I'll make a couple of photo's on my iPhone to clarify things a little. I'll add them in the evening.

 

[Geo]

The answers I gave is for metal only. If the problem is with the board itself, none of what I said will work. incinerating boards should only be done in an approved incinerator. Adding more metal to PCB's would not make much sense. Are you trying to dissolve the solder from the PCB's? If this is what you are working on, the layer of oxidation is most likely some other component of the solder that does no dissolve in HCl very well like silver or other hardener.

 

[Maurice]

Hi Geo,

What I'm tying to do is disolve the solder so that I can just pick up the components that where on the pcb

I have added a couple of images that should make it clearer what I'm doing. Or rather trying to do . I'm sorry that the quality of the images isn't very high.The image below is a photo from above with the arrows pointing to a couple solder points. The two arrows in the bottom point to two copper plates which where blank copper at the start. As you can see all the solder points and the copper places have a black layer. And now some of these seem to produce someting that looks like black sponge. On the right side of the glass you can see a couple of those "sponges" that loosened. The second picture is the same container but from the side.

Process
day 0 -> Little to no noticeable activity
day 1 - 2 -> Small bubbles are seen as the acid is working and the black layer is slowly forming
day 3+ -> The black layer is thick enough to pacify the action that going on
day 5+ -> Sponces seems to be growing on a couple of solder points.

The acid used is 5% hcl (10% hcl and normal water at a rate of 50:50)

 

[Geo]

If you are just using HCl, there's no danger in dissolving any precious metals. You can heat the HCl and force it to dissolve the tin from the solder. The black is more than likely the small amount of copper dissolved when you added chlorinated tap water to the mix.

 

[Maurice]

Hi Geo,

Thanks for the quick response. I'll create a experiment using 5% hcl and distilled water and see how well that goes )

I've got the same kind of pasification in another experiment. I have also uploaded a couple of photo's about that experiment.

This time it is undiluted 10% hcl, also cold.

Goal of this experiment was to see how fast/slow base metals would disolve if at all.

The material was blank on the first day and slowly developed the black pasification layer. Also as time passed small particals where collecting at the bottom of the container (second image). After less then a week no bubbles where noticiable anymore. The pasification layer does not seems to cover all the material as there is a thick layer on top and the lower you get the lighter the layer becomes. The acid isn't spend when I place a small piece of Al in the solution it is disolved quite quickly.

Questions:
- The small particals are they just smaller pieces of the starting material or some form of residue of undissolvable material (seems like the latter to me)
- Not all material seems to be coated with the layer, the acid isn't spend, yet no action has been hapening for a while now. So what is (might be) stopping the acid from working in this case.

 

[Maurice]

After filtering the HCl into another container I was left with a couple of pcb's that needed to cleanup. The components where not dislodged from the pcb's.

I added hot tab water to pcbs and let it stand for a while.. Soon after adding the hot tab water the solution went milky white. I poured the solution into another container and added some more hot water and repeated that a couple of times untill the solution wasn't miky white any longer. I let it stand for a couple of days. What happend afterwards is what surpriced me. The black solder points where partly disolved in the water and some components became loose. The white in the solution was comming from the blackened solder. I poured of the solution again and added boiling hot water onto the pcb's a couple of time to clearup the material.

The white substance is proberbly lead. I'll deal with that at a later stage.

So my experiment wasn't a total failure afterall