Went against my gut! Grrr...

[cnbarr]

Hi All,
I normally don't ask for help because I can usually find the answer on my own with the search function, but after a few days of searching I can't quite find what I'm looking for. With that being said, here is my issue, I have about five pounds of pins from backplane boards like this,


I processed them in 50/50 nitric in a stainless steel chaffing dish I received from glondor (first time I had a chance to use it, Thanks Mike worked great!). Anyway, after it had cooled I had a very prominent white precipitate which is virtually impossible to filter. But here is where I went against my gut, I was pulling all the pins with pliers, after three boards my hands were blister all to hell, (there is over 1600 pins per board) I had the bright idea to run the boards through my tile saw, (which I now immediately regret) since the pins were pressed in and not soldered. So I cut them as close as I could without touching the pins and through the section of board with pins into the nitric bath without paying attention to what material was under the solder mask. As you can see in the upper left corner of the first couple of pics, the silver layer under the solder mask, which I believe to be tin over copper, my first thought was silver but that didn't make sense in my head.

I now have over five liters of solution, that won't filter with foils in it, that I can't figure out what to do with. I have never dealt with this volume of solution before, every time time I encountered something like this I just dealt with the slow filtering and moved on with no issues.

Any input you guys can give me would be greatly appreciated.

Thank you,
Chris

 

[butcher]

I would screen out what I could, I have a cheap plastic screen with a handle, I bought from the dollar store, the plastic holds up well to the acids, I put the screen into a plastic funnel and this funnels solution into a collection jar, after screening out the larger pieces, I would put a little wad of fiberglass insulation in the funnel (something like Laser Steve's Charmin plug, and filter out more of the finer stuff, then the liquid from this would go to my distilling rig (I may even add some gold plated pins to this with elemental copper that needed to be dissolved, this would give me some copper in the mix which would help drive off the nitric acid when distilled), a little sulfuric acid added, and I would distill off the nitric solution (which could then be reused), the results would end up copper sulfate, which the gold is not soluble in, and I could separate gold from, the copper sulfate solution can also be reused.


http://goldrefiningforum.com/phpBB3/viewtopic.php?f=38&t=6199&hilit=killing+two+birds+one+rock

 

[NobleMetalWorks]

It's hard to tell what you might have in solution. It could be a lot of things. There may be some polymers, and the white may be silver nitrate. It could also be other things.

The silver nitrate will precipitate when your solution cools down. I feel that the white precipitant is Silver Nitrate, all you really have to do is put heat to the solution so that the silver nitrate dissolves back into solution, then filter it right away when the solution is warm, before the silver nitrate precipitates again.

After you figure out what is going on and how you resolved it, I would be interested to know what the problem was, and how you fixed it.

Scott

 

[ericrm]

i dont know how much help this is gonna be..................... so do not do anything until you get a real answer ,not just my guess..........................

from yahoo answer:
What is the word equation for the chemical reaction of tin metal and nitric acid?
Tin metal and nitric acid...produtcs are a solid, a tin oxide and a brown gas, nitrogen oxide

Gervald F Gervald F
A Top Contributor is someone who is knowledgeable in a particular category.
Best Answer - Chosen by Asker
Tin + nitric acid ----> tin(II) nitrate + hydrogen

followed by

Tin(II) nitrate -----> tin(II) oxide + nitrogen dioxide + oxygen

 

[philddreamer]

Eric, wether it's right or wrong, that's what I do. When I get a mix of old material that contains gold & solder, I run the material thru 50/50 nitric. The white gunk forms. After no more reaction, I let the solution settle overnite. I decant the solution, rinse the material with hot water & proceed to dissolve in HCl/Cl. Then proceed as usual.

Phil

 

[Palladium]

I think i would put it in something taller than wider and let settle for a day. Take a piece of hose and draw off as much solution as i could. Wash with water, let settle, decant, then put the residue in a pyroceram dish and evaporate slowly until dry. Then incentrate in a pyroceram dish. Pre wash with hcl to remove any tin, copper, or oxides and process with hcl/cl.

 

[ericrm]

Eric, wether it's right or wrong, that's what I do. When I get a mix of old material that contains gold & solder, I run the material thru 50/50 nitric. The white gunk forms. After no more reaction, I let the solution settle overnite. I decant the solution, rinse the material with hot water & proceed to dissolve in HCl/Cl. Then proceed as usual.

Phil

i have never tryed it myself that why i was very caucious in my answer. im realy happy to read that it work for you and that i will be able to use it myself. thank you

 

[Geo]

dealing with stannic acid is a pain no matter how you deal with it. if you incinerate it, it will lose an oxygen atom and turn back into elemental tin which then can be removed with hcl bath or you can dissolve the gold out of the material and spend time filtering solutions. in my opinion, if you dont remove the tin first, it will show up later.when you dissolve with hcl/Cl and let the solution sit undisturbed, does any white precipitate form? the tin will carry over and you may have to refine more than twice to clean it up.

 

[cnbarr]

Thank you all for the replies,

I would screen out what I could, I have a cheap plastic screen with a handle, I bought from the dollar store, the plastic holds up well to the acids, I put the screen into a plastic funnel and this funnels solution into a collection jar, after screening out the larger pieces, I would put a little wad of fiberglass insulation in the funnel (something like Laser Steve's Charmin plug, and filter out more of the finer stuff,

Butcher, I always use fiberglass to filter out the finer stuff (I started using fiberglass after reading one of your posts about 7 months ago), but this solution clogs it instantly. I like plastic screen idea, I'll give that a try.

It's hard to tell what you might have in solution. It could be a lot of things. There may be some polymers, and the white may be silver nitrate. It could also be other things.

The silver nitrate will precipitate when your solution cools down. I feel that the white precipitant is Silver Nitrate, all you really have to do is put heat to the solution so that the silver nitrate dissolves back into solution, then filter it right away when the solution is warm, before the silver nitrate precipitates again.

After you figure out what is going on and how you resolved it, I would be interested to know what the problem was, and how you fixed it.

Scott

Scott, I have tried heating it and it doesn't change anything. I don't feel it is silver of any form in the solution, the precipitant is a very very fine off white powder that settles quite slowly, i believe to be tin. I pulled out a couple dip samples just to be sure and tested one with salt and one with Hcl, there was no reaction in either.

Geo, Palladium, ericrm, Phil, I will try a combination of your responses and transfer everything into three large beakers and try to get everything to settle and filter out, and see what might work best. But, I may have to agree with Palladium and Geo that incineration may be the best route due do the amount of solids I have. The hard part is getting everything to settle and filter so I can proceed forward.

Thank you all again for the suggestions, I will report back later when I have some results.

Chris

 

[cnbarr]

dealing with stannic acid is a pain no matter how you deal with it. if you incinerate it, it will lose an oxygen atom and turn back into elemental tin which then can be removed with hcl bath or you can dissolve the gold out of the material and spend time filtering solutions. in my opinion, if you dont remove the tin first, it will show up later.when you dissolve with hcl/Cl and let the solution sit undisturbed, does any white precipitate form? the tin will carry over and you may have to refine more than twice to clean it up.

Sorry Geo, I missed you question in there. I haven't been able to decant the nitric and get to the foils and solids yet, so I have not made it that far just yet.

 

[glondor]

Hey Cnbarr. It's a small world. I am doing the exact same thing right now for a client from the forum. I had several large boards with press fit pins. They were wire wrapped on the back side so I had to pull them all by hand. About 12 thousand of them. 5 1/2 pounds. I used shop towel and electrical tape to mitigate the blisters. Made little finger jackets for the right places. Have nice hard callouses now.

Normally i would have soaked the pins in HCL to get rid of the tin but there seems to be a shortage of HCL in the local stores. It's swimming pool weather for sure and all I could find locally was 2 one liter bottles. Not enough. Sooooo I did what you did. I have done material with tin before so here is what I am doing.

I have a small stainless steel coffee filter that I set up as a sump in the pan. I tilt the pan a bit to drain the liquid to one end and draw from the sump with a little peristaltic pump i have. It is slow but it keeps the foils in the pan. I pump it to a paper coffee filter set up just to catch any fines for inspection, I will next wash the foils in the pan and let the lil pump do its thing again.

Next I will filter the foils thru the stainless coffee filter like so... Spoon the foils and dreck into the filter, not too much....and agitate the filter in a clean pan of water. The white dreck washes out and the foils remain.

Take the coffee filter and tip it sideways in a clean bucket of water, filling it up. Invert it and pull out quickly. The suction will pull out all the foils.

Reload the filter and ....

Run your solution (wash water) back through the coffee filter to catch any foils that may have got on the out side of the filter when you dumped to your "clean wash"

With practice you can get the foils fairly clean and it goes pretty fast. Incinerate and wash with HCL. Proceed as usual.

You can dry and incinerate the tin for hcl wash if you believe there is gold powder trapped in the tin. If you see dark bands or layers in the tin, It may be gold so proceed accordingly. Photos below for reference.

 

[cnbarr]

Hey glondor,
That looks like it does trick nicely, your ingenuity always amazes me, I'll print this one off for future reference. I already poured off the pan into separate 4000ml beakers to let them settle out, I do find it easier when you can see into a solution.

What still perplexes me is where the tin came from? The pins came from Ericcson backplane boards, some of mine were wire wrapped as well but I removed all the wires, there was not an ounce of solder on any of them, they were all pressed in. The only thing I can figure is the silver colored layer under the solder mask was a tin/nickle plating, which was my bad for trying to take a short cut and cut the sections of board away that housed the pins, when I knew I shouldn't have I knew I should have just pulled all the pins.

But that raises another question, where you ran all pins with no pieces of board, where did the tin come from in your batch? Unless the pins themselves have tin in them?

 

[philddreamer]

I too wonder where the tin sometimes comes from! :roll: These pins are pressed, too!
I bought a couple boards to run a test. there's over 500# available. The seller told me that there are 2 other persons that have bought the same material & both said they are recovering 1g of gold & 1g of Pd per pound of pins. Now, there's another, where is the Pd coming from? Are some pins also Pd plated? I let the solution settle overnite, will do a stannous test for Pd. Then I'll add fresh 50/50 in order to finish dissolution. I use nitric when running test to speed things.
Question, can Pd be de-plated in the sulphuric cell?

Thanks!
Phil

 

[goldsilverpro]

Yes, the original patent on the sulfuric stripper included Pd. Getting it out could be a problem though.

 

[maynman1751]

Phil, what is the silver colored material on the bottom half of the pins (second pic)? Are they possibly tin plated? It appears the holes they plug into are tin (solder) sockets.

 

[philddreamer]

Thank you, Chris!
That been the case, I hope I can drop the gold & save the Pd solution for the stock pot or, just set aside for further processing later.

May, That silver material is what I was told contains Pd. I don't know about tin, because they are not soldered, they are pressed into the sockets. I do know I have a white sediment at the botom of the solution that does resemble tin or Ag-Cl. As I continue the process today I hope to find out. I'll keep you all posted.

Thanks!
Phil

 

[qst42know]

glondor

Are you aware you can get heavy metal poisoning through your skin?

Many metal salts can cause permanent life altering health effects.

Please put some gloves on friend.

 

[Geo]

the tin comes from the pins. if the pins are springy, they could be bronze. bronze is copper and tin. if when you digest these pins in nitric acid or AP, you will have tin in your solution.

 

[glondor]

Thanks for the warning Quest. I just took the gloves off to take the pictures. Did a good wash up afterward and back to the gloves.

 

[cnbarr]

the tin comes from the pins. if the pins are springy, they could be bronze. bronze is copper and tin. if when you digest these pins in nitric acid or AP, you will have tin in your solution.

The pins are a bit springy, I didn't think they made pins from bronze, but that makes a lot more sense at this point. Thanks geo!

Hey glondor, I was looking at the pictures of the shape of some of the foils from your pins and looks like we're processing very similar if not the same type of pins? After reading Phil's comment on Pd, I tested mine as soon as I got home from work this evening and got a positive stannous and a positive DMG test for Pd. I guess just something to look into.

Just an update, I was able to decant and wash the solids once I transferred the solution to beakers (very slow to settle by the way, about 6-8hrs between each decant). I am know in the process of drying so I can proceed forward with incineration. If there was less tin I probably would have gone straight to AR or Hcl/Cl, but the tin is about 1 1/2in thick in the bottom of a 4000ml beaker, and I have fine particles of foils locked up in it. So I think incineration then an Hcl wash is going to be the most appropriate route at this point, If this sounds wrong or there is a better method for this please correct me in my intent to do so?

Thanks,
Chris