# Nitric 70% or AP



## Tauran (Oct 4, 2011)

hi guys and gals

i've been absorbing as much of this wonderful forum as i can and there is a question i still can't find the answer to.

i am dealing with about 3lbs of assorted plated pins from motherboards mostly from pci and DIMM slots, basically very low grade scrap.

my question is is it better to digest the pins in nitric acid to remove the base metals or am i better off using the AP method.

the cost of Nitric in australia is quite cheap (a 5 gallon bottle costs $65) so it's equally as economical as the Ap method.

i've had some success with nitric followed by AR however it's quite dangerous so i'm looking for something a little safer.

this noob would really appreciate some expertise on the matter.

matt


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## nickvc (Oct 4, 2011)

I'm no expert on e scrap but I think most members would suggest the AP method, it's advantages are that it is re usable and if done right will give you a good product for final refining. The other way to do pins is through the sulphuric cell which you will find on Lazersteves site, this again is a re usable method but has slightly more dangers as your using 95%+ sulphuric. Nitric will work but produces lots of hazardous fumes and will be considerably more expensive. 
I suggest you do plenty of studying here on the forum and read the forum handbooks which outlines many of the processes commonly used by the members, your scrap pile will only get bigger while you find which method suits your needs.


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## Tauran (Oct 4, 2011)

Thanks for the info.

My problem with using the AP method is that i'm not dealing with very large foils. Many of the pins are only plated at the tip so the foils are almost microscopic.

i've read most of Hoke's book and the majority of forum topics, however i can't find anyone who is dealing wth only partially plated pins

That aside my other question is how long would solid pins take to dissolve leaving just the foils. 

i'm not in any particular hurry just curious.

thanks


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## Geo (Oct 4, 2011)

you should be able to reclaim the gold at any size unless you throw it away. AP if done right will digest all the base metal and then you collect the solids that settle out in the bottom of your container. filter all liquid and collect all powders. the main reason i dont like using nitric acid to digest pins is you cant really eliminate all of the solder and tin in nitric acid creates some really nasty stuff called metastannic acid. its a jellie gooey substance that is not water soluble and isnt acid soluble either. it traps your gold and the only way to get rid of it is to incinerate it. if the material is clean and solder free nitric acid is much faster and will reduce the digestion time by days. if you need it in a hurry then nitric acid is a must. but if you have time AP is much better and much safer.


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## johnny309 (Oct 4, 2011)

AP

Pro: can be reused many times over,solder is not a problem(Just wash the filtered precipitates with warm water to eliminate the lead chloride),cheaper,not dangerous,small amount of wastes,works on Kovar alloys,and iron.

Cons: slow process,need of H202 or air bubbling,low recovery of Ag(making AgCl)

NITRIC

Pro: faster,recovery of silver from the raw material,adding H202 would reduce the amount of nitric and the fumes.

Cons: toxic fumes,problems with solder and kovar alloy,great volumes of waste byproduct.

In your case I'll go with with AP process...and save my nitric for silver(and silver cell)... :idea:


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## Tauran (Oct 4, 2011)

thanks guys

that answered my question. ive already got a small test batch of AP running so it'll give me an idea of duration. looks lke my next batch will be for realz.


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## Tauran (Oct 6, 2011)

Update:

The test batch of ap has been sitting for 2 days now. i increased the ammount of h2o2 and HCl (to steve's ratio) making a total volume of 1.8 liters. i figured that i will re use the same batch for incrementaly larger ammounts so the volume makes sense. 

i've just set up a fishtank pump to bubble air through the liquid and now it has gone a light brown and is a little cloudy. 

i think that the cloudyness is gold precipitate caused by copper saturation because when i leave the beaker untouched for a while it settles and goes clear again.

some of my pins are slowly turning a salmon colour the rest appear to be dissolving.

comments and/or critisism would be appreciated. 

p.s i can post pics if needed


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## moose7802 (Sep 15, 2013)

I have about a pound of assorted different types of pins, connectors, and other gold plated items from computers. My question is simply this, can I use copper II to boil my pins in or should I just use fresh hcl? I ask this question because I dont want to create a mess with the copper cementing itself back out onto my pins.


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## Pantherlikher (Sep 15, 2013)

Goto LazerSteve's website and use the search for AP...step by step how tos which if you read through, alot of posts there will give you everything you need to do it right.

AP can be used for a long, long time. I hit saturation and removed half the volume and just added more HCL. Now I barely get any brown powder from gold dissolving and then dropping.
You'll know when you hit saturation when you get the nice aqua green goo. Copper Cloride(I). Look under AP problems and you'll find lots of information on it.

B.S.


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## moose7802 (Sep 15, 2013)

Ok thank you. This AP is a nice green color but no sludge I have only processed 1lb of fingers through it and theres about 2,000ml. I think I should be good for a little while yet seeing as I dont do a whole lot of processing nor do I have tons of material.


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## butcher (Sep 16, 2013)

While I was typing with my one finger, Pantherlikher, beat me to the answer, it took me so long to type this I will post it anyway.

Copper would not cement back out onto the pins.

Read up on the document of this leach to get a good understanding of how it works (Laser Steve has a copy of the document on his website).

Cementing, is a reduction / oxidation process, a chemical replacement reaction, where we use a metal lower in the reactivity series to replace a metal in solution. 
Oxidation is:
Gain of oxygen
Loss of hydrogen 
Loss of electrons

Reduction is:
Loss of oxygen
Gain of hydrogen
Gain of electrons

There is no oxidation without reduction, for something to be oxidized something else has to be reduced, and like-wise we cannot reduce something without the oxidation of something else.
so we cannot reduce copper ions in solution back to metal unless something else is oxidized in the reaction.

When we dissolve a metal into solution we are making metal ions (or metal salts dissolved in solution).

Metal + acid = salt of that metal and acid
HCl alone will not dissolve copper, but it will attack copper oxide, so by adding air, or oxygen, in our case H2O2 to the acidic solution we can oxidize the copper to a copper oxide that the acid can attack.
copper is oxidized, H2O2 is reduced. 
Cu + H2O2 --> CuO + H2O + 1/2 O2
(oops)
oxidized copper and acid forms copper II Chloride and water (copper ions in solution)
CuO + 2HCl --> CuCl2 + H2O

overall reaction
2HCl + Cu + H2O2 --> CuCl2 + 2H2O

The above reaction put copper into solution as copper II Chloride.

Adding elemental copper metal to this CuCl2 solution will dissolve more copper (oxidize more copper into solution as the CuCl2 is reduced to Copper I Chloride (CuCl). Here the elemental copper gives up electrons and copper II chloride gains electrons.

CuCl2 + Cu --> 2CuCl

We see above adding copper metal to the CuCl2 solution will not reduce the copper from solution back into copper metal. But adding the copper metal will reduce the copper II chloride (green solution) to copper I chloride (brown solution with a precipitant of white copper I chloride powders).

Adding copper metal to copper I chloride will produce no reaction, we cannot oxidize the copper metal, and cannot reduce the copper I chloride in the reaction.

But we can regenerate the copper I chloride solution by adding HCl.
CuCl + HCl --> CuCl2 + H
putting the white powder of copper I chloride back into solution ready to dissolve more copper.

So we see here the copper ions from solution will not plate back out of the solution onto our copper pins, although we can form a copper I chloride.

To be able reduce the copper ions in solution back to copper metal we would need some other electro-chemical reaction, for example a metal lower in the reactivity series of metals.

Do a study on the reactivity series of metals this study is very helpful in recovery and refining of metals.

Here we can use elemental Iron (or another metal higher in the reactivity series than copper to give the copper ions back its missing electrons, to reduce the copper from solution (cement copper from solution), back into copper metal, here the copper is reduced to metal, as the iron is oxidized (dissolved into solution as metal ions), with iron giving up it electrons to the copper, copper gaining these electrons goes from being a copper ion missing electrons to copper metal with all of the electrons in the atoms, these copper atoms join together to form copper metal powder falling to the bottom of the vessel, while some of the copper atoms will plate out onto the undissolved iron until it is completely consumed in the reaction. Now we are back to our elemental copper with all of its electrons in its atoms, and Iron ions in solution missing electrons in its atoms.
We could also reduce iron from solution with a metal higher in the reactivity series than iron...

CuCl2 + Fe --> FeCl2 + Cu

(Reactions simplified for discussion).

Heating the solution can help it react a little faster, but you do not want to heat it too much if you do heat it too much you just waste the oxygen and acid needed in solution.
The reaction is slow cold, and faster if warmed.
Too much heat drives off the needed oxygen, gases in solutions are driven out with heat, while cold solutions retain gases much better.
Heating can concentrate solutions, once the free acid is concentrated to its azeotrope you will drive off your free acid as HCl gas changing the hydrochloric acid into hydrogen chloride gas, wasting your acids.

Keep studying, read the document on Steve's web site and study the reactivity series of metals, keep reading the forum, all of this will become more clear and you will gain a better understanding the more you study.


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## moose7802 (Sep 16, 2013)

Wow thank you for the great explanation it means a lot to me that you took all that time to type up this explanation!! I know I have a lot to learn but since I started this little venture I haven't stopped reading. There is soooo much to learn and understand it's almost a little overwhelming at times. I really do enjoy this a lot so reading and studying doesn't seem as bad as it did when I was in college or high school :roll: Thanks again guys for all the great info, you have definitely made it a lot easier to figure out and try to understand how each process works.


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## bswartzwelder (Sep 16, 2013)

Butcher,

I'm missing something in your explanation. You state:

Cu + H2O2 --> CuO + H2O + 1/2 O2

I can see where the Cu + 1 of the O combine to form CuO. That leaves H2) from the left side to be transposed to the right side. Again, no problems. But, where does the 1/2 O2 come from?


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## butcher (Sep 17, 2013)

bswartzwelder,

Oxygen is a gas of two oxygen molecules O2.
They actually like to travel in pairs

In my attempt to balance the equation, I messed up counting them darn little O molecules, I guess them things were just running around in solution busy oxidizing copper, that I lost count of them on the left side of the arrow, once I did I had to do something with it on the right side. :lol:


We sure do not want to leave them little O molecules out there all by themselves, they get kind lonely, always wanting to be with the other.

I will highlight that little oxygen molecule in red above to note it was a figment of my imagination.

Very good job, in catching my goof.

Thanks


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## bswartzwelder (Sep 17, 2013)

Butcher,

It wasn't as much catching you goof as it was just wondering about the little O's running around. I was thinking there might have been some O's added from the atmosphere which just jumped right out of thin air and into the mix. It's happened before. From your posts, I can see just how particular you are when it comes to getting things right. I am also very appreciative of all the work you put into the board. WE ALL BENEFIT from your explanations. Thank you for clearing that up. I'll be able to sleep tonight.

Bert


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## butcher (Sep 18, 2013)

Bert, 
I will make many more mistakes, it just seems to be part of my nature,.
For you to notice the mistake in the formula, it shows that you are reading and studying and that you have learned enough to recognize the mistake.
When you point them out to me it can help me to see where I may do better.
We all benefit.
I need to be able to sleep at night or I will be making many more mistakes for you to find.


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