# Nitric and pins



## Oz (May 10, 2008)

I had some pins that came off of early 90’s mother boards, these are the heavy squared pins that your ribbon cables plug into. I put 5 grams of these pins in 3/4 cup of 70% nitric cut in half with distilled water. It was about 50*F and started slow, I came back 2 hours later and found this…

I’m guessing that the reaction must have really heated up (the bottom of the container is warped from the heat) and being warm the acid could absorb more metals. After cooling off some of it came back out of solution, some of the nitric may have boiled off as well. What I’m wondering about is that the material you see in the picture is floating on top of the solution. I’m assuming it is copper based on the color but am not sure what metals are in the pins beyond the gold plating. Have any of you had this happen? I’m guessing I should just add more nitric to re-dissolve then process as usual?


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## Platdigger (May 10, 2008)

Are you on the beach?


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## lazersteve (May 10, 2008)

Oz,

If the pins are all dissolved then save your nitric, and move onto filtering the solution.

After filtering treat the foils/unknown with lots of water washes (3-4), then HCl to clean up the remaining base metals.

Process the washed foils as usual.

Steve


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## Oz (May 10, 2008)

Steve,

I was worried about loosing too much to the filter, and there are some small pieces on the bottom as well. Will HCl re-dissolve copper? To avoid loosing too much to the filter could I do what you are suggesting and just process the filtrate with the filter in AR? The stuff floating on top is so thin it is almost like an oil.

Platdigger,

I wish it was a beach! But alas it is just my back concrete patio with maple tree junk on it.


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## Platdigger (May 10, 2008)

:wink:


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## lazersteve (May 10, 2008)

Oz,

HCl will attack copper slowly. If the copper is very thin or powdered it will dissolve much quicker.

You can let everything settle and siphon off the bulk of the liquid and subsequent washes. Let everything settle well between each stage before moving to the next round of washing. The clean foils can then be dissolved in the same vessel they are currently in using HCl-Cl.

Steve


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## Oz (May 10, 2008)

Thanks Steve, I am away @ my girlfriends for the weekend but will try monday or tuesday and let you know how it worked out. I still find it odd to have what i am assuming to be copper floating on top.


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## Rag and Bone (May 10, 2008)

I've seen the same type of foils strip from low yield pins.


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## Harold_V (May 11, 2008)

Oz said:


> Thanks Steve, I am away @ my girlfriends for the weekend but will try monday or tuesday and let you know how it worked out. I still find it odd to have what i am assuming to be copper floating on top.



Had you undertaken a cleaning process, or incineration, you wouldn't be seeing anything floating, assuming you work with clean utensils and lab ware. 

Harold


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## Oz (May 11, 2008)

Well Harold what can I say, your right. I have seen you advise this time and again to others and read their results after taking your advise. I am just starting to develop procedures for different materials and there is no good reason not to incorporate incineration from the start. The one exception I see is that if I am sure there is nothing combustible other than oils that maybe washing in KOH would be appropriate then washing well in warm distilled water before processing. Thoughts?

Ps; You might also want to put under your tagline of “Buy Hoke’s Book!”
 “and remember, Incinerate! Incinerate! Incinerate!”


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## Platdigger (May 11, 2008)

and...."remove all base metals before dissolving gold"


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## Oz (May 11, 2008)

Platdigger,

Just in case I’m missing something??? That is nitric 35% in the pic I posted. i'm not sure i understand your comment.


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## Platdigger (May 11, 2008)

It wasn't meant for you Oz. I was just going along with your thinking of what could be added to Harolds..uh... tagline as you called it.

If I may tho, why only 5 grams? Doesn't seem like enough to bother with.

I mean if the stuff runs around 1 gram per pound......won't like it will be hard to deal with such a small amount of gold?
Randy


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## Anonymous (May 11, 2008)

I do not think that cooling would cause elemental copper to precipate out, it the solution was saturated at a higher temp then cooled copper nitrate should drop out, that may be your gold floating on the top.

Jim


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## Oz (May 11, 2008)

Platdigger,
Why only 5 grams? Well I have about 500 grams cut and ready to process and a kilo or so still in trash pc’s. I figured it might make sense to work a few small batches to see how it behaves before doing larger. As an example, this one getting so hot I now know that this is a reaction that should be done in glass only. The proportions are ok it seems so as to not boil over as well. Then you have Harold’s incineration that wasn’t done, lesson learned. Now picture it if I had done 500 grams at once in a bucket. The reaction would have probably been even hotter and of longer duration maybe even melting the bucket until the reaction was all over the floor. Now if the bucket didn’t melt I would still have some floating on top and some settled in the bottom and wondering how to handle gallons of this mix. After I learn what I can from this 5 grams, I will do another 5 grams using what I learned from the first. If I am happy with that reaction then I will start bumping up batch size.

James,
You could easily be right, I will have to see if there are any changes when I get back Monday as to how I proceed. I don’t yet know what I have on the bottom yet or what is floating on the top. I think Harold is right and there is enough oil there to float what I would want settled. I was unsure of the floating stuff but can say it looks like copper with a slight bronze hue.

I would still like to hear from Harold on the KOH since I am quite sure that oil is my only contaminate here as far as combustables.


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## Anonymous (May 11, 2008)

I have seen gold float on just water, if it is fine enough it gets trapped in/on? the surface tension. This happens when panning gold the really small stuff will float right out on you.


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## Harold_V (May 11, 2008)

Oz said:


> I would still like to hear from Harold on the KOH since I am quite sure that oil is my only contaminate here as far as combustables.



I have mixed emotions on the use of KOH. The hazards may well outweigh the benefits. 

Please let me explain. 

About 5 years after I started refining, I had occasion to have a drop of nitric acid get in my right eye, tech grade, right out of the container. I am fully responsible for what happened----having removed my safety glasses when I shouldn't have. I was but 20 steps from a sink, but the damage was done immediately---there was no stopping the acid from doing the damage it was destined to do. 

I was alone, so I drove myself to an ophthalmologist, who told me how fortunate I was to have been working with acid instead of a base (KOH, for example). Having already lost the surface of my eye, which immediately turned yellow, then sloughed off, he told me that the eye would repair itself and I'd be good as new. I wore an eye patch for about five days, and it turns out he was right. 

The good fortune, according to him, was that a base doesn't stop until it is consumed. He said that I had only 15 seconds to take the proper corrective action to avoid blindness in the eye, would it have been a base instead of nitric acid. The human body can't neutralize a base in the way it does an acid, according to what he told me. 

I think each individual will have to weigh what is most effective in their particular case. I found incineration was simple----and built my hood accordingly. I avoided using lye on a regular basis, although I'm sure it would be effective. 

I have a theory on your floating material. 

If you used a minimal amount of acid, barely enough to dissolve the base metals, I wonder if, possibly, traces of copper were precipitated on the nickel barrier that is commonly plated on copper before gold is applied. 

What little e scrap I processed through the years was always done with nitric acid-----so I'm not a stranger to its use in that given application. It wasn't uncommon for sparsely plated material to crumble to flakes, in keeping with those you created. That would be particularly true of wire wrap pins, which are extremely low in gold content. 

Difference was I always used heat, so the reaction time from start to finish might be only a few minutes, with the solids separated from the solution immediately. I didn't experience any of the copper colored floaters. 

A good test would be to decant the material and apply a few drops of fresh nitric. If you see more action, it's clear there was some cementing of copper. The gold should have a golden appearance unless it leans towards being colloidal, in which case it would be purple. 

Harold

Edit:

There is no need to use distilled water when processing gold plated pins. There is no silver present under ordinary circumstances. Tap water serves perfectly well. The use of distilled water is over rated.


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## Oz (May 12, 2008)

Well all, my solution remained unchanged through the weekend. I was more curious about what I had than anything else so I split the container into 2 new ones and tried to get the majority of floaters in one and the sinkers in the other. I then added a bit more 35% acid to each. The container with the floaters showed no change even after 4 hours. The container with the sinkers had some action for about 5 minutes then no more.
Conclusions…. What was floating on top was gold just very fine. 
There must have been oil or it would have settled.
I was very close on the amount of nitric needed since the settled particles reacted very little on addition of more Nitric.
The value of the gold is less that the cost of the nitric for these pins. 
Oh, and yes Harold. Incinerate, Incinerate, Incinerate.

Harold, thanks for the story on your experience with Nitric, I’m glad you were able to have a full recovery from your incident. I take safety with all of this very seriously, to the point I keep my goggles and gloves on the door knob to where I work. This way I can’t even open the door without removing them lest I am tempted to do something quick w/o at least minimal protection on. 

I agree with you as to the dangers with KOH as I used to make my own for precipitating potassium nitrate. Even this weaker stuff was bad news if you got it on your skin. 
As for distilled water….. I have a well and who knows what is in it as far as dissolved minerals. It is just as easy for me to use the distilled as I have a humid basement with a dehumidifier that gives me more than I need, and it is just one less concern as to contaminates in my reactions. The only thing it may add is a minute amount of Cu from the condensing coil which is no problem at all.  

Thanks again everyone!


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## eagle2 (May 14, 2008)

Wow, If you are going to use Nitric get some Pyrex beakers. 

The gold from those computer PCB`s square pins is extremely low grade and pieces will easily float, oil or not. Use some surfactant or just dish soap to make them settle.


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