Gold plated pins in aqua regia

[haveagojoe]

Gentlemen please, how is this pissing contest helping the OP get the gold off his pins? Regardless of the quantity of Gold?

I am just defending myself against a false accusation. I'm not interested in a pissing contest. I am merely proposing that empirically derived yield estimates are more reliable than those based on assumptions.

 

[4metals]

I am just defending myself against a false accusation. I'm not interested in a pissing contest. I am merely proposing that empirically derived yield estimates are more reliable than those based on assumptions.

Understood. Point taken and subject closed.

Now how do you think the OP should process his pins?

 

[haveagojoe]

Understood. Point taken and subject closed.

Now how do you think the OP should process his pins?

Personally I would try with a Sulfuric cell, it would seem most appropriate for this volume although of course in small batches not all at once. I agree with you that after the recovery stage it's easier and less problematic to combine the gold recovered from small batches for further refining all at once. That would basically happen by default in a Sulfuric cell.

 

[Yggdrasil]

Personally I would try with a Sulfuric cell, it would seem most appropriate for this volume although of course in small batches not all at once. I agree with you that after the recovery stage it's easier and less problematic to combine the gold recovered from small batches for further refining all at once.

It will take most of the Gold, but it will not touch the Gold inside the hollows of the pins.

Some kind of selective leaching would be best but most of them are out of scope for most of us.
Next it the Copper content is high enough one could smelt them and put it in a Copper cell.
Probably out of scope for the OP as well.

The easiest is the Cuprous Chloride etch aka AP but it takes time.
So if the OP is not in a hurry I would go for that.
Maybe heated to 40-50 C for speed.

 

[haveagojoe]

It will take most of the Gold, but it will not touch the Gold inside the hollows of the pins.

Some kind of selective leaching would be best but most of them are out of scope for most of us.

True.

I would suggest Sodium thiosulfate leaching but there isn't really enough information available for a beginner and I don't have any experience of it myself. But it seems like the chemicals needed are readily available.

You're probably right that a Copper Chloride etch is most practical, and also relatively low hazard. The nearest alternative of dissolving base metals with Nitric doesn't seem economical for this scale.

 

[4metals]

Let me give my perspective, from the world of commercial refining and drums of affordable Nitric acid.

The OP processed one pound of pins in 500 ml of 4:1 aqua regia. The result, no gold in solution (tested with stannous chloride). The solution saturated with copper and dropped some brownish mystery mud on the bottom of the beaker and left some undissolved pin bodies in the beaker. I would pick out the contacts that are on the bottom and rinse them into the beaker with the mystery mud. Add some rinse water and swirl the mystery mud and let it settle.

Next decant the liquid and cover the mystery mud with Hydrochloric Acid and with a dropper add nitric acid. It should begin to react and blow red. When it slows, if there is still mystery mud on the bottom, add more drops of nitric until the mystery mud dissolves. Careful nitric additions have assured that any remaining free nitric should be minimal. Now place a drop of the acid on your filter paper and test with stannous. If the mystery mud was gold you will have a purple stain, hopefully a dark purple stain. Now put this gold containing acid aside and tackle the 75 pounds.

The OP has learned that 1/2 liter of aqua regia dissolved almost an entire pound of pins, most of which was copper.

I would fashion a basket out of a small plastic bucket with tiny drainage holes to put a few pounds of pins into and mix up enough aqua regia to have a larger pail with aqua regia deep enough to cover the pins. Immerse the pin basket and agitate it in the aqua regia and it will immediately react blowing a red cloud (need I say in a hood or upwind from your body) Do not leave this in long, remove it and shake the basket to see if the gold has stripped, if it has shake as much acid off as you can. The reaction in the bucket, without metal will quiet down quickly. Put the pin basket in a bucket of rinse water and rinse it, drain it and refill it with more pins.

Repeat this until the immersion in the acid no longer strips the gold. At this point you can take some already stripped pins and put them in a basket and back into the now exhausted aqua regia. Over night the copper will dissolve and the gold will be out of solution. (Check the liquid with stannous chloride) Repeat as necessary to process all of the pins.

Now decant all of the spent aqua regia. You will have used a lot less aqua regia than expected because you are not dissolving the pins completely. Save the insolubles which at this point we know are gold, add the small amount of aqua regia from the original test, and add Hydrochloric Acid and nitric slowly with a dropper to digest all of the gold.

Now it's filter, and drop the Gold with metabisulfite normally. As an added step, toss some metabisulfite into the rinse water to drop that gold as well and add that to the re-refine lot.

This can be done in a few hours.

 

[4metals]

I think this thread has drawn out some useful information but unfortunately the title, "Does this look good so far?" may prevent future members from finding it. As a result, I have taken the liberty of changing the name of @Josecuervohr's thread to Gold plated pins in aqua regia. Maybe with the new name more folks can benefit.

I hope the OP comes back and posts some results when he is done, including which method he used.

Speaking of methods, we are still open for more!

 

[Shark]

How much experience does @Josecuervohr have?

This could have a large impact on the method selected. Not knowing the answer to this leads me to think 4metals has made the right diagnosis and answer to the OP's question. As well, yggdrasil has given a simple solution. Throwing out more advanced methods without knowing how well one (such as the OP) knows the chemistry behind this can more often create more issues than it fixes. With 75 pounds of mixed pins, I would use a sulfuric cell, but this may not be much help to newer members just starting out. @orvi has quite a bit of back ground in using AR in non standard ways, maybe he could add some to the information with the AR/pins questions.

 

[Yggdrasil]

How much experience does @Josecuervohr have?

This could have a large impact on the method selected. Not knowing the answer to this leads me to think 4metals has made the right diagnosis and answer to the OP's question. As well, yggdrasil has given a simple solution. Throwing out more advanced methods without knowing how well one (such as the OP) knows the chemistry behind this can more often create more issues than it fixes. With 75 pounds of mixed pins, I would use a sulfuric cell, but this may not be much help to newer members just starting out. @orvi has quite a bit of back ground in using AR in non standard ways, maybe he could add some to the information with the AR/pins questions.

That was the reason for my suggestion of using AP.
It is slow but probably the easiest and cheapest method we have.
And you do not need to babysit it.