Q on neutralising nitric acid in AR

[snoman701]

I know that sulfamic is preferred by others, but I now prefer to transfer the liquid (if it was a leach of computer chips) then use copper powder. A little excess copper simply begins the precipitation of the gold. I doubt it will be 99.9 though, so if that is your goal, a secondary refine will likely be necessary.


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[snoman701]

GSP's approach with incremental additions is great, especially when working with a known amount of gold, like lots of carat gold. Sometimes it is hard though to know how much gold you have, like when you have wet gold foils. Just take it easy and let the reactions take it's time.

I have a similar approach as GSP but with a twist. When I work with a known amount of gold I usually calculate 3-4 ml HCl per gram of gold and 0.75 ml nitric acid. I start with all HCl and up to 2/3 of the nitric acid if I'm working with solid pieces. For foils or fine powder I carefully add the nitric in small additions to avoid a boilover.
When the initial 2/3 of the nitric acid has been added and the reaction dies down it is usually just small pieces of undissolved gold left on the bottom of the beaker. I aim to dissolve around 90% of the gold in the first run.
Now I pour off the gold chloride into another beaker and add fresh HCl to the rest of the gold, the amount I use is depending on how much gold there is still undissolved.

This avoids the problem of having very weak aqua regia at the end and it is easy to see if I have a reaction or not before adding more nitric acid. All that gold chloride solution is diluting the aqua regia at the end and makes it easy to add too much nitric acid. With less volume and stronger AR it's easier to control the reaction and see if there still is nitric acid working.

Göran

I really like this method and have used it quite a few times.

The only thing I like more is using a gold button to consume the last bit of free nitric.


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[Shark]

I know that sulfamic is preferred by others, but I now prefer to transfer the liquid (if it was a leach of computer chips) then use copper powder. A little excess copper simply begins the precipitation of the gold. I doubt it will be 99.9 though, so if that is your goal, a secondary refine will likely be necessary.


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I am working on a lot now that I am using copper pipe to cement out the PM's. I ran into a problem and could not get the last bit to drop out of the solution. (it was a mix of many different types of materials) While it cemented out, it took on the shape of the copper pipe it was replacing. I really wish I had taken more pictures of it, as I have never had this same problem before. Even the cemented residues has a different look a to it than normal.

A neat thing about aqua regia, is that it takes about the same amount to dissolve a gram of many common metals we run up against. A gallon of AR will dissolve about 2 pounds of gold, 2 pounds of iron,2 pounds of nickel, or 2 pounds of copper. Easy to calculate, ball park wise, what is needed, and refining is a ball park art/science, in most cases. That's in my humble opinion, of course. You have you learn what you can get away with and what you can't get away with.

I never thought about it in that manner, but very useful to know those numbers.

 

[JanOlivier]

Thanks everyone for the great feed back. I realy like GSP's aprouch and going to try it as soon as my lab is up and running. Will then post of the progress

At the moment I'm still busy building my lab and depopulating circuit boards and learning on this forum

I work at a printing company and we have wat whe call the grave yard where all our copier machines go if thay beyond repair. The main boards are quite nice and some have up to 5 BGA chips and hundreds of ic chips on one main board. And lots of ics on the rest of the boards. Of 2 machine I have scraped about 2kg of different kinds of chips mostly look like old memory chips from Ram cards and just under 1kg of gold plated pins will post pic asoon as i can.

I'm still learning to find the best way of processing it all and before i get started. Like most of the chemicals are hard to find or so dam expensive like 55% nitric acid cost me ZAR500 for 2.5L So i dont just want to jump into thing before i waste