Solution Color Change during refinement

[Acidrain]

Something I haven't seen yet happened yesterday during 1st and second refinement. I'll go over the 1st and then 2nd and I'm hoping someone can help me understand what's happening.
Starting material was fully gold plated pins.
The plating is thick. In a previous test tube experiment, the pins sat in hot dilute 50/50 nitric for a LONG TIME without any reaction at all so in another experiment I clipped one in half a repeated procedure. That worked well so I scaled up to 229g, cutting each one in half. I disolved base metal (copper, possibly beryllium copper alloy) away with dilute nitric, 100ml lots. Each spent lot decanted into the stock pot, pins rinsed with water and repeat. When finished, I washed the foils well with water until wash water was clean.
I then placed the foils in a beaker and added 100ml hydrochloric acid 37% and heated on my coffee maker hotplate. Once hot, I started adding nitric acid with a pipette a few drops at a time until reaction stopped. This is where the first strange thing happened. The solution when from a greenish tint as the foils were dissolving, rapidly to black and then to the yellow/orange color that I expect! I added a couple drops of sulfuric acid and then added about 1/8 tsp sulfamic acid to be sure solution was denoxed. I then added urea to bring pH up to about 1.5 and took the solution off the hot plate. The solution was cooled with ice cubes, vaccuum filtered through #1 watman filter paper and gold dropped with ferrous sulphate. Gold powder hot water washed, hot HCL washed, then redisolved as before, same procedure. This time I dropped gold with SMB and this is where the second crazy color change happened. The solution was a beautiful yellow/orange color before SMB addition. I added SMB, gave it a gentle stir and instantly it changed to perfectly water clear! Then slowly the color changed to the brown that I expected which slowly settled to the bottom leaving water clear solution once again.
Can someone explain the color changes to me?

 

[Yggdrasil]

Something I haven't seen yet happened yesterday during 1st and second refinement. I'll go over the 1st and then 2nd and I'm hoping someone can help me understand what's happening.
Starting material was fully gold plated pins.View attachment 63555
The plating is thick. It previous test tube experiment, the pins sat in hot dilute 50/50 nitric for a LONG TIME without any reaction at all so in another experiment I clipped one in half a repeated procedure. That worked well so I scaled up to 229g, cutting each one in half. I disolved base metal (copper, possibly beryllium copper alloy) away with dilute nitric, 100ml lots. Each spent lot decanted into the stock pot, pins rinsed with water and repeat. When finished, I washed the foils well with water until wash water was clean.
I then placed the foils in a beaker and added 100ml hydrochloric acid 37% and heated on my coffee coffee maker hotplate. Once hot, I started adding nitric acid with a pipette a few drops at a time until reaction stopped. This is where the first strange thing happened. The solution when from a greenish tint as the foils were dissolving, rapidly to black and then to the yellow/orange color that I expect! I added a couple drops of sulfuric acid and then added about 1/8 tsp sulfamic acid to be sure solution was denoxed. I then added urea to bring pH up to about 1.5 and took the solution off the hot plate. The solution was cooled with ice cubes, vaccuum filtered through #1 watman filter paper and gold dropped with ferrous sulphate. Gold powder hot water washed, hot HCL washed, then redisolved as before, same procedure. This time I dropped gold with SMB and this is where the second crazy color change happened. The solution was a beautiful yellow/orange color before SMB addition. I added SMB, gave it a gentle stir and instantly it changed to perfectly water clear! Then slowly the color changed to the brown that I expected which slowly settled to the bottom leaving water clear solution once again.
Can someone explain the color changes to me?

The last color change was probably when the Gold Salt transformed to metal.
In the beginning the particles are too small to see, as they grow they become visible and forms the well known cinnamon color.

 

[Acidrain]

The last color change was probably when the Gold Salt transformed to metal.
In the beginning the particles are too small to see, as they grow they become visible and forms the well known cinnamon color.

That does make sense but I haven't seen it happen instantly like that yet. It was actually really neat to watch! I did to a stannous test and confirmed no gold left in solution but for a few minutes I was scratching my head wondering just where it had went! Non in solution and no visible precipitate. And then the power started falling. Super neat stuff

 

[4metals]

It is interesting hearing your descriptions and comparing it to what I have seen on a commercial scale of refining.

You painstakingly strip down e-scrap to yield a collection of pins. The pre processing you have done allows you to see the color changes which can be more subtle in production refining. In the long run you would never make money doing it the way you do it but the learning experience is priceless.

If you mix aqua regia and don't add anything to it it will turn a nice red orange color. If you add high purity gold to the acid it will stay a rich red color until you precipitate the gold and as you have seen and then turn clear. In mixed metal reactions, such as karat alloy, the green color of the acid is dominant. I have noticed that a karat digestion, which has a high percentage of gold, is still green but a vibrant green. Once the gold has been dropped, the solution is still green but a dull green. Once you see it enough you can tell when the precipitation is nearing the end. I was once told that the gold imparts a yellow color to the acid and once it drops out the lack of the golds yellow influence makes the solution the dull green.

Wait until you hit the world of dirty & multi-colored acids. Truly a horse of a different color! But it will help you appreciate the familiarization experiments you began with.

 

[Acidrain]

It is interesting hearing your descriptions and comparing it to what I have seen on a commercial scale of refining.

You painstakingly strip down e-scrap to yield a collection of pins. The pre processing you have done allows you to see the color changes which can be more subtle in production refining. In the long run you would never make money doing it the way you do it but the learning experience is priceless.

If you mix aqua regia and don't add anything to it it will turn a nice red orange color. If you add high purity gold to the acid it will stay a rich red color until you precipitate the gold and as you have seen and then turn clear. In mixed metal reactions, such as karat alloy, the green color of the acid is dominant. I have noticed that a karat digestion, which has a high percentage of gold, is still green but a vibrant green. Once the gold has been dropped, the solution is still green but a dull green. Once you see it enough you can tell when the precipitation is nearing the end. I was once told that the gold imparts a yellow color to the acid and once it drops out the lack of the golds yellow influence makes the solution the dull green.

Wait until you hit the world of dirty & multi-colored acids. Truly a horse of a different color! But it will help you appreciate the familiarization experiments you began with.

I want to try a different route with a small batch of the same pins. Instead of spending hours clipping them in half so the acid can work at the base metal and then using a lot of dilute nitric to remove it, I'd like to try completely dissolving the pins in AR and then cement the gold out with copper and then refine it. That seems like it would be much more cost/time effective.
What do you think?

 

[Acidrain]

It is interesting hearing your descriptions and comparing it to what I have seen on a commercial scale of refining.

You painstakingly strip down e-scrap to yield a collection of pins. The pre processing you have done allows you to see the color changes which can be more subtle in production refining. In the long run you would never make money doing it the way you do it but the learning experience is priceless.

If you mix aqua regia and don't add anything to it it will turn a nice red orange color. If you add high purity gold to the acid it will stay a rich red color until you precipitate the gold and as you have seen and then turn clear. In mixed metal reactions, such as karat alloy, the green color of the acid is dominant. I have noticed that a karat digestion, which has a high percentage of gold, is still green but a vibrant green. Once the gold has been dropped, the solution is still green but a dull green. Once you see it enough you can tell when the precipitation is nearing the end. I was once told that the gold imparts a yellow color to the acid and once it drops out the lack of the golds yellow influence makes the solution the dull green.

Wait until you hit the world of dirty & multi-colored acids. Truly a horse of a different color! But it will help you appreciate the familiarization experiments you began with.

Do you have suggestions on how I can change my processing to be more profitable? How would you go about it from a production standpoint?

 

[4metals]

Cementation will work but I would just do a first drop with whatever you prefer to precipitate with and filter it to re-dissolve. It's a time thing, difference between a customer waiting for a result and refining as a hobby.

Back in the day we would dissolve 1000 - 1200 ounce jewelry lots (melted and shotted first) in aqua regia, let them react overnight, and in the morning filter, precipitate, rinse, redissolve, filter, and drop a second time and hand off the lot to the melt shop before lunch.

 

[4metals]

Do you have suggestions on how I can change my processing to be more profitable? How would you go about it from a production standpoint?

This all depends on what type of scrap you are processing.

 

[Acidrain]

This all depends on what type of scrap you are processing.

Right now I'm working through about 17lbs of pogo pins and deutsch connectors. Copper, brass and bronze base metals. The only part that is bronze are the pogo bodies.
I think your previous reply answered my question though, you're right it's definitely a time thing. It took me a week to process that half lb working on it about an hour each weekday and then all weekend. These small batches I've been doing take a ton of patience waiting for acid to work and settling of the solution and if I hurry I'd lose a significant amount of finished product. I'm going to try as you said above

 

[4metals]

Stripping the gold off of anything electroplated is much more efficient. I do not know whether or not it would be possible for you to obtain cyanide but that would be my first choice. As a business, refiners can acquire cyanide as can many other industries, electroplaters rely heavily on cyanide as well.

17 pounds of pins could be completely stripped of their gold plating in an hour. The gold can be easily cemented overnight, and in the morning, the recovered (and well rinsed) powders can be digested and precipitated in a few hours.

 

[4metals]

Cyanide strip makes short work out of material like this

 

[Acidrain]

Cyanide is far outside my studies and completely different chemistry. Although a very attractive option, I am not set up for handling it. I am comfortable with acid/base chemistry and have much to learn still. I'd better stick to the path I have chosen already but I am going to study cyanide just for educational purposes. The brief bit of reading I just did on the topic was very mind expansive! It seems there is zero room for error with cyanide compared to marginal room for error with acids/bases with the difference being the finality of the outcome.

 

[4metals]

I just thought about this option. Another less used solution that will strip gold plating is iodine. Years back I used it to strip thick film gold from hybrid circuits. The gold was easily recovered with KOH.

 

[Acidrain]

I just thought about this option. Another less used solution that will strip gold plating is iodine. Years back I used it to strip thick film gold from hybrid circuits. The gold was easily recovered with KOH.

How ironic! I was actually just reading a post about iodine stripping and it sounds amazing!

https://goldrefiningforum.com/posts/2743/

Maybe you remember the post?
That's awesome that you've used it and verify it works. I'm going to study up on it and just may give it a try.

 

[4metals]

Yes it works and the iodine solutions can be regenerated and re-used. There was much talk about using iodine on ores but I have no experience with that. Ores can have widely varying chemistries so I would suggest caution.

However clean solutions of gold stripped with iodine produce a clean solution which is capable of re-use. And places like Carolina Biological Supply sell iodine, potassium iodide, and potassium hydroxide. All for reasonable prices. Carolina Biological Supply

 

[Acidrain]

Thank you 4metals!

 

[Acidrain]

Yes it works and the iodine solutions can be regenerated and re-used. There was much talk about using iodine on ores but I have no experience with that. Ores can have widely varying chemistries so I would suggest caution.

However clean solutions of gold stripped with iodine produce a clean solution which is capable of re-use. And places like Carolina Biological Supply sell iodine, potassium iodide, and potassium hydroxide. All for reasonable prices. Carolina Biological Supply

What a bummer. They will not ship Iodine to Oregon

 

[Martijn]

I was very enthusiastic like you and tried it once as a small test, and failed. it dissolved some gold, but i could only find info about dissolving the gold, and not getting it back out of solution, much like Shore chemicals, ECO goldex, or jinchan dressing agent.
It also took 'a lot' of H2O2 to regenerate, which is another off-limits chemical for private persons. It works with potassium iodide and iodine.
The waste treatment and health precautions are unclear to me with this process.

 

[minero74]

I hear some miners used Iodine with SSN
and the result is a very strong leaching solution for some types of Ores.

 

[anarxi]

Right now I'm working through about 17lbs of pogo pins and deutsch connectors. Copper, brass and bronze base metals. The only part that is bronze are the pogo bodies.
I think your previous reply answered my question though, you're right it's definitely a time thing. It took me a week to process that half lb working on it about an hour each weekday and then all weekend. These small batches I've been doing take a ton of patience waiting for acid to work and settling of the solution and if I hurry I'd lose a significant amount of finished product. I'm going to try as you said above

hello.
It seems to me that these pins are more practical to sell.
Considering that you know the real content, you can set a fair price for this scrap.