Excess HCL in aqua regia

[nizi72]

Respected Members,

I need you guidance on below matter.
I put finger strip (LCD MONITORS/LED SCREEN) in Nitric Acid (80%) and Water (20%).
I boiled the solution alongwith finger strips.
filtered the Solution (Nitric Acid + Water).
Covered foils and alongwith bit plastic with HCL..... approx. 140ml
I added little bit nitirc acid 10 ml to make aqua regia.
heat aqua regia for speedy process.
Stannous test is positive
denox with urea.
add SMB in water and mix with AQUA REGIA.
GOLD was not precipitated till next 10 hrs.
please help here.... what should I do next to recover gold.

 

[Geo]

Excess HCl will not cause the issue you have. Excess nitric acid will. You can not rinse acid completely from such material. It most likely had enough nitric acid left over from the leach that you really did not need to add more.

Heat the solution to near 200°F for an hour and then remove from heat and allow it to cool completely. Test the solution with stannous chloride. If it is positive for gold, remove excess nitric acid and try the drop again.

How much gold were you expecting? How much precipitated out eventually? Is it possible that all of the gold present precipitated out?

 

[butcher]

I suspect free nitric acid in solution along with base metal nitrate salts and now a mix of urea nitrate salts in solution.

Urea will not destroy nitric acid in solution, urea will not remove nitrate salts that with HCl acid reform aqua regia, urea and nitric acid make urea nitrate...

Try using sulfamic acid and ferrous sulfate, both will work to remove free nitric acid from solution, and will not make a nitrate salt to deal with...

 

[nizi72]

Excess HCl will not cause the issue you have. Excess nitric acid will. You can not rinse acid completely from such material. It most likely had enough nitric acid left over from the leach that you really did not need to add more.

Heat the solution to near 200°F for an hour and then remove from heat and allow it to cool completely. Test the solution with stannous chloride. If it is positive for gold, remove excess nitric acid and try the drop again.

How much gold were you expecting? How much precipitated out eventually? Is it possible that all of the gold present precipitated out?

Sir,

you are right that I did not rinse acid well, just add hcl and I feel in excess quantity.

Finger Strips are easily available and quite cheap here in PAKISTAN.

I was experimenting finger strips for recovery and need to know if I can have reasonable recovery to get some profit. Hence no idea of expecting gold.

Well very little brown particles precipitated now. AND aqua regia green color not change at this time.

NOW should I heat the solution or wait to get result??

 

[nizi72]

I suspect free nitric acid in solution along with base metal nitrate salts and now a mix of urea nitrate salts in solution.

Urea will not destroy nitric acid in solution, urea will not remove nitrate salts that with HCl acid reform aqua regia, urea and nitric acid make urea nitrate...

Try using sulfamic acid and ferrous sulfate, both will work to remove free nitric acid from solution, and will not make a nitrate salt to deal with...

SIR,

thanks for the assistance and valuable information.
at this time now very little brown/black particles precipitated.
I will check for chemicals in market if not precipitated after some time.

 

[nickvc]

Test your solution before you do anything, depending on how much gold was actually present you may well have recovered it all, when working with e scrap you need decent amounts to see any appreciable amount of gold so if you are only working with a small amount you will see very little return for the effort.
If your test shows positive then try one of the above suggestions to precipitate any remaining gold.

 

[g_axelsson]

Flat screen monitors generally doesn't have any gold fingers. Plating in these consumer devices are ENIG and doesn't contain a lot of gold.

How much material did you start with?

Göran

 

[nizi72]

Flat screen monitors generally doesn't have any gold fingers. Plating in these consumer devices are ENIG and doesn't contain a lot of gold.

How much material did you start with?

Göran

SIR,

I did experiment with 40 strips.
I had decided for experiment after seeing this video on youtube
https://www.youtube.com/watch?v=P38YaRmAaUI

While heating solutions (NITRIC + WATER), little foils came out on top of solution.
besides, after filter I had seen foils on filter.
Also got stannous test positive.

 

[nizi72]

Heat the solution to near 200°F for an hour and then remove from heat and allow it to cool completely. Test the solution with stannous chloride. If it is positive for gold, remove excess nitric acid and try the drop again.

SIR,

please advise, while heating solution, should I cover beaker or not??

if not cover the beaker, should I add water in solution if it is getting evaporate??

 

[nizi72]

Test your solution before you do anything, depending on how much gold was actually present you may well have recovered it all, when working with e scrap you need decent amounts to see any appreciable amount of gold so if you are only working with a small amount you will see very little return for the effort.
If your test shows positive then try one of the above suggestions to precipitate any remaining gold.

Noted Sir.

 

[rickbb]

The amount of gold from the plating on 40 "strips", PCB boards from LCD monitors will be tiny, almost microscopic.

As others have said, test your solution before doing anything else as you may have dropped all the gold there was.

As a test I processed a 5 gallon bucket full, (appx 250), of these boards and yielded less than a 1/2 gram of gold.

After depopulating them, soaking in HCL to remove tin solder and 2 weeks in AP solution with all my chems and labor I determined that it was a waste of my time.

Unless you can scale up to process tons of the material and have a very well tuned process I doubt you will turn a profit on just the plating. If you include all the chips and other components off the boards, (they do have a lot of MMLC's), then you may have a shot at a profit.

 

[nizi72]

The amount of gold from the plating on 40 "strips", PCB boards from LCD monitors will be tiny, almost microscopic.

As others have said, test your solution before doing anything else as you may have dropped all the gold there was.

As a test I processed a 5 gallon bucket full, (appx 250), of these boards and yielded less than a 1/2 gram of gold.

After depopulating them, soaking in HCL to remove tin solder and 2 weeks in AP solution with all my chems and labor I determined that it was a waste of my time.

Unless you can scale up to process tons of the material and have a very well tuned process I doubt you will turn a profit on just the plating. If you include all the chips and other components off the boards, (they do have a lot of MMLC's), then you may have a shot at a profit.

SIR,

I did test after 10 hrs, it was positive.
Once I feel some particle start precipitate, I did not heat or use sulfamic acid + ferrous sulfate (that was advised by respected members)…… BUT just wait and watch for any luck.
NOW Today I have checked and bit amount of brown powder dropped.
Color of aqua regia solution also changed from dark green to light green now.

YES, I have also start processing IC Chips.
for MLCCs I did not know, how to process them.....BUT I ll learn.

 

[Geo]

The need to heat and then allow to cool is to remove excess sulfur dioxide gas from the SMB you added. If you test the solution with stannous chloride after adding sodium metabisulfite, you will get a false positive reading. The SO2 will react with the tin in solution and create a brown to almost black result from the test. When you heat the solution it will drive out the SO2 and you will get a true test result.

After completing the heating and cooling process, test the solution again with stannous chloride. If you get a purple to black result after heating and cooling, it will be a true positive.

 

[jarlowski1]

I suspect you precipitated all the gold that was in solution. As other members have said the "finger strips" from lcds have very little gold on them. Just because you see gold on a circuit board doesn't mean it has any measurable amount on it. The newer boards like the lcd boards have an extremely thin layer of gold. My suggestion to you is to stop processing the stuff you have until you understand what you are doing. All the information you need to refine gold and other precious metals is on this website. Take some time to learn what to do and not to do so you can maximize your success while staying safe.

 

[nizi72]

The need to heat and then allow to cool is to remove excess sulfur dioxide gas from the SMB you added. If you test the solution with stannous chloride after adding sodium metabisulfite, you will get a false positive reading. The SO2 will react with the tin in solution and create a brown to almost black result from the test. When you heat the solution it will drive out the SO2 and you will get a true test result.

After completing the heating and cooling process, test the solution again with stannous chloride. If you get a purple to black result after heating and cooling, it will be a true positive.

SIR,
Thanks for detail guidance.

 

[nizi72]

I suspect you precipitated all the gold that was in solution. As other members have said the "finger strips" from lcds have very little gold on them. Just because you see gold on a circuit board doesn't mean it has any measurable amount on it. The newer boards like the lcd boards have an extremely thin layer of gold. My suggestion to you is to stop processing the stuff you have until you understand what you are doing. All the information you need to refine gold and other precious metals is on this website. Take some time to learn what to do and not to do so you can maximize your success while staying safe.

SIR,

After done my experiment. I agree with you and other respected members that on LCD finger strips has less gold recovery than the ic chips on LCD board has.....

finger strip powder settle down is lighter and less in weight than the IC chips of LCD boards.

my little experiment shows the result for me....