Help,Evaporation of excess nitric issues

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R

recycle69

Member
Joined
Nov 22, 2020
Messages
7
I had a bunch of gold filled jewelry which i tried to refine and recoop costs of investment.
I watched many videos,and read up on subject quite a bit,and I dissolved base metals using Hcl,and Nitric leaving gold foils behind to further process with aqua regia,and drop with Smb. But every time i tried dropping gold, I could not get it to drop. So I put my failed drop solution in to a bucket,thinking when i learned more,I would be able to recover it still. Well after many trial and errors,and failed attempts getting gold to drop, I started accumulating quite a bit of aqua regia and before I knew it i was near a whole 5 gallons of AR.
Meanwhile I read about the process in Hokes book like i was advised to do.
So with more jewelry still to process, I realized the large amount of AR i accumulated was getting to be too much,and after reading many times it is best to process all acids as you go, I decided I was not going to attempt to process anymore gold recovery until I dealt with my accumulated acids.
So i started the pain staking process of evaporating off excess nitric from the 5 gallons of AR i had, and have come to a point where I am unsure of what to do.
I finally got majority of all the AR and excess nitric evaporated after about 2wks or so of time and slow evaporation using 2 slow cookers,and a large evaporation type dish.
Looking back now, I am not sure if it was a mistake to continuously just keep adding acids to the pots as they lost volume from evap.But it is what I did.
When it was on the heat and evaporating, I noticed it seemed as if salts were trying to start to form.
I added some Hcl,and it bubbled and fizzed rapidly,and after some further evaporation I added Hcl again,and got same reaction,Upon doing this 2x, when i tried adding Hcl a 3rd time, it did not bubble or fizz.
But i did notice it seemed to start developing some type of salts or crystals and adding some more HCL had no effect on them.
So i turned off heat after it got to a syrup type consistency that looked similar to cream mixed with honey, a slightly brownish tan color with cream colored streaks,but none the less it was def a syrup type consistency,like warm honey or hot Caro syrup type deal.
These are some pics of it,and I am not sure how to go about processing this at this point in time.
I do not recall seeing in Hokes book anything about this type of stuff after evap of excess nitric from AR.
I did try taking a small sample,and added Hot boiling water,which the salts or crystals dissolved completely.
I tried adding Hcl,and they did not dissolve all the way, they dissolved some,but only partially.Even Hot Hcl,there was still white salts standing in bottom.
I tried to take many pics to show the different effects of hot water,hot Hcl,and cooled solution with brown top,and so on.
After this long tiresome process of evaporating all this Ar down to this point, I want to make sure whatever I do, I am not making anymore unnecessary waste products I dont need to,and also not making more work for myself and wastes.
A side Note, I did not add sulphuric acid to evap process,which am thinking would probable been good idea now, But I did not at the time.
I was careful watching for items that may been tin,since tin seems to melt fairly quickly at lower temps,and I normally can see it when heating item to redness if it is tin based.(not to say it cant be in the mix,but if there is then should be fairly minute amount)
I know there is quite bit gold in here somewhere. And It was all mainly just foils dissolved in all the AR solution I have evaporated down to this point.
tried to post the pics,please let me know if they dont show up.
Thank you in advance for help,and advice.

Edditted Post

Sorry for mix up, I know how vital it is to be accurate with chemicals and solutions using in any process,and I realized I made mistake in beginning of my post describing dissolving base metals with Hcl,and nitric.
But I used dilute nitric to dissolve all base metals from the gold filled jewelry.
Then Only foils went in to the AR solution,which I only used very small amounts of nitric with the Hcl to dissolve foils,but still had issues and could not get gold to drop using smb.
So with small experiments trying to get AR to drop using Smb, I still had no luck,and always tried adding more water here and there to the mix to see if gold would drop,but it never did,so it is how i ended up with so much AR to begin with and is what i evaporated down to what i have now.(excess of H2O and SMB)
After reading book of Hoke, i realized it is best to evap all down to syrup like consistency,which is what i did,and where I am at now.
But it seems it is saturated with a white and brown chlorides,which dissolve with hot boil water, but not with hot Hcl.(partially dissolves with hot Hcl)
Hokes book however does not mention the type of situation i have now, where once evap excess nitric, Now there is Alot of precipitate remaining in cooled dish,(temps were very cold last night) I am sure that there is Alot of Smb in the mix from trying to get gold to drop.
This AR solution has only had foils dissolved in it along with SMB,(lol I know there is alot of Au in the mix,however I cant say exactly how much i expect to recover,only that it should be a few decent Oz 3-4 or so )
My notes on weights of processed items have been mistakenly discarded by another,making it impossible for me to now know exact amounts of jewelry and foil weights processed in my solutions.(I still can't believe there gone but they are)
I have a friend who will help me get some pics up soon.
Thank you
 
No pictures came through.
Wow, that's a lot to take in. And you waited so long to ask for advice. The pictures would help but it sounds like the solution is over saturated.
Going back to the beginning. You leached gold filled scrap in AR until only foils remained? Did you test the solutions with stannous chloride to ensure that gold was in solution? Foils left from AR is most likely gold or even rhodium. Did you keep the solids or did you toss them out?
Quite a few mistakes. Gold filled scrap should be leached in a solution of tech grade nitric acid and distilled water at a ratio of 50/50. Save the HCl for later. There will be a certain amount of silver in each batch of gold filled scrap. Using only nitric acid and distilled water will allow you to recover the silver by cementing it out of solution onto copper metal. This leach is repeated until the nitric acid has no more reaction with the material. You should be left with karat gold foils and any stones from the jewelry.
Now is the time for HCl. Leaving the material in the beaker it was leached in, add HCl to 1/3 the volume of the beaker and heat. Residual nitric acid and left over nitrates will react as it warms. When this initial reaction stops, start adding nitric acid to the hot mixture in small increments and stir allowing the reaction to completely stop before adding more. Stop adding nitric when you can't see any more metal or there is no reaction when you add more nitric acid. Remove from heat and allow everything to cool completely. Filter the solution clear and observe the remaining solids. You are looking for metal of any kind. Any undissolved metal or black powder or dust or black solids is most likely undissolved metal. If you see any of this, add fresh HCl and repeat the leach. Once all of the metal has been dissolved and filtered, heat the solution and start adding sulfamic acid in small doses allowing the reaction to completely stop before adding more. This is removing any free left over nitric acid.
Once this step is complete, filter out any solids that may have precipitated and test the solution with stannous chloride. with a positive test, start adding your precipitant and drop the gold.

With what you have, add a gallon of fresh HCl and stir. Allow any salts to redissolve. Let it sit overnight. The next day, test the solution with stannous chloride. A negative will mean that either (1) the gold dropped and is mixed with any remaining solids or (2) there was never any gold in solution and all the gold is still with the solids the foils are in. If it is positive, decant to another container and filter the remaining solids adding that solution with the decanted solution. The left over solids will be chloride salts and will have silver chloride in the mix, so don't toss it out. Rinse and filter again. Add the clear rinse to the decanted solution. With all of the evaporation and additions of HCl, there should not be any left over nitric acid but that is not a definite possibility. Heat the solution in batches and add sulfamic acid in small increments like before until there's no reaction. Remove from heat and let everything cool and drop the gold.
 
Was finally able to get some pics up.
I guess the problem was my pic size was too large,and a friend showed me how to fix this.
I know the evap'd solution of AR is not in a see thru type container at moment, but am hoping with pics i posted showing a scoop of precipitate,that it may help to recognise what i am dealing with a little better.
I had a little bit of warm water earlier today,and it was maybe 40ml or less,and I poured it in to the evap'd solution to see what type reaction it would have on chlorides and precipitants out of curiosity,and figured worse case may be I would have to evaporate a little more if anything,But it did seem to melt or dissolve some of the chlorides in solution at the time.
I am not going any further with this solution until I get some advice on what should be done to process it and recover gold.
I have searched the forum and also have been reading book of Hoke, which is why and how I am to the point I am now with the evaporation of the AR down to the syrup type consistency,But can not find any info about the precipitates in container once container cools.
Only says to add 4x amount of water to solution,let stand for few days til absolutely clear,filter off and drop Au.
I had a question early on when first joined about my gold foils that dissolved in dilute nitric,and was advised to read Hoke's book. So I have read this book in Certain area's only. Not parts on refining cyanide solutions,or mirrors solutions,and I also have not yet read the Platinum metals part yet,but am starting on it tonight.
I have went back thru the book many times looking for everything pertaining to the AR process,and evap nitric.
But to no avail have i found anything about the precipitates present once AR is evap'd to syrup like consistency.
I was half tempted to add 4 parts of hot boil water to this solution,then let it settle for few days til clear and go from there, but do to the amount of AR i had to evap,and amount of precipitants I now have, I thought it be best to try seek advice before I just go and make another gallon of acidic solution,kind of like how I ended up with 5 gallons of AR to evap.
Here is a pic of precipitates after i added about 40ml of Hot water earlier today.IMG_20210114_181403.jpg
Any help and advice is greatly appreciated.
 
It doesn't seem to be too contaminated with copper. That's good. Keep adding water until all of the salt redissolves. Cement all metal out of solution on aluminum or zinc. This is done by adding a little of the sacrificial metal in at one time while stirring. This is a vigorous reaction and can boil over so make sure to have it in a container that has plenty of extra room. You can do it in batches. The process is complete when the solution loses all color except perhaps a very light green/blue color. This will be nickel and any iron and will not cement out of solution. All metals will come out of solution as a fine black powder. Allow all of the fine powder to settle completely. Decant carefully or siphon the solution off and transfer the solids to a smaller container. Continue until you have all of the recovered metal in one container. Remove as much solution as possible without removing any solids. Add HCl and your choice of oxidizer (preferably H2O2 or chlorine) and redissolve ALL of the solids in the smallest amount of solution possible. This will give you a more concentrated solution to work with without all of the salt. Test the solution with stannous chloride. With a positive for gold, add ferrous sulfate to precipitate the gold. After the gold has precipitated, you can test the solution again with stannous chloride for any PGM's. When using ferrous sulfate, you can test immediately after adding with stannous chloride without fear of a false positive.
 
Ok, that sounds a little more along the lines of what i was thinking to some extent.
And for now, I have taken around 300ml of the chlorides/salts,and added 4 x water to it.(hot Boil)
Which dissolved all solids/chlorides. and it turned to a brownish yellow color,I figured I would allow this to sit for another day or 2 to allow it to settle and clear,Just like Hoke Book says to do once evap'd excess nitric.
Although it did not describe having the precipitates in bottom once evaporated, it did say there would possibly be some chlorides in container when starting evaporation and to just leave them be while doing the process of evap.
So since I have tried small experiments earlier on,and tried Hot Hcl,and it only partially dissolved some of the solids, and The Hot Boil water dissolved all solids in the small experiments, I thought it might be best to just try a small batch,and continue to follow through with the Hoke instructions,seeing how the Boil water dissolved all matter.
I would really hate to have to cement out anything at this point, So I am hoping when the test solution settles and clears,that I can just precipitate with Coppera's,(ferrous sulphate).
However, I have never had any luck with my stannous chloride solution.
I purchased some stannous chloride dihydrate crystals,and tried making my stannous chloride solution,and even added some tin solder to the bottle after made,and it has never worked.
Not even on a AR solution,and dilute AR solution. And knowing the amount of gold foils in the amount of solution, It was a no brainer to me that the stannous was/is just bad.
I am not sure if you can get bad crystals or not,but i purchased from Lab and was a sealed container.
They were very clumpy and all stuck together like they were subject to moisture,but I was hoping it would not effect the integrity of crystals.
I tried adding a little more crystals to solution,and still had solder in bottom of bottle,but no change,the stannous just does not seem to be any good. I do not have any straight tin just 96/4 solder.
I know i really need some good stannous at this time, without it, I am more or less flying blind,and so only thing that keeps me going on the solution is knowing exactly what is in it.
Knowing it could not possibly cemented out anywhere else,it is all hiding in this evap'd batch of AR,Chlorides/salt solution.
Here is a pic from this morning after adding Hot boil water last nigh to some of the solids and liquids that were in the evap'd AR solution.IMG_20210115_103855.jpg 4 parts water added. color is clearing some, was brownish yellow last night..very bright light shining thru liquid for better pic
 
Your tin does not need to be pure to make stannous chloride, your solder will work. Others have used pewter.
There is a library thread on making stannous.
Good Luck
 
Lino1406 said:
Explain what in the photo? AR "with syrup consistency" should not contain solids
Click to expand...

The Photo is the evaporated AR solution that was originally evap'd to syrup/honey type consistency,which after first set of pics,showing the brown top layer of precipitate after syrup solution cooled overnight, Then the pic you are asking about was a pic of same solution with a small amount of hot boil water added to it,maybe like 30-40ml of hot water,which shows that the original brown top layer dissolved with addition of the hot H20.
 
If I understand the situation, you have still a white precipitate including SMB. This should include also AgCl, PbCl2, SnO2 and - the gold
 
Lino1406 said:
If I understand the situation, you have still a white precipitate including SMB. This should include also AgCl, PbCl2, SnO2 and - the gold
Click to expand...

Yes.Although I was trying to be careful to not process anything GF made from tin and lead
By being careful,I mean when heating to redness to burn off contaminants,The tin and lead would want to start melting fairly easily compared to other items with different base metals like brass,copper and silver.
So when i would run in to a item that wanted to start melting fairly easily,I simply did not put it in to the process for removing base metals with the dilute HN03. So by doing this I was trying to make sure tin and lead were very minimal.
However when i did do the evap process,looking back I did miss a important step,which was to add some sulphuric acid to the process to help take care of whatever lead/tin that may be in the mix,as well as help hasten process of to expell excess HN03.
And with the experiment I did, (following Hoke's instructions) by adding hot boil water to a test beeker of the mixture, the boil water did dissolve all matter.Just as described in book.
So test fluid is settling and will see if it clears,and what comes back or remains after another day or so.
As of yesterday,there was no signs of salts,or white chlorides of any type in bottom of vessel.
Just dark brown precipitate starting to form on bottom,and sides where test vessel is angled and tapered on sides,it is octagon shaped.
I am wondering since solution had so much SMB to begin with,hat perhaps once it was all evap'd down to syrup/honey matter,that perhaps some of the precipitates after cooled were from SMB,and once hot boil water was added and precipitates all dissolved,along with solution diluted with 4 x H20,That maybe the saturated SMB solution may not even need to be dropped once it sits and clears.
Wishful thinking,But I will test once its all settled and cleared with Ferrous Sulphate.
 
I would try to keep it simple: Evaporate the water, add some clean hcl (not a gallon!), then put all your gold safely back in solution by adding a small amount of nitric to create AR, add some sulfalmic (sp?) acid, then filter the pregnant AR solution. Then try to drop the gold again.

I may be wrong.

Save any filtered out materials too just in case.
 
Geo said:
When using ferrous sulfate, you can test immediately after adding with stannous chloride without fear of a false positive.
Click to expand...

What method would cause a false positive?

Sent from my iPhone using Tapatalk
 
thepickerexchange said:
What method would cause a false positive?

Sent from my iPhone using Tapatalk
Click to expand...
When using sodium metabisulfite, excess SO2 that is generated will react with the tin in the stannous chloride making a dark brown solid. This can be interpreted as a positive. Ferrous sulfate will not cause this effect.

EDIT : sulfate to sulfite
 
Geo said:
thepickerexchange said:
What method would cause a false positive?

Sent from my iPhone using Tapatalk
Click to expand...
When using sodium metabisulfite, excess SO2 that is generated will react with the tin in the stannous chloride making a dark brown solid. This can be interpreted as a positive. Ferrous sulfite will not cause this effect.
Click to expand...

Do you mean Ferrous sulfate, copperas?

Göran
 
Yes I do. Sorry. I was trying the talk to text on Cortana and I guess it "fixed" it for me. I'll edit and note. Thank you.
 
I have the same issue with the crystals forming at the bottom and I have evaporated out all the hydrochloric acid and the nitric acid and I will add hydrochloric acid and then evaporate again. before I did that my solution was a dark green to start out with and the Stanis chloride test would show positive but then it would disappear and I know that's because of excess nitric acid however the more I have done this process since ( evaporated the nygic acid down to the salts at the bottom being completely dry )then now the bluish color that was in the salts left over is starting to disappear and Stanis chloride test is no longer testing positive once I add more hydrochloric acid to the solution .the stannous chloride is actually turning the solution clear and I have also added SMB and it is just sitting at the bottom what should I do? I've seen numerous videos and I've never seen anybody completely evaporate everything is it possible to evaporate to the point to where it is no longer AR? I know for a fact that there is gold in there because the status chloride test has already tested positive once although it did disappear because of the excess Nitric. Also another question what are these crystals of salts? And is the gold in them and more importantly how do I get the gold out because hydrochloric acid alone is not working. Anyone who could help I would really appreciate it .thank you
 

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