Can't get gold to dissolve

[jeneje]

Hey guys need some help here, I started with 47 grams of 10K and 14K jewelry. As per Hoke, i cut the jewerly up and twisted it, washed in NaOH, rinsed well. I then added a 4 to 1 mix of HNO3 to remove base metals,(as you can see in the first pic at the back is my HNO3 with the base metals and the silver that droped out). After filtering and washing, i add HCL and started to add HNO3 a little at a time untill the reaction started and i let the reaction go untill there were no more. Filtered and resume the same process. I have done this 3-time over the past 36hours and I still have this black material in the vessel. Last night i mixed up AR 4 to 1 and covered the material some reaction and then nothing.

This morning i though it may need to be warmed, (as you can see in pic 2) after 45 minutes i still have the material and there has been no reaction.

I have tested with stannious and it is positive for gold but nothing else. What have i done wrong here for the material not to disolve?

Thanks
Ken

 

[jeneje]

After thinking about this a little more can this be silver oxide left over from the AR?
Ken

 

[jeneje]

Thanks guys but i think i can figure it now, I done another test using a folded tissue paper and can see all the color changes that will tell me what i have.
Ken

 

[butcher]

I am not sure how well you lowered the karat of the gold in the beginning.

If after the nitric treatment you still had pieces of metal and not just powers you probably did not remove all of the silver, even if you had only powers left after using nitric to dissolve base metals and silver, if you did not use enough nitric acid or if the solution was too concentrate, you may have not removed all of the silver or left some silver nitrate crystals.

It sounds like silver chloride passivation may be preventing you from getting the gold to dissolve easily, heat and stirring, knocking the gold around with a glass stir rod to try and knock off silver chloride crust, maybe a little water to help with evaporation from High heat, might help to remove the silver chloride crust if this is actually your problem.

If too much silver and you still have chunks of metal that will not dissolve, you may just have to remove the metal clean it off and start over, inquartering with silver again.

This is of course that is if this is actually the problem here.

 

[jeneje]

I am not sure how well you lowered the karat of the gold in the beginning.

If after the nitric treatment you still had pieces of metal and not just powers you probably did not remove all of the silver, even if you had only powers left after using nitric to dissolve base metals and silver, if you did not use enough nitric acid or if the solution was too concentrate, you may have not removed all of the silver or left some silver nitrate crystals.

It sounds like silver chloride passivation may be preventing you from getting the gold to dissolve easily, heat and stirring, knocking the gold around with a glass stir rod to try and knock off silver chloride crust, maybe a little water to help with evaporation from High heat, might help to remove the silver chloride crust if this is actually your problem.

If too much silver and you still have chunks of metal that will not dissolve, you may just have to remove the metal clean it off and start over, inquartering with silver again.

This is of course that is if this is actually the problem here.

Butcher, thanks for your reply. First i would like to tell you, i have never done any inquartering, i would have to reasearch how to do that. Here is another pic of what i have been left with. I have rinsed the material several times and now filtering the solution that has tested positive for gold and will later drop it.

If i dry this material and use a mortice and pestal to grind it up do you think that would help any? This is beyond my experience. Any thoughs here is greatly appreciated.

Thanks
Ken

 

[butcher]

from what I can tell, it looks like it is forming powders or porous lumps, or getting close to be becoming powders, if it is chunks still there can be several options to try, mortar and pestle probably not much good here.
Keep in your solution heating and trying to knock loose crust with glass rod and constant stirring, it would be slow work, try crushing them they may be porous, if nitric could get down under gold
You might even try small addition of hydrogen peroxide with this method, the actions of the oxygen bubbles may help to loosen and break free the silver crust.

You could try dissolving the silver chloride (moving the material back and forth between solutions) I do not like this Idea not only because of the work involved cross contamination of solutions but also of the solution you have to dissolve silver chloride (ammonia compounds which could become dangerous), sodium thiosulfate, ammonium chloride brine syrup, sodium chloride brine syrup.

http://www.saltlakemetals.com/index.html
Aqueous ammonia 3% at 25deg C (77 deg F) 1000g solution could dissolve up to 14g AgCl.
Aqueous ammonia 15% at 25deg C (77 deg F) 1000g solution could dissolve up to 75g AgCl.
Ammonium chloride brine at 110 deg C (230 deg F 1000g of solution can dissolve 10g of AgCl
Sodium chloride brine 110 deg C (230 deg F) 100g solution can dissolve 5g AgCl
Sodium thiosulfate 1000grams of 20% conc. solution can dissolve 1000g AgCl
Again I do not advise this method above.

Then there is incinerating and going back to nitric (I do not see this working well if it did not the first time),

Or just bite the bullet:
Rinse material the un-dissolved gold (I would wash in dilute NaOH solution and rinse in hot water to help remove chloride salts),
dry and weigh, we could try to figure about how much gold would be left from approximate karat from our beginning material (grams 10K melted with grams of 14K) and in quarter the gold from this figure, melt sterling with our gold, stir with a carbon rod and pour cornflakes (pour molten gold into stainless steel pot full of cold water), and start back with the nitric acid to part the silver and base metals from our gold

While you try to decide how you want to tackle the problem some else may have a better Idea.

if this is pretty much already gold powders and you are having a hard time trying to get it to dissolve into solution there may be some other problem we could discuss.

 

[butcher]

How much HCl are you using? The nitric is it home made or store bought what strength?
What I am getting at is are you using enough solution, could there be some other problem, beside silver chloride?


Those look like powders in the picture you should not have trouble putting the gold in solution if these were gold powders.

 

[jeneje]

How much HCl are you using? The nitric is it home made or store bought what strength?
What I am getting at is are you using enough solution, could there be some other problem, beside silver chloride?


Those look like powders in the picture you should not have trouble putting the gold in solution if these were gold powders.

Butcher i am using 4parts 35%HCL to 1 part HNO3 tech grade 68%, i just added some AR a weaker solution, just trying to get something started. I can tell you after stirring with glass rod the color changes to the emerald green color, testing with stannous it is positive with a deep purple.

I have added a small amount of water to my AR as per hoke mixture, I dont know if that is the prolbem? The black,- is a powder, not chunks. Maybe i'm just missing something here but i think i covered all the basic's.

Ken

 

[butcher]

jeneje,

You said you had 47 grams of metal, 10k and 14k twisted up.
Was this melted together?
That would make a big difference in what we are looking at.
Too much silver and too high of a karat would be very difficult to get dissolved with silver passivateing the metal, and you could have been driving acids off in the heated solutions as fume instead of reacting with metals.
My answers earlier I was assuming this metal was melted together which would have brought the karat of the 14 K down just a little bit.

How much of each of these metals, are involved.
If these were not melted together, and if you had to heat them strongly or there was still a lot of silver and base metals after the nitric treatment, if you just used a little acid, you may have consumed most of the acid dissolving up base metals or vaporized much of the acids off in heat as gas,
Mostly I am just throwing Ideas around here to try and figure out what is going on.

For each gram of pure gold you will need about 3.8ml of 32% HCl and 0.96ml of 70% HNO3,
Base metals can consume these acids faster, as we know it takes more nitric to dissolve copper than silver, I assume it also takes more nitric to dissolve silver and copper that it will to oxidize gold, not considering if we cannot even dissolve the silver chloride, and are vaporizing off acids in the gases trying to.
Heat can drive these acids from the vessel as gases.
Try of calculate how much gold is involved Xgrams 10K and Xgrams 14K
Xgrams of 10K times 0.416 = Xgrams gold
Plus
Xgrams of 14k times 0.583= X grams gold
Add the Xgrams of gold up, (for base metal subtract this from the total 47g of metals)
Now total Xgrams of gold use 3.8ml HCL cover powder,
In small clean jar measure 0.95ml HNO3 for each gram of gold.
Heat HCl do not boil medium heat will be ok, (note here I am assuming you have removed base metal).
Add HNO3 in small proportions, a pipette works well here, wait for reaction to finish and add some more, each time waiting, slow down adding nitric toward the end as most of the metals are dissolved, here we want to concentrate solution, if it has not concentrated by now, in the concentration the nitric can consume much more gold, and we want to make sure we use up all of the nitric, my goal here would be somewhat an evaporation to concentrate and dissolve the last bit of gold using any nitric additions needed before evaporation was to almost syrup or concentrated gold chloride orange in color, although many time I may leave a tiny bit of gold unreacted to insure I have used up HNO3, and can get that bit of gold nest run.

 

[jeneje]

jeneje,

You said you had 47 grams of metal, 10k and 14k twisted up.
Was this melted together?
That would make a big difference in what we are looking at.
Too much silver and too high of a karat would be very difficult to get dissolved with silver passivateing the metal, and you could have been driving acids off in the heated solutions as fume instead of reacting with metals.
My answers earlier I was assuming this metal was melted together which would have brought the karat of the 14 K down just a little bit.

How much of each of these metals, are involved.
If these were not melted together, and if you had to heat them strongly or there was still a lot of silver and base metals after the nitric treatment, if you just used a little acid, you may have consumed most of the acid dissolving up base metals or vaporized much of the acids off in heat as gas,
Mostly I am just throwing Ideas around here to try and figure out what is going on.

For each gram of pure gold you will need about 3.8ml of 32% HCl and 0.96ml of 70% HNO3,
Base metals can consume these acids faster, as we know it takes more nitric to dissolve copper than silver, I assume it also takes more nitric to dissolve silver and copper that it will to oxidize gold, not considering if we cannot even dissolve the silver chloride, and are vaporizing off acids in the gases trying to.
Heat can drive these acids from the vessel as gases.
Try of calculate how much gold is involved Xgrams 10K and Xgrams 14K
Xgrams of 10K times 0.416 = Xgrams gold
Plus
Xgrams of 14k times 0.583= X grams gold
Add the Xgrams of gold up, (for base metal subtract this from the total 47g of metals)
Now total Xgrams of gold use 3.8ml HCL cover powder,
In small clean jar measure 0.95ml HNO3 for each gram of gold.
Heat HCl do not boil medium heat will be ok, (note here I am assuming you have removed base metal).
Add HNO3 in small proportions, a pipette works well here, wait for reaction to finish and add some more, each time waiting, slow down adding nitric toward the end as most of the metals are dissolved, here we want to concentrate solution, if it has not concentrated by now, in the concentration the nitric can consume much more gold, and we want to make sure we use up all of the nitric, my goal here would be somewhat an evaporation to concentrate and dissolve the last bit of gold using any nitric additions needed before evaporation was to almost syrup or concentrated gold chloride orange in color, although many time I may leave a tiny bit of gold unreacted to insure I have used up HNO3, and can get that bit of gold nest run.

Butcher i did not melt the gold, i put it in as 10 and 14K. There was 28grams 10K and 19.7 14K. I put 100ml water to 25ML HNO3 to remove the base metals to start. I done 3 mixs of this. This may be where i made my mistake.

All the base metal may not have been removed, if this was the case - using AR to dissolve the remainder would it not just be dirty gold that could be re-refined again to purefy in the next run.

I guess i have alot more to learn here,

Ken

 

[Geo]

Ken, the reaction stops due to a coating of oxidized metal that forms on the outside of the pieces. its called "pacification". thats why its recommended that Karat gold be inquarted. more than likely its a layer of silver chloride coating the pieces. decant the solution and rinse the material. incinerate and rinse again in water. continue with the dissolution. you may have to do this again before its all dissolved if theres still quite a bit of metal.

 

[butcher]

Ken, that is what makes this forum so great, we all have a lot to learn, and there is so much we can learn here, do not forget to read yourself a bedtime story, Hokes is great as long as you do not get so excited with the story, that you cannot get to sleep, and end up running out to the lab to try what you learned from her book.

I know you will figure this out, and you will learn a lot from it, just be sure to share wih us what you learn.

 

[nickvc]

I have and do dissolve karat gold directly in AR and successfully but it takes experience to get good quality gold. The problems i uusually encounter are caused by the lower karat golds and white golds which can contain high percentages of silver which, as the guys are pointing out, causes pasivation as the chlorides cover the gold and the AR can't dissolve it. 14k and above is usually fine due to low silver content and many cheap alloys in the lower karats can be easy to process. English yellow 9k has 12% silver and can be stubborn to dissolve whereas Italian 9k replaces the silver with copper and more zinc and dissolves readily. Inquartation is really the easiest way to achieve 100% success, basically this means reducing the gold content of the material to 25% by adding silver ideally or copper at a push, this allows the nitric to do its magic and remove the silver and the vast majority of the base metals making the dissolution in AR easy. If you have lumps of green/grey material left that's due to the silver chloride forming a skin over your metal and the cure is to remove them rinse off into your AR and then melt and add silver or copper to reduce the gold % to 25% and ideally pour as cornflakes, melt and pour into a deep metal container with a good volume of very cold water, and redissolve in nitric and then back into AR. You can try getting your AR very hot, use a watch glass, this might start the reaction but in honesty I'd just go for the inquart method, that will work.
For all members new to working with karat scrap I'd have to agree with Harold about inquartation and say its the way to go, it works every time if done correctly. The use of silver is advisable for several reasons, it uses less nitric, it will act as a collector of PGMs if they are present and you can get it all back very easily to reuse in your next batches by cementation.

 

[jeneje]

First, thanks guys for all the help, second, i will not make this mistake again, I have one more question, as Geo suggested i decanted the gold last night and put water in it. Should i do a washing like Harold suggests before starting the process of inquarting and can i use the silver i have already refined for this or does it have to be .925. I hope i have enought oxy-acetylnen to this. Also not knowing the type of gold (Karat) now figuring the silver to use is a guess. To reduce the gold to 25% 1 gram gold to 4parts silver.

Butcher you are right about the bedtime story, it 3AM before i could go to sleep and yeah my wife told me stay away from the lab - there is always another day. She just did not see my 20 grams of gold traped wanting free :lol: !

nickvc, think you for the detailed solution. after my coffee i will be headed for the lab. Oh, i can use a regular melting dish for this right.

Thanks
Ken

 

[FrugalRefiner]

To reduce the gold to 25% 1 gram gold to 4parts silver.

That would give you less than 20% gold. If the gold was pure, adding 3 parts silver to one part gold would give you 25%, but of course, you would never inquart pure gold. I would estimate your remaining gold pieces at somewhere around 12 kt which would be 50% gold and 50% other metals. Adding an equal weight of silver will get you to somewhere around 25% gold.

Dave

 

[nickvc]

Ken if you know the starting weights of the mix you should be able to determine which karat is left, I'd bet on the 10k but it's best to check but even if your a litte out it shouldn't cause too many problems.
Yes your melting dish is fine, use an old one not the one for your fine gold, if your cant pour cornflakes a thin bar will do it just takes longer.

 

[jeneje]

Thanks Guys, i am heading to the lab now to try this, if i dont run out of gas.
Ken

 

[Geo]

keep this in mind, you cant add too much silver to achieve the effect you want BUT you can add too little. if you over shoot and add more than is needed, it only translates to using more chemicals which means more waste but it wont effect the outcome of the process at all.

 

[jeneje]

keep this in mind, you cant add too much silver to achieve the effect you want BUT you can add too little. if you over shoot and add more than is needed, it only translates to using more chemicals which means more waste but it wont effect the outcome of the process at all.

Thanks Geo, I will keep you all posted as i do this.
Ken

 

[jeneje]

Well guys, i can chalk this one to a learning experience. After washing and drying it came to 8.3grams. I now have a mess :roll: i forgot to prepare my dish and it stuck. I now have something :lol: just exactly what, i don't know! So i am moving along, i will drop what i have and be happy that i got that.

Thanks for everybodys help, this is one lesson i will not forget. Although expensive just the same a lesson. I can look back and tell myself i did give it a good go and more experience is needed.

Thanks Guys,
Ken
:mrgreen: