Unavoidable iron

[Alabama938]

So I have disassembled multiple Goldfilled watchbands, and have removed the tops on the vast majority. There are a few of the clasps and other connecting pieces that are gold plated, but I can’t remove them from the stainless steel strap. Needless to say even in this cleaned up pile of gold filled pieces, There is a fair amount of magnetic material.

I understand passivation is an issue when dissolving iron in nitric acid, how dilute does it need to be to avoid this? The last time I got some iron in a nitric boil there was a large amount of rust colored material that came out of solution… I assumed it was either iron oxide or copper cementing out on passivated iron. It really made for messy clean up but still got the job done. That run was also Goldfilled material, so I was just looking for pointers to improve.

So I have 430 g of cleaned watch bands and a few chains… Maybe 10% of the material is magnetic. Would it be a better idea to split it into two batches?

 

[nickvc]

Hot HCl will dissolve any steel even stainless but should you opt to try this make sure to wash well after and incinerate the material before going to the nitric.

 

[Alabama938]

Can I just do a hot acid w/ peroxide on the whole thing? Incineration step makes me feel like I’m going to lose some material.

 

[sayf]

Well, if i am in your place i would use a mixture of nitric sulfuric acid to dissolve the base metals as follows
Firstly dilute your sulfuric acid by adding 300 ml of concentrated sulfuric acid to 700 ml of distilled water so now you have 1000 ml of 30% diluted sulfuric acid,
add to that 100 ml of nitric acid (volume of nitric =1/10 of the diluted sulfuric volume) in two stages, firstly add 50 ml of nitric acid
Mix well and your solution is ready to be used
its very effective against both magnetic and non magnetic stuffs
now start adding your stuffs to the solution slowly piece by piece
any base metals should be eaten very quickly this way
But you need to becareful that such a reaction is exothermal (releases so much heat) and very violent even stainless steel cant carry such a reaction
so chose a big pyrex beaker for it to avoid any accidents and keep distilled water around, if you think that the reaction will get out of control just add some distilled water to calm it down
When the reaction cools down, slowly add the other 50 ml of nitric acid
when the reaction is done and all base metals are dissolved ,just add 1 litter of distilled water to the solution to precipitate any gold foils that have dissolved
(less than 1% of the gold will dissolve and all of it will precipitate again directly when you add the water so no worries )
Filter your foils wash them with distilled water and aqua regia them.... Eleminate nitric.... Precipitate with iron sulfate or smb or even zinc..

Good luck, work in well ventilated area or under a fume hood and please be safe

 

[kurtak]

Well, if i am in your place i would use a mixture of nitric sulfuric acid to dissolve the base metals

per the underlined - why in the world would you use sulfuric acid for dissolving base metals when you can use nitric for dissolving copper &/or copper alloys (like brass) - or HCl for dissolving iron &/or iron alloys - or even CuCl2 which although slow will dissolve both copper & iron

accidents with sulfuric can/will result in serious acid burns & are simply not worth taking the chance of getting burned when nitric &/or HCl will do the job

IMO only a fool would use sulfuric - when nitric or HCl will do the same job (dissolve base metals) --- sulfuric is a accident waiting to happen (IMO)

concerning gold on stainless steel (plating or gold filled) an alternative could/would be to go with the "reverse" AR process --- don't have time to explain that process right now - if interested will post about it

Kurt

 

[sayf]

Hi kurt thanks for your reply
If you read well the sulfuric acid here is not concentrated its only 30% like battery acid and not heated, with the mixture i mentioned you can get rid of base metals easily with one go and short time .

Danger exists is in every single step in this work even if you use nitruc or HCL or even vinegar
who wants to work in this field should take the risks and minimize them
so far i havnt used used concentrated hot sulfuric and i will not but you will need diluted sulfuric acid soon or later
Example : making iron sulfate
Another example urifying gold
Another example :nitric is forbidden in many countries so you can use diluted sulfuric acid yo do some jobs instead
am not arguing with you here, you guys are my teachers but am saying my thoughts
REGARDS

 

[Alabama938]

So I had taken the advice listed above and I did two hydrochloric acid boils… At least six hours each the solution got quite dark greenish yellow, I used 1600 mL of 20% HCl total. For the second one I added a small charge (10mL) of 30% peroxide to jumpstart everything, stannous test was negative.

There was some nasty brown grease like material that accumulated at the top of the fluid and trapped some of the gold foils that came off… I removed all of this with small pieces of paper towel and added to the batch to burn.

Currently I have everything drained and washed until the Rinse water has a neutral pH and it is drying for incineration. I don’t really have a ceramic dish large enough to accommodate the entire batch and filter papers, would an old cast-iron pan suffice?

 

[ssabovic]

hi ,
I m interested to know about reverse AR process ,
please if you can describe how it works,
I would like to know percentage of hcl/nitric, can sodium nitrate be used instead nitric (how much) ,
and whole process ,
thank you,
senad

 

[kurtak]

Don't have a lot of time to post today - but - here is a thread from back in 2015 about using the reverse AR method (there are a lot of other things discussed in the thread also so you have to kind of sort out the reverse AR process from the other things discussed)

Gold,Gold,and More Gold!!!!

The down side of the reverse AR process is - just as the name says - reverse AR - in other words - instead of using a lot of HCL & a little bit of nitric - you instead use a lot of nitric & VERY little HCl

Therefore - if you have trouble getting nitric &/or have to pay A LOT for your nitric it "may" (or not) be a good fit for you

What I can say is that if obtaining nitric is not a problem - the reverse AR process is the best way to "strip" gold "on" stainless steel (that is the best method/process other then cyanide if you can not get cyanide)

per the underlined - Edited to "can not" instead of "can"

Kurt

 

[kurtak]

Here is a post by 4metals about the reverse AR method

Anyone came up with a technique or process for watch bands ?

Kurt

 

[kurtak]

Danger exists is in every single step in this work even if you use nitruc or HCL or even vinegar

Yes - most everything we do in refining has an element of danger to it --- however - nitric - HCl (or vinegar) are not going to seriously burn you if you have an accident

However - on the other hand - an accident with sulfuric can/will result in VERY serious acid burns that can end up disfiguring you &/or blinding you --- for the rest of you life

Unless you have NO OTHER alternative I would NEVER use sulfuric for dissolving base metals when other acids will do the job --- its an accident waiting to happen

Again - IMO - unless you have ABSOLUTELY NO OTHER CHOICE using sulfuric is a BAD idea & therefore bad advice - unless you have absolutely no other choice :!:

Kurt

 

[kurtak]

but you will need diluted sulfuric acid soon or later

per the underlined - just not true :!: (at least not in larger amounts like liter(s) of it)

I spent 10 plus years refining for a living & in all those years the ONLY time a "had" to use sulfuric was to add "a few drops" of it to AR solutions to drop out any possible dissolved lead as lead sulfate

I don't even agree with the sulfuric stripping cell simply because there are so many safer ways to recover/refine gold

I would rather work with liter(s) of cyanide then work with liter(s) of sulfuric for stripping gold

So again - IMO - unless you have no other choice - working with sulfuric is a bad idea/advice

Kurt

 

[kurtak]

This is what can happen to you (almost instantly) when you have an accident with sulfuric & you get it on you

https://www.bing.com/images/search?q=pictures+of+sulfuric+acid+burns&qpvt=picyures+of+sulfuric+a

Nitric &/or HCl does not cause those kind of burns unless you leave on you for a LONG time

Kurt

 

[snoman701]

You aren't using sulfuric to strip, you are using it to hold the iron in solution at a higher pH.

Lou has posted an article on the forum somewhere called "The Iron Elephant", find it and read it.

I routinely do gold filled with a shot of sulfuric. It keeps the steel from passivating in the nitric, and keeps the iron from dropping out as ferric iron when the pH goes up. If you use HCl for the same, you end up dissolving gold.

I have never been successful with reverse AR on watch bands (the cheap stainless doesn't have the chromium content). It's not an easy process, and far, far more dangerous than using a little sulfuric. Recovering the gold is a pain in the butt without either solvent stripping or ion exchange. I have successfully used it on au brazed stainless quite a few times.

 

[Geo]

Why do people spend so much time pulling caps from watch bands? The base metal is mostly stainless steel. Roast the bands whole and leach them whole in nitric acid with a small sulfuric acid kicker to help with the high carbon springs. When all of the base metal is dissolved, decant to a clean beaker and drop the silver with HCl. The bands will be mostly untouched but the gold will be loose. Rinse well so that the metal can be handled safely. Now it is very easy to separate the heavy gold foils from the limp stainless steel bands. Limp because the springs are gone. It is not so hard to use a spray bottle to wash the loose gold from clean metal bands.

I'm sorry if I am letting out any trade secrets. I know many people rely on watch bands as part of their income and I'm sure they use this process as well. Not trying to step on toes, just trying to help people out.

 

[snoman701]

I'm sorry if I am letting out any trade secrets. I know many people rely on watch bands as part of their income and I'm sure they use this process as well. Not trying to step on toes, just trying to help people out.

i have trouble believing many people rely on watch bands as part of their income. i've had so many people surprised by the fact that i'm even willing to buy them. i think i brought home another pound of them today.

i will admit, i can rarely get them to wash away cleanly enough for my tastes. i just dissolve the stainless.

 

[cejohnsonsr1]

This must be a joke.

 

[Alabama938]

So I actually tried all of the above suggestions over the past month. The sulfuric wasn’t as dramatic as I thought it would be @30%sulfuric/10%nitric. I did about six bands, the first one left some of the marked stainless pieces behind, two of the stretchy ones became limp, it was a huge PITA to filter and clean up. The dilute nitric with a “small shot” sulfuric did as advertised. the solution was super volatile but was easier to filter in slightly. I used 25%nitric/2.5&5% sulfuric. They seemed about the same in volatility but really made a pretty solution.

I even tried AR (1:10) on a 1/2 fresh watch band, thinking it would dissolve the gold which would then cement out on the residual metal as the nitric ran out. This very nearly boiled over off heat, cold acids it expanded 8x initial volume and created this greenish black solution that when I washed sides of beaker fumed NO2, I only used 10mL! I’ve slowly diluted it a bit, boiling it has put gold in solution on stannous. Currently trying to decide how to recover that little mess. Can’t recommend against this enough.

I have since pulled all the caps on my remaining bands, and the recovery went smooth. C’est la vie