AR Process for gold, iridium, silver and platinum filings

[autumnwillow]

I have about 10 ounces of jewelry desk filings containing mostly gold but with traces of platinum, silver, iridium, palladium, copper, nickel, etc.

Is there an updated way of processing this? Or am I fine with following the procedures written in Hoke's book?

According to Hoke's book, the process should be:
1.) Clean the filings, burn, grind, sieve, magnet.
2.) Dissolve in nitric.
3.) Wash with water, sulphuric acid, wash with water, dry.
4.) Dissolve in AR. (Beaker 1)
5.) Get undissolved filings -> grind -> add little AR to check for undissolved gold (Beaker 2) -> return liquid from (Beaker 2) to (Beaker1) using a filter paper, -> Put filings in (Beaker 1) and dissolve the silver chloride with ammonia -> wash filings -> melt. (Why is Hoke assuming that there are no other traces of metal in the leftover filings? Such as rhodium or iridium?).
6.) Remove excess nitric on (Beaker 1), add hydrochloric acid then evaporate to syrup.
7.) Dilute syrup with water.
8.) Drop platinum with ammonium chloride -> filter -> calcine -> melt.
9.) Drop gold with copperas -> filter -> wash -> melt.

I have also read that processing platinum in AR is bad for the lungs, but which part? The calcining part? Or the part that it dissolves in AR?

If you were to process such filings what is the most effective and economical way?
Assuming that I am not really interested in refining the PGM's but just setting them aside for recovery purposes and refining when the quantity is already significant.
Is there a precipitant that could drop gold alone without dragging down the other PGM's?

 

[MarcoP]

All I could suggest to not drag down PGMs is to dilute the solution before using copperas. It's known that PGMs requires concentrated solutions otherwise they won't drop.

Marco

 

[rucito]

4.) Dissolve in AR.-cold AR
6.) Remove excess nitric on step 4, add hydrochloric acid then boil to syrup.-dont boil-evaporate
8.) Drop platinum with ammonium chloride -> filter -> calcine -> melt.-there is not Pt in solution
10.) Test,test,test!

 

[FrugalRefiner]

3.) Wash with water, sulphuric acid, wash with water, dry.

I don't recall the recommendation to wash with sulfuric. Can you tell me where that was? Since your next step is dissolving in AR, I don't see any need to dry the filings.

5.) Get undissolved filings -> grind -> add little AR to check for undissolved gold -> return liquids to previous AR at step 4, -> dissolve silver chloride in ammonia -> wash filings -> melt. (Why is Hoke assuming that there are no other traces of metal in the leftover filings? Such as rhodium or iridium?).

You've blended a few steps together here, making it a little unclear. Since you may end up with a bit more silver chloride after the dilution in step 7, you can combine them and process them together. If you use ammonia, be sure to promptly reacidify the solution to avoid creating any explosive compounds.

Then you mention washing the filings and melting. If you're expecting rhodium or iridium here, you'll probably struggle to melt them. Better to just keep them as is and accumulate until you have enough to make the effort worth while.

6.) Remove excess nitric on step 4, add hydrochloric acid then [stt]boil[/stt] to syrup.

You want to evaporate to syrup, not boil.

7.) Dilute syrup with water.

Diluting and chilling will help to cause any remaining silver chloride to precipitate. A bit of sulfuric will precipitate any lead. Then filter till the solution is perfectly clear before precipitating your precious metals.

8.) Drop platinum with ammonium chloride -> filter -> calcine -> melt.
9.) Drop gold with copperas -> filter -> wash -> melt.

Whether you drop the platinum first or the gold first depends on your circumstances. Be very careful if you're dealing with platinum salts. They're very hazardous.

I have also read that processing platinum in AR is bad for the lungs, but which part? The calcining part? Or the part that it dissolves in AR?

Both.

It's always difficult to critique a simple summary like this. There are many little steps along the way, a couple of which I've mentioned.

Harold has written quite a bit about this type of material as it was his primary feedstock. Search for some of his posts. I think kadriver has posted on the subject as well.

Dave

 

[autumnwillow]

I edited my post to make it more clear.

The sulphuric wash was to remove any traces of tin paste.

Are there any other ways to remove the excess nitric? Something faster than evaporating?

Can somebody point me to this pdf file where it shows a list of possible precipitants? I have downloaded it from this forum before but I could no longer find it even when using the search function.

Is processing Platinum dangerous even under a fume hood?
Should I just use cold AR so the Pt will not dissolve?
Hoke mentions in her book that some Pt will still dissolve especially if alloyed with the right metal.

 

[Dpetes]

Go here and scroll down about 16 replies and Butcher has the download for it.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=21140

 

[kurtak]

The sulphuric wash was to remove any traces of tin paste.

This is one case where Hokes is a bit misleading as the sulfuric wash does not really work well at removing the stannic tin --- if you have stannic tin (tin paste) you are much better off doing an oxidation roast to turn the stannic tin to tin oxide & then treating it with HCl

Are there any other ways to remove the excess nitric? Something faster than evaporating?

Yes - forget the evaporation method - it works but is rather difficult to do it & get it right - your other options are ---------

1) Sulfamic acid --- do a search with sulfamic as your search word - there is lots of info on the forum about it

2) copper powder (or "fine" copper filings) add in "small" increments this will precipitate a small amount of gold as cemented gold - let that set on the hot plate on low heat for awhile - if there is still free nitric it will re-dissolve the gold - if the gold dissolves add another "pinch" of copper powder & again let it sit for awhile (on the hot plate) do this till the gold that is cemented out by the "pinch" of copper powder no longer re-dissolves --- you can then drop your gold with the precipitant of your choice

3) put a gold button in the AR on the hot plate with low heat - let it react with the gold button until you see "absolutely" no more reaction taking place on the gold button - at that point the free nitric is used up & you can drop your gold with the precipitant of your choice --- Note; be sure there is more then enough HCl in the AR so that the HCl does not load with gold before the nitric is used up --- in other words it does not hurt to have an "excess" of HCl other wise the HCl can become loaded with gold - the gold will stop dissolving (because there is no more HCl to hold more gold) thereby fooling you that the free nitric is also used up

Option (3) is be far my preferred method to be sure there is no free nitric in my AR --- this is a method that Harold has posted many times on the forum & that is where I learned it from when I first joined the forum - I have been using it ever since & always keep some small gold buttons on hand just for this purpose --- if by chance I don't have some gold buttons on hand (which is rare) I go with option (2)

They (options 1 & 2) are no brainer methods - there is no guessing of did I evaporate enough & add enough HCl to drive off the free nitric &/or did I add enough sulfamic &/or to much sulfamic --- with options 1 & 2 when gold no longer dissolves the free nitric is gone - "provided" there is also enough HCl to take up all the gold

If you are doing your process for a client &/or want to know the exact yield of what you are processing - then weigh you gold button before you ad it to the AR & then weigh it again after the AR has finished reacting with it --- that will tell you how much belongs to the client &/or what the "actual" yield is & how much is from the button

Kurt

 

[autumnwillow]

Thank you kurtak, I think I will go with the gold button.

Speeding up this process, would it be better to do these steps?
1) Clean the filings by burning them then remove iron with magnet.
2) Melt everything in a button with soda ash and borax. Remove the slag after the melt.
3) Check the button for gold purity.
4) Inquart with proper amounts of silver to bring the gold purity down to 25%, melt and shot.
5) Dissolve the shots in heated nitric acid.
6) Filter the solution. Set aside the filtrate for palladium recovery by DMG then silver recovery by copper cementation later.
7) Get the solids from the filter paper and dissolve in heated AR. Filter.
8.) Weigh and put a small gold button in to remove excess nitric.
9) Drop platinum with ammonium chloride, check with stannous, filter powder, set aside for platinum calcining and melting. (I have an oxy-acetylene torch for this)
10) Drop gold with SMB. Check with stannous. Filter and put remaining acid in stock pot then wash gold and melt.

With this process it should be faster as I will be heating the acids, remove most(all?) of the base metals, no silver chloride to deal with?, recover palladium and silver, but this will consume more nitric acid and generate more wastes.
Without considering the wastes and more nitric consumed would it be better to go for this process?

I don't really want to calcine and melt the platinum salt yet, not until they are worth doing so, how do i store them? Do I just keep them in the dilute ammonium chloride solution?
I also have a few DMG-palladium yellow salts in a dried filter paper, I will read more on about this too once I know they are worth processing already.

 

[Anonymous]

A caveat for the gold button method.

Make sure that:

1. You haven't got a large amount of excess Nitric.
2. You have enough gold to use up what you do have!