Non-Chemical percipitate question

[NobleMetalsRecovery]

Are we talking about common household unscented ammonia?

I recently did the iron conversion of silver chloride. It was indeed very fascinating.

Steve

 

[Harold_V]

Thanks for the report on recovering from ammonia. It was never an issue for me, due to different procedures, but it would have been nice to have had that particular piece of knowledge tucked away in my mind. It makes lots of sense-----that's also one of the procedures for purifying palladium salts.

I also never tried the iron (steel) rod conversion of silver chloride to elemental silver. Because I had an abundance of aluminum on hand, I started using that instead. In retrospect, I can't help but wonder if, perhaps, iron would have been a slightly better choice. My single complaint with using aluminum was the solution after the fact. It was very confusing to see-----looking almost like there was silver in suspension. It took considerable testing over a long period of time before I became comfortable with tossing the solution. I imagine that isn't an issue with iron.

Back to my choice for using aluminum, I did all my conversions, such as they were, in a large handled Pyrex container. It was one I had managed to acquire in trade for a few ingot molds I made for another refiner. He didn't see a use for the container, but I had it earmarked for processing carpets, plus it was perfectly useful for converting silver chloride without fear of breaking, and was quite large in diameter, providing for a nice shallow layer of material that was easily visible. The last time I checked the cost of a replacement, it was well over $300, and that was many years ago, while I was still engaged in refining. To have risked breaking it with a steel rod wouldn't have been something I could have dealt with mentally. That would be my one and only reservation for not changing to iron, even today.

Great report, guys. Now I wish I'd have at least given it a try, so I'd understand the ease by which you can convert the chloride. I am now of the opinion it is easier than aluminum.

As I've said on countless occasions-------anyone that desires to learn refining is missing the boat without owning a copy of Hoke's book. There is so much useful information contained within that it makes it easy for most anyone to go from not having a clue, to being an astute refiner-------and it's all done in simple terms, easy to understand.

Harold

 

[lazersteve]

Steve,

I've used both types of ammonia (household 3-5% and concentrated 28%) for dissolving silver chloride. The concentrated works much better, but the household variety will work in a pinch.

Be sure you use the kind without additional soaps or scents. Clear ammonia is best of the household types. Heating speeds the dissolution of the silver chloride and produces unbearable ammonia fumes so be sure to do this in a ventilated area or better yet under a good fume hood.

My first post in this thread assumed the silver chloride was already dissolved in the ammonical solution such as when you are removing the purple crusting from karat gold placed in AR without inquarting first. ammonium hydroxide is a solvent for silver chloride.

Steve

 

[Platdigger]

Were do you get the 28% stuff Steve?
Randy

 

[lazersteve]

Randy,

I got mine at an old job where we etched large quantites of circuit boards. I have about two or three gallons of it. It's reallly nasty stuff and will bring tears to your eyes (literallly) just opening the jug. It's nothing to play around with.

As for where you could get some today... it's hard to say with all the chemical controls in place. I know several ways to produce concentrated ammonia, but the methods are beyond the average gold scrapper.

Steve

 

[NobleMetalsRecovery]

Maybe they still make ammonia for blue prints? I think it's pretty strong.

 

[NobleMetalsRecovery]

Zinc will work in place of the iron, "it is more rapid than iron, and equally effective". It is done with zinc foil and dilute (10 to 1) sulfuric acid. This info is from, "Recovering Precious Metals from Waste Liquid Residues", 1920, by Geroge E. Gee.

 

[Lino1406]

I suggest this is tin dioxide. It can be dissolved
in 60% sulfuric, or hydriodic acids (what fits)
Lino1406

 

[NobleMetalsRecovery]

Here are the results for the solution of silver chloride with an unknown white precipitate in the form of a fine white powder.

I added household ammonia and let it set for a day. A crystal like lattice formed on the top of the liquid, leaving the white powder still on the bottom of the coffee pot.

I assumed this to be the silver. I scooped the silver from the surface with a spoon and then converted the silver with zinc and then mixed it with soda ash and torched it to produce a nice silver bead.

 

[NobleMetalsRecovery]

Here are the results for the solution of silver chloride with an unknown white precipitate in the form of a fine white powder.

I added household ammonia and let it set for a day. A crystal like lattice formed on the top of the liquid, leaving the white powder still on the bottom of the coffee pot.

I assumed this to be the silver. I scooped the silver from the surface with a spoon and then converted the silver with zinc and then mixed it with soda ash and torched it to produce a nice silver bead.

 

[lazersteve]

Steve,

You should acidify the remaining ammonia solution after filtering out the white powder at the bottom. Silver should never be left in ammonia solutions because it can form explosive compounds. More silver chloride should precipitate from the filtered ammonia soluton after adding HCl.

You can then convert that silver chloride to silver also.

Steve

 

[Lino1406]

I am not sure what you used ammonia for if the white
precipitate remained
?Did you prove the nice silver bead is silver

 

[lazersteve]

Lino,
The remaining white precipitate was the mystery material that was mixed with the silver chloride. The ammonium hydroxide dissolved the silver chloride and the white mystery powder remained. If you read the entire thread you will see what he's talking about.

Steve

 

[Lino1406]

Thanks steve, although it's hard to conceive
from the "scooping" description. I refer you
again to my former post, suggesting the
"mystery precipitate" to be tin dioxide.
Lino1406

 

[Lou]

I don't know if you already checked, but try dissolving your mystery material in hot water. Silver chloride complexes with ammonia, but lead chloride (or any of the halides of lead) does not. So if you're left with a residue of white powder after ammonia water, try dissolving it up in hot water in which lead chloride is slightly soluble.

Tin dioxide is not soluble at all in water.

 

[NobleMetalsRecovery]

I have safely added the solution and unknown precipitate to my acid stockpot. I have not used ammonia in the past because of concerns of silver fulminate.

I did some testing to see if the bead is silver. I remelted it. No oxides formed. (I think the first time I melted it it did "spit" some). I then put the bead in boiling HCL. No reactions. If it were tin, zinc, or aluminum it would react strongly.

 

[Harold_V]

I did some testing to see if the bead is silver. I remelted it. No oxides formed. (I think the first time I melted it it did "spit" some). I then put the bead in boiling HCL. No reactions. If it were tin, zinc, or aluminum it would react strongly.

A test with Schwerter's solution will determine, instantly, if you have silver. Schwerter's is made of distilled water, reagent grade nitric and sodium or potassium dichromate. It reacts blood red when applied to silver.

Harold

 

[eagle2]

I would like to add that concd nitric acid produces an insoluble form of tin. Metastannic acid. I have found that it even is produced in somewhat dilute solutions and is one of my main bugaboos when preparing a gold solution for precip. This is a fine white powder that can pass through a coarse filter easily. It is also insoluble in ammonia.

I believe those white crystals on top of the ammonia are a silver complex. Don`t let your solution sit overnight. Separate it while its still warm and those crystals haven`t formed yet. My method is decant as much as possible, then filter the rest into the same beaker. I`ll heat this solution right away and slowly add HCl until its slightly acid. You will get a much nicer precip. from a hot solution. Then let this sit overnight to cool and get all the AgCl to settle. Also, when washing AgCl, its somewhat soluble in hot water. I use warm water then let it cool before suctioning it off.

Steve! What a great tip on reducing the AgCl in sulfuric with a iron stirrer!
I have looked at many ways of doing this and this has to be the best and simplest. Can`t wait to try it. ---- Al

 

[Lino1406]

Or, simply tin dioxide
Is soluble in:
1)boiling caustic
2)60% sulphuric
which is a bit difficult to decant,
3)HI
If the HI contains free I2
it can also dissolve the gold,
so use what fits according
to the case involved.
Lino1406

 

[eagle2]

Thank You for the info Lino:

Tin forms a lot of complex compounds. It seems every author has something different. It`s important to know something about its compounds, because we are always running into it.

The formula for Tin Oxide (or Dioxide) is SnO2, mol wt 150.70. Metastannic acid is given as approximately H2SnO3, mol wt 168.71. One author claimed some nitric acid is carried along with it. Another states it carries odd combinations of hydrates (water).

Most of it forms when AR is used. Its in the insolubles at the bottom of the beaker. When pure its a white powder. When you see it on the filter, its off white because gold and other elements have cemented to it. If the off white has a tinge of purple, thats gold you`re losing. So I save it and reprocess it later combining several batches.

Later on when I`m adjusting the Ph of my PM solution, it shows up again as a Tin oxide (and probably some Metastannic acid) precipitate and no doubt some cemented gold.

I hate to filter! This is the first place you start to lose gold.

The only reference to dissolving Metastannic acid I saw was prolonged heating in concd. HCl. (this would surely dissolve your gold precip), or heat it to break down the hydrate bond and produce a soluble form, or something called calcining.

Heres a good link to tin and its compounds.

www.1911encyclopedia.org/tin

Here`s a good tip on keeping your Stannous Chloride gold testing solution from going bad, Just keep a small piece of Tin metal in it.

Al