# Treating filters before storage



## qst42know (May 9, 2010)

After filtering a small batch of gold chloride and rinsing the filter as usual. I dropped the gold with SMB. I then left everything to settle overnight. Nothing unusual.

In the morning I went back to this and being a frugal sort and not wanting to miss any gold that tends to float I reused the same well rinsed filter to run the SMB rich solution through.

What I found was the filter had blackened a considerable amount. I would guess this to be gold chloride that was stuck in the filter.

A comment by Lou a while back mentioned no PM's should be melted as a chloride to prevent loses. 

Theoretically is it possible more gold can be recovered from incinerating filters if they are first treated to convert AuCl to metallic?

I know the amounts may be small but there is no sense in wasting any. :mrgreen:

edited spelling


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## samuel-a (May 9, 2010)

it's indeed good point...

i actually wonderd to what happens to PM's salts when burned....


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## qst42know (May 9, 2010)

Is there something that could be flushed through a silver chloride filter such as a weak solution of lye water to assist in it's conversion?


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## Lou (May 9, 2010)

I am not sure if I am fully understanding the nature of your question.

Gold, silver, and indeed all of the precious metals halogen salts have considerable vapor pressures when heated. Some of them also may volatilize (easily seen--heat HAuCl4 and watch as it decomposes to AuCl3 and HCl, and then further to AuCl and then deposits an Au mirror!) quite easily.

I also said never to heat precious metals with salts containing any member of the halogen family. Even gold may be attacked by heating it in the presence of ordinary table salt, and oxygen.


Lou


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## shyknee (May 9, 2010)

qst42know


> What I found was the filter had blacked a considerable amount. I would guess this to be gold chloride that was stuck in the filter.


gold powder in your case just processes the filter when you have a lot in AR or AP then drop again .

I do have a question about filters .
I have a jar and it is getting a little full of these silver chloride filters I do not want to burn them so i was thinking of the best wet procedure to take.
step 1: I would take 2 one liter jars (1jar 1/2 full with household ammonia + water 50/50) and (1jar 1/2 full with hcl+water 50/50 )
step 2: Put a bunch of filters in to soak in ammonia jar then remove filters and put them in hcl jar to make them acidic again and shake off any chlorides that carry over.
step 3: after repeating step 2 until out of filters.I would filter the ammonia solution into a larger container then add the jar of hcl+water .this would precipitate the silver chloride(I would add a little more straight hcl just to make sure the solution is well acidic)
step 4:convert silver chloride to metal (to be used for inquarting )

corrections needed ? please let us know if this is ok.

much appreciated


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## butcher (May 9, 2010)

I just heat them (slow heat I figure drives off chlorides) sprinkle some sodium hydroxide on them once all paper turns to char raise the heat slow then add flame, figure this just makes silver oxide then heat to silver. or mix them in with that other junk I am incenerating.


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## shyknee (May 9, 2010)

butcher
if that works for you great !
what I would prefer, is not to incinerate chlorides and filters and make smoke for neighbors


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## butcher (May 9, 2010)

ShyKnee, That sounds like it would be ok for most of the silver from the filters, a filter pile may have gold and PGM also.
I do not have close neighbors, and I missed your point about not wanting to incenerate in the post above. heck save them up till that next camping trip.


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## lazersteve (May 10, 2010)

Filter the pregnant ammonium hydroxide solution before precipitating the chloride again.

Steve


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## Oz (May 12, 2010)

Lou,

If I am reading the first post correctly he has taken your advice to heart more than most, you will lose PMs to vapor with heat if they are a salt compound. The rest of the thread seems to be about silver chloride, another animal.

Sticking with the gold chloride, instead of just setting filter paper that was used for filtering the gold chloride aside for incineration as is typically done (after a rinse), he is taking his waste solution that is still high in SO2 to reduce the gold chloride traces on the filter paper into elemental gold. Then he can incinerate his filter paper wastes with far less loss of Pms.

I do not see a flaw with his reasoning. It may not make a big difference in his yield from waste filters but it does not create additional wastes by practicing this method.


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## g_axelsson (May 12, 2010)

I don't think there is a big danger for losing the gold if you incinerate the filters without reducing the gold chloride. According to wikipedia gold chloride decomposes at 254 °C (527 K) forming metal Au and Cl gas. I would be more concerned that the gold is blown away together with the resulting ashes.

Silver chloride is a totally different animal...

/Göran


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## Oz (May 12, 2010)

I tend to listen to Lou since he has letters after his name that I lack. I will say that when de-noxxing by triple boiling if I let something boil dry by accident I consistently get a lower than expected yield, but that is only vague empirical evidence of what is happening. 

Having an explosives background I would ask if the decomposition of the elements in an explosive compound means that everything stays in an elemental state or do some elements form gasses? Gold fulminate would be an example as to precious metals but explain what happens to the elements in common gunpowder, do any of them become a vapor when they decompose? No matter the temperature there are many ways that things decompose. It is indeed a concern as to loosing gold to ash, but you have that problem incinerating filters either way.


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## qst42know (May 12, 2010)

Thanks Oz, that was my point to reduce the gold chloride in the filter rather than by incineration.

And along those same lines, silver chloride is more troublesome to reduce by incineration isn't it?

If I were to rinse the filters used for AgCl first with a NaOH solution would the incineration of these filters be improved? 

Keeping ash contained while incinerating has got to be easier than capturing the metal vapors.


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## Oz (May 12, 2010)

qst42know said:


> And along those same lines, silver chloride is more troublesome to reduce by incineration isn't it?



It is not only more troublesome and causing you to lose values but it can poison or kill you if in a great enough quantity without proper equipment (GSP has talked about someone that died from this if I am not mistaken). If you thoroughly wet your filters containing silver chloride with concentrated NaOH you will reduce your silver chloride to a silver oxide. The silver oxide does not lose near the amount of silver to vaporization as the chloride does when heated to a metallic state. Beyond that you need one of these guys with letters after their names to explain it in greater detail.


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