# Incineration and PM recovery from Rookie Filter Papers



## Lobby (Mar 9, 2012)

Folks,

I've no doubt entertained you with some of the rookie mistakes I've made as I've started the refining journey. But with experience comes expertise; at least I hope. 

In my first few batches, I've ended up with some filter papers with significant amounts of PM's: undissolved gold from the AR step, gold chloride that I didn't wash up, napkins that I used to pick up gold chloride solution spills, silver powder residues, silver nitrate and silver chloride containing filter papers.







I've read Harold_V's wonderful Incineration thread: 

http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=38&t=1997&p=16764&hilit=incineration#p16764

I've seen Kadriver's really good youtube video on this topic:

http://www.youtube.com/watch?v=GlozdhFuExk

And of course, I've read Hoke's book where she discusses this starting on page 216.

My questions relate to the salts (chlorides and nitrates) that are in the filter papers. Do fluxes in the melting dish reduce them to metals? If so, which fluxes? Soda Ash? 

Or do I need to do a multi step water / acid washes to recover those salts?

Thanks!


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## MysticColby (Mar 10, 2012)

Please wait for someone who knows more than me to respond before starting.
By using and saving all these, it sounds like you do similar to what I do, and probably most people on here. It's a little simpler for me, though, as I do almost entirely all silver.
That said, this is what I do with my PM-containing papers and filters: put them in a crucible (or melting dish), cover with borax with some sodium carbonate (soda ash) and melt to ~1100ºC. I still have the first crucible I got, it's not the prettiest, so I use it just for melting junk such as this that will later be refined.
What happens:
silver chloride melted with sodium carbonate will give you silver. silver nitrate heated to 444ºC should decompose into silver and NOx gas (DO NOT BREATH FUMES). silver oxide heated to 280ºC should decompose into silver and oxygen. auric chloride (AuCl3) heated to 254ºC should decompose into gold and chlorine gas (DO NOT BREATH FUMES). all pure metals will just melt together.
Needless to say, do this in a well ventilated area. It may be the case that the NOx and chlorine gas isn't good for certain refractory materials, but I don't know which ones and I haven't observed this to be the case with what I use (graphite crucible and insulating fire brick furnace).
Once melted, pour into large (~20 liter / 5 gallon) metal bucket (I use a 5 gallon plastic bucket with a metal dish that nearly covers the bottom - seems to work well enough) with water (do not get hot crucible / dish wet), wait for it to cool, recover metal flakes, refine as you estimate what's in it (maybe inquarter, maybe dissolve in nitric, etc.)
I remember reading on here once that sodium carbonate, when added to a melt, will reduce metal oxides (copper oxide -> copper, for example). ah, found it:
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=56&t=8264&p=77051&hilit=soda+ash+reduce+oxides#p77051

From reading Harold's post on incineration, I agree that a non-furnace burning is best/quickest. I've had success, though, with my furnace incinerating these papers. I've tried incinerating in an open pan, and it was really annoying when wind would pick up and blow dust away - furnace does protect against that. It does go slower than you'd expect of burning paper. But time was needed for metals to melt anyways, so I didn't see much harm.


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## Geo (Mar 10, 2012)

mystic, that is the proper process for silver. for gold, i don't think you need flux when you incinerate your filters. at least Harold never told me to. the main thing is to make sure the material is consumed to white ash. if you do this in a pyroceram dish you can go right to dissolution without moving the ashes. i use a stainless steel pan. ive gone through two so far as the acids are tough on the metal.


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## Harold_V (Mar 10, 2012)

MysticColby said:


> I've tried incinerating in an open pan, and it was really annoying when wind would pick up and blow dust away


Yep, dusting is a real problem when one incinerates. I learned that very early on. It's the reason that I included a filter system in my hood. I'd recover roughly eight ounces of gold about every two years when cleaning out the hood (I created an accumulation chamber as part of the design). That did not include the amount that was recovered from filters. That amount was never determined, as the ash was stored and processed along with all my other wastes, just prior to selling the refining business. 

Bottom line here is if you intend to incinerate (I don't understand how _*anyone*_ can refine and not do so), making provisions to recover values lost to dusting is a very good idea. 

Harold


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## NoIdea (Mar 10, 2012)

Hello - I have over come this problem with my pipe incinerator, see:

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=13166&p=132065#p132065

As for the portable filter unit, I have yet to clean it, but i did take a peek inside and it will need a clean soon, at which point i will take a photo.

P.S. Before making this unit, i performed the same process using a 50mm inside diameter quartz tube so i could watch. If you have ever seen zone melting, well, this was like zone incineration, a bright red ashing band about 5mm in thickness entering/moving into the black un-ashed material, whilst leaving behind a white/grey ashed product. Everyone should see it, its a bugger i did not take a photo. :roll: 

An Iron pipe will no dought behave differently.

Cheers

Deano


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## butcher (Mar 10, 2012)

When I incinerate chloride metal salts, (powders, or even filters), I will give them a wash in a hydroxide solution and rinse well first, my reasoning is that gold chlorides (or gold powder with a chloride salt) are volatile, and also the silver chlorides are volatile.

The wash of hydroxide is to help to convert the metal salts to oxides, and to help convert the chlorides to sodium chloride a soluble (table salt), which is rinsed out before incineration.

I believe this helps me reduce my losses in the metal burning off up in the smoke. 


Mystic Colby, method of using flux seems to also work on this idea.


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## Lobby (Mar 11, 2012)

Gosh, folks, you've answered my questions perfectly. I'd done some independent investigations concurrently, and had come to the conclusion that soda ash (sodium carbonate) would reduce metal chlorides (well, at least those of value to us) to the corresponding metal. I was set to do so.

But you've cleared my head on this. Thanks.

I'll let you know how much I get out of this recovery.


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## saadat68 (Oct 10, 2018)

butcher said:


> When I incinerate chloride metal salts, (powders, or even filters), I will give them a wash in a hydroxide solution and rinse well first, my reasoning is that gold chlorides (or gold powder with a chloride salt) are volatile, and also the silver chlorides are volatile.
> 
> The wash of hydroxide is to help to convert the metal salts to oxides, and to help convert the chlorides to sodium chloride a soluble (table salt), which is rinsed out before incineration.
> 
> ...


Hi Butcher
How are you?
Do you just grind filter papers and put them in NaOH solution? (Or burn them first with a little fire and put in hydroxide solution)

How much time we must putting them in NaOH solution to convert maximum of chlorides like silver chlorides to oxides?

Thanks


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## butcher (Oct 10, 2018)

hydrolysis, neutralization of metals salts and acids:
https://www.google.com/search?q=hydrolysis+neutralization+before+inceneration+of+acidic+chloride+salts&oq=hydrolysis+&aqs=chrome.0.69i59j35i39j69i57j0l2j69i60.9990j0j7&sourceid=chrome&ie=UTF-8


By raising pH the metals will form oxides and hydroxides, and acids will form salts of those acids, Much of the salts can be washed away from the insoluble powders.

Sodium hydroxide can be replaced by sodium carbonate, lime to raise the pH...


Filter papers will add carbon to the incineration process which is another reducing agent to help you keep your metals from volatilizing and going up in smoke.

In your study of the waste treatment, you will find a helpful chart for the pH of the metal hydroxides, showing at what pH they are less soluble, silver one of the last to be converted and to precipitate, for this reason bringing the pH of the slurry up to around pH 11, then back down to around pH 7 neutral, and rinsing the powders of the salt waters.

Caution, if high acid, raise pH slowly to minimize foam-overs.
Heating can help speed the reaction.


Rinsing the soluble salts away before incineration of the powders is an important step.
if drying the powders in a corning ware dish on a hot plate, do not fill bottom full of wet slurry, leaving about half of the bottom of the dish clear will allow you to raise the heat without bubbling and spitting, as it dries you can add more, making the job much faster in the long run.
After the powders dry you can raise the heat, the metal powders will fuse (melt together), they will need further heat to drive off the volatiles and should be stirred and crushed just before it bakes hard. after powders have dried and crushed back to powders bring the heat up to high, run a propane torch over powders while stirring bring them to a glowing red hot, stir powders so oxygen from the air can convert them to oxides...


Filter papers in the mix are helpful as it will add carbon to the incineration process which is another reducing agent to help you keep your metals from volatilizing and going up in smoke.
a little sodium carbonate in the incineration is also good.

I find a kitchen blender comes in handy if there is much silver chloride involved, it can speed the process and minimize the amount of liquid involved.

For small amounts of silver chloride in a mix of other metal powders, a good manual stirring, and the slurry may need a bit more liquid.

Water is normally a byproduct of many of the reactions involved as the metal chlorides and acids are reacting together.


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## saadat68 (Oct 11, 2018)

Thanks
Do you just *shred* filter papers and wash them in NaOH solution? ( Or we must *burn* them then wash in NaOH and then incinerate)

Can we use this process for residue from dissolve gold with qua regia? ( Which contains silver chlorides )


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## butcher (Oct 11, 2018)

The filter papers will shred when the slurry solution is stirred.

Yes, you can use this process for residue from dissolving gold with aqua regia? Which contains silver chlorides.

Like most of what we do, it depends on what the filters contained, if the filter paper was loaded full of silver chloride, the silver chloride powder would go to my silver chloride stock pot( which is kept wet) for later processing, while the filter paper would be saved for use in an incineration process.

Waste hydroxide solutions can be used to help neutralize your waste acid solutions.


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## saadat68 (Oct 11, 2018)

Thanks again 
My last question is:
As you know in silver chlorides conversation we continue stirring solution until all of white traces convert to gray 
But in filter papers we can't see white silver chlorides. How much time is needed for washing filter papers in NaOH solution/in blender? 15 minutes is eunugh?


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## butcher (Oct 12, 2018)

If the filter papers carry mostly silver chloride, add that to your stock silver pot.
I did not want to discuss converting silver chloride here as there are several methods like dilute sulfuric in cast iron or with nails...


silver chloride NaOH and hydrogen peroxide in a blender it does not take long if you have silver (it's the outer shell of the crystals will darken in sunlight (in the mechanical cutting/grinding action of the blender with the sodium hydroxide and hydrogen peroxide and the work goes much faster than stirring...



If papers are base metals, with small amounts of silver chloride and say gold and other trash where your incinerating the lot.

Our goal is to reduce as much metal as possible to oxides, hydroxides, making the solution basic, to precipitate these, neutralizing the acids and converting them to soluble salts which can be washed away, and we can also attempt to convert as much silver as possible to oxides.

Although the discussion above I was not focusing on using this as a method of converting silver chloride, just a step before and or during incineration to minimize loss due to chloride salts in the incineration process.

Silver chloride can become harder to convert if it is contaminated with base metals and trash, my guess is the base metals will convert easier, and the silver chloride may just convert to a metal coating over the silver chloride crystals.

With dirty filters and other junk you may be incinerating, here we may not get every bit of silver chloride converted, but we can convert as much as possible and then convert more during the incineration process itself, with carbon from the paper as a reducing agent and other junk in the fusion, as base metals oxide give up oxygen to the carbon many of these base metals like copper metal will also act as a reducing agent.
We can also add sodium carbonate as a reducing agent to our fusion, adding it dry late in the fusion process can also help with the moisture involved and help to give the fusion a place for this moisture to escape (bubbling problems as mentioned above).

By slowly drying, then slowly raising the heat to fusion, we can slowly drive off some of the remaining salts and acids in the fusion process, as water is driven out along with most any acid formed in the heat, stirring the fusion till dry, then crushing to powder before it hardens to a cake or breaking the cake and powdering (much more work), many of the metals will again oxidize as we bring the crushed powder up to a red heat and add oxygen (or air by stirring the red-hot powders) many of the base metal will again oxidize (making them more soluble in acids later)...

Again my thoughts are of incinerating without having so many values in fume losses, not as a method of silver chloride conversion.


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## everydayisalesson (Oct 16, 2018)

Hey Butcher,
I wanted to try your trick with hitting the waste filters and paper towels with sodium hydroxide before incineration as it sounded like a good idea. My question here, if you can see in the picture, the solution has a reddish brown color. As you can see, I am wick filtering. You don't think there is any PMs present do you? I thought about a stannous test but I don't think that will work since the metals should all be dropped. Should I run the solution through a coffee filter a bunch of times or am I worrying for nothing. 

Thanks,
Mike

BTW, anyone can answer, I was asking Butcher cause I am sure he has seen this.


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## butcher (Oct 17, 2018)

I am not really sure and cannot tell from the picture and your post, is the solution acidic or basic?

The colored solution has metals involved, cementing or using a metal higher in the reactivity series will remove some metals.

https://en.wikipedia.org/wiki/Reactivity_series

You can also remove others raising the pH of the solution, the amphoteric metals are soluble in the acid and the caustic or basic solution, and have a lower solubility at a certain range of pH of the solution.

Remember what you have studied in waste treatment, the same principles will apply here.


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## nickvc (Oct 17, 2018)

If there are any values in the waste solution you will be unlikely to be able to filter them effectively, my suggestion is to evaporate the solution, collect any dried residue, incinerate and wash with Hcl, test this solution, and if anything is left dissolve and test again.


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## everydayisalesson (Oct 17, 2018)

Thanks guys. Im not used to seeing any color after hydroxide treatment so it threw me off. I will follow your directions Nick just in case. Thanks.

Mike


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## butcher (Oct 17, 2018)

The solution could be a colloidal solution, holding reduced metals in the liquid.
Nickvc's advice will break the colloidal bonds.


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## everydayisalesson (Oct 23, 2018)

Just posting an update. The container on the right has been on for 2 days basically, it gets down about half way and I fill it back up. The container on the left I just put on because this is taking so long. The cold nights have not been helpful.

When I finally get it down and concentrated enough. Is it OK to let it run dry in the glass or should I transfer it to something else like a stainless steel pan?

Mike


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## g_axelsson (Oct 24, 2018)

Take a small sample, dry it out, dissolve in AR and test for precious metals. If there are no precious metals then there is no reason to evaporate the whole batch.

Göran


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## everydayisalesson (Oct 24, 2018)

Goran, I wish I would of thought of that sooner thank you. Will try today.

Mike


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## snoman701 (Oct 24, 2018)

I just did my filter papers today. There is a lot of bandwidth for such an easy process.

I put them in to a crucible and heated it to around 500c. I held it there until smoking stopped. After that I ground the residue in the crucible, added silver cement, soda ash and borax then mixed and covered and heated slowly until melt temp. 

Then once at melt temp I just stirred until everything was uniform and poured.

Had I had more filters I would have milled them and roast them following the pyrolization, but honestly....they are my filters. They aren't worth much unless I'm sloppy as heck. There's probably more rhodium than gold from the plating on white gold. 


Sent from my iPhone using Tapatalk


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## Geo (Oct 25, 2018)

Working with escrap produces some Pd waste. As the filters contain a trace amount, I incinerate to ash and try to remove metals as selectively as I can. Nitric acid first to remove copper, silver and Pd and decant to another beaker. Without adding more nitric acid, I then add HCl. The residual nitric acid is usually enough to dissolve any gold and Pt. Anything that doesn't dissolve here goes in my solids for smelting.


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## everydayisalesson (Oct 29, 2018)

Ok everyone, I boiled it down and to a crisp, about a liter to begin with. While still hot, I incinerated from above. I scraped and smashed and scraped and smashed. Finally I hit about 2 tablespoons of ash with bleach and hcl. No stannous color at all, absolutely nothing. 

Im confused as to what it could have been. A liter of fluid produced about 6 tablespoons of ash. Any guesses? I guess the good news is that I dont have to worry about this ash, going to boil it all down and throw it out just in case.

Thanks for the help guys.

Mike


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## Platdigger (Oct 29, 2018)

You could now try "hitting" as you say some of the untested ash with nitric, checking again for silver.
I think the color you are seeing is some base metals that did not form hydroxides because of the window some of these have, and the ease to swing past this window without forming hydroxides.
Also, if you do this nitric test I would also check it for pd.


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## everydayisalesson (Oct 30, 2018)

Will do Platdigger. I may get a little time this evening. I have potassium nitrate, could make a little poor mans nitric or poor mans AR. I had thought about that as I was posting yesterday, just haven't had the time. I think I may take a sample and add some more hydroxide to see if it does anything separate from all the other filters. 

Thanks again,

Mike


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## Geo (Nov 14, 2018)

Could have been iron. Looks rusty to me.


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