Processing my used filters

[Rreyes097]

Hello and good morning to the forum! So after a few years I have gathered quite a bit of used filters. So I went ahead and incinerated them. Sifted them and I came out to about 500 g of material. I then put half of that in a thousand milliliter beaker with distilled water and added 15 mL of nitric acid. When no reaction happened even with heat I added 15 more milliliters of nitric acid and still nothing has happened. Can anybody tell me why this might be the case? This process seems so straightforward. And as with all all things in refining and recovery it is not. So any advice would be helpful thanks guys!

 

[Yggdrasil]

Hello and good morning to the forum! So after a few years I have gathered quite a bit of used filters. So I went ahead and incinerated them. Sifted them and I came out to about 500 g of material. I then put half of that in a thousand milliliter beaker with distilled water and added 15 mL of nitric acid. When no reaction happened even with heat I added 15 more milliliters of nitric acid and still nothing has happened. Can anybody tell me why this might be the case? This process seems so straightforward. And as with all all things in refining and recovery it is not so any advice would be helpful thanks guys!

What did you expect to happen?
Was this from Gold dropping or what kind of processes did they come from?
Was the ash completely whitish grey?

 

[Rreyes097]

What did you expect to happen?
Was this from Gold dropping or what kind of processes did they come from?
Was the ash completely whitish grey?

What did expect to happen? I'm sorry but is this a rhetorical question? What I expected to happen was the nitric acid to dissolve anything there was to dissolve in this material. The material came from standard gold recovery and silver recovery and refining as well.

 

[Yggdrasil]

What did expect to happen? I'm sorry but is this a rhetorical question? What I expected to happen was the nitric acid to dissolve anything there was to dissolve in this material. The material came from standard gold recovery and silver recovery and refining as well.

Nitric will not dissolve Gold as you know. And uf it was Gold Chloride you will not need Nitric at all.
Hot AR will dissolve the papers.
So what did you expect to happen and how do you know if what should have happen have not happened?

So no, it was not rhetorical.
You need to have a plan and that includes having an idea on what will happen.

 

[Rreyes097]

Nitric will not dissolve Gold as you know. And uf it was Gold Chloride you will not need Nitric at all.
Hot AR will dissolve the papers.
So what did you expect to happen and how do you know if what should have happen have not happened?

So no, it was not rhetorical.
You need to have a plan and that includes having an idea on what will happen.

I incinerated the filters. Then sifted them. Then put distilled water and nitric acid in there so I was thinking that the nitric acid would dissolve any base metals that were in there. Also any silver that may have been in there I was hoping to dissolve. According to streetips videos on processing filters.

 

[Yggdrasil]

I incinerated the filters. Then sifted them. Then put distilled water and nitric acid in there so I was thinking that the nitric acid would dissolve any base metals that were in there. Also any silver that may have been in there I was hoping to dissolve. According to streetips videos on processing filters.

When you incinerate filters you will have losses. But its one of these catch 22 things.
If you decompose the filters in hot AR, there will be filtering issues. If you incinerate you will have losses.
Why do you expect the process to not be sucessful?

 

[Rreyes097]

When you incinerate filters you will have losses. But its one of these catch 22 things.
If you decompose the filters in hot AR, there will be filtering issues. If you incinerate you will have losses.
Why do you expect the process to not be sucessful?

I'm not expecting it to be unsuccessful I just don't see the nitric doing anything. That's all. I know there are losses.

 

[Yggdrasil]

I'm not expecting it to be unsuccessful I just don't see the nitric doing anything. That's all. I know there are losses.

So what colour is there then?

 

[Rreyes097]

Greenish blue? I'm just unsure if the nitric acid is working. I see no reddish brown fumes. Or really none of the usual indicators that's working. Other than the color changing to that color. But it's far less than what I expected according to the videos. And normally I don't go off of YouTube videos anymore but Streetips is pretty reliable and very articulate when explaining whatever the video is about. I suppose it's working and I just don't realize it.

 

[Ohiogoldfever]

I’d test the solution. If nothings present try AR. Then test again. Should be something there.

 

[Rreyes097]

I did try taking a small sample out and put some HCl to try and see if the silver, if any, was in solution but no silver chloride precipitated. But yeah, I probably need to just do what you suggested and use some AR. Because that's why I'm using nitric first is to get the silver first correct? Also thanks for taking the time to give me a solid suggestion.

 

[Yggdrasil]

Greenish blue? I'm just unsure if the nitric acid is working. I see no reddish brown fumes. Or really none of the usual indicators that's working. Other than the color changing to that color. But it's far less than what I expected according to the videos. And normally I don't go off of YouTube videos anymore but Streetips is pretty reliable and very articulate when explaining whatever the video is about. I suppose it's working and I just don't realize it.

Since it is greenish blue you have dissolved the Copper and possibly the silver.
With the minute amount of metals in the filter you will not se any brown fumes.
There are not enough metals to dislodge more NOx than it keeps dissolved.
Hence the greenish tint to it.

 

[Rreyes097]

Since it is greenish blue you have dissolved the Copper and possibly the silver.
With the minute amount of metals in the filter you will not se any brown fumes.
There are not enough metals to dislodge more NOx than it keeps dissolved.
Hence the greenish tint to it.

I suppose that makes sense. Thank you so much! I'll filter solution and go ahead and rinse then AR. Unless I'm missing something?

 

[orvi]

Yggdrasil is right about the point - what should dissolve in nitric, when filter papers came from hydrometallurgical processing ? There is not much to be dissolved with nitric alone - you dissolve it beforehand, on the filters (if nicely washed), only insoluble portion is retained, that is most of the times AgCl, small gold particles and insoluble tin compounds + other ceramic/plastic/miscell junk.

Wet route for filter papers is doable, just you need to boil it for some time in AR to disintegrate the paper to cellulose sludge. Drawback of this method is - recovery of silver is practically impossible - unless you opt for ammonia leaching of the cellulose/whatever/AgCl/tin oxohydroxides/junk sludge Not pleasant at all. But it will certainly work.

Personally, I incinerate them. Blend the papers, or press them that way they are not completely loose, but also not tightly hammered together - to allow gasses to escape and simultaneously saving the space in the pot you are using. It is wise to layer the papers with sodium carbonate - to help reduce AgCl to metallic silver (AgCl vaporize easily and melts just above 450°C). No reducers are needed as you have plentiful of carbonaceous material - which will easily reduce all metals down to zinc

Cover the pot with preferentially mineral wool and start heating very slowly - to the point you dry up the charge and it start slowly smoking. Light up the smoke and continue till you reach around 500°C (starting to see some dull red). If the smoke/flame is no longer going out of vessel, put the heatgun/torch aside and carefully open up the container. There should be carbon residue with all the ashes and stuff. There comes a fun part

Now, you need to burn all of the carbon from the residue. So in cheap DIY setup holding the temperature above 500°C in open container with VERY CAREFUL stirring of the carbon/ashes, till they come nicely greyish coloured and nothing is burning inside when swirled with steel or graphite rod - no sparkles of unburnt carbon emerge. Be gentle, residue is often very dusty and "floaty", with hot air currents tend to "fly out" the material form the pot. Depending on the ammount of paper, this coul take few minutes to few hours.

When you are left with thoroughly burnt ashy residue, now you have two options. Hydro or pyro processing. As the composition of this material is most of the times quite complex, you need to preferentially decide on what to do - based on what you have thrown into the container with filter papers Main problem now is tin - it is all reduced down to metallic form now. So if you ever put the metastannic filters into the pot, you will have awful lot of tin inside. If you try to smelt this in graphite, you will obtain high tin alloy and that is painful to process ba any means. If you want to smelt it in clay, good luck with fluxing the SnO2 out. Better go with drilled magnesia brick and very basic NaOH or sodium carbonate flux, maybe with additions of nitrate to oxidize the base metals from the melt to the slag. But Air/better oxygen will also accomplish this conveniently

For hydro treatment of the ashes, it is wise crank up the temperature to around 600°C (good IR thermometers can reliably measure this) and hold for hour or two. With plenty of carbonate in the charge, all AgCl would be reduced to elemental silver by now, and the residue would stay porous. If you then take this residue and suspend it in water, all NaCl and Na2CO3 will dissolve, leaving all other junk from tin, and elemental silver together with gold in easy to filter form. But you need to reliably hold that temperature and DO NOT PASS THE 650°C. Otherwise NaCl will start to cake the residue to rock like structure and game over to the easy leaching This process was developed by Wasyl Kunda, and it is used to convert AgCl to metallic silver on industrial scale.

Then you go from there, NOW apply nitric acid to dissolve the silver, and what is left is leached with AR to recover possible gold present

Processing multicomponent, full of junk, full of organic mixtures like filter papers is often quite PITA. I personally do it in bulk, when I accumulate few L bucket full of them, otherwise not worth it Also, think about what you are adding into the container, have separate ones for silver, gold and PGMs and try to add as little junk as possible. Not all filter papers hold values and need to be added as "dead mass" to the pot.

It is said that "miligram to miligram, it all counts", but you will remember that phrase when you will be incinerating the carbon from filters for third hour in row and not nearly done or going through washing of cellulose sludge from filter papers leaching, willing to sacrifice hundreds of miligrams of that same gold just to stop this suffering

 

[Rreyes097]

Thank you so much for the reply. It is appreciated and gives me a lot to think about.

 

[Rreyes097]

For hydro treatment of the ashes, it is wise crank up the temperature to around 600°C (good IR thermometers can reliably measure this) and hold for hour or two. With plenty of carbonate in the charge, all AgCl would be reduced to elemental silver by now, and the residue would stay porous. If you then take this residue and suspend it in water, all NaCl and Na2CO3 will dissolve, leaving all other junk from tin, and elemental silver together with gold in easy to filter form. But you need to reliably hold that temperature and DO NOT PASS THE 650°C. Otherwise NaCl will start to cake the residue to rock like structure and game over to the easy leaching

So this part is probably the best way but I'm not thoroughly understanding it. I'm going to for sure do it the hydro way.

So here's where I am. I took all filters and incinerated them in a pot. These filters were from everything I've done to this point. Which includes every process I have ever tried. Successful and many unsuccessful. Silver and gold only but I've tried many of the common methods for both. So what I'm saying is there was a lot of junk in there. Well I incinerated until my pot started to melt. And I probably didn't incinerate enough. But I'm not sure. After I took the pot off the heat it was red coals for a few hours or a couple hours after that. I then sifted out all large pieces. Then separated it roughly in half. The first half I put distilled water and what ended up being a good amount of nitric acid and put on heat for over an hour. So from here I planned on filtering and using that liquid to precipitate any silver chloride. Then I should rinse the material with more water? Then use AR. For gold recovery. Is this correct? If not I got another half of the material that I can try to follow what your instructions said if I can. I might need some help with that though.

 

[Rreyes097]

So I took the solution and filtered it and put some copper in it for its cement on copper if there is any silver at all. Nothing is being cemented as of yet so either I have no silver. Or something's blocking it from cementing on copper any suggestions?

 

[orvi]

So this part is probably the best way but I'm not thoroughly understanding it. I'm going to for sure do it the hydro way.

So here's where I am. I took all filters and incinerated them in a pot. These filters were from everything I've done to this point. Which includes every process I have ever tried. Successful and many unsuccessful. Silver and gold only but I've tried many of the common methods for both. So what I'm saying is there was a lot of junk in there. Well I incinerated until my pot started to melt. And I probably didn't incinerate enough. But I'm not sure. After I took the pot off the heat it was red coals for a few hours or a couple hours after that. I then sifted out all large pieces. Then separated it roughly in half. The first half I put distilled water and what ended up being a good amount of nitric acid and put on heat for over an hour. So from here I planned on filtering and using that liquid to precipitate any silver chloride. Then I should rinse the material with more water? Then use AR. For gold recovery. Is this correct? If not I got another half of the material that I can try to follow what your instructions said if I can. I might need some help with that though.

If you didn´t added up any base, you were likely to smoke off volatile chlorides like AgCl, maybe also some AuCl3 (but realizing plenty of carbon - I think loss there wouldn´t be that huge). Silver chloride in particular is only very slowly reduced by carbon (slow enough to be smoked out of the crucible), and realizing very low melting point of 450°C, it has quite high vapor pressure even at like dull red (500-600°C). That being said, smoke that you seen when incinerating the charge was not only quite expensive, but also quite toxic.

Completion of incineration isn´t measured by temperature, but the complete burn-out of carbon residue. Term for this is dead incinerated - meaning nothing that can burn will remain in the pot When you swirl the powder in the pot (preferably in dark) and very gently blow air over it, nothing should become burning or glowing more - that will mean you still have left carbon to deal with.

If you put nitric on burnt residue, that wasn´t cranked to like 1300+°C (to enable all chlorides to vaporize), you will still have chlorides in the charge. Meaning that if you add distilled water, they all become solubilized. Then you pour nitric acid in - so any silver that has the chance to dissolve is immediately precipitated out as AgCl. And rest of it will be passivated by layer of AgCl.

More sense would be first washing with water to wash away any soluble chlorides. And only then applying nitric - if your aim is to dissolve possible silver.

So now, you created some funky kinda "AR" in the pot, that will definitely dissolve gold after some time (if you have gold present), but with silver, I do not think you will be able to any kind of efficiently recover it from this solution.

 

[Rreyes097]

If you didn´t added up any base, you were likely to smoke off volatile chlorides like AgCl, maybe also some AuCl3 (but realizing plenty of carbon - I think loss there wouldn´t be that huge). Silver chloride in particular is only very slowly reduced by carbon (slow enough to be smoked out of the crucible), and realizing very low melting point of 450°C, it has quite high vapor pressure even at like dull red (500-600°C). That being said, smoke that you seen when incinerating the charge was not only quite expensive, but also quite toxic.

Completion of incineration isn´t measured by temperature, but the complete burn-out of carbon residue. Term for this is dead incinerated - meaning nothing that can burn will remain in the pot When you swirl the powder in the pot (preferably in dark) and very gently blow air over it, nothing should become burning or glowing more - that will mean you still have left carbon to deal with.

If you put nitric on burnt residue, that wasn´t cranked to like 1300+°C (to enable all chlorides to vaporize), you will still have chlorides in the charge. Meaning that if you add distilled water, they all become solubilized. Then you pour nitric acid in - so any silver that has the chance to dissolve is immediately precipitated out as AgCl. And rest of it will be passivated by layer of AgCl.

More sense would be first washing with water to wash away any soluble chlorides. And only then applying nitric - if your aim is to dissolve possible silver.

So now, you created some funky kinda "AR" in the pot, that will definitely dissolve gold after some time (if you have gold present), but with silver, I do not think you will be able to any kind of efficiently recover it from this solution.

I'm getting confused. So I might have burnt off the silver? And also not burned it enough? So again carbon is going to hide my gold?
Okay so this half of the material is going to be what it's going to be. The second half I'd like to do it right to the best of my abilities. Should I go back and incinerate more? And instead of going straight to nitric and distilled water what steps should I include?

 

[orvi]

Certainly not all, but it does happen fairly often that it could be significant portion. Most of the times, filter papers are acidic and full of chlorides. That is bad enviroment for incineration, as nearly all chloride salts are volatile.
If it is properly incinerated I cannot say as I did not saw the behaviour during the incineration.

First step to include is to not make mess beforehand second time keep waste filter papers/towels for silver and gold separated. Now you see why.
Now, you can leach out the gold (if you have some inside), then filtering the residue with AgCl and either rinse out AgCl with ammonia or smelt/bake that down with good ammount of carbonate.