Incinerated filters and PM salts recovery

[Bluebloomer]

Hi all,

I incinerated a bunch of paper filters with traces of precious metals, and I roasted the collected salts from all my failed recovery attemps.
Incinerated about 30 paper filters and roasted around 38 grams of salts containing precious metals.

After incineration I added HCL to make a black sludge. When the reaction seized, I washed the sludge with dilluted amonia and twice with hot water.

Then I added nitric acid to the washed sludge to recover the silver. There should be close to 20 grams Ag to be recovered, going to cement it with Cu.

Plan is to rinse the sludge again until free of nitric, and then add it to AR to recover about 10 grams of Au.

I was thinking about putting it straight into nitric acid, but because there should be a lot of Copper and Aluminum in the sludge HCL plus some H2O2 seemed the better choice.
Let it boil for about 2 hours.

I just wanted to ask you guys if this was the right thing to do, or should I of made and AR solution right after the HCL wash to recover the silver as AgCl, filter and then recover the gold ?

The way I am doing it now means extra acid, washing and filtering, but I felt like it was the better way to go because of the thick black sludge.
But any input would be most welcome.

 

[gold4mike]

When you added nitric to the washed sludge you made AR. You should have some dissolved gold in your solution now.

Washing it with HCl was a good idea but the addition of nitric should have been preceded by incineration.

 

[goldsilverpro]

Hi all,

I incinerated a bunch of paper filters with traces of precious metals, and I roasted the collected salts from all my failed recovery attemps.
Incinerated about 30 paper filters and roasted around 38 grams of salts containing precious metals.

After incineration I added HCL to make a black sludge. When the reaction seized, I washed the sludge with dilluted amonia and twice with hot water.

Then I added nitric acid to the washed sludge to recover the silver. There should be close to 20 grams Ag to be recovered, going to cement it with Cu.

Plan is to rinse the sludge again until free of nitric, and then add it to AR to recover about 10 grams of Au.

I was thinking about putting it straight into nitric acid, but because there should be a lot of Copper and Aluminum in the sludge HCL plus some H2O2 seemed the better choice.
Let it boil for about 2 hours.

I just wanted to ask you guys if this was the right thing to do, or should I of made and AR solution right after the HCL wash to recover the silver as AgCl, filter and then recover the gold ?

The way I am doing it now means extra acid, washing and filtering, but I felt like it was the better way to go because of the thick black sludge.
But any input would be most welcome.

What PMs were in there? Any gold? PGMs? Mostly silver? Silver chloride? I've found it best to save filters from these 4 categories in 4 different buckets and treat them separately. Makes for easier refining.

One thing that bothers me is that the only source I can think of that would produce a black sludge is unburned carbon. You've got to burn to at least a medium-to-light gray. If there is any black, keep on burning. PMs have ways of attaching themselves to carbon.

Why the HCl? If you're looking for silver, whether or not there is gold in it, you should first leach with about 50/50 or weaker nitric, diluted with distilled water, hot in a big container (heavy non-magnetic stainless works great). If you have introduced no chlorides, the silver should be in a form that will dissolve in the nitric.

 

[Bluebloomer]

Hi, thanks for the replies.

When I was messing around this summer trying to recover gold and silver from old jewelry I made one big mistake after another.

In the end I dumped silver chloride into the AR containing gold and at that point I knew I made such a mess of things I'd better stop doing what I did.

So, I cemented all salts with iron, aluminum and copper, recovering as many salts as I could so I could try and retrieve the Ag en Au later on.

So the HCL was to eliminate the iron and other base metals. But I forgot I also added a lot of soda ash. That was before I understood that neutralizing the acid was the last step.

All in all a giant mess..

And yes, I read that carbon will bind to the gold preventing it from precipitating. But since the ashes from the burnt filter were flying all over the place when I put a butane torch over it, I thought I better save the ashes this way and start recovery.

Needles to say it didn't go that well..

Was it perhaps a better idea to introduce sulphuric acid to the ashes eliminating base metals ? And what should be the best way to proceed now ?

I have a dirty AR solution with probably a lot of carbon that is preventing the gold from dropping properly.

Add aluminum foil to the AR drop the metals and start over, or will the carbon in the solution prevent it too ?

I know understand I should of boiled the roasted salts in HCL, then start the nitric bath. But how would you deal with the incinerated paper filters when they are flying all over the place ?

 

[butcher]

Incineration, is best started from the bottom of the pan, focusing the heat on the bottom of the pan first.
It somewhat depends on what your tools are your using to do the incineration with, and what your incinerating in.
Another thing is it depends on the materials being incinerated and how they react...

Much of this will come from your own experience, I can try to explain some things the best I can, which may be of help.

Say your using a rosebud torch, or a gas flame stove top, and a stainless steel pan, if you are heating a stainless steel pan until it and its contents become red hot, and then introduce a stream of oxygen over the crushed powders as you stir them the carbon will burn easily in the oxygen, with the heat involved. no need to heat from above and take the chance of blowing out powder.

If your initial heat source is an electric hot plate, and your powders are in a ceramic Corning pyro Ceram casserole dish.
It becomes a bit more tricky, the heat from the hot plate is not great enough to incinerate the carbon.

The heat is hot enough to carbonize the filter paper with the powders, and hot enough to begin the fusing process of many metal salts, here we can crush the carbonized paper in with the powders.

Depending on the material or powders involved, you may form fused salts, the heat from the hotplate is hot enough to begin forming this fusion, but is not hot enough to complete the process, if the powders do fuse, here you need to re-crush the fused salts, and keep them crushed until the incineration process is completed.

Many times what you will see is the dry powders fuse forming a syrup like substance, then this will dry again with more added heat to form a hard cake, you need to begin re-crushing this cake before it is completely hard again, begin at about the point it is dried the second time , or it becomes more difficult to crush the cake.

At this point you can add heat from above with a torch, propane torch or another torch of choice, with an appropriate tip, learning to adjust and control the flame, so you do not blow your powders from the dish, a lower flame to begin with, just lapping the powders with the heat from the tip of the flame, focusing first at heating around the outer portion of your dish, and bringing the flame in only as the powders can handle to blowing force of the flames, then as they can, bring the torch on in, until we can lap the powders with the more forceful blue cone portion of our torch, and bring the powders up to red hot, while stirring them and exposing them to plenty of heat, and air, or oxygen to oxidize the base metals involved.

Note, when we roast with a carbon source (filter papers included) the carbon source can reduce metal salts to elemental metals, for example copper sulfate to copper metal, getting these red hot in plenty of air or oxygen with the oxidizing flame of the torch, keeping the metal powders stirred and exposed to the oxygen source while holding them red hot for a long enough period of time, we can oxidize the base metal powders, example change the fine copper powder to black copper oxides, so they are easier to dissolve in acids of later steps.

Another thing to consider when roasting or incinerating some types of metal powders of chlorides, several metals can be volatile as chlorides, like gold or silver, here a good prior wash in NaOH, and rinsing well, can be helpful to wash out the salt, and form oxides or hydroxides of some base metals, lowering the chloride content, here also I sometimes find it useful to add a carbon source (if one is not already involved) like filter papers(or another carbon source like flour, or sugar), to the roasting process, it can reduce some base metals in the beginning but they can be re-oxidized again when we get them red hot and exposed to air or oxygen, it can be helpful also to keep your values from going up in smoke with the fumes.

 

[Bluebloomer]

Very nice Butcher ! Thank you for another valuable lesson that will aid in a future incineration process..!

But, what to do with the above problem ? The black slush is drying, since it looks like a big black pancake, it will be easy enough (I think) to roast it, like you described Butcher.

Is the carbon polluted AR lost, or will aluminum still precipitate all the metals out ?

And if so, precipitate the metals, dry and roast the salts until redhot, and then retry the recovery process starting with nitric first ?

For the salts, let them dry, and roast as Butcher described ? Or would it be an option to melt some silver, and add the salts and cast the molten fusion as shot and then retry a recovery ?

 

[butcher]

The metals in solution will be reduced by the aluminum, but the carbon can absorb your values and non values alike, the aluminum can form a gelatin that can also trap values.

You may be able to collect some of the insoluble in a filter, or if too hard to filter a funnel and a wad of fiber glass insulation, this may help to separate the two portions solids and liquids, that can be joined again later in the incineration process after evaporation of the liquid.

I would try evaporation of the liquid to dryness, it will form a syrup, which you may need to lower heat to keep it from bubbling and spitting out of your dish.

There are a couple of tricks you can try as the syrup tries to dry.
Lowering heat below the boiling point, where acid fume can vapor off more mildly, and slow drying.
Having more surface area in the dish than you have syrup, or fused powders, so you can separate it by stirring, this helps the gas bubbles to be relieved from under the mush, instead of flowing up through it forming large bubbles and popping and splashing them out of the dish.
Adding your filter papers,or some tissue paper, to absorb the fused liquid's, so you can stir and break the fusion up to globules so gases of the acids or salts can easily escape without bubbling and splashing the contents out of your dish.
Sometimes if doing large batches, and several runs of incinerating powders from a large batch, I will add a small portion of the already incinerated powders, to absorb moisture and prevent bubbling assisting in drying the sludge enough it will separate it in the dish to prevent large bubbles from rising and bursting...
controlling heat is a big portion in these processes.

Many salts as I said will dry after forming a syrup, and can be crushed to powders, adding more heat many of these will fuse again to a syrupy substance that still needs to drive off the acids, as gases of those salts, and will dry again as the acids portion is removed, to form the cake which will need crushing to fine powder before bringing them up to the glowing red hot metals that can be oxidized in air or with oxygen...
Keeping the powders stirred, and red hot long enough, and in plenty of air or oxygen for the conversion to take place (with sulfides they suggest 20 to 30 minutes or even more)...

Each acid or its salts have a boiling point, some acids or its salts are more volatile, like the salts from nitric or HCl and will leave the powders sooner. than others like sulfuric, sulfates, or sulfides that take more heat and longer to leave as gas of SO2, SO3 or SOx...

NaCl (sodium chloride) (table salt), has a high boiling point very close to AgCl, a lot of times we have both of these together, in our powders, this makes it hard to drive off the chloride as gas and not lose our silver as white smoke in the fumes and gases, whenever we try to melt or incinerate the silver powders.
The salt seems to share or give up the chloride ions to the silver which is volatile at High heat.
I suppose it may be possible to heat very slowly at a certain rate and drive off chlorides and not the silver, although in reality, it is not practical and really does not work that easy, or at all.
The problem is controlling the heat just perfect, and knowing how much heat, when and how to raise the heat...
This is where converting silver chloride to metal or silver oxide , or even prewashing with NaOH and rinsing out the salts can help before incineration, or like when using a lot of soda ash (sodium carbonate) or (washing soda) as a flux when trying to convert the silver chloride to elemental silver in a temperature controlled melt...

One problem you will have with a dirty sludge of mixed base metals and carbon base materials is getting any kind of controlled conversion with all of the reactions going on in the mess, the sodium hydroxide can help to lower the acidity and convert many of the metal chloride salts to oxides and hydroxides, making a salt that can more easily be washed out, but with carbonous materials even some of this salt will be absorbed into that carbon...

Aluminum can form a gelatinous substance with chlorides (aluminum will not dissolve in strong nitric acid), making filtering troublesome, making washing the gelatin out of your salts a problem, this problem becomes worse if we remove the acid and make it more of an aluminum hydroxide which is even less soluble.
If you have much aluminum you may want to try to remove it first with HCl, and filtering even if you have to use a Charmin plug or fiberglass...

Aluminum and tin (along with many of the base metals oxides) would wash out better with HCl after incineration as Harold has suggested so many times.

Keep in mind, you will again form silver chloride from and silver powders , and they take time to settle, so when decanting the HCl washings, give the silver chlorides time to settle

Remember also if you wish to change acids and not dissolve gold, you will need to incinerate your powders again, other wise you could just move on to aqua regia or one of the work around's like HCl/NaClO...

When you have a mess, you have a mess to deal with, to try and recover your values, and keep them from going up in smoke or to be lost in the waste...

The best way to deal with a mess is not to make one.

 

[eastky]

blue I haven't recovered or refined any precious metals yet. I have read this forum front to back top to bottom.
One thing the forum has taught me is patience. A great bunch of people here and I am thankful to them for the knowledge I have gained.

Being that I haven't refined anything yet I am kind of reluctant to give advice on the subject matter. So I mainly just read and learn from other people at this time. The good thing about the forum is you can learn from other peoples mistakes.

Butcher gave you excellent advice as always in tough cases here on the forum.

This is what I would do even though I haven't recovered or refined anything yet. If I am leading you in the wrong direction
someone will or should correct me. That's a good thing not only for you but for me to.

Let your sludge dry. If not completely dry when you start to incinerate start with low heat to avoid steam explosions.
Add your material in thin layers instead of just dumping it all in at one time.

After everything is incinerated I would put the powders in a dilute sulfuric acid and heat for a bit. Make sure that the powder is broke up well and not in clumps. That way all the powders are exposed to the acid. This should remove the copper. The copper is in salt form and should dissolve in dilute sulfuric if I am not mistaken. GSP has mentioned using dilute sulfuric acid on copper on the forum and if I am not mistaken Harold has also. The acid has to be diluted sulfuric.

After that I would let the powders settle decant without disturbing the powders wash with hot water.

Go to nitric acid to remove the silver and other base metals. When you have no more reactions going on let settle decant.
Wash the powders with hot water maybe with some heat. Incinerate to remove all traces of nitric acid.

Wash with HCL acid to remove aluminum and help to remove iron. Switch between water washes and HCL.
I wouldn't worry about washing this to many times like this. You are wanting to get the aluminum out of the mix.

Go to AR don't over do it with the nitric acid. I feel that you are pretty much home free at this point. I believe you should know the steps at this point and if you don't you need to do some reading.

You need to concentrate on one of the precious metals at this time. Don't step over a dollar to pick up a dime.
Recover the gold first and then if you want go for the silver.

 

[Bluebloomer]

Well, thank you very much Butcher and eastky for a detailled explanation, allmost a manual of sorts, to help fix this mistake.

It's obvious now I just did a pyrolysis and not an incineration.

Recover the gold first and then if you want go for the silver.

Correct me if I'm wrong, but I thought it's not possible to get to the gold without removing the silver first, if they are both in an acidic solution ?
Any silver in an AR solution will precipitate first as a chloride, unless I use the HCL/CL method to get to the gold ?

Butcher it's obvious you are very passionate about recovering and refining precious metals, that I can't thank you (and all of you in fact) enough for the education like information you are sharing.
People like you make it so much easier and understandable for people like me..

I think I understand the process now, and I realy understand where I went wrong (again). It did cost me some acids, but I also gained some valuable inside.

Recently got a nice acetylene torch set, on a holder with wheels. It was sitting at someone's attic and he gave it me. The hoses are in perfect shape and the torch itself looks almost new, and if I spent 40 euro I get 2 new bottles of gas to do the incineration, the right way.
BTW at the hardware store it will cost me around 80 euro for a bottle of MAPP gas and a bottle of oxygen, while at an online hardware store it's about half that price.. Nuts he ?

Just one more question; if I was to buy a small gold melting furnace, (China 350 usd inc shipping - 1100 C) would it be overkill to incinerate the recovered salts and paper filters that way ?

And would that same furnace be suitable to incinerate (IC)chips ? I have around 12 pounds of chips, from flatpacks, to IC's and the chips from PC memory modules. My second idea would be to set a stainless steel pot on a barbeque and incinerate it that way, or should I just use a flame ?

Once again thank you all so much, and I do hope you all got a wonderfull Christmas.

Bluebloomer.

 

[nickvc]

I'd stay away from cheap furnaces they are usually rubbish.
Spend some time and look up all you can here on the forum about incineration and how others do it, you will be amazed at the ingenuity of many of our members and something will be what you need without spending big money buying something you don't.

 

[Bluebloomer]

Well, I believe you nickvc, I'm guessing it's all been done before so and the Chinese aren't known for their superiour quality

I have seen some DIY kilns or ovens to incinerate and even melt PM's so I guess I look around and borrow some idea's...

BTW I got 3 boxes with 6 drinking glasses, on the box is said "24 ct gold crystal glassware" handmade in Turkey. So I smashed one of the glasses to pieces and tried the HCL/CL method, aswell as AR but nothing is happening.. Guess it's fools gold, gold colored paint or something like that. Bummer would of been fun with 18 of those glasses which had a real think layer of "gold", although my first impression was that it must be paint. It was too good to be true..

 

[eastky]

Bluebloomer

Recover the gold first and then if you want go for the silver.

Correct me if I'm wrong, but I thought it's not possible to get to the gold without removing the silver first, if they are both in an acidic solution ?[/quote]

When doing a batch of AR I would consider silver a base metal even though it is a precious metal. AR is for gold and platinum group metals. Removing as much of the silver as possible before AR. Then you add a bunch of silver chloride along with carbon from burnt filters and the wheels fall off.

You are past worrying about silver being in the AR. Some of your gold is locked up in the carbon from the filters. You have a mess on your hands. I would go back to square one and start over. Like I said it is really hard to understand what you have done so far.

If you have an AR solution and you havent added anything to it yet. Add some iron to drop the metals out. Any gold that was absorbed by the carbon will stay in the carbon. Let everything settle and decant retrieve the sludge and filter material. Let dry and incinerate.

Being that I don't have any interest in silver. I don't do a lot of reading on recovering and refining silver.
You need to do some reading on silver chloride and see if nitric acid will dissolve it.
You may have to do some reading on converting silver chloride back to elemental silver.

If you have to go this far to recover or remove the silver you might as well melt it and pour shot or flakes to remove the silver with nitric acid along with the other base metals. If so you need to read up on inquartation.

Keep the aluminum out of the process at all times if possible is my suggestion. If aluminum will be dissolved or attacked by an acid it doesn't need to be added in the recovery or refining stages.

 

[butcher]

AgCl silver chloride is insoluble even in aqua regia.

Basically you will not have silver and gold in the same solution.

In highly acidic and concentrated aqua regia, or high concentrations of chlorides involved, you can have a tiny amount of silver which will dissolve as AgCl2, (Note the difference of AgCl and AgCl2 Here), but unless very concentrated and with a very high chloride content, even aqua regia will not hold a heck of a lot of silver this way (so we say: basically you will not have silver in solution with your gold). Maybe just enough to contaminate your solution.

Gold will not dissolve in nitric acid (unless chlorides or a halogen is involve. or another acid like HCL).

Silver will not dissolve in aqua regia, its surface oxidizes and quickly builds a protective layer, forming a layer of passivation of silver chloride, which is insoluble in aqua regia, if large pieces of silver or High silver mixed with gold (karat gold this passivated layer of silver chloride can keep the other metals like gold from being exposed to dissolve in the aqua regia.

If the silver metal is finely divided, in aqua regia, (or some other oxidizing chloride solution which dissolves gold Like HCl/NaClO or HCl/Conc.H2O2) finely divided silver like filings, silver in fine granular form, the silver may partially or even completely become converted to silver chloride, much of this depends on size of the silver, and conditions under which the reaction is run.

AgCl is insoluble in nitric acid (so silver chloride will not dissolve in nitric acid).

Note that if you mix nitric acid and a chloride you create a form of aqua regia (even if it is not the same proportions we normally deal with) this aqua regia will dissolve gold.

 

[eastky]

Butcher if you would be so kind as to grade me on the advice that I have given? Just wanting to know if my advice is acceptable. Having not recovered or refined anything yet just wanting to know if I have understanding of things.

 

[butcher]

eastky,
I will not grade you, it does look like you have a pretty good understanding of most things, and overall your advice here is good, you did state you did not understand some things like how the silver reacts, I will just try to add some to your comments.
Dealing with a recovery process, or a mess, is not easy, and much of how we go about it, can depend much on the mess we have to deal with, we have to consider what is involved and how it will react in different treatments. or reactions.


Correct me if I'm wrong, but I thought it's not possible to get to the gold without removing the silver first, if they are both in an acidic solution ?[/quote]

Silver will not be in a chloride solution with gold.
Silver forms insoluble silver chloride, in a chloride solution that dissolves gold.
If the silver is alloyed with gold in a percentage that will form a passive layer of silver chloride keeping us from dissolving the gold when we try to dissolve the gold we may need to in-quarter the gold to raise the silver content, and part the silver and base metals with nitric first, before going after the gold. The other option is to raise the portion of gold to silver ratio, by adding gold to lower the silver content of the overall alloy.

When silver and gold are finely divided, such as in powders or filings this may not be as much of a problem, where we may be able to fairly easily break up the silver chloride crust with heat and stirring using the vigorous mechanical actions, and the acid can more easily get past the silver chloride crust to attack the gold, where silver will form an insoluble silver chloride powder, and dissolve gold into solution.

When doing a batch of AR I would consider silver a base metal even though it is a precious metal. AR is for gold and platinum group metals. Removing as much of the silver as possible before AR. Then you add a bunch of silver chloride along with carbon from burnt filters and the wheels fall off.

Any time we can remove the other metals, or any thing that can interfere with the oxidation and reduction process of the target metal, the better we can perform the chemical reaction we are after, the more trash in the reaction the more trash out of the reaction, too much trash in the reaction and the reaction does not take place as we expect it to, you cannot expect to get your baby clean by washing him in muddy water, the muddier the water the less likely the baby will come out of the water in better shape than he went in, with gold we can lose our baby in the mud.

You are past worrying about silver being in the AR. Some of your gold is locked up in the carbon from the filters. You have a mess on your hands. I would go back to square one and start over. Like I said it is really hard to understand what you have done so far.
Great advice

If you have an AR solution and you haven't added anything to it yet. Add some iron to drop the metals out. Any gold that was absorbed by the carbon will stay in the carbon. Let everything settle and decant retrieve the sludge and filter material. Let dry and incinerate.

If I thought gold was in solution My choice here would normally be to use copper to cement values, instead of iron, although treating this mess like a stock pot and using iron may be a good choice also.
Here we can have gold in several states of oxidation, or even in colloidal form, we need to keep this in mind so we do not lose values, we may not be able to cement some of the gold from solution.

With a mess from electronic scrap, where tin is most likely to be involved, and gold can be held in the solution as colloidal gold, and it may be a high probability in solution of this state, I know I can not make the colloid precipitate, as the colloid is already a metal and cannot be reduced, or cemented.
The static charge of the colloidal particles keep the ultra fine gold metal in constant motion in the solution, where it will not settle, the colloids are so fine they can flow through a filter, the tin or other metals like aluminum can create problems with filtering, we cannot test for the colloidal gold in solution with a stannous chloride test, we will either need to break the colloid, (this may work with a fairly clean solution), or just evaporate the whole of the solution to dryness, and incinerate the powders to oxidize the base metals, remove the organic content and wash the troublesome material with a HCl boil as suggested by Harold to improve the state of our powders (removing trash or putting it into a state it does not create as much trouble...

Being that I don't have any interest in silver. I don't do a lot of reading on recovering and refining silver.
You need to do some reading on silver chloride and see if nitric acid will dissolve it.
You may have to do some reading on converting silver chloride back to elemental silver.

Nitric acid will not dissolve silver chloride, (it will dissolve elemental silver), many times I try to avoid making silver chloride any where I can, but many times in recovery it may be easier to just form the silver chloride to deal with, as it does have less value than gold.
In recovery many times we have to make decisions on which route may be the best way to go, many times either route will have its problems, Choices are made by our target metals and the conditions involved. Understanding of the problems we are faced with in either route we choose is helpful in making a decision. Understand the reactions can also help us to decide on a method that will create less trouble and get the most value out of the recovery process that we are working on. Basically not every mess or recovery project is the same, and can sometimes require different methods to solve a problem. This is where our study and education pays off.

If you have to go this far to recover or remove the silver you might as well melt it and pour shot or flakes to remove the silver with nitric acid along with the other base metals. If so you need to read up on inquartation.

If the silver is finely divided or in a chloride form. Or you have gold powders with a chloride salt, I may look at a different option, as both can be volatile if you just tried to melt them you are taking a chance of putting gold and silver up into the smoke evolving from that melt.

Keep the aluminum out of the process at all times if possible is my suggestion. If aluminum will be dissolved or attacked by an acid it doesn't need to be added in the recovery or refining stages.

Tin and aluminum are just trouble. Organics are trouble. Base metals are trouble. we need to remove the troublesome substances before we try to put our values in solution.

If this was a small batch of little value, and ended up as a mess, it may just go to the stock pot, to deal with it when I have to deal with the stock pot and its mess...
sometimes it is better just to wait and deal with the stock pot as a big mess instead of wasting time on a small failed batch with little value...

Filter papers normally have a lot of garbage, organics, salts of metals, chloride salts and possibly other salts such as sulfate, base metals, silver chlorides...

Treating them with a hydroxide solution to attempt to convert most of the metal salts to oxides or hydroxides, and wash out the more soluble sodium chloride that forms as much as possible, to lower the chloride content as much as possible, in an attempt to lower the chloride content where silver and gold are volatile at high heat, before drying and incinerating the powders and filter papers.

Where in the heat of incineration we can drive off the salts of acids as volatile gases, and burning off the organic, carbonous material. In the red heat, and stirring the powders exposing them and providing oxygen, we can convert, or reduce the metal powders to oxides, forming metal oxides in a state of powders which are more easily dissolved into the acid treatment later.

The tin involved can be put in a state in which it will be easier to deal with in the following hot HCl acid washes, (removing problems with the later filtering steps). The silver is finely divided, (and if this was not just a batch of silver, where we are basically trying to recover mainly silver).

If there are pieces of metal, screening the powders after incineration to remove the chunks of metal, and sending them to your stock pot.

A boil of the powders in HCl will normally be the best choice, to help remove the troublesome metals like tin, we may need to do a couple of these hot HCl acid washes, (the color of the wash will usually tell us if we are still dissolving copper or base metal oxides forming soluble chlorides), Hot water rinses also help to remove the base metal chloride salts like PbCl2...

(This treatment may convert the silver metal powders, or silver oxide powders to insoluble silver chloride powders, but if we are not mainly dealing with silver as a recovery then we will just have the small amount of silver chloride to deal with later.)

The HCl wash will not dissolve the gold, or PGM metals if so involved, which can be dissolved into solution, leaving the silver as a chloride powder...

the silver chloride powders and other metal powders are finely divided, so we can reach the gold and PGM with our acids, and with stirring to dissolve the gold or PGM from the small amount of silver chloride powders.
Silver chloride is normally a very fluffy substance, (when its not a in a state of the passive coating on the gold as it is when we deal with karat gold), the fluffy silver chloride once stirred takes time to settle, stirring helps to put silver chloride up in the solution in motion as the acids attack our gold or PGM powders, stirring and heat can also help our acids to get better exposure to these harder to dissolve metals...

If the filters papers were mostly just full of silver chloride, with out much organics besides the filter paper, and not a bunch of other metals or salts, or other materials from electronic scrap that would hold metals or compounds like tin and other troublesome metals, then how you went about recovering the silver would be a bit different...
The process of recovery and your choice of method to use, can be subject to the conditions and what your trying to recover, and what you have involved to recover the metal from...

 

[Bluebloomer]

Wow, that's amazing, a lot of information I can use, and helps me understand the process better.

I thought I read up enough to understand what I was doing, but what I thought I knew where just the basics..
Now I can try to clean up this mess the right way.
Will try and make a photo report when I take another go at this mess, but before that I will make a list of steps to take before I make them so you guys can correct me if I go wrong.

You guys have thought me that I :

- did things in a wrong order
- should of started with sulphuric acid to wash first, or go straight to nitric acid to wash
- did not incinerate but just burned the filters, causing trouble with carbon
- can't escape the fact that AgCl is sometimes impossible to avoid, perhaps even a necessity in a recovery process
- AgCl is insoluble, unless you want to use a litre of 5% ammonia per gram of agcl - see link
(http://www.saltlakemetals.com/Solubility_Of_Silver_Chloride.htm)
- Silver can remain in an AR solution, and pollute the dropped gold making it necessary to re-refine in some cases
- should always go for the gold first and not the silver, otherwise things get overcomplicated

By now I almost doubled the amount of salts and ashes due to the failed "incineration" and using aluminum instead of iron or copper. There is a good deal of AgCl in that mess. Perhaps I should try to explain what I did wrong and why thing have become sucht a mess.

- Before reading anything but the forum, I messed around trying to recover some gold filled/plated items, aswell as some silver jewelry. I had some 5 batches going on, totaly oblivious about the how and why of a good and safe recovery. At some point I cemented some silver with copper in one jar, and had a nice batch of AgCl in another jar, while the gold recovery was in 2 other jars.
- When I tried washing the silver I accidently mixed the silver chloride with the cemented silver. When I realized my mistake I made another one by discarding that silver mix in with the dillute AR with some dissolved gold that was not precipitated yet.
- So, now I have a big batch of dissolved gold, cemented silver and silver chloride and perhaps 20 coffee filters with traces of salts both AgCl, cemented Silver and other base metals.
- I put aluminum, and copper and iron in the bucket, because I wasn't sure what I should of been using.. I was kind of hoping that the copper would cement that last silver out, and the aluminum and iron should cement all other metals out, for a recovery attempt later.
- It took days to settle the liquid, decant and filter.
- The final result was a salt in different colors, from the different buckets, and a huge stack of filters..

That is in short what went wrong. Wasting loads of acids, and just fooling around like a headless chicken, not knowing what the heck I was doing..
From there I made things a bit worse by not incinerating the filters, but only burining them.
The only thing I did was remove the base metals, but I added those again with the aluminum.. So I repeated the mistake all over again sort of, lol.

When the weather is good again (snow and heavy freezing here in the Netherlands now) I know how to deal with this mess the right way. I have the materials to incinerate the right way, and I know the sequence of thing to do.

Now I think the gold can be recovered using the correct methods. The AgCl that has been clogging up the filters, is a very fine powder now. Is it a write off and totaly lost ?
When I incinerate and roast the powders, ash and filters the right way there will be not much left of the silver chloride. What is happening to the silver chloride at that time ?
I will concentrate on the gold only, and deal with the silver once the gold has been recovered.

So to clarify things: I have a big black pancake that has gold, silver, agcl, carbon, ash and aluminum in it. The carbon will be removed after a good incineration, then I will roast it red hot, and wash in nitric acid, or hot sulphuric acid, rinse and go for the AR to get the gold. The silver chloride traces are now converted or detroyed or what ?

ps

I tried filter the waste acids, then neutralize it using soda ash, and I added some ammonia I used to wash some other things with. Thinking it would bring the PH up a bit before using soda ash.
The result is a thick brown liquid. I know now that HCL + Ammonia makes ammonium chloride. So did I turn my acid waste into a dirty NH4Cl ? The waste is PH neutral now, and I am trying to filter it, before discarding it, but I would like to understand what is happening to the acid waste. By the looks of it, it might be 200 grams of thick brown residue that's left in the filters.
The ammonia was a mistake, should of kept it separate from the acids.. But what is the brown residue and how should I deal with it ?

 

[butcher]

You do have a mess, the use of ammonia can make it dangerous even explosive if dried or heated.
You need to acidify, HCl can be used (or nitric but it can put gold into solution here), acidify the solution and powders giving the powders a good stir to expose all of the powders get exposed to the acid well, crushing any lumps as you stir the powders in the acid, if silver is in solution the acid will cause it to precipitate out as silver chloride (with either acid used).

I would be careful when drying or heating of what containers were used, you may even try testing a few samples before doing the larger batch, just for safety.

How I would probably chose a recovery would depend much on what I had, if the majority of this is silver powders and silver chloride (some of which was reduced by the acids and aluminum), I would probably go for pretreatment washes, drying, an incinerating roast, and then a careful smelting process with soda ash based flux for a conversion of silver chloride during the melt.

It is hard to help someone get out of a mess ( or do a recovery of values), when you cannot see how the mess was made, and do not know all of the details involved, or know what it actually is that you have.

Here I suggest you acidify this mess for now, to make it safe to dry, (being careful about the drying, doing test batches), being sure to get the powders good exposure to acids, with plenty of stirring and crushing of any clumps, (a kitchen blender would be helpful), then dry the powders label them and save them, until you have done some more study so that you understand better of how to deal with them.

 

[Bluebloomer]

Butcher, the mess was made by collecting the washing liquids, the nitric acid and the neutralized AR. I wanted to neutralize this batch to store it for when I went to the disposal/recycle plant.

In a bright moment I thought, hey I still have some amonia/water let's add it to the batch and neutralize it, so all the waste liquids are gone.

That's when the brown sponge like precipitant appeared. I now had 4 filters with a thick red/brown sponge like cake substance. The liquid is drained and allmost clear, 6 litres in total with a PH of around 6.

At first I thought to just dry the sponge, and offer it as chemical waste along with the liquid. But then I started to doubt. And with good reason if I see what you just said.

The gold/silver/carbon mess is dried crumbled, and stored in a bin. So the sponge and liquid I am refering to now is just the waste, neutralized AR, and rinsing water.
Why the heck did it turn red/brown and why is it so much ? If I'm guessing it's about 400 grams of this red/brown sponge, but it's still pretty wet, like jellow.

That's what I did, and I totaly forgot that ammonium chloride is made with hcl/nh3 in equal parts, so perhaps traces of silver, aluminum, copper, smb, nacl etc is what's turning it red/brown ?

I just wonder what was going on with the red/brown sponge.

Since the jelly like substance is now in a paper filter, and the liquids have been separated. I should add some of the liquid back to the sponge, and acidify it again, or could I dry the jelly and offer it as chemcial waste ?

 

[eastky]

Blue good luck on your recovery.

Butcher thanks. At least now I know I have a pretty good understanding of things.

 

[butcher]

I cannot say for sure but the red brown sounds like iron, the gelatinous substance is most likely the aluminum oxide.
Colors are just clues, but really do not mean much unless in a specific test, or reaction...

To treat the waste solution I would raise it pH to 9.5, this is where most of the metals will precipitate from solution, let settle and decant the sludge formed in solution here, some metals are amphoteric and will dissolve in excess base, lower pH back down to 7, and decant the sludge that forms here, this way you remove most of the dangerous metals leaving mainly a salt water solution, to dispose of.

The waste sludge I dry and roast it, to change the hydroxides to the more safer (less water soluble) Oxide, before disposal.

The safety section has some very good topics on waste disposal.