Incinerated filters and PM salts recovery

[Bluebloomer]

Eastky, thank you for your contribution, you have been very helpfull. Those salts from the failed re-recovery attempt are dry, and safely stored. Didn't realize I could also mess up the waste ..

Butcher, I have already filtered the gelatinous substance, and it's sitting in 3 large coffee filters. The liquid that remained after 3 times filtering was allmost clear, and PH neutral. I stored it in a container.

What's left is the red/brown sludge pancake. I do have a batch of liquid with a PH of around 10. Are you advising to add the filtered red/brown substance to that liquid with a ph of 10, and then follow your advice ?

 

[butcher]

If you already have metals or salts out of solution, I see no reason to take a chance of dissolving them back into solution again at this point.

 

[Bluebloomer]

Ah darn, I thought it would be the logical step, and then deal with the solids later. The solids that formed are a mixture of copper, aluminum, iron, and perhaps even traces of some precious metal, but those are neglable. I'm sorry I was too fast with filtering, before I could get your previous advice to work..

The red/brown pancake is now drying, because it's tearing up in the filter.

Butcher, do you think I would have to wait and then roast it, or should I try to force dry it in a hot bowl and should I offer it as a whole to the disposal plant, or should I save it and separate the metals at some later time? It now looks like coffegrinds after making a large pot of coffee. Only it's a massive volume, about 500 grams is remaining now.

I now know never to mix dirty hcl with nh3 and to neutralize acids the right way I need to use the appropriate methods. Just got ahead of myself again..
Once I know how to add photo's on the board, I will post them, so you might get an impression of what it looks like and what to do.

 

[g_axelsson]

Picked from the top thread on every section in the forum, thank you FrugalRefiner.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=69&t=21374&p=220514#p220509

Göran

 

[Bluebloomer]

Thank you Göran. I have resized the pictures, and I'll place them here on the server, as I know it's annoying to have posts on a forum with missing pictures.


The recovered precious metals salts, with carbon and used filters. It has been reduced to about a third, and the ashes and salts are mainly under the filters.

The still drying red/brown sludge after getting it thru a coffee filter.


Close-up of the sludge

After filtering the remaining liquid, that is now as good as clear, it turned bright red, iron oxide ?

Hope this sheds some light on the situation.

What remains is a 3 litre jug with almost clear liquid with a PH of around 6-7

Before I got your advice Butcher, I already filtered it, thinking It would settle down to just a little bit of sludge.. But got stuck with a big pile of this sludge..


And in about 11 hours it's new year, so in case we don't talk before that, I wish you all a very nice new years eve, and a healty, fortunate and happy 2015.

Gilbert

 

[Bluebloomer]

First of all, Happy New Year to you all.. !

Second, Butcher, it didn't sit with me well, that I filtered the slimey red/brown substance before I could take your advice and set it to action.
Well, I took some of the dried goo, al added base to it, with a Ph of about 9-10 according to the color of the paper.

The slimey goo dissovled in minutes, and now there is this black liquid with no visible solids.

Added a third of water to the solution, then some HCL. The solution started to warm up, so I let it cool, and then measure PH.

As the acidity went up, and the PH went down, the liquid became more and more greyish, and solids began to settle at the bottom of the jar.

Is that what you had in mind with your previous advice ?

I think I can siphon the liquid, and then filter the solids, or evaporate the remaining liquid ?

 

[butcher]

Bluebloomer,
I have to admit I am confused on what your doing now and why.

If you have powders and dissolved them in an alkaline solution pH. 9-10, (which sounds a bit strange as this is where most metals are least soluble, although some (actually many) metals that are amphoteric will precipitate with a base and re-dissolve, if the solution becomes more basic.

With metals dissolved at pH 9-10 this leads me to believe, you either had invaluable amphoteric, metals in solution, metals as colloids, or did not give the solution time to settle the insoluble metals.

Not really knowing what the powders you had that dissolved into this alkaline solution, or the details involved, it is hard to make any comments on what they could have been.

Normally when I treat a waste solution that is acidic, (after cementing the more dangerous metals from the acidic solution with a less dangerous metal like iron), I raise the pH. towards 7, let it sit to settle, and decant the insoluble sludge from the solution, then raise the pH of the remaining solution to 9.5 and precipitate more insoluble metals, then lower the pH back to neutral 7, so that the metals that are amphoteric will also settle out of the neutral solution as sludge and can be removed, leaving a clear salt water solution.

With the powders you have (loaded with carbon and all kinds of metals), attempting a separation with pH probably will just be pretty much fruitless, or a waste of time.

This will not be of much use with the mess you have now but it may help you understand better the solubility of metals at differing pH.

Although mess like what you have, the solution bound with organics or carbon will not follow these charts.

Take a look at these:
https://www.google.com/?gws_rd=ssl#q=solubility+charts+of+metals+at+different+pH
https://www.google.com/?gws_rd=ssl#q=amphoteric+metals

 

[Bluebloomer]

Butcher, I now see I totaly misunderstood it..

The goal was to make the red/brown sludge turn liquid again and separate the metals in it.

That worked with the solution with a PH of around 10. But now I see I should of used acid, and raise the PH in steps, letting the solution settle and siphon in between steps.

After reading more about amphoteric metals and the solubility of metals I understand I tried to do the process backwards.

The filters with the red/brown sludge were realy heavy, so this let me to believe there was a lot of metal in it, now I wonder if the weight was just the reaction between the ammonia and the hcl that clogged together.

There will be a lot of aluminum, carbon, iron and copper in the solution still. It's from old AP, AR, failed recovery attempts, and rinsing liquids. Some gold and silver will be in there, but I consider it a loss as those values are just too low. The only concern now is to make the solution safe enough to discard as waste.

Because I read this message too late, I am now back to square 1; an alkaline solutiuon polluted with a bunch of metals with a PH of around 10.

The salts from the failed recovery are safely stored, so this is just the waste. What do you think I should do now? Start over again and acidify the solutiuon and do it as you described ?

And yes I should read better, and perhaps ask before I do...

 

[butcher]

For the filtered solution see the safety section for dealing with waste.

As far as the sludge the carbon has somewhat complicated the waste treatment.

For the carbon based powders, dry and incinerate them, this will form oxides, (which are less soluble than the hydroxides of many of the base metals in this compound of salts), the section in dealing with waste in the safety section will also apply.

You could go chasing after the values in this mess, but you could also spend a lot of time, trouble, and acids, and reagents, and still have most of this as just waste to deal with, again, costing you much more than you may possibly get back.

If you knew there were values worth recovery here, incinerating and saving the roasted powders labeling them for storage. Storing them until after you have done more study, to learn how metals react. You could then try to remove much of the metals from this roasted sludge with your acid wastes from future batch's, dissolving many of the base metal oxides into the waste solutions, similar to how the stock pot works, but even that will take some more study, to understand how metals react, to be able to recover the values, you have a wide range of metals involved, some of which can be dissolved in acids, after roasting to red hot forming oxides, but some like the iron after forming an oxide you may, or may not be able to dissolve it back into an acid solution, depending on it oxidation state.

 

[Bluebloomer]

You're right Butcher, this is a waste of time and materials.
I did manage to recover a good 2 ounce of solids from all the waste I had left.

Next time I will not be using waste to treat waste, as it creates more waste.. Duh..

I had some nice 15 inch tall jars, and I kept siphoning the settled solids until the liquid did not settle anymore.

I acidified the waste, with used acids, then raised the PH and kept patient to let it all settle. The remaining fluid is a mixture of ammonia, dextrose, HCL, HNO3, Cl, SMB (used way too much) and sodium hydroxide all mixed into 1 brown syrup like fluid. Luckily I can dispose of it free of charge at the recycle plant.

The solids I have left are drying and I'll take a look at those later when I have a good testing solution.

All in all I failed miserably again, I ended up with allmost the same amount of paper filters again, and a lot of mixed metals and salts all because again I misunderstood the process..

At least all of the waste is disposed of now, and again it has been a learning process. Dealing with waste is just as tricky as dealing with a recovery of refining..
Thank you once again for all your input. Next time I will ask before I do when I'm not sure...

 

[DylanDownright84]

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.

I know this is from quite a while ago, but I've always wondered that if we incinerate filters from AR processes, would values be lost since the gold hadn't been in its elemental metal form? I've just ran AR filters in AR because of this fear or losing values. I've read and researched on this subject and never seem to find a simple answer. Same goes for my silver nitrate filters. I know heat can reduce metals to salts, but.... again, I've always worried that I would lose values if I incinerated AR or silver nitrate filters.

Edit: when talking about the incineration of filters hoke doesnt mention the loss of values, but I still find myself thinking about it. She suggests using petrol as fuel if needed, haven't needed to go that route, thankfully. Haha. But wouldn't some of the value vaporize and go up in smoke?

 

[Jmk88]

I believe if it’s in the form of gold chloride (III) you would indeed lose your gold by burning the papers.

The chemistry principle of this I will not comment on as I think I understand but I am not sure. In which case I will leave it to someone who does.

But my understanding is, from reading countless posts here, you certainly would be losing values if you incinerate soaked filters. Otherwise everyone would just get their gold out that way, rather than the processes we use.

 

[Jmk88]

Here is a related post:

https://goldrefiningforum.com/phpBB3/viewtopic.php?t=7455

I personally disagree in part with Phildreamers opinion; I don’t believe you would lose values strictly via “vapours”. You will if the solution begins it’s evaporation at the top of your pot as it will indeed splash out.

However in the sense of “evaporating gold”, this isn’t possible fundamentally at the temperatures we use.

Simply use an Erlenmeyer flask or a boiling flask to stop this happening. Boiling flasks will take a lot longer.

But I Digress a bit.

 

[butcher]

DylanDownright84,
Gold will dissolve in chlorine gas and some of the gold can be carried off in these volatile gases of chlorine.

Some silver is also lost in vapors if silver chloride is melted without conversion.

I normally use NaOH sodium hydroxide to help convert the HCl to NaCl salt which can be rinsed from the filter media, the base metal chloride salts will form hydroxides or oxides, a little sodium carbonate can also be added to assist in the fusion process (before burning the carbon in the papers)...
HCl + NaOH --> NaCl + H2O
CuCl + 2NaOH --> Cu(OH)2 + 2NaCl
2AgCl + 2NaOH --> 2Ag2O + 2NaCl + H2O


Heating too strong at the beginning and raising the heat too fast is also a place for loss.
Slow heating and raising the heat slowly can help to remove or convert chlorides and helps to minimize gold or silver losses, heating the salts slowly will minimize loss as this can help to fuse the salts and drive off acids and vapors as the metals convert, and the volatile gases leave or are converted slowly in the heating process.

 

[Jmk88]

And there is my newly found knowledge for today.

Thank you butcher.

 

[Yggdrasil]

Butcher!
Just out of curiosity, will all the PMs react and form hydroxides?
Gold will form Auric acid, H₃AuO₃ and then Auric Oxide when heated, but what about the PGMs?
Personally I have sprinkled a bit of NaOH on moist filters and dried it before incineration,
but I suspect I have overdone it, so I will go for a dedicated spray bottle in the future.

 

[butcher]

The more valuable metals are less reactive and do not oxidize easily, they are generally extremely difficult to get them to form oxides and hydroxides, for the most part normally needing extreme conditions like high heating to accomplish. Silver seems to be an exception.


Sprinkling a bit of NaOH on moist filters and dried it before incineration, would leave the NaCl salts in the papers which when heated provide a source of chlorides and chlorine if the filter paper are burnt. The table salt NaCl and any other soluble salts should be washed or rinsed from the filters before drying and incinerating them otherwise you are just back to square one from where you started.

 

[Yggdrasil]

Thanks
Duely noted.

 

[kurtak]

I believe if it’s in the form of gold chloride (III) you would indeed lose your gold by burning the papers.

Although that "can" be true it most certainly is not true in the absolute - ashing (which is the proper term for burning) filter papers to recover the "traces" of gold chloride that is "always" left in filters from filtering AR is "common" practice

Can you loose your gold when ashing filters - Absolutely - if not "done right" you can/will loose most if not all of it up in smoke

On the other hand - if done right the "vast" majority can be recovered (like 90 - 95% - & even as high as 98 - 99%) & for what it is worth the 5 - 10% lost during the ashing of the filters can be "captured" for future recovery

Note; - this holds true for silver nitrate &/or other metal salts trapped in filters

The question of loosing the values - or recovering the values is answered in the conditions of how you go about preforming the ashing of the filters

In chemistry we have two reactions - oxidation - or reduction --- gold chloride &/or silver nitrate are metals in a state of oxidation --- so when we ash filter papers we want to cause reduction of the metal oxides in order to recover those "trace" values trapped in the paper

The reduction of the metal oxides is called calcination which is a reduction of the oxides by way of heat - at "controlled" temp

Example; - you can actually reduce gold chloride (&/or silver nitrate) by evaporating a solution down to its sold crystal salts - then continue to apply heat to a point that the chloride &/or nitrate salts will reduce to the metals of gold &/or silver

In "fact" that is a common method used for reducing PGMs once they have been precipitated from solution as PGM salts

So the question is the conditions under which you ash the filters - temp plays a roll as well as whether done in the presence of oxygen - or the lack of oxygen

I you burn a single paper in the open air with a torch most if not ALL the gold chloride will go up in smoke because there is no control of the temp & the oxygen prevents the gold from reducing

Crumple the filter up into a "tight" wad - put it in a melting dish - put a torch to it & MOST of the gold will go up in smoke (because of the above) however "some" gold - in the "center" of the wad will reduce to gold because the oxygen can't get to the center of the wad

In other words a "flat" filter burned in open air exposes the entire "surface" of the filter to oxygen -where as a waded paper reduces the surface exposed to oxygen

So what does that all mean - it means when ashing papers it needs to be done in a lack of oxygen

So - I ash my filters in one of my "vision ware" pots - with a SS lid on it that has three or four 1/2 inch holes drilled in the SS lid (you want "some' smoke to escape but NO oxygen to entire (with out the holes in the lid - pressure can build up & blow the lid off)

Now then - I talked about temp as well - the "proper" (ideal) temp to cause calcination (reduction) of the chlorides/nitrates is 380 C - or 717 F - so temp control is important - the best way to do that is to do it in an electric furnace where you can "set" the temp - or you can do it on a hot plate but you should have a hand held laser temp reader

One more note to make when ashing filter papers (& I am not sure why this is true) but loses "will" be less if the papers are damp rather then dry --- I "think" its because the steam - at the beginning of heating starves the oxygen in the covered pot

I also talked about surface area (exposed to oxygen) there for you are best served doing more papers rather the less papers with the papers being wadded up

That said - you can over load the vessel with filters (&/or pack them in to tight) so that they don't completely ash to the middle of the vessel - that part is a bit of a learning curve --- the point being if you do only a couple/few filters at a time you "may" only achieve 90 - 95% recovery - by doing more filters at a time there should be no reason not to achieve 98 - 99% recovery

Once this part of the ashing is done the papers/filters will be mostly carbon - however you have now accomplished the task of calcination of the metals (the chlorides &/or nitrates have been driven off under controlled temp with no oxygen) so you can now complete the ashing by "incineration" --- meaning high enough heat in the presence of oxygen so as to turn the carbon to true ash with out worry of losing values

In other words - once the chlorides &/or nitrates have been driven off in a controlled manner - there is no longer a worry of losing values at higher temps

You can now ether recover the metals from the ash by leaching the ash or smelting the ash --- personally I prefer smelting with an added collector metal (copper or silver) - but that's because I do "a lot" of other smelting - so I just add the ashed filters to those smelts - in other words I "collect" my values in one larger batch rather then in several smaller batches

Bottom line - yes you can ash your filters with VERY little to next to NO lose - IF you do it right

Like EVERYTHING else in refining - there is a learning curve to it & can certainly be done with "little" to no lose

Kurt

 

[Jmk88]

And there is my second lesson of the day.

Not too bad for one day, by my reckoning.

Thank you Kurt.

My chemistry understanding is definitely improving with posts like this. I will sit and read this in the bath shortly.

Thank you Sir.