Incineration

[Harold_V]

A recent inquiry by PM concerning incineration has prompted me to post on the subject.

Those of you who have read my ravings know that I endorse the process, and recommend it for almost everything you may encounter. When your material gets incinerated and why may vary, but rarely will a process not benefit by the procedure.

These are my thoughts, based on years of practice:

Hoke, in her book, talks freely of tossing on gasoline when incinerating. That, of course, is insane. Gasoline should never be used as an accelerant, especially when working indoors. The risk of a fire out of control is immense. I strongly advise against using anything when incinerating aside from the material in question. None is required.

Do not incinerate in a kiln. The most desirable condtion is one whereby the material in question can be ignited, not just heated and permitted to smolder. It's one way to limit the amount of smoke created by the roasting process. An ample supply of oxygen is required, which would be limited in a kiln. Open incineration is the answer.

If plastic items (bags containing polishing waste, for example) are incinerated, they should be monitored closely. The bulk of plastic items don't burn well, turning to oil instead when heated. However, once they reach critical temperature, they often erupt in flame much like you'd expect from burning fuel.

Do not incinerate in a hood that is flammable, nor on a countertop that has a wooden base under the burner. Prolonged heating will slowly convert the wood to charcoal, with a fire the outcome, assuming there is enough oxygen. A smoldering fire could result easily after prlonged incineration.

My method for incinerating was simple. My heat source was the same one that I used for the refining process, although when incinerating no other process was in motion because of the excessive heat.

The heat source in question was a three burner natural gas hotplate. They are relatively inexpensive (I used to pay $60), and were used as purchased, with one modification. I adjusted the valve on one position so it would be opened with greater flow, and adjusted the air full open. If natural gas is not an option, one could use propane, although with the propane tank out of doors, piping the gas inside.

A discarded fry pan serves very well as the incineration container. It should never be made of aluminum, which would melt, nor cast iron, which will be difficult to heat well, plus they will crack when heated as is necessary for proper incineration.

I found that stainless pans held up very well, and could be used for many cycles before they perforated. They do have a finite life, especially if acid bearing materials are incinerated, and that's one of the things you'll do routinely once you understand the benefits.

Second-hand stores (Goodwill, for example) are an excellent source for pans of this nature. Boy Scouts used a small pan, about 6" in diameter, which serves very well for small lots, so if you encounter one, don't pass it by.

I am assuming that the greatest interest here is the processing of E scrap. In that case, incineration may not be required until after the gold has been stripped. I would assume that the material would be stripped by a sulfuric cell, or one of the work-around methods promoted on the forum.

Once the values have been removed from the base metals, the step I would recommend is to get all of them in a filter, where they can be drained and dried. When well drained, they should be introduced to the pan, filter and all. Heat the lot until the filter combusts, then add sufficient heat to the pan to achieve a dull red heat. Apply heat to the sides and bottom of the pan, not to the material inside, and do not melt the material. A Hoke type torch, or a rose bud serves very well for the additional heating. This should remove all oils and grease and plastic bits from the material, and burn off all carbonaceous substances. Heat should be maintained until there are no glowing embers.

After incineration, crush the material well in a mortar, then screen the lot, removing anything that's magnetic, which should be added to the stock pot. It will likely carry traces of values, and they'll be recovered in the future when the stock pot is refined or furnace reduced.

The now crushed and screened material can be treated by two methods, each of which will remove unwanted substances. If nitric is your choice, the material would be boiled in nitric/water until no more fumes evolve, then the beaker filled with water. Decant when the solids have settled well, and rinse once again, using water.

If the material in question has the risk of containing tin, either from E scrap (solder) or it came from gold filled objects, which often have a soft solder bonding the gold surface, the material will benefit by a boil in HCl. This process will make for very easy filtration of the gold chloride solution that is yet to be produced.

Going from nitric to HCl presents a serious risk of dissolving values prematurely. To get around the problem, once again, the material should be incinerated. Once well heated, all nitric would have been expelled. Once again, crush the material well in a mortar, then place it back in a beaker. There should be no need to screen after the first time. Cover the material with 50/50 HCl and tap water and bring to a boil, holding there for several minutes. Remove the beaker from the heat source, and add water. Allow to settle well, then decant. Rinse with water, stirring well, then allowing the material to settle. None of these processes require distilled water. Tap water should be more than adequate.

After decanting, the material is ready to be dissolved to extract the gold. The resulting solution should be various shades of yellow, depending on the level of concentration. For the most part, the base metals will have been eliminated because of the acid washes. That serves to provide much cleaner gold.

All of these operations may sound like they are labor intensive, but they are routine-----easily accomplished, and paying huge benefits in the overall quality of gold recovered, plus ease in handling of the gold solution. Another benefit is you won't experience floating of precipitated gold, assuming you keep your vessels well washed, and don't get finger prints on the insides of beakers that are used in precipitation.

If you are involved in refining wastes from the jeweler's bench, the only material that doesn't require incineration is large pieces of karat gold, which would be inquarted, thus freed of oils when they are melted.

Something to ponder.

Regardless of how much you may wash filters when filtering your gold chloride solutions, traces of values will usually remain. If you do not wish to spend the time, and prefer to not dilute your solutions by rinsing, do not discard the filter when finished with filtration and a fast rinse with water (I always used tap water). They should be dried, then incinerated, with the resulting ashes stored. By incinerating, any free acids are eliminated, limiting the amount of rust you'll experience in your work area.

Don't discard anything that is in the filter. Everything should be stored for future processing by furnace. There is often silver chloride included, along with traces of other metals. They will serve to act as a collector when the material is processed, so they provide a valuable function.

The bottom line here is that incineration should be a part of your refining processes. The benefits far outweigh the results of avoiding the process.

Contrary to the belief of some, incineration does nothing to degrade the quality of gold, nor does it complicate refining. Yes, it is ugly from heating, but otherwise not changed. Incineration will not complicate the refining process, and the washing process will restore the bulk of luster to the material.

Harold

 

[Buzz]

Excellent post Harold, thanks.

How much of the values do you reckon actually "go up in smoke"?

Reason I ask is the fume hood.
Due to my location and facilities, i would have to incinerate outdoors and i doubt a fume hood would be very effective due to draughts etc.

I'd hate to stand there and watch all my precious just fly away!

Regards
Buzz

 

[Harold_V]

In my opinion, not much unless you incinerate polishing wastes. They were quite smoky and liberated a great deal of wax, especially if they were heated but not yet ignited. Once they ignited, they weren't bad. The vapors carried traces of the solids, but they were not lost, thanks to filtration.

As for losses due to breezes, you'd have to design around that problem, but it's certainly possible. The size of the opening in the hood would serve well enough, or you could provide a complete cover, with fresh air vents placed in appropriate places.

If you incinerate only small batches of materials, there really isn't much smoke. The worst things to incinerate are fume hood and polishing waste filters, along with the polishing wastes. Each of them smoke like crazy. I used to do a lot of my incineration in the dead of night to avoid the limited smoke plume being visible. Worked fine for years. My early refining years were in a sub-division, where houses were spaced 4 per acre. I had no complaints from neighbors while refining there.

There are losses by various procedures, so a filtered fume hood is a great idea. Even when dissolving values, if there's the slightest bit of effervescence, the tiny bubbles that surface burst with enough energy to carry off minuscule traces of vales. A filtered fume hood can capture the bulk of the losses and return them, assuming it's filtered and can be cleaned appropriately on occasion. I used 20" x 25" fiber glass furnace filters in my hood, which were easy to change. Once fully contaminated, I'd pull the filter and incinerate, then store the wastes that were generated. It the filter had punched steel faces, that portion went in the stock pot, and the incinerated ashes were stored, just as I recommend.

If you incinerate out of doors, as long as you can keep the hood dry, there's no reason to not use one----especially a filtered one. A good paddle type blower would be clog free and provide enough draft to keep the exhaust running through the filter, assuming you designed the hood properly. You can even include a scrubber of sorts, which would also recover lost values. A little creativity could go a long ways towards designing something that functioned well.

Assuming a scrubber is created, a cascading water type would likely work, but it, like the filters in a hood, should have provisions for the recovery of values. Anything solid that accumulated in the scrubber would be incinerated and processed by furnace. Assuming water was used, it could be introduced to the stock pot when it was changed, insuring that any values contained would be recovered. I had plans like that, but sold the business before they materialized.

I don't feel comfortable disclosing the amount of gold, silver and platinum group I recovered from my waste materials (after more than 20 years of operation), but there's not a person reading this board that wouldn't be impressed. It was a wonderful savings plan-----especially with the inflated values of those metals on today's market. Damned shame I didn't keep the platinum group longer than I did.

I encourage anyone that refines to pursue a hood and a scrubber of sorts. Do it for all the wrong reasons (recovering losses), if ecology alone isn't a good enough reason. You'll be justly rewarded, assuming you keep refining.

Harold

 

[skippy]

I'd advise against anyone incinerating e scrap. Dioxins and brominated hydrocarbons are not something you or anyone else would want to breathe. If the incineration was nice and hot, with sufficient exygen I suspect most of the nasty stuff would be decomposed though. Watch out for the solid residue too, heavy metal oxides, etc.

http://www.aseanenvironment.info/Abstract/41015197.pdf

 

[Platdigger]

Skippy is right about incinerating this E scrap stuff.

This is a whole different ball game.

Randy

 

[Harold_V]

I'd advise against anyone incinerating e scrap. Dioxins and brominated hydrocarbons are not something you or anyone else would want to breathe. If the incineration was nice and hot, with sufficient exygen I suspect most of the nasty stuff would be decomposed though. Watch out for the solid residue too, heavy metal oxides, etc.

http://www.aseanenvironment.info/Abstract/41015197.pdf

I trust you took note of my comment:

I am assuming that the greatest interest here is the processing of E scrap. In that case, incineration may not be required until after the gold has been stripped.

I made no recommendation to incinerate E scrap, but incinerating the stripped values is advised. Assuming you've done your work well, there would be precious little in the way of noxious fumes created, and the benefits of incineration would be far greater than ignoring the procedure.

Harold

 

[skippy]

Harold, I know that you wern't recommending incinerating e-scrap. Though I can see how my message came across like that - sorry.
I just wanted to caution anyone against trying this with motherboards on their BBQ in their subdivision .

 

[Harold_V]

Chuckle!

Yep! I get your point. Especially if the barbeque were to become the heat source. I can't imagine food prepared after incineration of boards would be in anyone's best interest, to say nothing of the noxious fumes that would be generated in the process of incineration.

Fact is, if a person could get around the initial incineration, tossing entire boards in the furnace to be melted is not a bad idea. The base metals would serve as a collector for values, so you'd achieve quite good recovery with minimum effort. Problem is, you're left with a mess that would require parting with nitric. It's beyond that which the home refiner should entertain unless a cheap source of nitric is available.

One of my customers was a recycler, many years ago. He had incinerated a huge quantity of E scrap, fusing it into a common mass. I processed enough of the material to determine values, and realized it was a losing proposition for a small scale operation. I ended up shipping the balance (over 20 pounds of metal) to a refinery that is known to me (now, not then) to be dishonest. They reported half the content that I had determined to be present----and took their fees from the half due my customer. That was the beginning of my negative experiences with major refiners.

Harold

EDIT:

It has been brought to my attention that the very fact that I've discussed the process of incineration and furnace processing of boards may be an inducement for those that have less than good sense to attempt recovery of values by that method. I do not endorse the concept unless one has a certified incinerator. It has long been known that burning plastic compounds results in the liberation of toxic gases. It would also be an invitation for a visit from the local authorities. It would be difficult, if not impossible, to mask the stink and visual signs.

I hesitate to remove the information above, if for no other reason, it's a fact of life. That's one of the processes that is used for recovery of values. That in no way should be construed as a suggestion for the home refiner to attempt the process. Those who don't have the wisdom to adhere to good practice would likely engage in it, in spite of being well informed of the hazards. We see that daily in other processes. Use good sense, folks.

Harold

 

[skippy]

I suspect if the boards were charged into a retort and the gases generated upon heating were piped out and through a burner with sufficient oxygen that the toxins would be minimal. Improvise some sort of exhaust scrubber and it would be even. Might be an appropriate way to incinerate a small amounts for assay.

 

[Anonymous]

I used a old toaster oven or heat gun to depopulate the boards, catch a lot of the solder in a pan and all of the parts. Then I use a belt sander with 36 grit to wipe the traces off.

I have a slucie box to seperate the metal from the small amount of fiber from the boards.
I should add that obvius gold plating is removed by grinding seperately first.

I was doing pretty good till copper dropped so low.

I still have all of the chips and stuff to process.

Jim

 

[butcher]

James this can be so fine your tailings may also be rich, fine gold floats, and especially if stuck to solder mask etcetera,maybe catch tailings letting them settle, decant, and leach them to test for values.if you are not just after the copper in your processes, and the parts depopulated have value to electronic hobbiest.of coarse check switchs and older components for gold, tantalum capacitors, silver capacitors,and stuff like that. newer circuit boards are mutilayer and can have more copper in between fiberglass sheets than they have on the outside layers.
fiber Cpu's have multilayers with gold plating and copper between each fiberglass layer

 

[kjavanb123]

All,

Is this the same "incineration" process required after I nitric leached some CPUs to remove the base metals before I leach the materials with AP? Because last time, only 0.22 grams of gold powder was recovered from 3 of the following CPUs which is just a major loss in value somewhere.


I read Harold's piece on this, so after nitric leach, rinse and decant with water, I should boil in dilute hcl? then proceed with AP leach?

Thanks
Kevin

 

[maynman1751]

Incinerate between acids(nitric/HCl) or you could produce AR and lose values.

 

[kjavanb123]

hi,

what you mean by incinerate between acids? do i have to heat the CPUs after they are being leached with nitric to remove base metals?

Thanks and regards,
Kevin

 

[Geo]

incinerate between processes using nitric solutions and hcl solutions. you cant wash either acid out of the material. if you leach in nitric, and go to a hcl solution without incinerating to remove the nitric acid first, you will create a weak AR solution that will dissolve some of your values. if you did not know this beforehand, you could discard the solution and thus throwing out your gold with the wash water.

 

[kjavanb123]

hmm I still can't get the "incineration", I got the part leaching in nitric then adding hcl would create weak AR, so what do i do?? after I leached in nitric, then just heat the beaker with CPUs in it dry? boil in water? if you could elaborate on this part.

Thanks
Kevin

 

[Geo]

if you just dry the chemical, it forms a salt. when you add water, it hydrates back to the chemical it was. to completely remove the nitric or the hcl from material, it needs to be brought to (at least) a dull red heat for a few minutes. you cant do this in a glass container. Harold recommends a stainless steel pan. any heat source that can get the material that hot will work. if the material contains carbon, it needs to be kept at a red heat until all the black carbon is gone and chalky white ash remains, if its solids (like ceramics or metal) just a dull red heat for a few minutes will work.

 

[kjavanb123]

Thanks a lot Geo, I saved some left over solution after nitric leach and it seems positive for gold.

Regards,
Kevin

 

[pesco]

Hi guys,
I know its an old topic, but situation have changed, at least from point of view :mrgreen:

Back in early nineties every two weeks I was getting bucket load of sand papers and around 1.5 kg workbench dust (mainly paste) along with spent electrolytes. Propane costed me next to nothing, so all solids were incinerated. I never used steel pan and would not recommend it as some values form alloys with steel very easily. Container of choice was around 3 litres, deep ceramic dish and was doing all papers and paste in small batches.
The yield was good enough to return more then twice as much values as my competitor (to be clear - he wasn't sloppy or uneducated, he was just greedy :x ) and still make very nice profit. Problem were losses and I was joking to my mates that if I carry on like that for next 20 years or so I will be proud creator of new gold ore deposit around my garden :mrgreen:

Today I would rather experiment with pyrolysis. Last year I have done pilot batch of RJ45 connectors, gold plated tapes and sim cards. Plastics simply vanished, but still there is a bit of carbon left from paper labels, some tapes etc.. That batch is still waiting for further processing but I am thinking of replacing incineration by heating the batch up on hotplate and very slowly blowing oxygen over it. Should work in theory, but practice is often quite different animal. Anyone tried ? :mrgreen:

 

[Geo]

what you describe is the general process for incineration. heat the material until only a small bit of carbon remains and then play oxygen over the heated material to convert the last bit of carbon to carbon dioxide.