Chip incineration - Leftover carbon

[VanMarco]

Sorry in advance for asking something that is already most likely answered multiple times.
So i incinerated a small batch of gold corner bga tops, flatpacks, mix.
My method is this. I take a tin can side , place the chips flat on it, then place the the sheet of metal with the
chips in my coal boiler, right onto the hot coals. the chips turn white and glow red but some that's a bit thicker,
inside a certain percentage is still black. Now, I ask. Is this a very big problem? I know that carbon would steal gold,
but also i will mill this in the ball mill, then i plan to wash the finer stuff with water (and not discard anything just in case), won't the carbon float with the fine ash?
I caught 99% of the ones that weren't fully white. Can I simply heat these black parts with a blowtorch?

Thanks

 

[Yggdrasil]

Sorry in advance for asking something that is already most likely answered multiple times.
So i incinerated a small batch of gold corner bga tops, flatpacks, mix.
My method is this. I take a tin can side , place the chips flat on it, then place the the sheet of metal with the
chips in my coal boiler, right onto the hot coals. the chips turn white and glow red but some that's a bit thicker,
inside a certain percentage is still black. Now, I ask. Is this a very big problem? I know that carbon would steal gold,
but also i will mill this in the ball mill, then i plan to wash the finer stuff with water (and not discard anything just in case), won't the carbon float with the fine ash?
I caught 99% of the ones that weren't fully white. Can I simply heat these black parts with a blowtorch?

Thanks

After it is ball milled and cleaned you can run the powders again.
The best way to process this is to Pyrolize where you run the gases back into the fire and combust them completely.

 

[andu]

Might want to mix the ash a tiny bit to make sure oxygen allows a more complete burn imo.
I wouldn't discard anything as your gold is probably going to a colloidal stage. Gotta love the nothing goes to waste policy.

 

[VanMarco]

Sometimes i think if you don't ball mill it, then bond wires will remain intact an separate better. but literature and members experience tell otherwise
Also, thanks!

 

[FrugalRefiner]

During your first incineration, the layer of white ash forms. It acts as an insulator and as a block for more oxygen to get to the center. Pull the partially incinerated ICs, Wash off the layer of ash, and incinerate again.

Dave

 

[VanMarco]

wow, thanks! that's a very good idea! Infact, thin chips, fared the best. thicker, got longer. some that remained somewhat carbon-y, are the flat packs that have a big copper heatsink inside. Will do as you say

 

[dannlee]

I found I was being stingy with propane use and shorting the overall time required - once they are past flames and turned to red glow coals thats when lower heat and a lot more time can finish it at one go.

Also - Antimony can be 2 or more percent of the epoxy and is used as a flame suppressant in many many electronic components - leaves the ash 'gummy' and I found a water boil with a tiny bit of HCl turned the silicon frit dust a bright white and let gold gather together easier...

Photo is example of a hurried burn, water washed to get black inky dregs out but not mild HCl washed - note the wires melted to balls from extreme temperature flame-out to reduce smoke & soot discharge...



EDIT: Wow, that was 7 years ago - sheesh, time flies by : (

 

[speed]

Ultimately carbon will be washed away during your wash process anyway so it's not really a problem.

 

[stella polaris]

Ultimately carbon will be washed away during your wash process anyway so it's not really a problem.

Exept that it can hold gold, that will be lost.

 

[jphayesjr]

During your first incineration, the layer of white ash forms. It acts as an insulator and as a block for more oxygen to get to the center. Pull the partially incinerated ICs, Wash off the layer of ash, and incinerate again.

Dave

If you're processing a lot, it might be a good idea to save the wash water, and accumulate over time. You may be pleasantly surprised how much colloidal gold shows up.

 

[Rreyes097]

So simply filtering with 2 coffee filters isn't going to catch any of that colloidal gold? I haven't saved all my rinse water because I've been using 2 filters to try and catch anything I might be accidentally pouring out.

 

[goldshark]

Has anybody ever added an oxidizer like Sodium Nitrate in with the chips? I am wondering if it may help, much like adding oxidizer to sulfides during a smelt or assay, to aid in the carbon's reduction.

 

[jphayesjr]

So simply filtering with 2 coffee filters isn't going to catch any of that colloidal gold? I haven't saved all my rinse water because I've been using 2 filters to try and catch anything I might be accidentally pouring out.

Not micron sized particles, but filtering will catch larger particles. Lab filter paper is available to catch the micron gold dust.

 

[kurtak]

Ultimately carbon will be washed away during your wash process anyway so it's not really a problem.

This is correct - the carbon is of absolutely no concern until ------------

1) After you are done washing away the carbon/ash to get your "concentrates" - and --------
2) Before going to the leaching step (if you intend to leach rather then smelt)

In other words - the only time the carbon becomes an issue is when you go to leach your concentrates which is easy to deal with by simply incinerating the concentrate to complete ash before leaching

Exept that it can hold gold, that will be lost.

If you are talking about the carbon holding gold & being lost during the washing/concentrating process that is only true if you do not mill the carbon to at least 80 (minus) mesh

In other words - pieces of carbon larger then 80 mesh can hold/trap bond wires so a (larger then 80 mesh) piece of carbon attached to a bond wire can cause that bond wire to wash away during the concentration process

That problem is solved by milling the carbon (the chips) to 80 mesh (& finer)

In other words - an 80 mesh piece of carbon is to small to stay attached to a bond wire - so - if (after milling) anything that goes through an 80 sifting screen means ALL bond wires have been liberated & those bond wires will concentrate just fine

At 80 mesh (minus) if you lose gold (bond wires) it's not because of the carbon - rather there is a problem with your washing/concentrating method

On the other hand - if you are talking about the leaching part of the process - then yes - you can/will lose gold if you do not turn the carbon to complete white ash before leaching because gold ions in the leach solution can & will be absorbed by the carbon

Kurt

 

[kurtak]

If you're processing a lot, it might be a good idea to save the wash water, and accumulate over time. You may be pleasantly surprised how much colloidal gold shows up.

This is completely irrelevant to the incineration - milling - & concentration part of the process (which is being discussed here)

There is NO colloidal gold formed/made during the above part(s) of the process

colloidal gold particles should only be an issue when washing the gold sponge (powders) AFTER precipitating the gold from the leach - in which case - yes - you should ALWAYS pour your gold sponge washes into a "settling" vessel (bucket/beaker/jar)

depending on the size of the colloidal particles that pour off during the sponge washing process those particles can take from a day to a week to settle --- they add up & yes can be pleasantly surprising

Kurt

 

[kurtak]

So simply filtering with 2 coffee filters isn't going to catch any of that colloidal gold? I haven't saved all my rinse water because I've been using 2 filters to try and catch anything I might be accidentally pouring out.

Not micron sized particles, but filtering will catch larger particles. Lab filter paper is available to catch the micron gold dust.

If we are talking about the gold sponge AFTER precipitation of the gold from the leach solution there is absolutely NO reason to filter in the first place - why tie up ultra fine gold particles that get stuck in the filter which means the filters then need to be processed to recovered the gold from the filters

This is especially true if you are dealing with less then an ozt of gold sponge

In my 15 years of refining the ONLY time I used a filter for my gold sponge was when I was dealing with more then 3 - 5 ozt of sponge in which case vacuum filtering worked well for dewatering (sucking) that much water out of that much sponge

IMO - anything under 3 ozt of sponge you are better served to simply decant the original leach (after precipitation) into a settling vessel --- then put the sponge through the HCl/water washing process & decant each wash into the same settling vessel

Once the sponge has gone through the washing process dry the sponge in the same beaker you precipitated & washed the gold in & then pour the dried gold into your well glazed melting dish & melt it

IF (the BIG IF) you are doing things right in the first place you should have a VERY SMALL amount of ULTRA fine gold that goes off into the settling vessel during the above decanting process - so little it is not of any real concern

However - it will add up over time - so just keep using the same settling vessel each time you do the decanting/washing process until it builds up to enough to process on it's own - or go into a future (other) batch

IF (again the BIG IF) you are having a problem with your precipitated gold pouring off when decanting then you are doing something wrong in the first place --- something that is causing gold to precipitate as ultra fine gold particles instead of larger heavier particles that stay well flocked together & well settled

Things such as precipitating from a "to dilute" solution or from a very dirty solution that causes co-depositing of garbage

When that happens - you have a problem - you need to figure out what that problem is & fix it

Because when gold is precipitated from WELL filtered solutions &/or a solution that is (Edit to add word > NOT to diluted the VAST majority of the gold will flock together into large enough (& heavy enough) particles that it will stay in your beaker during the decanting & washing process --- with NO NEED for filtering

Kurt

 

[kurtak]

Has anybody ever added an oxidizer like Sodium Nitrate in with the chips? I am wondering if it may help, much like adding oxidizer to sulfides during a smelt or assay, to aid in the carbon's reduction.

Hmmm - not sure just what you are asking here --- at what point in the process are you thinking of adding the nitrate (oxidize)

This is what I can tell you based on my experience processing IC chips which I used to process in 50 - 60 pound batches & doing 500 - 600 pounds per year (at the peak of my refining)

The steps (basically) -----------

1) turn epoxy chips to complete carbon by way of pyrolizing/incineration

2) mill the chips to turn the carbon to at least 80 mesh (& finer) powder

3) sift the milled carbon powder through 80 (or 100) mesh sifting screen to remove over size junk (silicon dies, larger Kovar legs heat spreaders etc.) if all carbon did not mill to 80 minus re-mill & resift the over size --- if you skip this step it will lead to gold loss down the road

4) use magnet to remove small Kovar wires & other magnetics that go through 80 (or 100) sifting screen --- if you skip this step it will lead to gold loss down the road

5) do a prewash of the carbon to somewhat reduce the amount of carbon - this prewash will reduce the carbon by 1/3 to 1/2 --- I do this in a 5 gallon bucket which I can explain in more detail if need be

This next step goes to somewhat answering your question about the effect of oxidizer on carbon

6) after the prewash (which has somewhat reduced the amount of carbon) it's time to remove the fine copper wires that go through the 80 mesh sifting process by leaching the carbon with nitric --- if you skip this step it will lead to gold loss down the road

What happens here - besides leaching the copper out is that the carbon absorbs nitrate turning it to sort of a (slower) burning black gun powder (in other words it's carbon plus nitrate but minus the sulfur) much the same as the principle as how gun cotton is made

7) wash the nitric/copper leach out of the carbon

8) do final concentration of carbon by method of your choice (panning, tabling etc.) to get final bond wire concentrates for leaching or smelting

If you intend to leach the concentrates you need to turn any (& all) carbon in the concentrates to complete ash by incineration & the nitrate in the carbon will assist in getting good complete ashing of the carbon in this step

If you smelt the concentrates you don't need to do the above incineration step as the carbon plus nitrate will ash the carbon (& slag it off) during the smelt

So - I don't know about using just sodium (or potassium) nitrate in the process - but you could certainly use "poor mans" nitric in step 6 if you can't get actual nitric &/or have to pay a high price for actual nitric

Just make sure you use poor mans nitric in step 6 & NOT poor mans AR

Kurt

 

[VanMarco]

I washed the chips, and what's left is a bunch of half charred stuff, and heatsinks. so to turn into all white ash, i need to place it on top of coal and leave it to glow? possibly using a thicker steel plate.

 

[FrugalRefiner]

Excellent post Kurt!

Dave

 

[VanMarco]

Today I build a contraption/thing to incinerate chips better, will post pictures