Processing clean ENIG plated PCB's

What is the most environment friendly yet cheap way to process clean (no solder, most likely only Cu,Ni,Au) ENIG plated PCB's for Au and maybe also Cu?

Filtered Incinerating, crushing, smelting, electrolysis?
Bio leaching after grinding? (probably not practicable without housing the bacteria/archaea - however the most environment friendly i suppose)
Chemical process? I always read that it will create too much waste; true?
Mechanical filtering, crushing, weighting/washing + smelting?

Anything else?


This is basically new land for me as i usually just sold the traces, but boards (about 10% top layer only, the other ~90% are multilayer with many having 7+ layers of hefty copper >1000µm) are stocking up and i really want to process this myself, at least the Au if the Cu would be too hard.

So any input is welcome, also for crazy ideas :wink:
Thanks

Theoretically, If you have a lot of them, the best and cleanest way to go would be shredding & milling followed by gravity concentration, If done properly you should end up with primo stuff - easily assayable and thus easy to sell or even refine yourself... but you would most likely need a dedicated machinery for that (i think there have been some successful DIY efforts documented here, though)

Keep in mind - ENIG is disappointingly thin, thus low-yielding - to see for yourself try running few kg of your boards through AP (copper (II) chloride, look it up); You`ll get all the gold but without mechanically destroying the structure of the boards it will be next to impossible to dissolve inside copper layers... You can try to recover the copper that does dissolve by cementing on scrap iron or electrolytically, but I would guess that there is many times more value in copper than ENIG in most cases

Most processes if run in a proper setting and taking care of the waste could be environmental friendly. Since we are talking ENIG and all gold is exposed I think a cyanide bath is both the cheapest and clean way to recover the gold. It all depends on the scale of the operation what is the most economical way and how the boards is processed later on.
Warning : Cyanide can kill you if you don't take proper care. No second chances.

For recovering the copper both chemical leaching and smelting could be used in theory. At larger scale copper is recovered only by smelting. A lot of companies have tried to develop a chemical leach process for circuit board scrap but I have never heard of one succeeding.

Talking about that, wasn't there a company a year or two ago that built a large pilot plant somewhere in the USA? I can't seem to find that thread right now.

Göran

Thanks for the input, it helped me to decide to take a differnt approach untill i got more gear and experience;
I figured i would decide later how i finish, but for now i would do this:

1. Seperate boards by thickness (pcb and copper, most boards have their copper thickness marked) and weight/whole surface.
2. Cut of the gold plated parts of the board or remove the whole traces if possible.
3. Seperate traces from cuts.


Explanations:

1. Some boards are very very very thin and as stated before just one layered, they are not >1000µm Cu but ~100-300µm(marked) i made some calculations on the surface/1000g - they are worth sorting out.
2. Removing traces is sometimes very hard, especially with thin boards, but cutting the gold plated parts on the other hand is way easier on thinner boards.. This step further increase the quality of the scrap and will make it easier to refine.
3. Obvious i guess, traces are >95% (>99%?) metal while cuts contain lots of fibres/epoxy.



Then i will see what i got left, i figured it is way harder to estimate than i thougt when i grabbed examples for evaluation (calculation) because the thickness of the boards and the thickness of the traces, leave alone the amount of layers giving so many different results per 1000g..

Sorting out it is, for now.

@niks neims

I am aware that ENIG is very thin, i use 0.01µm to 0.1µm as an min to max, and 0.01-0.03µm as possible result yields in my calculations, depending on the weight/surface this material can still be better than fingers by weight, sadly most of it isnt ("7 layers of thick Cu").

@g_axelsson

Most processes i know about will create waste, bioleaching seems to be the only almost (some claim completely) clean process. However, yet no option for someone like me (and most others) considering the 'low' copper price.

May be best to keep my copper refining shut for now and sell it to a professional in this field instead, or on ebay :roll:

The only people who manage to get out all the copper efficiently and profitably are the refineries. The price of copper is actually pretty alright at the moment too.

A lot of people have tried to treat the copper in a less commercial environment and in many cases it causes as many issues as gains.

After going trough one pack of 10kg (22lbs) yesterday, i ended up with ~8kg/17.6lbs thick pcbs with gold still on (left unprocessed), ~1.6kg/3.5lbs thin pcbs as copper scrap with all gold removed and about 415g/0,91bs of very thin boards which thickest is <0.6mm/0.027inch (remember, some other boards have copper traces thicker than that, this is a very good hint if u ask me), at least 50% of the surface is gold plated, most are 90% plated and are not completely shiny (greater surface).

@anachronism
Yes i will try to sell the not gold plated parts to an copper refinery or salesman, these are no use for hobby builders or collectors.
Burning it is very cheap but very toxic so i can not sell it to my neighbour :twisted:

I have come across a lot of erroneous platings, i will upload a picture the next days..

Is it possible that with errors in the process, gold builds an alloy or thicker plating than usually on the boards?

Thanks experts

Picture of example:

Syn said:

I have come across a lot of erroneous platings, i will upload a picture the next days..

Is it possible that with errors in the process, gold builds an alloy or thicker plating than usually on the boards?

Thanks experts

Click to expand...

Yes there are times with older plating where the thickness is different from what it was supposed to be. That given you must never base the prospective value of a job on that. Assume the lowest thickness, and price accordingly.

I thought the picture might be helpful to identify different errors and their possible changes. This would help to cherrypick from thicker boards (so far selling the unprocessed very thick boards on ebay seems to be best value).

Clearly there are not many people who know about this, but why not give it a shot?