What went wrong here ? - Solved

[kernels]

Hi guys,

I've built up a bit of experience with recovery and refining from E-waste, so no everyday I end up stumped . . .

I recently harvested some ceramic logic ICs with gold braze under the die and broke them up into medium sized chunks (around 6mm /0.25") The main reason for breaking them up was to remove all the kovar legs, which I did.

I then placed the chunks and powder that came out of the chip smasher into a beaker, and as per usual, added a good volume of HCl and heated up to hot, but not boiling temperature around 90deg C

Almost immediately after adding the cold HCl I started noticing a white powder, but assumed that it would be just ceramic powder in suspension in the HCl.

I kept the solution hot for around two hours, but never observed any real reaction (I've seen the reaction of hot HCl with solder many times)

I then washed out the HCl containing a lot of cloudy particles, re-filled with clean HCl and proceeded to add HNO3 to put the gold into solution.

I then filtered the solution . . .

So, I've ended up with this post filtering :



And after letting the filtered solution sit for a while, I got a white crystal precipitant:



So, I didn't think I had Tin in the source material, didn't get any reaction with hot HCl. Could this be the result of Lead ? Any other metals that can cause these problems ?

 

[4metals]

The solids in the filter were that color all along or did they get that grey purple hue on standing? Was the solution warm or even hot when it was filtered?


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[kernels]

I think the filtered material has turned more grey than it was at first, solution was still medium hot when I filtered it, probably around 50 deg C or so.

These are the same questions that led me to wonder whether I had Lead in the source material, but couldn't see why I would have lead (without Tin) inside ceramic Logic ICs

 

[kernels]

Sorry, left out that the color of the filtered material is more grey than purple, I think the color of the first image was slightly off because of the LED illumination I was using.

 

[4metals]

My guess is it is silver.

Silver chloride has a low solubility in aqua regia but if it is chilled it is exceptionally low. I would say it is silver chloride. The combination of coffee filters which are a rather coarse filtration medium, combined with an increased solubility of silver chloride in warm / hot acid, allowed the dissolved silver to pass through the filter. When the solution cooled off, the solubility decreased and it comes out of solution.
Try washing the solids with hot hot water, if it's lead chloride it will dissolve and pass through the filter.


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[kernels]

Thanks for that great insight 4metals, when looking at the dies on the chips, It did look like the bonding wires could have been silver! Not sure why that didn't click for me, haven't actually come across much silver in E-waste so far!

Now I guess it will probably be worth trying to separate the silver chloride from the left over ceramic chips . . . Any advice here ?

 

[4metals]

Ammonia


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[kernels]

Thanks, will search and research. Very much appreciate your contributions 4metals.

 

[Geo]

The actual bonding wires should never be made of silver. There may be something out there that I'm not aware of but if the wire looks like silver, it's most likely aluminum. The silver is under the die. The base the die sits on can be silver, palladium or an alloy of the two. Gold was also used in the bases.

 

[kernels]

So, I'm still at a bit of a loss, I went out and bought some Cloudy Ammonia (Ammonium Hydroxide 18g/L) from the local hardware store yesterday, added about a teaspoon full of that material in the filter into a beaker, added about 200mL of the ammonia and couldn't seem to dissolve any of the white powder.

Geo - yes, doesn't really make sense that they would use Silver for bonding wires. The die appeared to be set in gold braze, which is why I processed these, I did get a little bit of gold out of the solution, but am still stumped about what the white powder mess is.

 

[glorycloud]

You may need to heat the ammonia solution to get the silver chloride soluble.

 

[kernels]

After a few more small experiments, I now don't think the mystery material is Tin or Silver.

1. Take a small quantity of source material, treat with Nitric Acid (warm) - No Reaction (Not Silver)
2. Take a small quantity of source material, treat with boiling Hydrochloric Acid - Solution color turns very dark (Dark grey / purple color) - 'white' powder appears to dissolve slowly.

 

[kernels]

Update - I'm pretty sure these ceramic logic ICs are made from pressed Alumina, which is pretty much inert. The process of smashing them up has produced a lot of fine powder, which looks bad, but really it filters out pretty well (just a bit slowly).

So my process with these chips will basically be to smash them up, then move straight to a AR leach, then filter the gold bearing solution off. I might also have to cool + settle and siphon the solution since some of the fine powder is almost guaranteed to make it through the filters.

 

[Tzoax]

My guess is that the white stuff is the glue reacting with acids, take a look. I also had that white powder when processing this type of chips, and it was very slow to dissolve all of that "glue" (i dont know the composition of it).



Alexander

 

[kernels]

Hi Tzoax, AWESOME! That must be exactly what it is. I think having smashed my chips quite has caused a lot of that glue to end up as powder. It doesn't seem to affect the AR leach much, just have to filter and settle the solution to get rid of it.

 

[g_axelsson]

When you mention it, I have run into this purple sludge too. I learned that the glass frit that "glues" together the two ceramic parts of a ceramic DIL capsule (for example in EPROM:s) dissolve in diluted nitric acid. I now wash them in nitric first giving a lot cleaner scrap to work with later on.

I made a post about this last summer. http://goldrefiningforum.com/phpBB3/viewtopic.php?f=34&t=22611&p=237368#p237368

Göran

 

[Geo]

The white layer or middle layer between the top and bottom alumina layers is sintered glass. The glass is the white powder that will not dissolve in any acid. The bond that holds the sintered glass together is broken by any strong acid. Sulfuric acid, nitric acid or HCl acid will all work at breaking the bond though Sulfuric works fastest follow by nitric with HCl being the slowest. Direct dissolution by AR or course will also break the bond in the sintered glass and really makes a mess. Once the glass is broken down, the legs are loose. The legs terminate at the bonding wires. Separating the legs by magnets at this stage will cause you to lose gold bonding wires because they are still attached to the legs. After it has reached this point, any remaining legs must be dissolved to reclaim all of the gold bonding wires. The legs should be removed well before this stage while the chip is still whole. The best way I have found is to use CuCl2 in any capacity whether it is new or old or even depleted. The exchange of iron for copper will remove the legs and leave copper dust and whole chips with no legs or very little iron in the ceramic bodies where the legs were.

 

[kurtak]

My guess is that the white stuff is the glue reacting with acids, take a look. I also had that white powder when processing this type of chips, and it was very slow to dissolve all of that "glue" (i dont know the composition of it).

4.jpg

Alexander

Pictures really can be worth a thousand words - If the OP had provided a pic of that type chip this would have been resolved earlier (nothing wrong with the way this thread went - just saying)

Thanks for posting Tzoax 8)

as I side note - when I first read the problem I was for some reason picturing "white" ceramic chips (maybe I wasn't reading close enough)

Kurt