AP solution producing blueish green sludge?

[goldfinger3]

So I posted my process a long time back and I got tied up with life in between then and now also took some advice from last time and changed how I was handling my materials.

Fast forward I am processing old tv remote boards I use a 5 gallon bucket with sealed lid as my overflow and a internal glass jar for my reaction vessel I place 30 or so boards at a time in Muratic and Peroxide solution the process had been running smoothly for quite some time processing roughly 200 boards or so at this point with 2 filtering process and then reusing the AP. I usually leave the boards for 2 or 3 days between swapping and yesterday I noticed a large buildup of a blueish green sludge. It washes off easily when i spray the boards down before removal but it has gunked up my reaction container and will be a nightmare to filter out. I remove as much forign material from the boards as possible before processing them but they will still contain some solder. The build up appears to start from the location with the solder, so my question is what might this blue/green sludge be and how do I handle it going forward. http://imgur.com/a/TLQHd

I have halted my processing for the time being until I can find a solution. I do not currently have anything to do a hot sandbath before processing, but I assume this is going to be the easiest way to prevent this going forward?

 

[g_axelsson]

I guess it can be three different things...
1. Copper chloride, have you tested to dissolve it in some extra HCl?
2. Metastannic acid stained with copper chloride. To deal with that... do a search on the forum. Here is a link to a few threads.
http://goldrefiningwiki.com/mediawiki/index.php/Metastannic_acid
3. A reaction with the plastic in the boards.

My money is on alternative 2 or 1.

Göran

 

[Refining Rick]

Am I wrong? If it is A/P then there should be no metastannic acid as I do not see any nitric acid was used. This point any tin would become tin chloride (stannous chloride).
My guess is the "coating" on the boards. I have had some of the coating get pretty messy. Especially if left for long periods to soak. Like in a nasty stomach....
Or copper chloride as Göran said. Easy enough to check for. Scoop some of the slime and add some fresh HCl. See If it dissolves.

 

[g_axelsson]

Yeah, metastannic acid. What do you think happens when stannous chloride goes bad? In an aerated copper chloride bath there is all possibility to oxidize tin to it's next state.
It looked like there were some gunk on the solder pads, but it might have been a coincidence.

Göran

 

[upcyclist]

:idea: Ding! This discussion (and the linked threads above) finally made me realize that while metastannic acid is formed when you mix nitric acid & tin, it is NOT a nitrate or anything of the sort. Just because we commonly associate it with nitric acid doesn't mean it isn't formed in other ways.

Thanks, guys!

 

[Refining Rick]

Yes. I was under the same assumption as it is normally discussed as a result of having tin in your A/R.

 

[Geo]

Metastannic acid is not really an excepted name for the chemical make up. It is more accurate to call it hydrated tin oxide. There is more than one species of hydrated tin oxide. Nitric acid on tin metal creates hydrated tin oxide directly while stannous chloride has to decompose into hydrated tin oxide. In the AP process, the very act of keeping the solution oxygenated converts the stannous chloride to hydrated tin oxide faster. Whether you are bubbling air through it or adding H2O2, the effect is still the same.
As far as the OP, it looks like some kind of coating on the board. HCl is a solvent to polyvinyl chlorides (pvc) so it could be some type of moisture barrier. If you have never noticed it before, it could be localized to just that one or just that one board type or part number.