Reclaiming Copper from Sodium Persulfate #4: 6B Pencil Lead Anode
As previously noted I’ve decided to give softer sketch pencil leads a try.
It looks like the electrodes are more efficient and a bit more stable. I’ve also noticed that the solution seemed to have taken on a lighter blue color and the copper cathode seems to have gotten thicker. In principle it seems to work!
However, the thicker anode too started to disintegrate after a few hours at 2 to 2.1 V.
It’s time to go back to the drawing board and see if it would make sense to get either a properly manufactured graphite or coal electrode or even go all out and get a platinum one.
Reclaiming Copper from Sodium Persulfate #3: Bigger Graphite Anode
I tried scaling up the graphite anode by connecting several sketch pencil leads together.
I’ve done this using single strands of stranded copper wire to weave and knot the individual pencil leads together. Once tightly woven into place I’ve finalized everything by adding generous amounts of solder.
With regards to being able to use higher voltages this was no help (of course) and the pencil leads still disintegrated.
What I’ve learned:
- Fellow hacker reloc pointed out that the softer a pencil lead, the more graphite it contains. I’ve picked 2H leads for my tests so far and will switch to 6B leads (the softest I could find at short notice).
- What is going into solution depends on the voltage applied (potential) and which materials of lower potential are still there (if available, the lowest energy bond breaks first, even with high voltages).
- Documented potentials (see: Pauling electronegativity) are usually defined for platinum electrodes. If you’re using something else, you have to apply a correction value. Also thanks to reloc for helping out with all the theoretical science behind the experiment!
Reclaiming Copper from Sodium Persulfate #2: Stainless Steel Anode
I got my hands on some pieces of stainless steel to replace the graphite anode.
Reader’s Digest version: the mess got bigger. Green is the new blue.
What I’ve learned:
- Stainless steel doesn’t seem to work well, the solution quickly turns green.
- The green color could be Iron(II)-Sulfate, though that is not yet verified. Anyway it’s not really a success.
Reclaiming Copper from Sodium Persulfate #1: The Naive Approach
At shackspace we’re somehow in the business of collecting sizable amounts of used up etching solution. We’re using Sodium Persulfate which on its own is also used as a bleach, detergent or disinfectant.
However, with plenty of copper ions in the used up solution it’s a very potent poison and you should not by any means pour it down your drain, ever.
A quick search on how to get rid of the stuff yielded Marc Schaffer's page (German) who explains his electrolysis setup using a 12 V 900 mA Photocell, a copper cathode and an anode made from either stainless steel, coal or platinum.
Platinum was no option because of its high price. I didn’t have any stainless steel that I could verify to be stainless steel at hand, so I opted for coal.
The closest thing to coal I could think of was graphite.
And since I’m a lazy person, I simply got some sketch pencil leads. All the core, none of the casing :)
The result of the first experiment can be seen in the pictures above:
- The pencil lead disintegrated
- A huge mess
What I’ve learned:
- 12 V won’t work. Anything much higher than 2 V will cause the lead to disintegrate
- Electrolysis should start at around 1.8 V, that’s when bubbles (Oxygen) start to form at the anode
- Graphite particles can be filtered out quite easily using a piece of paper towel
- More electrodes should have better yield
Teardown: Water Flow-Sensor
Recently the shackspace lasercutter started to act up a bit. Turns out that I’ve probably put a bit too much copper sulfate into the cooling water and it started to react with the aluminium connector pieces which then corroded and closed up on themselves.
However, after having just cleaned them, the lasercutter complained again that there was no flow. So this time around I suspected the flow sensor itself. Turns out I was wrong (it was the just recently cleaned connectors, again) but I took apart and cleaned the flow sensor anyway.
The sensor itself is genius in its simple design. It has a single moving part: a small flap that blocks flow in one direction but lets it pass with close to zero force in the other. The flap position is then detected, I’m going out on a limb here, most likely using a hall sensor or something similar.
What I also found is a piece of horrible engineering.
One side had a connector screwed in, secured with Teflon tape and a small O-ring. The O-ring was pressed to the casing by the face of the screw-in connector tube. So as soon as you start fastening the connector, the O-ring will inadvertently end up being squeezed into the tube and bunch up there, restricting flow and doing actually a worse job with water proving than if it simply wasn’t there at all.
Long story short, I’ve left out the O-ring entirely, put everything back together and it worked beautifully.
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