Sciencemadness Discussion Board

Graphite from dissolved electrode

Neme - 5-8-2016 at 09:55

I tried electrolysis of copper sulphate with bad graphite electrode and it dissolved into the solution. After many filtrations is the solution still black-ish and after short googling I did not find easy way to get rid of it.

So, does anyone know if there is an easy way to remove graphite from solution to get solution of clean copper sulphate for other uses?

MrHomeScientist - 5-8-2016 at 10:28

Well graphite doesn't dissolve in aqueous solution. More likely it's lots of tiny carbon particles that are so small they just sail through filter paper. You can wait a long time (several days, probably) and they should settle out, and you can decant from there. I've heard that boiling solutions with suspensions can cause particles to aggregate and fall out quicker, but somehow I doubt that will work with graphite. You could also try adding a flocculant like alum which should encourage precipitation. A recrystallization or two will get rid of any contamination it adds.

Edit: Wikipedia has a good explanation of how flocculants work:
Quote:
Particles finer than 0.1 µm (10−7m) in water remain continuously in motion due to electrostatic charge (often negative) which causes them to repel each other. Once their electrostatic charge is neutralized by the use of a coagulant chemical, the finer particles start to collide and agglomerate (collect together) under the influence of Van der Waals's forces. These larger and heavier particles are called flocs.

Flocculants, or flocculating agents (also known as flocking agents), are chemicals that promote flocculation by causing colloids and other suspended particles in liquids to aggregate, forming a floc. Flocculants are used in water treatment processes to improve the sedimentation or filterability of small particles. For example, a flocculant may be used in swimming pool or drinking water filtration to aid removal of microscopic particles which would otherwise cause the water to be turbid (cloudy) and which would be difficult or impossible to remove by filtration alone.

Many flocculants are multivalent cations such as aluminium, iron, calcium or magnesium.[1] These positively charged molecules interact with negatively charged particles and molecules to reduce the barriers to aggregation. In addition, many of these chemicals, under appropriate pH and other conditions such as temperature and salinity, react with water to form insoluble hydroxides which, upon precipitating, link together to form long chains or meshes, physically trapping small particles into the larger floc.

So maybe it will work with graphite after all.

[Edited on 8-5-2016 by MrHomeScientist]

Neme - 5-8-2016 at 10:50

Well just curious, where did I say that graphite dissolved? The only thing that dissolved was the graphite electrode. Settling does not work since the particles are so small that they're still in the solution after more than week.
The flocculant idea sounds good, I will look into it, thanks for advice :)

MrHomeScientist - 5-8-2016 at 11:40

"Graphite from dissolved electrode"
"graphite electrode and it dissolved"


In chemistry, "dissolve" has a very particular meaning:

from: https://en.wikipedia.org/wiki/Dissolution_(chemistry)
"The dissolution of gases, liquids, or solids into a liquid or other solvent is a process by which these original states become solutes (dissolved components), forming a solution of the gas, liquid, or solid in the original solvent." (emphasis mine)

from: https://en.wikipedia.org/wiki/Solution
"Characteristics:
[1] A solution is a homogeneous mixture of two or more substances.
[2] The particles of solute in a solution cannot be seen by the naked eye.
[3] A solution does not allow beams of light to scatter.
[4] A solution is stable.
[5] The solute from a solution cannot be separated by filtration (or mechanically).
[6] It is composed of only one phase."

Your liquid may satisfy some of those, but it violates 2, 6, and probably 3 and 4.

This may seem a bit pedantic, but it's important to be precise in science. Perhaps a better word for your situation would be that the electrode "disintegrated."

Anyways I'm interested to hear how this turns out. Let us know if you make any progress.

Xenoid - 5-8-2016 at 15:43

You could try diatomaceous earth, I used it to clean up the graphite in some of my chlorate cells.

It is sometimes available as a swimming pool filtering agent and also from some gardening centres.

Put a thin layer on top of your filter paper, you'll need a straight sided funnel with a flat bottom (Buchner) and possibly vacuum or pressure.

Neme - 6-8-2016 at 00:57

Quote: Originally posted by MrHomeScientist  

"Graphite from dissolved electrode"
"graphite electrode and it dissolved"


Sorry, but I don't see a mention about dissolved graphite. That bad electrode was containing mainly graphite and bonding material under coating that I removed. After I turned the electrolysis on, sulfuric acid, which was produced, reacted with bonding material and dissolved it. So the electrode dissolved and left very small particles of graphite in solution. I want to get rid off these small particles that can't be filtered or settled.

j_sum1 - 6-8-2016 at 04:11

As MHS said, "dissolved" is not the word you are after for this phenomenon. Corroded is more like it.

I have used graphite rods from batteries and copper sulfate to produce sulfuric acid from electrolysis. You are right that the electrodes do not last -- although it is better if you keep the current low.

It takes a few days but the black crud does settle and you can decant or pipette the liquid you want from the top. Gravity filtering with a good filter paper also works but is not actually much quicker.

For future reference, a strip of lead makes a far superior anode. It quickly builds up a layer of lead dioxide which performs its function admirably. Mine was an old piece of lead flashing which I cleaned up. This is a simple but slow way of making sulfuric acid. It is a great way of making lead dioxide electrodes. (Although I admit to not having tested them under extreme conditions.)