# Recycling copper sulfate electrolyte



## Martijn (Dec 30, 2021)

Hello fellow refiners. I was going through my used and dirty CuSO4 electrolyte after all the leftover pins from the sulfuric stripping cell were processed. 
My cell is a 10 liter paint roller bucket and I had three 8 liter runs to process. 
I had the electrolyte stored in a 30L jerrycan. 
The bottom is layered with white/yellow base metal pollution. 

To concentrate the used copper sulfate I filtered it and evaporated it down in a pyrex bowl in a sandbath at around 70 degrees C. Kept adding electrolyte until the other base metal (sulfates?) were forming a layer on top and the color of the solution was dark blue. 

To collect the copper sulfate I took it out of the sandbath and let it cool. 
Next day a thick layer of blue crystals formed on the bottom and the concentrated solution, also containing the free sulfuric acid, was poured off in a filter to get more pollution out before it went back in the evaporation bowl.

The white/yellow pollution, ( I think nickel and zinc sulfate precipitate mostly) falls to the bottom, polluting the crystals on the bottom. 
To get the most pollution out, I broke up the crysral layer and carefully spray rinsed the white spots off with cold water until the rinse water was clear blue and no longer milky. The crystals will dissolve a bit during rinsing, but keeping the rinse water cold will keep that to a minimum. 
The rinse water is fed back into the evaporation bowl. 

I then dissolved the 'dirty' crystals in hot water and poured it in a beaker to crystallize out.
Since there was still a small amount of white precipitate on the bottom, I suspended a wire in the solution to let crystals grow free from the bottom. 

Now this is just for fun and hobby, but I also want to replenish my clean copper sulfate supply for future cell runs. 
Crystalizing is an easy way to purify certain salts.
Ì'm sure you can scale it up by hanging a plastic mesh or something in there with more surface for crystals to form on. 

To get crystals growing faster on the wire, I 'seeded' one wire by dipping it in the still warm concentrated solution and let it cool, hanging above the beaker. This forms small crystals that kick start the growth on the wire. I repeated this a couple of times while the solution was cooling off. 

Once there are crystals forming in the beaker on the bottom, saturation was reached at that temperature and from that point you can leave the wires hanging in while it cools down further. They will not dissolve anymore because of the solution being saturated. 

Once there are a lot of crystals on the bottom of the beaker, the crystallization process slows down and I restart it by taking the wires with the crystals out, and heating the solution back up to dissolve the crystals on the bottom again.
You can also add more new washed crystals during heating to raise the concentration. 
Let it cool a bit and put the wires back in when the first tiny crystals start to form on the bottom. 

To harvest the clean pure copper sulfate, hang them to dry and just pinch them off with pliers or redissolve them in a bit of clean water to let it crystallize out. A very concentrated solution heated up so far that its super saturated will form very fine crystals, like you get when you buy it. 

A good way to clean the last bit of evaporated and crystallized out solution is plating out the copper on a copper sheet, using a inert anode like platinum. I use a plate of lead to avoid getting more metals in solution from the anode. I don't have a platinum electrode. 
The lead sheet does wear down in time but it seems to fall off as brown black powder in stead of going in solution. Lead is insoluble in sulfuric acid. 

The cleaned solution will contain only sulfuric acid and other base metals in solution that cant be filtered out. You can let the dirty acid settle out and decant or filter while the H2SO4 concentration is still low. 
Then you can boil it down to get a higher concentration. 
It will still be dirty, but it can be reused to distill copper chloride or copper nitrate waste to get some hydrochloric or nitric acid back from your waste. You could also use it to make nitric acid from nitrate salts. Converting your waste that way will also create more copper sulfate to harvest. 

Endless fun! 

Some pictures of my experimenting: 


Evaporation bowl in sand on a hotplate. 



Filtering the poured off dirty solution after colling down to harvest crystals. 



Cristalizing beaker with wires. Electrowinning cell tryout in the back. That's going through evaporation first. This is just a setup for later use. 


Close up of one wire with crystals. 

A lot more fun than the usual waste treatment! 

I hope this is usefull to someone. 

Martijn.


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## FrugalRefiner (Dec 30, 2021)

Very nice Martijn!

Dave


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## Martijn (Jan 4, 2022)

Growing result of first crystal after three times in re-concentrated juice. 
It's a real shame Christmas is over.. this would be a great tree decoration


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## Abdoulapapatte (Jan 25, 2022)

thank you


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## Declan O'Reilly (Feb 7, 2022)

Very cool, thanks for the explanation of the process!


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## yellowfoil (May 9, 2022)

Is it wires or strings hanging in solution to grow crystals on? I know you mentioned wires, but they look like strings in the picture. Very cool process, I will use it for purifying of copperas as well. Thanks for sharing.


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## Martijn (May 9, 2022)

Some sort of plastic string. Sorry. Language error. Here in NL its the same name for wire, thread and strings of both metal and fibers.


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## Martijn (May 9, 2022)

Just looked in my year old test beaker with iron sulfate waste and found some big square-ish green crystals formed on the bottom. Just by letting it evaporate slowly. It seems to separate itself from other contaminants in there like zinc by the crystallisation process.


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## yellowfoil (May 9, 2022)

Would you please specify exactly the process you got copper sulfate from. I just wat to be sure I understand how copper sulfate was created.

Exactly what happened to me with iron sulfate. Nice big crystals at the bottom of the container in brownish sediments. Hanging it on strings is better. Easier to remove crystals from dirty solution. You gave me inspiration, thanks.


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## Martijn (May 10, 2022)

yellowfoil said:


> Would you please specify exactly the process you got copper sulfate from. I just wat to be sure I understand how copper sulfate was created.
> 
> Exactly what happened to me with iron sulfate. Nice big crystals at the bottom of the container in brownish sediments. Hanging it on strings is better. Easier to remove crystals from dirty solution. You gave me inspiration, thanks.


It came from the copper sulfate cell to purify copper and brass pins and get the last bit of gold out. I replaced the electrolyte when it got too dirty to keep a clean deposit of copper on the cathode.
You could also electrowin it out but it will be impure. 
I wanted to get fresh clean copper sulfate crystals for future runs. 

The result of all those stripped pins was negligible by the way. 99% of the gold came off with the sulfuric stripping cell. 
But now i have a box full of copper plates for the stockpot. And a bit of experience gained. 

I've just put an iron bar in the remaining acid to make more copperas. 

Martijn.


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## Edlin (May 10, 2022)

Martijn said:


> Growing result of first crystal after three times in re-concentrated juice.
> It's a real shame Christmas is over.. this would be a great tree decoration
> 
> View attachment 47682


Haven’t seen this process used since first year university. Great job Martijn.

Ed


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## Martijn (May 29, 2022)

Continued with electrowinnng to get more copper out, filtered and then added some iron to cement out more copper and convert free sulfuric to make more copperas. I also added some sulfuric to furhter raise the concentration while evaporating. 

Slowly evaporating in the sun with a reflector. It can get the temperature up to 45 degr. C. 
First crystals showed up after a cool night. They will probalby dissolve again in the heat from the sun. Started at 14 degr. C, after one hour in the sun it's at 30 C.


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