Copper Chloride ("AP") cleanup - Experiment writeup

[kurtak]

Nice thread haveagojoe

Because you are running a winning cell - rather than a parting cell it is important that the anode is "inert" to the electrolyte in the cell --- in other words - as metal ions are won to the cathode the anode can not be made of a metal that will react with the electrolyte

I bring this up because you said -------

I had read that Stainless Steel could be used for the anode

Stainless steel will react with HCl & therefor SS is not a good option as CuCl2 is a HCl electrolyte & the SS anode would most certainly be destroyed

On the other hand SS would work (at least to a degree) in a nitric electrolyte (such as copper or silver nitrate) &/or cyanide electrolyte as SS does not really react much to nitric - or cyanide

Therefore your choice of graphite is a good choice as graphite in "inert" to nitric, HCl & cyanide

The problem with graphite is that it erodes (sooner or later) due to the hydrogen being produced at the anode

So depending on the "density" of the graphite will depend on how long the anode holds up --- I bring this up because you said ------------

Graphite is also available as solid sheets or felt mats

per the bold print -I don't know this for sure but I am guessing carbon/graphite "felt mats" would likely fall apart in relatively short order due to erosion caused by the production of hydrogen at the anode & "sheets" may have the same problem

You want "high density" carbon/graphite solid "blocks" &/or rods

I've seen people on Youtube extract carbon rods from zinc-carbon batteries, which I would have tried if I could find one.

Yeah, those type of batteries are few and far between these days. Mainly found in the big, boxy 6V batteries. The downside is they've been immersed in the battery's electrolyte, so when you apply heat (voltage) to them, they start oozing electrolyte that's been absorbed in them

The problem with the electrodes out of those batteries is that they are made with a very porous "low density" carbon/graphite so they erode "very" quickly due to the hydrogen production at the anode --- they will work they just don't last very long --- you need high density carbon/graphite anodes if you want them to last for any real time

the felt has the highest surface area

Concerning the surface area - you want the surface area of the anode to be no more then the surface area of the cathode - it can be less but not more --- to large of a surface area at the anode & all you do is produce more hydrogen by splitting the H from the O from the H2O in the electrolyte

the reaction is now depositing the other contaminant metals such as Iron, Tin, Nickel and Cobalt

I don't believe iron will electrowin at all to the cathode - the tin nickel yes - but not the iron - not sure about the cobalt

In other words not all metals will electrowin - iron is one of them

& concerning mixed metals in the electrolyte (those that will electrowin) they will ALL start depositing to the cathode as soon as you turn on the power supply - It becomes a question of which metals win - more - or less - depending on several factors - such as - what is the dominant (starting) metal(s) - what voltage the cell is run at - effected by where the metal(s) sit in the electromotive series etc. etc.

Now the deposits are jet black and powdery, and don't adhere well to the cathode.

This is because as the metal ions become more & more depleted from the electrolyte it starts depositing smaller & smaller particles of metal at the cathode - smaller particles of metal don't "reflect" there color the same as large particles - so they start to become darker in color & as well they don't adhere to the cathode as tightly & as well because you are "freeing up" acid the longer the cell runs that acid "starts" to cause "some" oxidation on the surface of those smaller metal particles - which also cause them to look darker in color

For what it is worth

Kurt

 

[haveagojoe]

That's some nice copper powder to strain wet with 400 mesh and use to clean the stockpot or if you clean it up with some waste sulfuric to clean other base metals out and use to precipitate gold.

The cathode copper powder came up quite nice after sieiving and washing, I did a dilute sulfurc wash and water rinses followed by HCl wash and water rinses. Not the highest purity and I don't have a 400 mesh but it left a lot behind with a coarse sieve, I think it came out fine enough to use for something...

 

[haveagojoe]

You want "high density" carbon/graphite solid "blocks" &/or rods

Thanks, yes in the end I have ordered three 10mm rods for the anode, I think more than that will cause the chlorine production to become excessive, and will draw more current than the little buck convertor can offer (3A), although for the next batch I will run it at 1.8-2V from the start so it should be a bit slower.

Concerning the surface area - you want the surface area of the anode to be no more then the surface area of the cathode - it can be less but not more --- to large of a surface area at the anode & all you do is produce more hydrogen by splitting the H from the O from the H2O in the electrolyte

I found that as the black powder started depositing, it started to produce Hydrogen at the cathode. Increasing the surface area of the cathode seemed to resolve this- as you indicate, it must not be less than that of the anode.

I don't believe iron will electrowin at all to the cathode - the tin nickel yes - but not the iron - not sure about the cobalt

In other words not all metals will electrowin - iron is one of them

I think you must be right. The black powder does not seem to respond to a magnet.

The solution in the cell is getting quite clear now but still has a slight green colour, so I think it must now be Iron (II) Chloride remaining.

So while the experiment was successful in removing copper and probably most of the other metals, it has not solved the problem of Iron in solution.

 

[Shark]

Ferric chloride will eat quite a bit of copper.

 

[haveagojoe]

Ferric chloride will eat quite a bit of copper.

That's true but I think what I have remaining is ferrous chloride (FeCl2) which is pale green rather than ferric chloride (FeCl3)which is yellow-brown. Perhaps eventually when all the other contaminant metals have been deposited, the FeCl2 will be oxidized to FeCl3 by electrolysis and the solution will go brown. If so then I think it can be precipitated out by heating.

 

[haveagojoe]

Update on day 12

The solution is almost clear but still retains a slight green colour. Black powder is still being deposited, gradually slower and slower. I am filtering it every 12 hours. On day 9 I switched from a copper cathode to graphite, using one of the sticks I had been using as an anode. With less surface area at the anode it will be running at a lower current but the black powder seems much slower to deposit than the copper anyway.

I did some tests on the black powder, it's definitely not copper, I think its oxides and hydroxides of mostly nickel and tin. It has a faint but distinct earthy metallic smell which to me indicates nickel- a lot of British coins are nickel plated or nickel-brass, the smell is very recognizable and I find it quite unpleasant. The powder does not burn but imparts a green colour to a flame, also supporting the presence of nickel. I think the black deposits are mostly nickel oxide, which is sold as a very similar-looking fine black powder; and I think the remaining solution contains mostly nickel (II) chloride.

I will let the experiment run for another 2 days to try to remove the last of the contaminants but I think I won't be able to get it perfectly clear. Also I suspect that the HCl has lost some of its strength as some of the reactions of oxidation towards the end of the process may have produced water. Also towards the end I am noticing some black deposits below the anode, which I think are due to degradation of the graphite.

 

[haveagojoe]

Update on day 14

I ended the experiment today with mixed but generally positive results. Below is a photo of the original solution (left) and the solution after 2 weeks of electrolysis (right). It retained a green colour which I think is mostly Nickel Chloride. I think it would have continued to clear very slowly, but frankly I ran out of patience and want my workspace back to work on other processes.



In conclusion:
- Electrowinning of copper from used Copper Chloride solution is quite easy, fast and effective.
- 3V will deposit the copper quite quickly but can cause dendrites to form, and possibly co-deposits of other metals; 1.8V is slower but produces fewer dendrites and the rate of Chlorine production is lower.
- Copper tends to deposit first; removal of other contaminant metals is slower and requires a lower voltage to prevent excessive hydrogen production, 1.8V seemed to work well for both copper and other metals.
- A copper cathode is fine for electrowinning copper but graphite was better for the other contaminant metals.
- The other metals do not readily deposit in metallic form but rather as a black powder of oxides and hydroxides, which do not adhere well to the cathode and require regular removal by filtration, although since they are fairly heavy, most can be removed by decanting. A coffee filter can remove most of the black powder deposits but a finer filter would be better as they are very fine.
- The cathode must have an equal or larger surface area than the anode.
- The current draw is primarily determined by the surface area of the anode.
- Spacing of the electrodes affects the rate of deposition, closer spacing is faster but risks short circuiting by dendrites.
- Production of Chlorine gas is significant when electrowinning copper, but once the copper has been removed much less gas is produced as the other metals are being deposited.
- Electrolysis will not easily remove all contaminants but can revive the acid quite adequately for recycling in further Copper Chloride solutions.
- The main advantage is to remove copper in metallic form rather than as Copper (I) Chloride produced by settling, and to produce cleaner HCl rather than Ferrous or Ferric Chloride produced by cementing the copper onto Iron.
- The slowest contaminant to be removed is probably Nickel.


I think to run this process on a larger scale it might be advantageous to operate two cells, the first one to remove copper only using copper as the cathode, which would require management of chlorine gas; and then to transfer the solution to a second cell using graphite as the cathode to remove the other metals, which would produce minimal gas but would require regular filtration. Perhaps a basket below the cathode on the second cell to catch the black powder would make their removal easier and reduce the frequency of filtration required.

I have purchased better graphite electrodes for the next experiment but I'll take a break from it now while I work on some gold.

I will dry the black powder deposits to determine their weight.

 

[FrugalRefiner]

Joe, I appreciate your experiment, your approach, and reporting the results to us all. It's been very interesting.

Dave