Chemical Recovery of Hydrochloric Acid from Copper Chloride solution

[haveagojoe]

I have tried to recover HCl from used Copper Chloride solution using electrolysis, see thread here:
https://goldrefiningforum.com/threads/copper-chloride-ap-cleanup-experiment-writeup.35323/

The experiment seemed to produce reasonable results in depositing Copper from solution at the cathode, but I wasn't happy with the amount of Chlorine gas produced, and I was not able to test the strength of the resulting acid. I suspect that it was significantly weakened by the release of Chlorine and resulting production of water by the electrolysis.

In my ongoing quest to find a workable method to renew my acid I came across this excellent and thorough video which came out a few days ago, which I'm sure will be of interest to members:

Video

Distilling off the HCl from the Copper Chloride salts seems to be a much more practical and effective approach than electrolysis.

The video creator performs the extra steps of fractional distillation to bring the concentration of the acid up to its azeotope, and then bubbling Hydrogen Chloride gas through it to increase the concentration further. However for reuse in Copper Chloride etches, I think it would be sufficient to simply reuse without fractional distillation or further concentration, at low strength ~10%.

The drawback of this approach is that, as the creator notes around the 1:40 mark, only free HCl can be recovered. In heavily saturated solutions, the Chloride is bound to the Copper ions and remains behind in the Copper (ii) Chloride salts.

I am wondering if there is any way to address this in order to recover Chlorides which are bound up with Copper? I was thinking that prior electrolysis might help by removing metallic Copper, but I think the release of Chlorine gas during oxidation simply depletes the HCl, producing water.

Would there be any benefit in dropping the Copper out with Iron first instead to create Iron Chloride solution, and distill that to recover the HCl?

This video details the process of HCl recovery from Iron Chloride solution, but it seems far too advanced to replicate at the hobby level... Video

 

[haveagojoe]

I think I found an answer- conversion of the Copper Chloride into Copper Sulfate using Sulfuric acid as in this video: Video
This should allow the remaining HCl to be evaporated off, and then the Copper can be recovered by electrolysis without production of Chlorine gas.

The video says to every 1g of dry Copper Chloride salts, add 7ml water and then 1ml concentrated Sulfuric acid; bubble with air to ensure Copper (i) Chloride is dissolved, and then distill to recover HCl, leaving behind Copper Sulfate which can be rehydrated with water prior to electrolysis. Unfortunately it appears a platinum coated anode is necessary; a copper cathode is fine. Small platinized titanium mesh anodes seem to be quite affordable though.

 

[Martijn]

I think I found an answer- conversion of the Copper Chloride into Copper Sulfate using Sulfuric acid as in this video: Video
This should allow the remaining HCl to be evaporated off, and then the Copper can be recovered by electrolysis without production of Chlorine gas.

The video says to every 1g of dry Copper Chloride salts, add 7ml water and then 1ml concentrated Sulfuric acid; bubble with air to ensure Copper (i) Chloride is dissolved, and then distill to recover HCl, leaving behind Copper Sulfate which can be rehydrated with water prior to electrolysis. Unfortunately it appears a platinum coated anode is necessary; a copper cathode is fine. Small platinized titanium mesh anodes seem to be quite affordable though.

I tried electrolysis with a seemingly affordable platinized electrode, it got eaten pretty fast. You need a good quality.
Another way could be evaporating your copper chloride to crystals and add sulfuric and then 'evaporate' the HCl, which comes down to distilling actually, as the HCl will form an azeotrope and you need an excess of sulfuric to evaporate the chlorine out of solution. if you keep it stoichiometrically balanced to exactly use up your sulfuric, you need to evaporate to dry copper sulfate.

edited: this part makes no sense, i confused Cu chloride with Cu sulfate.
Mind that if you go for stoichiometric conversion, 'dry' copper sulfate will be anhydrous, there is a tridydrate( greeinsh) and a pentahydrate(the cobalt blue crystals) which contains resp. 3 or 5 H2O molecules for every CuSO4 molecule. Sovadding 7ml of water to dry copper sulfate means anhydrous, i think.

To measure how strong your HCl is, use tritation: make a molar solution of NaOH by adding 40grams of lye to 1 liter of distilled water.
Put a small beaker on a scale (with a good accuracy of 0.01gram) and add a couple of grams of your HCl or copper chloride. Then write down the starting weight and tare your scale.
Put a tiny piece of pH paper in the beaker.
Slowly add the molar NaOH with some stirring until the paper shows neutral pH.
Write down your added NaOH weight.
Now it takes 1mol of lye to neutralize 1 mol of HCl. NaOH + HCl > H20 + NaCl.
1ml of a molar lye solution neutralizes 1ml of a molar HCl solution.
As 1ml of molar lye will weigh about the same as 1ml of molar HCl, 1.04gr resp. 1.03646gr, you can guesstimate the strength.
So lets say you started with 5 grams of HCl and you needed to add 25gr of lye solution (5 times as much as the HCl) it's about 5 mol HCl. If you calculate that in weight and mol, you will get 5×36.46gr > 182.3grams of HCl per liter> 18.23%HCl.

Source: wikipedia HCl page.

Another way to calculate it: you added 25ml of Lye which is 1/40 of a mol of lye, so your 5gr of HCl solution contains 1/40 of a mol of HCl, which is 36.46/40= 0.9115 gram. That is a percentage of 0.9115grHCl / 5gr HCl solution = 0.1823 or 18.23% strength.

 

[otto]

you could consider dropping out the copper as the basic carbonate with HCO3- that will deal with all the Cu with very low residual Cu2+ and avoid tainting your mix with Fe3+ or compromising the Cl- concentration. if you dont need highly conc. HCl you can boil the mix down and used a "paired container" method of cleaning up HCL tainted with Fe, by placing a container of distilled water in a sealed system with the contaminated HCl. the gas will migrate to the distilled side producing roughly 10-12% HCL but very pure

 

[haveagojoe]

you could consider dropping out the copper as the basic carbonate with HCO3- that will deal with all the Cu with very low residual Cu2+ and avoid tainting your mix with Fe3+ or compromising the Cl- concentration.

Doesn't that just neutralize the HCl?

if you dont need highly conc. HCl you can boil the mix down and used a "paired container" method of cleaning up HCL tainted with Fe, by placing a container of distilled water in a sealed system with the contaminated HCl. the gas will migrate to the distilled side producing roughly 10-12% HCL but very pure

This could work, but still only recovers free HCl, the chlorides which are bound up with copper will just stay as they are. It could only recover half of the available free HCl as well, since it only migrates until it reaches equilibrium between the two containers.

I think the copper sulfate conversion should work well to recover HCl from copper chloride. It looks like it shouldn't work, because both copper chloride and copper sulfate are soluble, so it's not precipitating, it just makes a mixture; but it's the heating which makes the sulfuric displace the HCl to form copper sulfate.

I think it would also still work if the solution contains iron and nickel as well as copper - as it usually does with escrap etching. It would leave behind iron sulfate and nickel sulfate along with the copper sulfate.

 

[Martijn]

Doesn't that just neutralize the HCl?

Yes, it does, and even before any carbonates are formed. Once pH goes over pH 1, most of the acid is already neutralized.

if you dont need highly conc. HCl you can boil the mix down and used a "paired container" method of cleaning up HCL tainted with Fe, by placing a container of distilled water in a sealed system with the contaminated HCl. the gas will migrate to the distilled side producing roughly 10-12% HCL but very pure

I doubt that works. How do you know when to stop "boiling" (I assume you mean "evaporating")
So after boiling the dirty HCL is at or even still below the azeotrope? Because evaporating any HCl down will yield 20% max, not any stronger.
No HCl will leave the vessel to migrate to clean water.