Chemical Using Zinc to deal with Tin Oxide from dirty Copper Chloride etches- experiment writeup

[Yggdrasil]

The colour looks a bit more normal after filtering, dropping out the lead with sulfuric, and then double filtering again. Maybe it was just the lighting.

I tend to get impatient at this stage and use an excess of SMB rather than off-gassing the chlorine properly. But this time there's no point rushing as I'm waiting for a new crucible to arrive anyway so I'll just wait. I think I ought to cement it really but the excitement of seeing it drop with SMB is very alluring

My first solution was practically red, but it was just 10 ish ml and quite concentrated.

 

[haveagojoe]

My first solution was practically red, but it was just 10 ish ml and quite concentrated.

Yea this time I made a bit more of an effort to keep the volume down as my last one was such low concentration that the drop was ultra-fine and took a long time to settle.

 

[haveagojoe]

Your call.

I decided to take the sensible route of cementing with copper and was pleasantly surprised.

In the past I have found cementation to be a slow process, but this time my solution was still warm after driving off the chlorine on the hotplate, and when I suspended a coil of heavy-gauge electrical wire into it, the whole solution turned dark and cloudy almost instantly, nearly as quickly as an SMB drop.

Shaking the coil after a few minutes released a crust of black powder which quickly settled in a layer at the bottom of the beaker, while the solution continued to darken.

I will leave it to proceed for 24hrs but I think most of the gold will have cemented long before then.

I would be interested to hear if others use gentle heat to aid cementation, as I think this is something I will do again in future.

 

[Yggdrasil]

I decided to take the sensible route of cementing with copper and was pleasantly surprised.

In the past I have found cementation to be a slow process, but this time my solution was still warm after driving off the chlorine on the hotplate, and when I suspended a coil of heavy-gauge electrical wire into it, the whole solution turned dark and cloudy almost instantly, nearly as quickly as an SMB drop.

Shaking the coil after a few minutes released a crust of black powder which quickly settled in a layer at the bottom of the beaker, while the solution continued to darken.

I will leave it to proceed for 24hrs but I think most of the gold will have cemented long before then.

I would be interested to hear if others use gentle heat to aid cementation, as I think this is something I will do again in future.

Circulation is important so all the solution comes in contact with the Copper.

 

[haveagojoe]

Circulation is important so all the solution comes in contact with the Copper.

You're right- after about 90 minutes of continued aggitation, the solution is almost clear with only a slight yellow hue remaining, and only black powder at the bottom and on the coil. I'm amazed how effective it was and I will no longer hesitate to use cementation as a first stage recovery method.

 

[orvi]

You're right- after about 90 minutes of continued aggitation, the solution is almost clear with only a slight yellow hue remaining, and only black powder at the bottom and on the coil. I'm amazed how effective it was and I will no longer hesitate to use cementation as a first stage recovery method.

Cementation is a great first step in rough recovery, because it kills residual nitric acid too. Chlorine isn´t very problematic (pool chlorine/hypochlorite), because solubility of gasseous chlorine in HCl is relatively low. And chlorine is very effectively reduced by SMB too.
But if you are refining with nitric, using cementation on copper assure complete de-NOx-ing and also complete gold precipitation.

It is beneficial to heat the solution below boiling point - it not only speed up the process, but also convection in the hot liquid mix it around and effect better precipitation. Not to mention that precipitates from hot solutions "pack" better and particles clumping together means faster clear-up time and settling/decanting.

 

[orvi]

Yup

The Control of Poisons and Explosives Precursors Regulations 2023:

The Following Substances Are Classified as Regulated Explosive Precursors:
Ammonium Nitrate 16% N
Nitromethane 30% W/W
Potassium Perchlorate 40% W/W
Hexamine
Nitric Acid 3% W/W
Sodium Chlorate 40% W/W
Hydrochloric Acid 10% W/W
Phosphoric Acid 30% W/W
Sodium Perchlorate 40% W/W
Hydrogen Peroxide 12% W/W
Potassium Chlorate 40% W/W
Sulfuric Acid 15% W/W

I never thought you will be worse off than us... I very much hate the people who regulate what I can and what I cannot. As a veteran in making all kinds of stupid things in my younger years, experimenting with many kinds of energetics... I really do not see how you will use say phosphoric acid or HCl for explosives preparation...

Here, they totally pissed me off by banning regular battery acid. Like, why ? Who ever misused battery acid ? How ?

 

[haveagojoe]

precipitates from hot solutions "pack" better and particles clumping together means faster clear-up time and settling/decanting.

Yes, this was what surprised me the most, the cemented gold is granular rather than dusty, much larger clumps than I have seen before.

Chlorine isn´t very problematic (pool chlorine/hypochlorite), because solubility of gasseous chlorine in HCl is relatively low.

Well I'm not sure, I seem to have encountered a problem:

After cementation, I let the solution sit for about 18 hours and then drove off the residual chlorine with heat on the hotplate for an hour. I could not smell any chlorine after this.

I decanted the solution from the cemented gold, and then boiled the gold in HCl. The colour improved, going from black to a nice brown which I would normally recognize as a sign of improved purity. Initially the HCl showed no colour change. However, after I left it to cool, the HCl began to turn yellow.

I decanted it off, and in the decanted yellow solution I placed a fresh piece of copper. Black powder began to cement out onto it! So the yellow colour must have been gold going back into solution again!

I added fresh HCl to the cemented gold, and again it began to turn yellow!

I can't figure it out. Perhaps I had not sufficiently driven off the chlorine after cementation, or perhaps there is something in the tablet to keep it in solution and prevent off-gassing. (I imagine that could be beneficial in swimming pools)

The only other possibility I can think of is that rinsing my beakers in tap water left a tiny amount of chlorine residue which allowed the gold to be redissolved.

 

[haveagojoe]

Who ever misused battery acid ? How ?

There have been a few nasty acid attacks here in the last few years, I think Sulfuric is the main one used.

 

[haveagojoe]

My new crucible won't be here for another week, so in my impatience and in the spirit of experimentation I opted to melt up the cemented gold in a potato

Produced this rather sorry-looking little fella, just over 1g:



The potato crucible works but not very well, the gold refused to melt properly to a liquid, it just glowed dull red and gradually came together in a lump. I think a lot of heat was being wasted in cooking the potato, I just couldn't get it hot enough. I'll melt it up again with borax when my crucible arrives.

All good fun and my 1oz goal is a small step closer