# Is Hoke relevant today? The Stock Pot.



## g_axelsson (Jan 18, 2017)

I got a pm from a member asking if I thought that Hoke is still relevant for the stock pot in the days of e-waste.

I thought it was a good question and a good start for a discussion thread. 

Exactly how does the content of the stock pot differ between old times and the stock pot from electronic sources?
Is there any better techniques to handle the stock pot today that wasn't available to Hoke?

In Hoke's book the chapter XIII on Stock Pot starts at page 143 and runs through to 155.
Here are some quick links.
Page 143 - THE STOCK POT - MATERIAL HANDLED
Page 144 - EQUIPMENT AND CHEMICALS - COLLECTING THE PRECIOUS METALS WITH ZINC
Page 145 - REFINING THE BLACK POWDER
Page 146 
Page 147 - THE IRIDIUM RESIDUE - THE DILUTE AQUA REGIA SOLUTION-PLATINUM, PALLADIUM, GOLD
Page 148 - PLATINUM - PALLADIUM
Page 149 - BURNING THE RED PALLADIUM POWDER
Page 150 - FURTHER TREATMENT OF THE SOLUTION FROM WHICH PLATINUM AND PALLADIUM HAVE BEEN REMOVED
Page 151
Page 152 - DISPOSAL OF THE FINAL TAILINGS
Page 153
Page 154 - QUESTIONS AND ANSWERS
Page 155
Part IV of chapter XIX contains alternative methods for Stock Pot recovery. It starts at page 162 and runs through to 168.
Page 162
Page 163
Page 164
Page 165
Page 166
Page 167
Page 168

Here are a couple of GRF links on the stock pot
Harold's five quart ice cream bucket
Harold, sending iron filing to the stock pot
Harold, filtering and incinerating the cemented metals
Harold, emptying the stock pot
Harold, 20 year stock pot savings plan
Harold, hydrogen from the stock pot ignites
Harold, short introduction
Another discussion about the stock pot

What do you think? Is the information outdated? Something to improve on? Any other links?

Most people here is using a stock pot different from the description in chapter XIII (evaporation in large vats) but in chapter XIV, page 164 she describes using scrap iron or copper to cement the stock pot and in page 165 she talks about refining the stock pot with acids. Pretty much the same way many of us is running our stock pots.

Göran


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## aga (Jan 18, 2017)

The underlying Chemistry hasn't changed since Hoke's time, so her logic/methods still hold perfectly true.

There have been many advances in organic chemistry and materials technology in the past 70 years, so maybe there are some benefits to be had there.

For example, chelating agents such as EDTA (1960s) (https://en.wikipedia.org/wiki/Chelation) 'complex' with metal ions, radically altering their chemical behaviour. Being organometallic materials, they should decompose/burn in a furnace, leaving the metal behind.

Molecular filter materials (beads) can be bought which selectively adsorb different chemicals depending on their specification. E.g. 3A molecular filters selectively adsorb water. Heating them drives the water out so they can be re-used.

Personally, i've not even recovered anything from a 'normal' stock-pot yet, so will stick with the 'normal' procedures for now. Sounds like some fun experimentation though :wink:


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## snoman701 (Jan 18, 2017)

I would think more-so relevant with e-waste.

E-waste is a rich ore, but not concentrated to the point of being as rich as karat scrap (usually). Thus it is more difficult to recover the very small amount of PMG's, especially when doing chemical assays. 

If you are just recovering gold, then not likely, as the testing is so sensitive you should know if your solutions have gold in them (as long as it's ionic gold). 

And I'm new, so anything that I wrote that is wrong, please point out and I'll happily ammend to include correct details.


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## Topher_osAUrus (Jan 18, 2017)

I don't know how it could ever become outdated, really.

To recover the trace values, it would have to be done with copper. Then to get all the other junk out and begin to make it safe, the copper and crap would have to be displaced by iron or zinc, maybe aluminum.. 

How could it be improved upon? ...unless there was some magical resin to capture the values, then just cement directly on iron, skipping copper.. But, I think there would be a trade off somewhere.... ...maybe its just me, but, I think ths "tried and true" way is still very relevant and practical today, even with escrap.

Heck, its probably much safer now than 30 years ago, since they have been weeding out some of the nastier metals... But, I am curious as to snomans other thread question.

-is cadmium hydroxide/oxide cake the same hazard as our other metal cakes from the neutralization of the stock pot? Or must we keep the nitric stock pot waste separate from the AR waste stream?

As far as processing the stockpot. I think there are so many different methods, because there are so many different precious metals that can be contained in the pot. If you process alot of platinum group metals, it would probably be in your best interest to process the black sludge differently than if you were just running gold and silver. There are so many different ways to skin that cat, because there are soo many types of fur!


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## anachronism (Jan 18, 2017)

Hi Goran

Does the chemistry of Hoke's stock pot still hold relevance today? 

Yes it does. The theory of not throwing away valuable metals is never going to get old. 

That given I don't think that the message of stock pots given out over the last few years on this forum is the actual message that Hoke was giving out. She makes reference to "picking and choosing" what goes into a stock pot based upon the contents whereas the message here has been more geared towards considering every "barren" solution to be stock pot material in the hope that one can recover a few grains later on.

There is also mention of keeping the acidity low. Probably for reasons detailed in my last few paragraphs. 

Your thread is simply brilliant, and I thank you for it because it's opened up doors for me personally and I hope for many other people. 

To open up one door in specific response to your question. Hoke was never around the kind of materials we treat today in ewaste. I feel that if the lady had been, then her book would have been very different. Assuming that she would have known the additional elements that are brought into play, she would probably have been able to present a cracking set of processes. That given, her best skill has always been to be able to explain complex chemistry in terms that the layman can understand. I would love to see a comparison between the metals the lady worked with and the metals we work with now, accompanied by details of the inter reactions between those metals and how they affect the recovery and refining processes.

Another door is opened on page 145. Given that your stock pot is supposed to be devoid of Nitric, yet mention is made of your black powder redissolving, then possibly the discussion about base metal salts dissolving gold in HCl very readily could be addressed because it's not something I have seen much mention of here to date. This is also mentioned on page 153. Hoke obviously knew about this yet the general silence about it is interesting.

Actually the more I read this chapter the more I feel that Hoke has been used in the same way as another text in that the message being given out can be interpreted and preached about in a multitude of ways, and that the base message can be lost in this translation. Especially if the mouthpiece doesn't understand the real message. The most valuable part of this exercise for me has been being able to read this with much more chemistry knowledge than I had before and being able to see what has been misinterpreted, and how those misinterpretations have been passed into refining "lore."

I am not going to lie. I have never once read this chapter before you presented it here Goran. To say that it is an eye opener is putting it mildly for the reasons stated above. As such, I thank you.

Jon

Edit for clarity my point about mouthpieces is NOT aimed at anyone in particular, I mean that- it's more the overall "lore" thing and the whole urban myth process.


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## aga (Jan 18, 2017)

anachronism said:


> There is also mention of keeping the acidity low. Probably for reasons detailed in my last few paragraphs.


Which paragraphs ?

Hoke says to add some HCl, also some members here, but not Why, although i can guess.

Guessing got me nowhere the first time round, so stuff like that is confusing for a noob like me, as i cannot find the 'paragraphs' mentioned and have obviously missed something important.

Edit: missed a quote mark


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## Topher_osAUrus (Jan 18, 2017)

Well, adding HCl would keep the ph low, since its acidic..

but, I'm going to go with it helps keep the base metal salts in solution and aides the displacement reaction, in turn liberating the wee-bits of pm's in solution.


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## anachronism (Jan 18, 2017)

Hi Toph

Actually I mistyped- the reference was to keep the pH close to neutral. My apologies because it makes a mess of the context I was trying to put across. 

Look at the opening line of page 153 on the link Goran kindly gave, and see the reference to the acid possibly dissolving the precious metals. 

Aga I was referring the the last few paragraphs of my own post.


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## Topher_osAUrus (Jan 18, 2017)

link...hah, I'll grab my original copy 8) 

She is speaking of the washing, or tailings, not the stock pot itself, but the settling tank. Which would be a different beast than the stock pot, I believe.
edit to add:

Yes, she is speaking strictly of the washing/settling tanks. The stock pot and its need for acidity is spoken of on 144.
"..sometimes the solution suddenly becomes thick and muddy, with a scum on top. In that case, add HCl and stir, until it clears up. Try to avoid this thick mud, by having plenty of acid in your solution"

edit again to fix my fat fingers


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## Topher_osAUrus (Jan 18, 2017)

Hoke does advocate for working the stock pot with zinc though, instead of copper. I believe that was her chosen example as zinc completes the process pretty quickly. I think it has the drawback of having to be closely tended too, else the metals will redissolve in the acidic solution. If copper is the cementing metal, I don't believe that would be possible, as the solution would already be saturated with copper, and there would be no room for the precious metals.


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## anachronism (Jan 18, 2017)

Topher_osAUrus said:


> Hoke does advocate for working the stock pot with zinc though, instead of copper. I believe that was her chosen example as zinc completes the process pretty quickly. I think it has the drawback of having to be closely tended too, else the metals will redissolve in the acidic solution. If copper is the cementing metal, I don't believe that would be possible, as the solution would already be saturated with copper, and there would be no room for the precious metals.



You might want to check over your chemistry here mate.


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## Topher_osAUrus (Jan 18, 2017)

Care to clarify Jon?

Edit:

Or anyone?... I would very much like to know where I am off on my line of thinking. Id rather be wrong and corrected, than a fool spreading misinformation


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## g_axelsson (Jan 19, 2017)

Topher_osAUrus said:


> Hoke does advocate for working the stock pot with zinc though, instead of copper. I believe that was her chosen example as zinc completes the process pretty quickly. I think it has the drawback of having to be closely tended too, else the metals will redissolve in the acidic solution. If copper is the cementing metal, I don't believe that would be possible, as the solution would already be saturated with copper, and there would be no room for the precious metals.


This is a misconception coming from too many explanations that "copper pushes the precious metals out of solution". There is nothing like "pushing" in chemistry. It's all about concentration, solubility and oxidation state.

Going a bit off topic here, this "pushing" is something usually seen when discussion of gold dissolved by HCl and hydrogen peroxide when starting a copper chloride leach. What is happening (as far as I understand) is that the hydrogen peroxide changes the oxidation potential so much that gold can be oxidized and then dissolved by the HCl. Gold will in it's turn cement on copper (via a displacement reaction) but if it falls off it will be dissolved again.
When the oxidation potential (i.e. the concentration of peroxide) goes down gold stops being dissolved and any cemented gold stays metallic.
It has nothing to do with the solution being full of copper, it's just out of peroxide and the oxidation potential has dropped.

Coming back to the stock pot, if you have the liquid saturated with copper chloride then cementing won't work as the surface of any copper passivate when new copper chloride is formed but can't dissolve again. That means that any precious metals in solution stays in solution since there is mo exposed metal left to cement on.
In this case you have too much metal and not enough with water and the stock pot isn't working.

As a side note, CuCl2 has the ability to not only dissolve copper, it can also dissolve palladium.

Göran


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## Topher_osAUrus (Jan 19, 2017)

I understand Goran.
I shouldn't have used the term push. I knew it was a displacement reaction, but, thats just how i "viewed" it as happening. The gold in solution was reduced/pushed out when it came in contact with a metal that was higher in the reactivity series.

And, i didn't think of the excess oxidizer in the pot, since Hoke says to keep free nitric out of the stockpot.

Thank you for the clarity


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## g_axelsson (Jan 19, 2017)

Topher, you didn't mention "push", I used it as a possible explanation of why you thought "there is no room for precious metals".

Göran


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## aga (Jan 19, 2017)

g_axelsson said:


> What is happening (as far as I understand) is that the hydrogen peroxide changes the oxidation potential so much that gold can be oxidized and then dissolved by the HCl. Gold will in it's turn cement on copper (via a displacement reaction)


Sounds pretty good. A bit of chemistry study has revealed that many (if not all) reactions can be very complex, with only the final results being simple.

This overall reaction might be written something like 2 AuCl + H2O2 + Cu => 2 Au + CuCl2 + H2 + O2 with the 'simple' result being elemental gold and copper chloride.

In reality it will happen through a series of reactions, each producing some unstable intermediate chemical species to eventually reduce the Au+ down to Au0, i.e. elemental gold without too many/too few electrons.

The specific details of the exact mechanism (and how the peroxide acts as a catalyst) is beyond me.
The details will be posted if i can find a full explanation anywhere.


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## anachronism (Jan 19, 2017)

Sorry Toph I was in bed when you replied. Goran picked it up though!

Yeah Aga that's basically what I was getting at, that it's simple to look at the end result and assume nothing complicated has taken place.  

Jon


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## Topher_osAUrus (Jan 19, 2017)

No worries.

So, it would be best to do as I have then and keep the stockpot "active" by keeping an aquarium bubbler in it, constantly agitating the old solution. Right? That way accomplishes a couple things, keeping the metals that have displaced out off the copper/keeping fresh surface on the copper, as well as keeping pregnant solution that has yet to cement in motion, so it can be reduced down .

But, how far off was the line of thinking that cemented values have less chance to redissolve in a copper cementing pot vs the zinc one? 

Actually, why is it so easy for pm's to redissolve after being reduced by zinc cementation?


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## anachronism (Jan 19, 2017)

Sure I'll try although I am sure a real chemist will explain it better.

Imagine your stock pot. By definition it's a swirling mass of base metals of all kinds of descriptions. You add a load of Chloride ions with the HCl when you precipitate with the zinc. The excess ions don't go away and when the zinc reaction has finished they react with the base metal ions and create an environment that can and will dissolve gold and other precious metals. Hence Hoke's comments. 

An analogy- how many times have you been sure that you have denoxxed a dirty solution entirely, dropped the gold, and then when you do your first HCl wash you're left with a pregnant solution? You'll also probably notice that this occurs much less with a second refine where your gold is purer and your base metal content in the solution is almost non existent. Excuse the lay explanation Toph.

Jon


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## Topher_osAUrus (Jan 19, 2017)

That's a fine explanation Jon. I do appreciate it. (afterall, I am a pretty "lay" person.  )
..and, it adds a bit to another book that had mentioned ferric chloride will dissolve gold to a minor extent. He also mentions a couple other acids that will dissolve a minute amount of gold too, but, I haven't had my coffee yet and I can't recall which ones Wise mentioned... And which ones were more apt to do it than others.

I do remember though, that sulfuric can hold gold in solution if it has any free halogens in it.


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## aga (Jan 19, 2017)

The main thing to remember is that is the Chloride ions (Cl-) that are reacting with the PMs to create soluble compounds (hypochlorous acid also appears to play a role). The existence of each species (i.e Cl-, HOCl etc) is strongly governed by the pH (i.e. how much H+ is in there) which is why Hoke says to add HCl to the stock pot.

It's the Clorine in HCl that gets reduced, presumably by water, then attacks the gold/PMs, which could even be guessed as it makes HAuCl4. The nitric acts as a catalyst and does not end up in the result, although it does take part in the reaction.

https://www.sciencemadness.org/whisper/viewthread.php?tid=63606#pid419262

In a 'Stock Pot' the chemistry is mind-bogglingly complicated, due the the mix of so many chemicals in random amounts.

Where Hoke excelled was in doing all the seriously complicated chemistry and maths, then 'refining' all that work down into a book giving procedures that Work, so no, Hoke is not outdated at all, at least not for the forseeable future.


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## FrugalRefiner (Jan 19, 2017)

aga said:


> It's the Clorine in HCl that gets reduced, presumably by water, then attacks the gold/PMs, which could even be guessed as it makes HAuCl4. The nitric acts as a catalyst and does not end up in the result, although it does take part in the reaction.


 :shock: Chlorine in HCl getting reduced by water, then attacking gold? Nitric acting as a catalyst? Aga, I think your time would be better spent learning about refining here on this forum than posting what people are posting elsewhere. I mean no disrespect to Sciencemadness, but in five years of studying refining, I've never heard any explanation like that. 

I'm not a chemist. I could be wrong.

Dave


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## Topher_osAUrus (Jan 19, 2017)

If it was HOT water, it could liberate the Cl in the HCl. Since it is just a gas dissolved in water, and solubility drops with temperature increase. (...maybe not though, as there would be extra water for the Cl to stay in the solution... heck, I don't know..) And, I believe I understand what he meant by the nitric as a catalyst (I think). As the addition of nitric to HCl makes NOCl (nitrosyl chloride) which is the workhorse in dissolving gold. (I believe)

edit to add a thought


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## aga (Jan 19, 2017)

FrugalRefiner said:


> I mean no disrespect to Sciencemadness, but in five years of studying refining, I've never heard any explanation like that.


Certainly i need to spend a lot more time studying Refining before i can hope to get anywhere !

I only have 3 years Chemistry study on a hobby basis, and just a few weeks attempting to Refine, so i could be completely wrong about many things.

SciMad was just the first place i knew those Pourbaix diagrams were available.

The Fact is that that Gold dissolves in HCl and makes HAuCl4 ONLY if nitric is present as well. Logically that means the NO3 is a catalyst, as the AR mix does not predominately produce AuNO3 (which appears not to exist).

A common misconception is that a Catalyst does not get involved with a reaction. They do, lots, which is why they work.

The underlying mechanism is that the catalyst reacts first, reducing the Energy required for the next step, which ends up with the catalyst back as it was, and the desired material formed.



Topher_osAUrus said:


> If it was HOT water, it could liberate the Cl


In some circumstances, yes. Heating makes a big difference to all chemical reactions as you already have seen.

If you altered the pH enough, it might not.

One of the barriers to two chemicals reacting with each other is the _activation energy_ required : they will react instantly if they are hot enough, not at all if they are cold.

Everyone has seen a firecracker. It won't start reacting unless it gets some heat, i.e. a flame.

Catalysts basically reduce the activation energy required for the overall reaction to get started.


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## aga (Jan 19, 2017)

FrugalRefiner said:


> ... posting what people are posting elsewhere ...


These are my own opinions, not something i found elsewhere and copy-pasted.


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## FrugalRefiner (Jan 19, 2017)

aga said:


> The Fact is that that Gold dissolves in HCl and makes HAuCl4 ONLY if nitric is present as well. Logically that means the NO3 is a catalyst, as the AR mix does not predominately produce AuNO3 (which appears not to exist).


Please stop posting things like this. It is not a fact that gold dissolves in HCl ONLY if nitric is present. All you need is an oxidizer. Hydrogen peroxide will work. Even the oxygen from the air will do if you give it enough time.



> A common misconception is that a Catalyst does not get involved with a reaction. They do, lots, which is why they work.
> 
> The underlying mechanism is that the catalyst reacts first, reducing the Energy required for the next step, which ends up with the catalyst back as it was, and the desired material formed.


A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Nitric acid is an oxidizer, not a catalyst in this case.

We strive to not have misinformation on this forum. Please stop posting things like this until you are sure of the answer, not your opinions or what you think is logical.

Dave


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## aga (Jan 20, 2017)

aga said:


> It's the Clorine in HCl that gets reduced, presumably by water


Further reading says that this is 100% wrong. 

The Cl was already reduced before water came into the picture.



FrugalRefiner said:


> aga said:
> 
> 
> > We strive to not have misinformation on this forum. Please stop posting things like this until you are sure of the answer, not your opinions or what you think is logical.


Point taken.

I will not post anything similar without some reference/evidence to back it up.


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