HCL Zinc reactions

[Yggdrasil]

I'm sorry I saw this today but had already done my process over the weekend. I did as I'd mentioned earlier:

Zinc granules immersed in Dilute HCl => Decant => Added boiling distilled water to let loose the particles held together => a fractional difference observed => Added HCl => 10 minute boil => unfortunately there was no GOLD in the solution at all

The solution turned a light brown transparent colour the same as we have our sulfuric acid drain openers at 93 % conc.

Added a little SMB to see if there is any reaction, fizzing was there but nothing more...

I'm a little confused here.
You added Zinc granules to dilute HCl, is this the granules created by the cementing?
If so, the HCl do not dissolve any Gold only the Zinc, so there should not be any Gold in solution.
The Gold should be black powder in the bottom.

 

[J.Najam]

is this the granules created by the cementing?

Yes, the granules that can be seen in the first pictures were a result of cementing. So I guess there may be an excess of Zinc and the HCl did not have much surface to attack all the zinc at once so I wasn't able to expose these. So I added fresh HCL

so there should not be any Gold in solution.

And yes unfortunately so came down to this...

 

[Yggdrasil]

Yes, the granules that can be seen in the first pictures were a result of cementing. So I guess there may be an excess of Zinc and the HCl did not have much surface to attack all the zinc at once so I wasn't able to expose these. So I added fresh HCL

And yes unfortunately so came down to this...

HCl do not dissolve Gold so the Gold if there, will be the slime left over after.

 

[J.Najam]

HCl do not dissolve Gold so the Gold if there, will be the slime left over after.

Yeah, HCl doesn't. Also there was no slime. The solution was clear dilute brown.

 

[Shark]

I have 99% glacial acid, if i prepare a 50% vinegar solution with it and add salt to the solution do you think it could do the job too? Would it be considered environmentally safe because glacial acid had its own awful smell

No this is not environmentally safe. Once metals are introduced to acids they are now toxic to the environment. Even vinegar (glacial acetic acid). Please study on safety and dealing with the wastes produced. As mentioned elsewhere, this produces hydrochloric acid and introducing metals brings you back to toxic materials.

Now back to regularly scheduled programming.

 

[Yggdrasil]

Yeah, HCl doesn't. Also there was no slime. The solution was clear dilute brown.

It can be that it is so fine that the particles are suspended in the liquid.
Try to add one drop of Nitric, bleach or Peroxide into a somewhat concentrated solution, then test it with Stannous.

 

[J.Najam]

Yep, tried. No result. Thanks for everyone who commented and supported . Will be posting up new experiments

 

[Golddigger76]

No need to experiment as there are known procedures posted over and over, but even better is for you to read the book written by hoke, almost any information you may need to refine.

Obviously the book was written long before modern electronics were made.
we no longer need urea, but for the most part the methods she wrote still applies

 

[J.Najam]

No need to experiment as there are known procedures posted over and over, but even better is for you to read the book written by hoke, almost any information you may need to refine.

Obviously the book was written long before modern electronics were made.
we no longer need urea, but for the most part the methods she wrote still applies

I completely agree with you regarding the experiment bit. I do have Hoke's book but I'm almost finding it hard to go through it given my job and timings, so usually I refer to it when I have decided to go through a certain process.

 

[Yggdrasil]

I completely agree with you regarding the experiment bit. I do have Hoke's book but I'm almost finding it hard to go through it given my job and timings, so usually I refer to it when I have decided to go through a certain process.

If you are finding it hard to read the book, how do you have time to experiment?
Even worse it implies you have not read the safety and dealing with waste in the forum.
I will urge you to stop all dealing with chemicals until this is done.

 

[J.Najam]

Uh, no. I went through the waste dealing post you had shared with me earlier like you do with newcomers. So I have went through it, discussed a couple pointers with my relative who's a chemical engineer regarding the disposal as well. He recommended me to neutralize any solutions that I suspect may not have much metals into it and dispose of safely. But to be careful of any that may have a saturation of the same.

I had just a couple of questions after going through the waste treatment post,

1, are we supposed to seal the stock pot or we have to leave the lid loose? If loose, is it a hazard to environment?
2, Lets suppose im dealing with nitric, peroxide, HCl and may be even sulfuric in my refining. All done separately, should they go into the same stock pot?

If you are finding it hard to read the book, how do you have time to experiment?

I take out some time for the intended process and study it during my work hours when in office

 

[Yggdrasil]

Uh, no. I went through the waste dealing post you had shared with me earlier like you do with newcomers. So I have went through it, discussed a couple pointers with my relative who's a chemical engineer regarding the disposal as well. He recommended me to neutralize any solutions that I suspect may not have much metals into it and dispose of safely. But to be careful of any that may have a saturation of the same.

I had just a couple of questions after going through the waste treatment post,

1, are we supposed to seal the stock pot or we have to leave the lid loose? If loose, is it a hazard to environment?
2, Lets suppose im dealing with nitric, peroxide, HCl and may be even sulfuric in my refining. All done separately, should they go into the same stock pot?


I take out some time for the intended process and study it during my work hours when in office

The stock pot is a rather vague and sometimes multipurpose description.
It is both a place to put your "waste" before waste treatment
and also a place to recover the values that has slipped past you during processing.

I put all acidic waste there. And as long as you do not process it it can be closed,
even though if left open some will evaporate and as such reduce the amount to process in the end.
I cover it with a piece of cloth in my lab.

When the level get high enough you put in a piece of Copper and set up some kind of stirring or bubbling for a day or three.
Then let it settle for some day to a week and gently siphon off the liquid without disturbing the slimes/powders.
Remember to brush the Copper clean in to the container before removing it.
This liquid is the one you run through you waste treatment, but obviously the first step of cementing on Copper is already done.

 

[J.Najam]

Thanks for the insight, this clears a load off my mind. Will find out later how to process the slimes or powders for the precious metals that we may have caught over there. On another note, using copper we're cementing out any metals that are lower than that in the reactivity series. So in order to now get the copper back out, we're gonna have to siphon the liquid out and place an iron or aluminum in the solution?

This procedure would be correct?

 

[Yggdrasil]

Thanks for the insight, this clears a load off my mind. Will find out later how to process the slimes or powders for the precious metals that we may have caught over there. On another note, using copper we're cementing out any metals that are lower than that in the reactivity series. So in order to now get the copper back out, we're gonna have to siphon the liquid out and place an iron or aluminum in the solution?

This procedure would be correct?

Read my post again and then dealing with waste again.
When you are finished with each step of cementing you remove the solids and treat the liquids in the next step.

 

[Ultrax]

Did you get a description from the producer?
I think the Zinc is used directly in the Cyanide solution, not sure.
But anyway Active Carbon is the preferred method of stripping the Gold from Cyanide based leaches.
And why didn't you go for straight Cyanide or Ferro/Ferri Cyanide, much less issues and usually much cheaper then these "green" concoctions.

Edit to add:
The reason of the trouble dissolving the Zinc may be due to the PMs passifying the Zinc so the HCl can't reach it.

In general, there should be no problem with the dissolution of zinc in hydrochloric acid. There can only be problems with proportions (obvious and large lack of acid).
The black color of zinc during the reaction is NOT passivation, but an optical effect due to the rapid detachment of zinc ions from the metal surface (many microscopic pits absorbing light are formed, so the surface of zinc granules appears black). But yes, this funny effect is misleading

 

[Yggdrasil]

In general, there should be no problem with the dissolution of zinc in hydrochloric acid. There can only be problems with proportions (obvious and large lack of acid).
The black color of zinc during the reaction is NOT passivation, but an optical effect due to the rapid detachment of zinc ions from the metal surface (many microscopic pits absorbing light are formed, so the surface of zinc granules appears black). But yes, this funny effect is misleading

Thanks Ultrax.
I weas not sure what happened if the surface was saturated by Silver or Gold.

 

[Ultrax]

Here I assume that the zinc on which the precious metal was precipitated is simply dissolved by hydrochloric acid and this is not a replacement reaction.

In this case, the reaction of zinc dissolution in hydrochloric acid has an electrochemical priority to the reduction of traces of gold salts by zinc from the unwashed mass of the Au-Zn metal filtrate.

If we are talking about cleaning the mixed silver and gold precipitate from zinc, it is better not to use HCl. Zinc is easier to remove with moderate hot 15%-20% acetic acid.

If the situation involves the precipitate of gold by zinc in an acidic solution (pH < 3), it is necessary to calculate the electrochemical potentials for specific conditions in the solution to determine the priority direction of the dissolution/replacement reactions to minimize consumption of zinc and also minimize reducing the rate of gold or silver recovery due to losses of the active surface of zinc.

Specifically, if you have a large quantity of silver in solution - the zinc granule is immediately covered with grey loose powdered metallic silver and further reduction takes place not on the zinc surface, but on the previously formed silver (slowly). That's why intensive mixing is required. Without mixing, in this situation, you will see the dark grey color of silver on the zinc granules' surface.

 

[J.Najam]

Here I assume that the zinc on which the precious metal was precipitated is simply dissolved by hydrochloric acid and this is not a replacement reaction.

Hello,

How are you doing? Thanks for your increasing my knowledge though I had to read your comment multiple times to understand what you'd written.

And thanks to god I understood it to some extent but would need some clarification.

1, As per highlighted above, yes zinc was used to precipitate the gold from the solution and HCL was used to dissolve the excess powder that remained. So how and when does a replacement reaction not occur? (Other than metals not present)

If we are talking about cleaning the mixed silver and gold precipitate from zinc, it is better not to use HCl. Zinc is easier to remove with moderate hot 15%-20% acetic acid.

2, I have often read in many places that HCL, HNO3 and H2SO4 are the acids that are best suited for zinc dissolution because of their strengths. So again, how would only only 15-20% acetic acid do the same job? I believe to an extent can be possible but would it really give me the same purity as the other 3 as mentioned above? If yes, would it be safe to say that I can further use only acetic for future uses and the rest won't be required for the same?

If the situation involves the precipitate of gold by zinc in an acidic solution (pH < 3), it is necessary to calculate the electrochemical potentials for specific conditions in the solution to determine the priority direction of the dissolution/replacement reactions

3, My pH here was 4. I dont know if its regardless or useful in the next step. How do we calculate the electrochemical potentials for specific conditions like you have mentioned?

Anxiously awaiting your reply.

Many thanks

 

[Ultrax]

Hello,
1) From which solution do you precipitate gold with zinc? Tetrachloroaurate, thiosulfate complex, thiourea complex, cyanide complex?
2) How do you control pH? Do you know how to use the Pourbaix diagram for gold compounds? Eh-pH dependency?
3) The replacement reaction between zinc and gold will run in almost any case (except for really incorrect, chemically absurd conditions).
In practice, the question is the time spent on gold precipitation and the percentage of productive output/tailings.
If ions of other metals are present, they shift the standard electrochemical potentials of all metals in solution, but how and in which direction exactly is a relatively difficult case for the forum.
For example, gold itself does not quantitatively dissolve in thiosulfate (unlike silver) but in the presence of copper, nickel, or cobalt ions, the process of dissolving gold is faster than in the cyanide process, and forming one of the most stable gold complex compounds.
Beginners usually get it accidentally, dissolving electronic scrap and trying to precipitate gold with metabisulphite). As a result, very often, gold doesn't precipitate but redissolves very quickly. And since it is a very non-trivial task to precipitate the gold from the thiosulphate complex, and it can mask the tin chloride test, such solutions are usually poured into the sewer as empty by beginners
There are hundreds of such ionic combinations, so you will need to study at least a course in general inorganic chemistry to be able to calculate a specific set of electrochemical conditions. If you have a mining enterprise with more or less stable ores, it makes sense to do such work, for random sources of gold (electronic scrap, etc.) it is difficult and usually impractical. It is easier to provide a large excess of precipitant metal.
For a one-time operation, it is cheaper than any chemical calculations.

About acids:

If there is only gold and zinc in the precipitate, any acid can be used.
There are mnemonic rules for solubility: NAG-SAG-PMS-Castro Bear
If there is silver in the precipitate: nitric will dissolve it, hydrochloric will not work (zinc won't dissolve), sulfuric will not work (zinc won't dissolve, except concentrated - then with silver together), and acetic will only dissolve zinc. Acetic acid is relatively safe, very cheap and widely available, and therefore convenient. Why do we need a concentration of acetic acid of no more than 20%, this is a question, the answer to which is worth finding on your own

 

[J.Najam]

Hello again,

1) From which solution do you precipitate gold with zinc? Tetrachloroaurate, thiosulfate complex, thiourea complex, cyanide complex?

Cyanide derivative.

2) How do you control pH? Do you know how to use the Pourbaix diagram for gold compounds? Eh-pH dependency?

Used citric acid to bring pH from 12 - 4.5

As for the Pourbaix diagram, no idea but will definitely check it out.

For example, gold itself does not quantitatively dissolve in thiosulfate (unlike silver) but in the presence of copper, nickel, or cobalt ions, the process of dissolving gold is faster than in the cyanide process, and forming one of the most stable gold complex compounds.
Beginners usually get it accidentally, dissolving electronic scrap and trying to precipitate gold with metabisulphite). As a result, very often, gold doesn't precipitate but redissolves very quickly. And since it is a very non-trivial task to precipitate the gold from the thiosulphate complex, and it can mask the tin chloride test, such solutions are usually poured into the sewer as empty by beginners

Though I have no experience nor enough knowledge about thiosulfate, I love how accurately breif and crisp these two paragraphs were in context to highlighting the issue as well as studying the pointers mentioned.

There are hundreds of such ionic combinations, so you will need to study at least a course in general inorganic chemistry to be able to calculate a specific set of electrochemical conditions. If you have a mining enterprise with more or less stable ores, it makes sense to do such work, for random sources of gold (electronic scrap, etc.) it is difficult and usually impractical. It is easier to provide a large excess of precipitant metal.
For a one-time operation, it is cheaper than any chemical calculations.

Most certainly so. In fact I do believe I may have to do some in depth study of chemicals alongside Hokes to know exactly what im doing in this field.

For the calculations part, you're right. Though I look forward to the day I do. Maths => brain teaser => mental growth

If there is silver in the precipitate

Was working on ram fingers. So i dont think it'll be silver anymore. There may be a presence of AuZn and CuZn for sure.