HCL Zinc reactions

[Ultrax]

Hello,
Which cyanide derivative are you using? Cyanate? Ferrocyanide + oxidizer/persulfate?
Have you tried to increase the specific surface area of of zinc by treatment with lead nitrate?

You didn't wrote how you control the resulting exact pH? Au(CN)2- is stable up to pH =3 (in theory), but without precise control, free CN - may still appear in the solution. For what purpose do you use citrate buffer? (unless it's a gold plating electrolyte) Why not phosphoric acid?
In weakly acidic solutions, citric acid can be oxidized to acetodicarboxylic acid, which is then decarboxylated to form acetone. At shifted potentials, white flaky citric acid oxidation products can form in the volume of the solution, which are captured by the gold precipitate (usually, of course, this only appears during electrolysis).

If you are sure that there is no silver in the RAM contacts, then you probably do not need to do any calculations for competing reactions. In my country, in the manufacture of substrates and contacts for RAM chips, silver was first used, and only then a thin layer of gold was applied. As far as I know, the same principle was used by Intel in the contacts of the first Pentium CPUs. I don’t know how the matter is with electroplating in modern contacts of RAM chips. Once upon a time, I got into electroplating and we couldn't do an abrasion-resistant(!) electroplating of gold without silver.
Maybe you would like to read this https://www.researchgate.net/public...lver_and_gold_from_cyanide_leaching_solutions

 

[Yggdrasil]

Hello,
Which cyanide derivative are you using? Cyanate? Ferrocyanide + oxidizer/persulfate?
Have you tried to increase the specific surface area of of zinc by treatment with lead nitrate?

You didn't wrote how you control the resulting exact pH? Au(CN)2- is stable up to pH =3 (in theory), but without precise control, free CN - may still appear in the solution. For what purpose do you use citrate buffer? (unless it's a gold plating electrolyte) Why not phosphoric acid?
In weakly acidic solutions, citric acid can be oxidized to acetodicarboxylic acid, which is then decarboxylated to form acetone. At shifted potentials, white flaky citric acid oxidation products can form in the volume of the solution, which are captured by the gold precipitate (usually, of course, this only appears during electrolysis).

If you are sure that there is no silver in the RAM contacts, then you probably do not need to do any calculations for competing reactions. In my country, in the manufacture of substrates and contacts for RAM chips, silver was first used, and only then a thin layer of gold was applied. As far as I know, the same principle was used by Intel in the contacts of the first Pentium CPUs. I don’t know how the matter is with electroplating in modern contacts of RAM chips. Once upon a time, I got into electroplating and we couldn't do an abrasion-resistant electroplating of gold without silver.
Maybe you would like to read this https://www.researchgate.net/public...lver_and_gold_from_cyanide_leaching_solutions

I think reading the whole thread will give you some insight to his challenges and difficulties.

 

[Ultrax]

Thanks, Yggdrassil I think I got carried away.

 

[J.Najam]

cyanide derivative are you using?

Jin Chan

but without precise control

I do believe it still is present, to take care of it heres what I did:

1, decant to the lowest volume closest to the sediment.
2, filtered and washed the residue multiple times on the filter paper to remove any CN traces there might be.

I did not wash off the excess zinc hence the problem.

Citrate buffer was recommended by the seller. And it does work just fine. Although the procedure was not very clear. But this forum is a refiners paradise after Hokes I believe.

Many confusions and mistakes were pointed out. Many issues were clarified on how this process can also be a lot LOT less pain. I don't plan on using it with a full heart but I may again, once Im fully sure of the safety and the right techniques to carry out this procdure.

At shifted potentials, white flaky citric acid oxidation products can form in the volume of the solution, which are captured by the gold precipitate

YES! It definitely does that, but since you have a very clear undertsanding. Help me with this :

What if we create a 2M aqeuos citric acid solution, filter it and then use it.. Should it be effective enough? I last tried it without any metals in the same solution so im unsure of the result but it did buffer the pH down to my desired outcome without any gassing or heating effect. The solution remained as cold as it was.

 

[J.Najam]

I think reading the whole thread will give you some insight to his challenges and difficulties.

Just on another note, I checked the MSDS certificate for LD50 > 5000mg/kg. I can even share an image if you'd like. Just how dangerous could this be?

 

[Yggdrasil]

Just on another note, I checked the MSDS certificate for LD50 > 5000mg/kg. I can even share an image if you'd like. Just how dangerous could this be?

Depends on the state.
New unused in powder form do not relate well to a solution with salts of metals and Cyanide.
Then add pH and complexes.

Companies tend to describe the most favourable conditions for their products.

 

[J.Najam]

Depends on the state.
New unused in powder form do not relate well to a solution with salts of metals and Cyanide.
Then add pH and complexes.

Companies tend to describe the most favourable conditions for their products.

I see.

Could make sense then why other seller of this product claims it to be non toxic

 

[Ultrax]

I see.

Could make sense then why other seller of this product claims it to be non toxic

In the case of the Chinese reagent Jin Chan, the declared lethal dose is an outright lie. Jin Chan at the time of our research a couple of years ago was ordinary sodium cyanide in organic granules for transportation safety.

It is far better to buy reagents from official chemical companies that explicitly list them as "extremely dangerous". Yes, it may not be possible to buy from an individual, only companies with a license, but it is at least relatively safe for uninformed people.
I generally don't recommend using cyanide in any form unless you have HCN control, a pressurized reactor, and a powerful fume hood with an absorber and filters.
As has been written more than once, the cyanide process is not well suited for working "on your knees".
In addition, its selectivity for gold is high only at very low concentrations, which directly contradicts the desire to dissolve gold quickly. If you have more than a few micrometers of gold to leach, it generally does not fit well. A person sees that the dissolution is not going in the desired way and begins to add more cyanide - as a result, other metals begin to dissolve and the risk of poisoning greatly increases.

For comparison:
If the relative dissolution rate index of gold in cyanide is about = 1, and for aqua regia (with all its inconveniences), index is about 250 (without even heating). That means that the dissolution rate of gold in AR is 250 times faster,than in cyanide.
For hydrochloric acid + hydrogen peroxide index = 4,
For Thiosulfate dissolution 60
For Thiourea dissolution 50-65.
I recommend you switch to thiosulfate dissolution + electrolysis.
Calmly, fast enough, and relatively safe.

 

[J.Najam]

In the case of the Chinese reagent Jin Chan, the declared lethal dose is an outright lie. Jin Chan at the time of our research a couple of years ago was ordinary sodium cyanide in organic granules for transportation safety.

That's an interesting insight. I think Dave aka Frugalrefiner also mentioned a similar concern earlier in one of my threads about their reagents being safe only for shipping or transport.

"extremely dangerous"

Sorry sir, but if you visit Alibaba, there are hundreds of suppliers selling the same stating either non toxic or low toxic. But nothing at all as you have mentioned. Each providing their MSDS certificate.

Be it Jin Chan or LVJIN. One LVJIN seller however mentions that it may be a substitute but the components of their agents actually comprise some cyanide therefore precautions must be taken before actually carrying out with the procedure.

In addition, its selectivity for gold is high only at very low concentrations, which directly contradicts the desire to dissolve gold quickly.

I may have to disagree to a certain extent. As many operations I have carried in the past, the leaching rate has been more than satisfactory with the solution concentration being at 1 - 3 %. For instance I was able to dissolve platings from 100 grams of cpu pins in less than 5 minutes with very little agitation. Solution was 5 grams JinChan with 150Ml boiling distilled water.

unless you have HCN control, a pressurized reactor, and a powerful fume hood with an absorber and filters.

I didn't. In fact last year i was struck with Covid and was restricted to my room. Sir believe you me. I carried my first procedures in my bedroom in those days. Now I know seniors could come bashing down on me and I dont blame any of them. But this is only because I was purely told it was non toxic and I beheld myself thinking Alibaba is a huge platform and not many could just fraud you like that. Trusted sellers and trade assurances were the key factors I just believed. By the grace of God, im alive as well as any one around me alhamdulillah.

Hence the toxicity remains a contradiction in my POV. Im still unsure of its toxic degree. I didnt use any acid inside though. It was just the leaching process ans pH adjustments with Citric.

P.S. Moderators, please don't ban me for this.

For Thiosulfate dissolution 60

Having said all that, I am really more inclined to learning this process. But since Im a newbie, do you really think pulling off a non trivial procedure like this should be undertaken? I really don't want to go through a new mess altogether given what I have already gone through and still going through with the current reagent.

 

[Ultrax]

Hence the toxicity remains a contradiction in my POV. Im still unsure of its toxic degree. I didnt use any acid inside though. It was just the leaching process ans pH adjustments with Citric.

Hydrogen cyanide is a gas, so when you feel that something is wrong, it may be too late. Therefore, the HCN sensor (like this 7-CL2-20 Chlorine Cl2 SS gas sensor, 0-20ppm Cl2) should be in any chemical lab that works with any kind(!) of cyanide. Of course, following these tips or not is only your personal choice.

 

[Ultrax]

Having said all that, I am really more inclined to learning this process. But since Im a newbie, do you really think pulling off a non trivial procedure like this should be undertaken? I really don't want to go through a new mess altogether given what I have already gone through and still going through with the current reagent.

Yes.

 

[Yggdrasil]

That's an interesting insight. I think Dave aka Frugalrefiner also mentioned a similar concern earlier in one of my threads about their reagents being safe only for shipping or transport.

Sorry sir, but if you visit Alibaba, there are hundreds of suppliers selling the same stating either non toxic or low toxic. But nothing at all as you have mentioned. Each providing their MSDS certificate.

Be it Jin Chan or LVJIN. One LVJIN seller however mentions that it may be a substitute but the components of their agents actually comprise some cyanide therefore precautions must be taken before actually carrying out with the procedure.

I may have to disagree to a certain extent. As many operations I have carried in the past, the leaching rate has been more than satisfactory with the solution concentration being at 1 - 3 %. For instance I was able to dissolve platings from 100 grams of cpu pins in less than 5 minutes with very little agitation. Solution was 5 grams JinChan with 150Ml boiling distilled water.

I didn't. In fact last year i was struck with Covid and was restricted to my room. Sir believe you me. I carried my first procedures in my bedroom in those days. Now I know seniors could come bashing down on me and I dont blame any of them. But this is only because I was purely told it was non toxic and I beheld myself thinking Alibaba is a huge platform and not many could just fraud you like that. Trusted sellers and trade assurances were the key factors I just believed. By the grace of God, im alive as well as any one around me alhamdulillah.

Hence the toxicity remains a contradiction in my POV. Im still unsure of its toxic degree. I didnt use any acid inside though. It was just the leaching process ans pH adjustments with Citric.

P.S. Moderators, please don't ban me for this.

Having said all that, I am really more inclined to learning this process. But since Im a newbie, do you really think pulling off a non trivial procedure like this should be undertaken? I really don't want to go through a new mess altogether given what I have already gone through and still going through with the current reagent.

We don’t ban folks for mistakes done in the past.
But as you are now better informed, do not do them again.
And as Ultrax said in his last post, Yes but with the proper precautions, which means not in your home or outside among others.
And get the cyanide first aid kit and a proper sensor!!!!
If you plan to press on.

 

[J.Najam]

Hydrogen cyanide is a gas, so when you feel that something is wrong, it may be too late. Therefore, the HCN sensor (like this 7-CL2-20 Chlorine Cl2 SS gas sensor, 0-20ppm Cl2) should be in any chemical lab that works with any kind(!) of cyanide. Of course, following these tips or not is only your personal choice.

Thankyou! This is certainly what I'd been looking for. Ill save this link to my archives. Certainly not getting it anywhere locally. So I'll procure it in the future. And if course I want to follow the tips. Safety better than money or gold.

 

[J.Najam]

We don’t ban folks for mistakes done in the past.
But as you are now better informed, do not do them again.
And as Ultrax said in his last post, Yes but with the proper precautions, which means not in your home or outside among others.
And get the cyanide first aid kit and a proper sensor!!!!
If you plan to press on.

Much appreciate your understanding. Definitely not doing it again like that ever hopefully.

Proper precautions with a fumehood and scrubber. I'll search for the cyanide first aid and a sensor, but rest assured the solution has been sealed up in a bottle and kept aside until complete arrangements have been made to proceed.

On the other hand I'd like to share my latest recovery in the other thread.

 

[J.Najam]

Yes.

Great. You're my coach in this process. Let me read up a little about thiosulfate first and then ill proceed with the questions hopefully.

 

[Shark]

One of the great things about refining is all the different ways to do the different processes. Learning how to do them is great and often easier than knowing when to use them. The more ways we know how and when, the better prepared we are to deal with different materials. I am hoping to see another thread later on some of the ways (like thiosulfate for example) of dealing with other materials. This one has been a very informative and easy reading pleasure.

 

[sincha978]

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

I have a similar situation here.
Before I always used SMB for precipitating Gold, but from few months ago, new laws were brougth in my country, and from then only companies can buy SMB, and individuals can't.
So after using all of my supplies I had left, 2 days ago I tried using Zinc for precipitation.
For clarification: We are here talking about ram memory pins, cpu plating, and cellphone scrap.
I first dissolved base metals with diluted nitric acid, since it was faster than AP.
Then washed and filtered it.
Then dissolved gold in aqua regia and after that neutralised it with boiling and adding Hcl three times.
After that I used Zinc from AA batteries cut in small pieces for precipitation, which worked great but I am left with gold and excess zinc at the bottom.
Now my question is, which one of the acids would work the best for removing zinc from gold powder?
I have 35% Hcl, 80% acetic acid, and 68% nitric acid.

 

[Ultrax]

Now my question is, which one of the acids would work the best for removing zinc from gold powder?
I have 35% Hcl, 80% acetic acid, and 68% nitric acid.

Any of them.

 

[sincha978]

Any of them.

Thanks a lot.

 

[Yggdrasil]

I have a similar situation here.
Before I always used SMB for precipitating Gold, but from few months ago, new laws were brougth in my country, and from then only companies can buy SMB, and individuals can't.
So after using all of my supplies I had left, 2 days ago I tried using Zinc for precipitation.
For clarification: We are here talking about ram memory pins, cpu plating, and cellphone scrap.
I first dissolved base metals with diluted nitric acid, since it was faster than AP.
Then washed and filtered it.
Then dissolved gold in aqua regia and after that neutralised it with boiling and adding Hcl three times.
After that I used Zinc from AA batteries cut in small pieces for precipitation, which worked great but I am left with gold and excess zinc at the bottom.
Now my question is, which one of the acids would work the best for removing zinc from gold powder?
I have 35% Hcl, 80% acetic acid, and 68% nitric acid.

As Ultrax say any of them will remove the Zinc, but since Zinc drop all the other metals including Copper.
I think Nitric is your only viable solution, unless you have Tin in your Mix.